EXPLOITING THE INSECTICIDAL POTENTIAL OF THE INVASIVE SIAM
WEED, Chromolaena odorata L. (ASTERACEAE) IN THE MANAGEMENT OF
MAJOR PESTS OF CABBAGE, Brassica oleracea var capitata AND THEIR
NATURAL ENEMIES FOR ENHANCED YIELD IN THE MOIST SEMI-
DECIDUOUS AGRO- ECOLOGICAL ZONE OF GHANA
BY
GODFRED NWOSU EZENA
10397344
THIS THESIS IS SUBMITTED TO THE UNIVERSITY OF GHANA, LEGON IN
PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD OF
MASTER OF PHILOSOPHY ENTOMOLOGY DEGREE
INSECT SCIENCE PROGRAMME*
UNIVERSITY OF GHANA
LEGON
JULY, 2015
*Joint Inter- Faculty International Programme for the Training of Entomologists in
West Africa.
Collaborating Departments: Animal Biology and Conservation Science (School of
Biological Sciences) and Crop Science (School of Agriculture), College of Basic and
Applied Sciences
University of Ghana, Legon
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DECLARATION
This is to certify that this thesis, with exception of references to other works which have
been duly acknowledged, is the results of research work undertaken by me, Godfred
Nwosu Ezena, at the Forest and Horticultural Crops Research Centre (FOHCREC)
towards the award of Master of Philosophy (M. Phil.) degree in Entomology at the
African Regional Postgraduate Programme in Insect Science (ARPPIS), University of
Ghana, Legon.
GODFRED NWOSU EZENA
(STUDENT)
DR. CLEMENT AKOTSEN- MENSAH
(SUPERVISOR)
DR. KEN OKWAE FENING
(SUPERVISOR)
DR. ROSINA KYEREMATEN
(ARPPIS CO-ORDINATOR)
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DEDICATION
I dedicate this thesis to my dear wife, Mrs. Helena Ezena and my lovely daughters, Irene
Ifeoma Adomah Ezena and Jessica Nkechi Dansowaa Ezena, for their sacrifices during
this course. I was away and denied you of my comfort, yet you prayed for me to endure
all hardships to complete this programme. I say I would forever be grateful and God
bless you!
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ACKNOWLEDGEMENTS
I wish to express my sincere gratitude to the Almighty God for his numerous blessings,
divine protection and direction throughout my studies.
My profound gratitude also goes to Dr. Clement Akotsen- Mensah and Dr. Ken Okwae
Fening, my supervisors for suggesting this topic and I appreciate their valuable
criticisms, suggestions, corrections and support which have helped me greatly in
preparing this dissertation.
My special thanks also go to Mrs. Evelyn Opare, District Director of Agriculture, and my
colleague staff of MoFA, Gomoa West District Assembly, for their support and advice.
I am also grateful to the ARPPIS Coordinator, Dr. Rosina Kyerematen, and the thesis
Coordinator, Dr. M.K. Billah of African Regional Post-graduate Programme in Insect
Science (ARPPIS), Legon and all the lecturers for making my dream come true as an
Entomologist.
My deepest appreciation is extended to my wife, Helena Ezena, my daughters, Irene
Ifeoma Adomah Ezena and Jessica Nkechi Dansowaa Ezena and my mum, Mad.
Georgina Adomah and my entire family and Mr. Samuel Adu- Acheampong for their
support, love, encouragement and prayers throughout the study.
I also wish to express my sincere thanks to all friends and ARPPIS classmates especially
Angelina Fathia Osabutey, Charles Adzim Amankwah, Derrick Asante and Owusu
Fordjour Aidoo for their valuable contributions which sustained me throughout the
course.
I express my sincere appreciation to all FOHCREC staff especially Mr. C. Adu- Gyamfi
(Technician) and Mr. Isaac Amoh and also the inhabitants of FOHCREC. I finally say a
big thanks to Sampson Addae, Ruth Ansah, Musah, Attakora, Koby and all national
service persons.
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TABLE OF CONTENTS
Content Page
DECLARATION ................................................................................................................. i
DEDICATION .................................................................................................................... ii
ACKNOWLEDGEMENTS .............................................................................................. iii
TABLE OF CONTENTS .................................................................................................. iv
LIST OF TABLES .......................................................................................................... viii
LIST OF FIGURES ............................................................................................................ x
LIST OF PLATES ............................................................................................................. xi
LIST OF ABBREVIATIONS........................................................................................... xii
LIST OF APPENDICES................................................................................................. xiii
ABSTRACT .................................................................................................................... xiv
CHAPTER ONE ................................................................................................................. 1
1.0 GENERAL INTRODUCTION ............................................................................ 1
1.1 Background .......................................................................................................... 1
1.2 Problem statement ................................................................................................ 2
1.3 Justification .......................................................................................................... 3
1.4 OBJECTIVES ...................................................................................................... 6
1.4.1 Main objective .................................................................................................. 6
1.4.2 Specific objectives ............................................................................................ 6
CHAPTER TWO ................................................................................................................ 7
2.0 LITERATURE REVIEW ........................................................................................ 7
2.1 History of cabbage as an edible leafy vegetable .................................................. 7
2.2 Description and agronomy of the cabbage plant .................................................. 8
2.3 Cabbage production and their constraints in Ghana .......................................... 10
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2.4 Nutritional and health benefits of cabbage ........................................................ 11
2.5 Cabbage production as a source of employment ............................................... 12
2.6 Diseases of cabbage ........................................................................................... 13
2.7 Insect pests and other arthropods ....................................................................... 14
2.7.1 Diamondback moth, Plutella xylostella (L.) ............................................... 15
2.7.2 Cabbage aphid, Brevicoryne brassicae (L.) ............................................... 22
2.7.3 Cabbage looper, Trichoplusia ni (Hṳber) ................................................... 25
2.7.4 Cabbage webworm, Hellula undalis (F.) .................................................... 25
2.7.5 Cabbage flea beetle, Phyllotreta spp. ......................................................... 25
2.7.6 Variegated grasshopper, Zonocerus variegatus (L.) ................................... 26
2.8 Management of cabbage pests ........................................................................... 26
2.8.1 Biological control ....................................................................................... 26
2.8.2 Host plant resistance ................................................................................... 28
2.8.3 Mating disruption using sex pheromones ................................................... 28
2.8.4 Insecticides ................................................................................................. 29
2.8.5 Cultural practices ........................................................................................ 33
2.9 Use of botanicals and their importance in pest management ............................ 34
2.10 Common plants used as botanicals .................................................................... 38
2.10.1 Siam weed, Chromolaena odorata (Asteraceae) ......................................... 38
2.11 Neem tree (Azadirachta indica A. Juss) ............................................................ 40
2.11.1 Importance of neem as botanicals ............................................................ 42
CHAPTER THREE .......................................................................................................... 44
3.0 MATERIALS AND METHODS ....................................................................... 44
3.1 Study location .................................................................................................... 44
3.2 Preparation of treatments ................................................................................... 44
3.2.1 Preparation of Chromolaena odorata leaf extracts .................................... 45
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3.2.2 Preparation of neem seed extracts .............................................................. 45
3.3 Field experiment ................................................................................................ 46
3.3.1 Nursery establishment ................................................................................ 46
3.3.2 Land Preparation, field layout and transplanting ........................................ 46
3.4 Experimental design, treatments and agronomic practices ................................ 47
3.5 Data collection, yield and damage assessment .................................................. 47
3.5.1 Data collection ............................................................................................ 47
3.5.2 Multiple head formation and head damage assessment .............................. 48
3.5.3 Yield assessment ......................................................................................... 49
3.6 Cost- benefit Assessment ................................................................................... 50
3.6.1 Costs of treatments ..................................................................................... 50
3.6.2 Assessment of economic benefits ............................................................... 51
3.7 Data Analyses .................................................................................................... 51
3.7.1 Field experiments ........................................................................................ 51
3.7.2 Economic analysis ...................................................................................... 52
CHAPTER FOUR ............................................................................................................ 53
4.0 RESULTS .......................................................................................................... 53
4.1 Insect fauna found on cabbage field during the growing seasons...................... 53
4.1.1 Observed damage caused by the major pests on cabbage during the study
period .................................................................................................................... 54
4.2 Effects of botanicals and conventional insecticides on insect pest populations 59
4.3 Effects of treatments on natural enemies ........................................................... 61
4.4 Effects of treatments on cabbage head damage ................................................. 63
4.5 Effects of treatments on cabbage multiple head formation ................................ 64
4.6 Effects of treatments on marketability of cabbage ............................................. 65
4.7 Effects of treatment on weight of cabbage head ................................................ 67
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4.8 Economics of cabbage production ..................................................................... 68
4.8.1 Yield and income ........................................................................................ 68
4.8.2 Cost: benefit ratio ....................................................................................... 69
CHAPTER FIVE .............................................................................................................. 72
5.0 DISCUSSIONS .................................................................................................. 72
5.1 Effects of the treatments on insects population ................................................. 72
5.2 Effects of treatments on natural enemies population ......................................... 74
5.3 Effects of treatments on cabbage head damage ................................................. 75
5.4 Effects of treatments on multiple heads formation ............................................ 75
5.5 Effects of treatments on marketability of cabbage ............................................. 76
5.6 Effects of treatments on weight of cabbage head .............................................. 76
5.7 Cost: benefit ratio ............................................................................................... 77
CHAPTER SIX ................................................................................................................. 79
6.0 SUMMARY AND CONCLUSION................................................................... 79
REFERENCES ................................................................................................................. 80
APPENDICES ................................................................................................................ 109
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LIST OF TABLES
Table 1: Some major insect pests of cabbage in Ghana…………………………… 14
Table 2: Pesticides used by farmers in Ghana to control insect pests on cabbage.... 32
Table 3: Some plants traditionally used to control pests and diseases …………..... 36
Table 4: Modified scale of Dreyer, M. used for damage scoring on cabbage
varieties at Kabete field station, Togo…………………………………… 49
Table 5: Insect pests of cabbage found during the experiments…………………. 53
Table 6a: Mean (±S.E) populations of insect pests on cabbage sprayed with
botanical and conventional insecticides and tap water as control
during 2014 major rainy season………………………………………… 60
Table 6b: Mean (±S.E) populations of insect pests on cabbage sprayed with
botanical and conventional insecticides and tap water as control
during 2014 minor rainy season………………………………………… 61
Table 7a: Mean (±S.E) numbers of natural enemies of pests of cabbage
sprayed with botanical and conventional insecticides during 2014
minor rainy season……………………………………………………..…62
Table 7b: Mean (±S.E) numbers of natural enemies of pests of cabbage
sprayed with botanical and conventional Insecticides during 2014
major rainy season…………………………………………….………… 63
Table 8: Mean (±S.E) scores for cabbage head damage during 2014 major and minor
seasons……………………………………… ………….……………….. 64
Table 9: Mean (±S.E) of number of multiple heads, weight of cabbage heads and
yield of cabbage under different spray treatments during 2014 major rainy
season…..………………………………………………………………… 67
Table 10: Mean (±S.E) of number of multiple heads, weight of cabbage heads
and yield of cabbage under different spray treatments during 2014 minor
season.……………………………………………………….………........ 68
Table 11: Evaluation of cost and benefit in managing cabbage pests with
crude water extracts of siam weed, neem and sunhalothrin® during
2014 minor rainy season........................................................................... 70
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Table 12: Evaluation of cost and benefit in managing cabbage pests with crude water
extracts of siam weed, neem and sunhalothrin®, during 2014 major rainy
season…………………………………………………………………….. 71
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LIST OF FIGURES
Figure 1: Effects of treatments on cabbage multiple heads formation during 2014 major
and minor cropping seasons ...................................................................................... 65
Figure 2: Effects of the various treatments on the mean yield of cabbage head
marketability in the major season. ............................................................................ 66
Figure 3: Effects of the various treatments on the mean yield of cabbage head
marketability in the minor season. ............................................................................ 66
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LIST OF PLATES
Plate 1: The cabbage plant .................................................................................................. 8
Plate 2: Life cycle of diamondback moth ......................................................................... 16
Plate 3: Siam weed plant (Chromolaena odorata) ........................................................... 40
Plate 4: Fresh neem seeds ................................................................................................. 41
Plate 5: Aphids infestation observed on a cabbage plant during the experiment ............. 54
Plate 6: Cabbage webworm attacking the apical meristem of a young cabbage seedling.
................................................................................................................................. 55
Plate 7: Hellula undalis attacking a developing cabbage leaf. ......................................... 56
Plate 8: Leaf damage caused by a variegated grasshopper on cabbage. ........................... 57
Plate 9: A millipede causing damage to cabbage. ............................................................ 58
Plate 10: A snail feeding on the cabbage leaf ................................................................... 58
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LIST OF ABBREVIATIONS
ANOVA Analysis of variance
ARPPIS African Regional Postgraduate Programme in Insect Science
Bt Bacillus thuringiensis
DBM Diamondback moth
DDT Dichlorodiphenyltrichloroethane
EC Emulsifiable Concentrate
FOHCREC Forest and Horticultural Crops Research Centre
GH¢ Ghana cedis
GMT Greenwich Meridian Time
Ha Hectare
IPM Integrated Pest Management
NPM Non- pesticide management
PSBs Pods Sucking Bugs
SE Standard error
Ton Tonne
TRT Treatment
US$ United State Dollars
WAT Weeks after transplanting
WHO World Health Organization
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LIST OF APPENDICES
Appendix 1: ANOVA for the effects of botanicals and conventional insecticides on
insect pest population in the major and minor seasons ........................................... 109
Appendix 2: ANOVA for the effects of the treatments on the natural enemies in the
minor and major seasons ......................................................................................... 112
Appendix 3: ANOVA for the effects of treatments on cabbage head in the major and
minor seasons .......................................................................................................... 115
Appendix 4: ANOVA for the effects of treatments on multiple head formation in the
major season and minor seasons ............................................................................. 116
Appendix 5: ANOVA for the effects of treatments on marketable and unmarketable
cabbage heads in the major and minor seasons ....................................................... 117
Appendix 6: ANOVA for the effects of treatments on weight and total yield of cabbage
head in the major and minor seasons ...................................................................... 119
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ABSTRACT
Cabbage is an important crop for many smallholder farmers in Africa and Asia, due to its
nutritional and financial benefits. It is one of the popular vegetables consumed and
cultivated by both urban and rural dwellers in Ghana. The production of cabbage in
Ghana, however, is faced with numerous constraints especially insect pest infestations.
Farmers have limited control options and therefore resort to the use of synthetic
insecticides. Indiscriminate use of these insecticides has led to insect pest resistance
problems, and also toxic residues in cabbage heads, posing high risk to humans, animals
and the environment. Botanicals, which are derived from plant products are reported to
be effective against many insect pests and are considered cheap, easily degradable and
environmentally safe. Field experiments were carried out to determine the insecticidal
potentials of siam weed, Chromolaena odorata L. at different rates (10, 20 and 30 g/L)
in the management of the major pests of cabbage and its effect on their natural enemies
during the major and minor seasons of 2014. The treatment consisted of three doses of C.
odorata (10, 20 and 30g/L of water), 50 g/L of neem seed extract (as standard botanical),
a conventional insecticide, Sunhalothrin® (with active ingredient Lambda cyhalothrin,
EC) and tap water as a control. The treatments were laid out in randomized complete
block design (RCBD) with three replications. The numbers of insect pests were recorded
weekly on eight innermost cabbage plants per plot from transplanting until maturity. At
maturity, cabbage heads obtained from each treated plots were counted and weighed and
then classified as marketable or unmarketable depending on the level of damage. Cost-
benefit analyses of the different management options were also carried out. The
diamondback moth (DBM), Plutella xylostella L. occurred only during the minor rainy
season. The three rates of C. odorata had significantly lower number of aphid,
Brevicoryne brassicae L. as compared to the Sunhalothrin. The 10 and 20g/ L of C.
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odorata sprayed plots recorded the highest build up of natural enemy populations as
compared to 30g/ L of C. odorata and Sunhalothrin during the major rainy season. The
cabbage plots sprayed with neem seed extract and siam weed extract (especially 10 and
20 g/L of water) had the highest yield, followed by the 30g/ L C. odorata and
Sunhalothrin treated plots and the control The study also indicated that, the neem seed
extract treated plots had the highest cost- benefit ratio followed by 20, 10 and 30g/L C.
odorata treated plots, with the Sunhalothrin treated plots being the least. The findings
from the current study, therefore, attest to the potential of 10 and 20g/ L of C. odorata as
effective and economically feasible option for the management of insect pests of cabbage
and other related vegetables, especially in smallholder farms and backyard gardens and
other organic farming systems.
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CHAPTER ONE
1.0 GENERAL INTRODUCTION
1.1 Background
Cabbage, Brassica oleracea var. capitata (L.) originated from the Mediterranean Region,
Southern England, Wales and Northern France (Norman, 1992). It belongs to the family
Cruciferae and is cultivated from the arctic to sub-tropic and at higher altitudes in the
tropics as well as in the tropical lowlands on the West African coast (Hill, 1983).
Cabbage is a very important vegetable produced in mostly the southern parts of Ghana and
is consumed by both the rural and urban populations (Obeng-Ofori and Ankrah, 2002). The
crop has replaced many indigenous green vegetables and is now cultivated all year round
on mainly rented lands in the urban centers, and near streams in the peri-urban and rural
areas (Timbilla, 1997; Timbilla and Nyarko, 2004; Fening et al., 2013, 2014). The
cultivation of cabbage provides a good source of employment for both rural and urban
dwellers (Norman, 1992). Furthermore, middlemen who purchase the vegetable from farms
and send it to the urban centres as well as transport operators who convey the heads to the
market centres, all obtain their source of livelihood from the crop (Asare- Bediako et al.,
2010).
Cabbage has traditionally been used to cure certain ailments as well as for food. It has anti-
inflammatory property and contains chemicals which can prevent cancer (Lin, 2008). The
ancient Greeks used fresh white cabbage juice to relieve sore or infected eyes and juice
from the cabbage stem is a good remedy for ulcers (Norman and Shealy, 2007).
Traditionally, the Romans and Egyptians drink cabbage juice before big dinners to prevent
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intoxication from alcohol (Lin, 2008). Cabbage seeds are also believed to prevent
hangovers (Norman and Shealy, 2007).
1.2 Problem statement
Cabbage production, like many other crops is faced with numerous constraints. These
include high cost of inputs such as pesticides, seeds, fertilizers and also attack by insect
pests and diseases (Fening et al., 2013, 2014). Among these production constraint, insect
pests and diseases are the most important factors that reduce the quality and marketable
yield of cabbage (Timbilla and Nyarko, 2004). Insect pests and diseases can devastate
cabbage to a nearly zero yield. For instance, the diamondback moth (DBM), Plutella
xylostella L. (Lepidoptera: Plutellidae) is the most important pest of cabbage in Ghana
(Obeng-Ofori and Ankrah, 2002; Timbilla and Nyarko, 2004). This insect is one of the
greatest threats to crucifer production in the tropics causing over 90% crop losses
(Charleston, 2004). The cabbage webworm, Hellula undalis L. (Lepidoptera: Pyralidae)
and cabbage aphids, Brevicoryne brassicae L. (Hemiptera: Aphididae) are also important
pests of cabbage in Ghana (Ninsin, 1997).
Moreover, damages caused by these insect pests have over the years been reduced by
various synthetic insecticides which are applied at different stages of the plant‟s growth
(Ninsin, 1997). It is well established that, pesticides play a major role for the production of
adequate and high yielding food, especially vegetables for an increasing world population
through the control of insects and insect-borne diseases. Many synthetic insecticides are
however, toxic and persistent (Kluive, 1981). These synthetic insecticides cause
toxicological and environmental problems which include toxic residues in food, soil, water,
adverse effects on non-target insects and other beneficial organisms, as well as the
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development of resistant strains in insect pests (Ninsin, 1997; Amoako, 2010; Fening et al.,
2013). The indiscriminate and improper use of synthetic insecticides has been an issue of
much concern to consumers (Fening et al., 2013; Fening, 2013). Typical examples of
insecticides used are Polythrine C® and Cypercal 50 EC® (Barbara, 1993; Amoako, 2010).
1.3 Justification
Vegetable farmers frequently apply synthetic insecticides to manage DBM, cabbage aphid
and other prevalent insect pests of cabbage (Grzywacz et al., 2010; Gerken et al., 2001;
Macharia et al., 2005) because they are quick in action and are easy to apply and less
labour intensive (Weinberger and Srinivasan, 2009). There has been an increase in the
resistance of DBM and other insect pests of cabbage to insecticides in recent times, making
their management difficult (Obeng-Ofori and Ankrah, 2002; De Cássia Seffrin et al., 2010).
Synthetic insecticides have also been associated with health hazards to humans and
animals, environmental pollution and are unavailable to many peasant farmers such as
those in the Ghana‟s rural communities (Devanand and Rani, 2008, De Cássia Seffrin et al.,
2010; Fening, et al., 2013). Synthetic insecticides are often mishandled and misapplied
especially by inexperienced farmers (Ntow et al., 2006; Coulibaly et al., 2007; Fening et
al., 2013).
In order to avoid the negative impacts of these synthetic insecticides, alternative approaches
to managing pests of cabbage and other vegetables have to be considered (Ntow et al.,
2006, Coulibaly et al., 2007; Fening et al., 2013; Amoabeng et al., 2013). Botanical
insecticides can be a good option to promote sustainable pest management because they
have lower environmental impact than synthetic insecticides (Devanand and Rani, 2008;
Rath and Gopalakrishnan, 2006). However, botanical insecticides such as pyrethrum and
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azadirachtin are relatively expensive and difficult for most smallholder farmers to obtain
(Amoabeng et al., 2013). To provide a viable alternative for resource- poor farmers,
botanical insecticides must be based on plant materials that are cheap and readily available
and can simply be prepared rather than requiring organic solvents and complex apparatus
(Fening et al., 2013). Also, extracts from plant materials have to be benign to natural
enemies in order to avoid secondary and resurgent pests, as well as having low
phytotoxicity whiles protecting yields (Fening et al., 2013). Though simple, plant extracts
are commonly promoted for use in home gardens, so there is growing interest for use by
farmers in developing countries (Amoabeng et al., 2013).
Some plant species which have useful insecticidal properties are in the families of
Meliaceae, Rutaceae, Asteraceae, Piperaceae, Compositae, Lamiaceae, Euphorbiaceae,
Combretaceae and Annonaceae (Amoabeng et al., 2013). Some of these species are also
considered as weeds in and around farms (Devanand and Rani, 2008). Pest control using
local materials offers farmers the opportunity to reduce production costs, as the plants often
grow wild in and around farms and so can be obtained with little effort and zero or minimal
cost (Amoabeng et al., 2013).
Siam weed, Chromolaena odorata (L.) (Asteraceae), an invasive shrub is believed to have
originated from South America and the Caribbean (McFadyen, 1988). It was first reported
in Ghana in 1969 (Hall et al., 1972) and has since spread to cover about 60% of the land
area of the country (Timbilla and Braimah, 1996). It is particularly, prominent in areas with
an annual rainfall of about 2000 mm and has become a major weed of arable land and
plantation crops, forests and rangelands. Chromolaena odorata grows very fast and
smothers other vegetation beneath it by forming dense thickets or canopies that are difficult
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to penetrate. The plant is known by several local nicknames such as „Acheampong‟, „Busia‟
and „Abaafo‟ across its range in Ghana (Timbilla and Braimah, 1996).
The introduction of C.odorata has brought new challenges to bear on agricultural
productivity in Ghana. For instance, the management of C. odorata in plantation crops such
as cocoa, oil palm and citrus is reported to contribute to about a third of the cost of
production of such plantations (McFadyen, 1988). The high cost of plantation maintenance
and other problems associated with the management of this weed have forced some farmers
to abandon their plantations (Timbilla and Braimah, 1996). Chromolaena odorata has also
contributed significantly to the recent forest fires in the country because it produces large
quantities of dry leaf litter, stems and twigs that contain chemicals which act as fuel for
fires (Braimah and Timbilla, 1991).
However, C. odorata when utilized as a botanical has proven to be effective against pods-
sucking bugs (PSBs) infestation in the savannah region of Northern Nigeria, and this, can
sustain greater cowpea yield (Degri et al., 2013). Chromolaena odorata can therefore serve
as a better alternative to synthetic insecticides usage for managing the populations of pod
sucking bugs (PSBs) on cowpea. It has been considered advantageous, because they are
readily available and bio-degradable bio-insecticides which are friendly or safe to the
applicators, farmers, consumers and the environment (Degri et al., 2013).
However, some botanical insecticides may also adversely affect beneficial insects (Buss
and Park-Brown, 2002; Dubey et al., 2011). For example, Amoabeng et al., (2013) have
indicated that 30 g/L of C. odorata applied in controlling DBM larvae in the field among
other botanicals was effective in reducing the pest population. However, this rate of C.
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odorata was found to significantly reduce the population of natural enemies in the field
(Amoabeng et al., 2013). Fening et al., (2011), also cautioned that, higher concentrations of
botanicals could possibly have some detrimental effect on natural enemy populations
because their numbers reduced with increasing concentrations. Hence, the need to optimize
the dose of crude extract from C. odorata for effective control of major pests of cabbage
with minimal or no adverse effect on the natural enemies of these pests and other non-target
organisms.
1.4 OBJECTIVES
1.4.1 Main objective
The main aim of this study was to optimize the dose of Chromolaena odorata leaf extract
to manage the major pests of cabbage and also ensure the survival of their natural enemies.
1.4.2 Specific objectives
1. To assess the performance of three rates of crude extracts of siam weed to manage
insect pests of cabbage.
2. To ascertain the effect of the different rates of the siam weed extract on the natural
enemies and other non-target organisms in the field.
3. To determine a cost- benefit analysis for the use of siam weed as a local botanical
insecticide.
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CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 History of cabbage as an edible leafy vegetable
The cabbage plant is native to the mediterranean region of Europe and it is somewhat
similar in appearance to a leafy canola plant (Andongma, 2010). The cultivation of the
plant started soon after the domestication of plants began (Sinnadurai, 1992).The people of
the Mediterranean region began growing the first ancient cabbage plant as a leafy
vegetable. Because leaves are the part of the plants which are consumed, plants with the
large leaves were selectively propagated (Obeng- Ofori, 1998). This resulted in large and
larger-leafed plants slowly being developed as the seed from the largest-leafed plants were
favoured. By the 5th century B.C., continued preference for ever-larger leafed plants had led
to the development of the vegetable we now know as Kale. Kale is known botanically as
Brassica oleracea variety acephala which translates to mean cabbage, of the vegetable
garden without a head. Kale has since been grown as a leafy vegetable for thousands of
years (Baldwin, 1995).
The crop was probably introduced by the British into Ghana (Sinnadurai, 1992). There is no
record of the time of its introduction but the crop was grown on a small scale around 1940.
It is still not a popular crop in the rural areas. It is a popular crop around urban towns and
cities where the bulk of the crop is produced for Ghanaians and foreigners in the country
(Obeng- Ofori et al., 2007). Cultivars such as Copenhagen Market, Drumhead, Suttons
Tropical, Japanese Hybrid cabbage, Golden Acre, Suttons Pride of the Market, KK Cross,
Oxylus and Marion Market are suitable for production in Ghana (Obeng- Ofori et al.,
2007).
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2.2 Description and agronomy of the cabbage plant
Cabbage (Brassica oleracea var capitata L.) is the most important vegetable in the family
Cruciferae. The edible portion is called the head which is made up of many overlapping
thin smooth leaves covering a small terminal bud (Sinnadurai, 1992). The head forms
halfway through the growth of the plant and thus is not seen in young seedlings. When the
head is removed, buds arise in the axils of the lower leaves and these may form small heads
called “cabbage sprouts” or multiple heads and do not have any commercial market value
(Obeng- Ofori et al., 2007).
Cabbage could be described as a very large terminal bud with foreshortened stem and
tightly packed in rolled leaves (Plate 1). If flowering is allowed to occur there are
appropriate internodes elongations terminating in the formation of an inflorescence. The
head shape may be pointed or round and the leaf colour and shape are variable (Rice et al.,
1993; Andongma, 2010).
Plate 1: The cabbage plant.
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Cabbage like other brassicas is grown from the seed. The seeds can both be sown in a
seedbed and later pricked - out on to a nursery bed or sown directly in the nursery bed
(Schmutterer, 1992). Close spacing of the seedlings in the nursery can cause the hypocotyls
to elongate and such seedlings will not stand erect when transplanted in the field. Close
spacing may also cause damping - off disease which enhances insect infestation. Seedlings
may be ready for planting about 21 to 30 days after nursing. Nursery beds should be
manured and sterilized before sowing the seed. Shade the nursery immediately after sowing
and remove the shade after the seedlings have emerged. Hardening of seedlings before
planting is essential when the crop is to be grown under rainfed conditions. Spacing in the
field will depend on the cultivar (Obeng- Ofori et al., 2007).
Cabbage is a cool season crop which prefers a cool moist climate with a monthly average
temperature of 15oC to 22oC (Hill, 1983). When the temperature is high, small heads are
produced. However, varieties have been bred which produce large heads under high
temperature in the warm tropics. In the warm tropics like West Africa, the head will crack
when mature and eventually deteriorate without flowering. Cabbage as a vegetable is
treated as an annual crop. In West Africa, the growing season is during the cool months
from July to September in the South as a rain fed crop and from November to January as an
irrigated crop. It can be grown during the same period in the north. In the forest zone, three
crops a year have been in low - lying areas with supplementary irrigation (Hill, 1983;
Obeng- Ofori et al., 2007).
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2.3 Cabbage production and their constraints in Ghana
Cabbage is an important exotic vegetable grown on both large and small scale farms in
Ghana (Obeng- Ofori, 1998). In Ghana, it is a popular vegetable among urban and peri-
urban dwellers (Timbilla and Nyarko, 2004). Fresh vegetable production farms for city
residents are located on outskirts of cities or cleared areas in highlands accessible from the
cities. Production of healthy looking and damage free cabbage for wealthy city dwellers are
important considerations in cultivation of cabbage (Talekar and Shelton, 1993). Insecticides
are frequently used for the control of insect pests. The sole reliance on insecticides for the
control of insect pests can result in the rapid build- up of resistance (Andongma, 2010).
Cabbage production can be a very profitable activity, with a quick return on investment
(Mochiah, et al., 2011a). The total harvesting period for cabbage in the field varies from 3
to 4 months, but some varieties can be harvested in about 70 days after transplanting
(Obeng- Ofori et al., 2007). There is no seed recycling but the total seed cost for cabbage
production represents only 5% of the farmers‟ total costs (Mochiah et al., 2011a).
Meanwhile, fertilizers and insecticides together account for 17% of the total expenses and
labour cost is 60%, with a high proportion being family labour (Horna et al., 2007). The
main activities are nursery management, land preparation, transplanting, weeding, watering
and harvesting. Cabbage production tends to be very intensive with high levels of pesticides
and fertilizers applied which can run off into drinking water sources (Obeng- Ofori et al.,
2007). Producers usually use low quality water from drains, shallow wells and streams to
irrigate their fields (Horna et al., 2007). Cabbage marketing and prices are determined by
the seasonality of demand (Obeng- Ofori et al., 2007). Cabbage demand peaks around
December festivities and continues throughout the dry season (Mochiah, et al., 2011b). The
compact head of Oxylus is the most preferred variety and transports and also stores well.
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Lack of variety diversity however, is a problem that needs to be addressed (Obeng- Ofori,
1998; Horna et al., 2007).
Although cabbage has enormous benefits to the growth of humans and the nation as a
whole, its production is associated with a lot of problems. These include difficulty in land
acquisition; high cost of inputs such as fertilizers; labour; lack of good water for irrigation;
high weed infestation and attack by diseases and insect pests (Obeng- Ofori, 1998).
Prominent among these problems in Ghana is pest attack. These pests include aphids,
Brevicoryne brassicae, Bagrada bug, Bagrada hilaris, flea beetles, Phyllotreta sp.,
diamondback moth, Plutella xylostella and cutworm, Agrotis sp. (De Lannoy, 2001). The
most devastating pest that causes severe damage in cabbage production is the diamondback
moth (DBM) (Kwarteng and Towler, 1994). Pest infestation normally leads to reduction in
market value and in some cases total crop failure (Joel, 1994).
2.4 Nutritional and health benefits of cabbage
Cabbage is a good source of protein, carbohydrates, calcium, iron, carotene, thiamine,
riboflavin, niacin, as well as vitamin C (De Lannoy, 2001). Cabbages can also serve as food
for cattle, pigs and other farm animals. Mashed and juiced cabbage used in poultices has
helped to treat boils, warts, pneumonia, appendicitis and ulcers (Hatfield, 2004).
Tindall (1983) listed the nutritive components of cabbage leaves per 100g edible portion as
follows: water – 93ml, calories – 23J, protein – 1.5g, fat – 0.2g, carbohydrates - 4g, fibre –
0.8g, calcium – 40mg, iron – 0.5, vitamin potency – 30iu, thiamine –0.05mg, riboflavin –
0.05mg, niacin – 0.3mg and ascorbic acid – 40mg.
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Cabbage has been used daily in dishes as a relish and has curative benefits such as in the
control of bronchitis, cataracts, diabetes, Cronhn‟s disease, diverticular diseases, heart
attack and hypertension (Reuben et al., 2006).
A study in Utah revealed that those who ate more cruciferous vegetables had a much lower
risk of colon cancer (Lin, 2008). On the side of caution, however, consuming excessive
amount of cabbage may contribute to thyroid problems, possibly goiter (Nisit et al., 2006).
A well-known remedy for healing peptic ulcers is drinking cabbage juice (Allen and Allen,
2009). It has been known for the past 20 years that phytonutrients work as antioxidants to
disarm free radicals before they can damage DNA cell membrane and fat containing
molecules such as cholesterol (Norman and Shealy, 2007). Now, new research is revealing
that phytonutrients in crucifers such as cabbage work at a much deeper level (Nisit et al.,
2006). These compounds actually signal our genes to increase production of enzymes
involved in detoxification (Allen and Allen, 2009). Recent studies show that those eating
more cruciferous vegetables have a much lower risk of prostate, colorectal and lung cancer-
even when compared to those who regularly eat other vegetables (Lin, 2008).
2.5 Cabbage production as a source of employment
Cabbage provides a source of livelihood to all individuals who are engaged in its
production from its cultivation till it gets to the final consumer (Sinnadurai, 1992; Asare-
Bediako et al., 2010).
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2.6 Diseases of cabbage
Cabbage is not only affected by insect pests but also diseases. Although there are many
diseases that affect cabbage, only a few are prevalent or cause much damage (Rice et al.,
1993). Diseases in plants occur when a pathogen is present, the host is susceptible, and
when the environment is favourable for the disease to develop (Guerena, 2006). Altering
any one of these three factors may prevent the disease from occurring. Organisms
responsible for plant diseases include fungi, bacteria, nematodes, and viruses (Obeng- Ofori
et al., 2007). If these organisms are present, then the manipulation of the environment and
the host may make it less susceptible and help it to be more sustainably managed, causing
the diseases on cabbage and other brassica crops (De Lannoy, 2001; Obeng- Ofori et al.,
2007).
Some common diseases of cabbage and other brassicas include; black rot and soft rot which
are caused by bacteria, Xanthomonas campestris and Erwinia carotovora respectively.
These bacteria occur as a result of infection on seeds, on crop residue in the field, or on
weeds in or near the field and under favourable weather conditions. These diseases cause
large V-shaped spots on the edges of the leaves. These spots have a yellow margin, and the
veins in the spots are black. In severe cases, the whole leaves may be blighted causing great
reduction in yield (Guerena, 2006).
Other diseases of cabbage are mostly caused by fungi. These include; Downy mildew,
Fusarium wilt, Damping off and Alternaria leaf spot. Most of these diseases are favoured
by wet weather conditions and have caused stunted growth in the crop and also caused
large grayish- black ringed spots on the leaves down to the stem, making the crop
unmarketable (Ninsin, 1997).
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2.7 Insect pests and other arthropods
Like other brassicas, cabbage has a wide spectrum of pests. The continuous cultivation of
the crop has led to the proliferation of insect pests such as Hellula undalis (Fab.)
(Lepidoptera: Pyralidae), Plutella xylostella (L.) (Lepidoptera: Plutellidae) and Brevicoryne
brassicae (L.) (Hemiptera: Aphididae) (Timbilla, 1997). Obeng- Ofori et al., (2007) have
listed the major types of insect pests of cabbage in Ghana (Table 1). These include aphids
which transmit viral diseases and leaf eating caterpillars, which can completely defoliate
plants during severe attacks.
Table 1: Some major insect pests of cabbage in Ghana
Scientific Name Common Name Order Family
Plutella xylostella Diamondback moth Lepidoptera Plutellidae
Brevicoryne brassicae Cabbage Aphid Hemiptera Aphididae
Hellula undalis Cabbage webworm Lepidoptera Pyralidae
Athalia sjostedti Cabbage sawfly Hymenoptera Tenthredinidae
Phyllotreta spp. Cabbage flea beetle Coleoptera Chrysomelidae
Source: Obeng- Ofori et al., (2007).
Other pests of cabbage reported in Ghana include the cabbage looper, Trichoplusia nii, the
whitefly, Bemisia tabaci and the variegated grasshopper, Zonocerus variegatus (Mochiah et
al., 2011b; Fening et al., 2011; Baidoo et al., 2012). In 1970, Nigeria declared Z.
variegatus a major pest and subsequently it had become a problem in Cote D‟ Ivoire,
Ghana, Congo, Benin, Uganda, Senegal and Burkina Faso (Modder, 2004).
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2.7.1 Diamondback moth, Plutella xylostella (L.)
Plutella xylostella is one of the most important pests of cruciferous crops throughout the
world, and can cause serious economic losses if not controlled (Talekar and Shelton, 1993).
In the warm, humid tropics, this insect breeds throughout the year, and can have more than
ten generations annually. The destructiveness of DBM, coupled with the fact that it has the
capacity to develop resistance very rapidly to any chemical control measure used singly,
has made this pest the focus of IPM research in many parts of the tropical world.
Practically, all the available methods and pest control technologies have been tried at some
time or another for the management of DBM (Glare and O‟Gallagham, 2000). The global
cost of controlling this pest has recently been estimated between 4 and 5 billion US dollars
(Zalucki et al., 2012).
2.7.1.1 Biology
Life cycle of diamondback moth is dependent upon temperature, and typically it completes
its life cycle in about 25-30 days (Harcourt, 1957)(Plate 2). It is not known whether any of
the life stages of diamondback moth undergoes diapauses or hibernate (Talekar and
Shelton, 1993).
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Source: A. M. Varela. Icipe
Plate 2: Life cycle of diamondback moth.
2.7.1.2 Egg stage
The egg is minute, yellowish white to yellowish green cylindrical to oblong with average
dimensions of 0.48 x 0.25mm (Bhallaa and Dubey, 1986). The incubation period ranges
from three to six days depending on the temperature (Talekar and Shelton, 1993).
2.7.1.3 Larval stage
The larvae are gray-green with a dark head in the first three instars and green with greenish
brown head in the final instars, measuring 10-12mm in length and moderately stout, and
smooth with short scattered hairs (Bhallaa and Dubey, 1986). The larval body form tapers
at both ends, and a pair of protruding prolegs from the posterior end, forming a distinctive
"V" shape and the prolegs are five in pairs (Harcourt, 1957). The diamondback moth has
four instars: the range of days per instar is 3-7; 2-7; 2-8, and 2-10 for the 1st - 4th instar
(Talekar and Shelton, 1993). Overall, length of each instar rarely exceeds 1.7, 3.5, 7.0, and
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11.2 mm, respectively, for instars 1 through 4. Mean head capsule widths for these instars
are about 0.16, 0.25, 0.37, and 0.61 mm (Harcourt, 1957).
The first instar larvae initially wonder over the leaf surface and feed as the miners, whereas
older larvae feed from the lower leaf surface by scraping the epidermis of the crucifer
plants and usually consume all tissue except the wax layer on the upper surface, thus
creating a “window” in the leaf (Bhallaa and Dubey, 1986; Talekar and Shelton, 1993). The
fourth instar larvae, consume the largest quantity of leaf tissue (Salinas, 1986). At the
slightest disturbance, the larvae wriggle rapidly and drop down from the leaf, suspending
themselves by silken threads (Bhallaa and Dubey, 1986).
2.7.1.4 Pupal stage
The mature caterpillar forms a loose silken cocoon. As a result, its body becomes shortened
longitudinally but remains active (Bhallaa and Dubey, 1986). The mature pupae are 6mm
long and light in colour. The pupal stage is between 7 to 11 days (Salinas, 1986). The
newly formed pupa is yellowish green, but in a day or two it becomes brown in color until
the time of adult emergence (Bhallaa and Dubey, 1986).
2.7.1.5 Adult stage
The adult is a small, slender, grayish-brown moth with pronounced pair of antennae. It is
about 10-12 mm long, and marked with a broad cream or light brown band along the back.
The band is sometimes constricted to form one or three light-coloured diamonds on the
back when in rest position, which is the basis for the common name of this insect. When
viewed from the side, the tips of the wings turn upward slightly. Adult males and females
live about 12 and 16 days, respectively (Harcourt, 1957), and for 3 to 6 days without food
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and for 11 to 16 days provided with food (Salinas, 1986). Adults emerge during the evening
and rarely in the morning hours. Females deposit eggs for about 10 days. Some moths may
be weak fliers, but populations are known to migrate long distances (Talekar and Shelton,
1993). However, they are readily carried by the wind (Harcourt, 1957).
The male moth is dark brown with a pattern of three consecutive white diamonds on its
back. The female moth is tan coloured and its diamond patterns are less distinct than those
of the male (Borror et al., 1992). Adults are active at dusk and throughout the night. During
the day if plants is disturbed the moth would be seen flying from their resting places
(Talekar and Shelton, 1993).
Salinas (1986) reported the adults started copulating almost immediately after emerging
from the pupae because the females produce a strong sex pheromone, which attracted the
male. The individuals copulating pair face opposite directions and hang downwards with
the female above. Mating lasts one to two hours with the females mating only once.
Oviposition begins in the evening; the majority of the eggs are laid before midnight with
peak oviposition occurring between 19:00-20:00 hours (Talekar and Shelton, 1993). The
ratio of eggs laid on the upper and lower leaf surfaces is approximately 3:2 and very few
eggs laid on stems and petioles (Harcourt, 1957). Eggs are laid preferentially in the cavities
of leaves rather than on the smooth surface. Temperature, trichomes and waxes on leaf
surface all influence oviposition (Talekar and Shelton, 1993).
The oviposition period lasts three to ten days depending on environmental conditions and
peak oviposition occurs on the first day of emergence (Salinas, 1986). The fecundity of
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diamondback moth depends on many factors including genetic and nutritional condition of
the larvae, morphological nature of the host plant, climatic conditions, and the presence or
absence of host plants for oviposition (Salinas, 1986). Fecundity as low as 18 eggs, and as
high as 306 eggs per female was reported by some workers (Chelliah and Srinivasan, 1986;
Talekar and Shelton, 1993). The incubation period is influenced mainly by temperature and
lasts 5 to 6 days (Talekar and Shelton, 1993).
2.7.1.6 Ecology of Diamondback moth
Diamondback moth occurs wherever crucifers are grown and is believed to be the most
universally distributed of all Lepidoptera (Talekar and Shelton, 1993). There are numerous
insects, which, like diamondback moth have a worldwide distribution. These cosmopolitan
insects have certain common characteristics, which enable them to survive in the varying
climatic conditions present over wider areas of their distribution. Besides, the potential to
colonize under varying conditions, their strong dispersal or migrating capacity is
indispensable to the increase of their distribution range (Chu, 1986). Although the origin of
diamondback moth is not clear, judging from its close relationship with the cruciferous
plants it is assumed that this insect originated in Asia Minor (Talekar and Shelton, 1993).
There the moth further spread to other areas with the increase of cultivation of cruciferous
vegetables.
Generally, the strong flight ability of the moth helped its distribution to even wider areas
(Harcourt, 1957). This moth can remain in a continuous flight for several days and cover
distance of 1000 Kms per day (Talekar and Shelton, 1993). Wind is reported to be a major
factor in diamondback moth migration from one area to the other (Chu, 1986; Honda, 1992;
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Talekar and Shelton, 1993). Honda (1992) suggested that density of source population,
meteorological conditions when the adults take off, the physiological condition of the
migrants and the temperatures of the upper air in which they migrate affect diamondback
moth migration. Seedlings contaminated with diamondback moth were reported as sources
of infestation in the United States (Talekar and Shelton, 1993). The presence of crucifers
throughout the year in the tropics and subtropics allows the pest to be active throughout the
season and hence the simultaneous occurrence of all stages of the insect. The mechanism of
its occurrence in the temperate areas where crucifers are not found year round is not clearly
known (Talekar and Shelton, 1993).
Diamondback moth larvae only feed on plants in the family Cruciferae, which contain
mustard oil and their glycosides (Hillyer and Thorsteinson, 1971). Nayar and Thorsteinson
(1963) stated that the glucosides sinigrin, sinalbin, and glucocheirolin produced by crucifer
plants are important to stimulate diamondback moth feeding. Virtually, all cruciferous
vegetables are attacked by diamondback moth including cabbage (B. oleracea. var.
capitata), broccoli (B. oleracea var. italica ), cauliflower (B. oleracea. var. botrytis),
collards (B. oleracea var. acephala), kale (B. oleracea var. alboglabra), kohlrabi (B.
oleracea var. gongylodes), mustard (B. juncea), radish (Raphanus sativus L.), turnip (B.
rapa var. pekinesis), Chinese cabbage (B. rapa cv. gr. pekinensis ), watercress (Nasturtium
officinale R. Br.), and Brussels sprouts (B. oleracea L. var. gemmifera) (Capinera, 2001).
Diamondback moth also feeds on many different cruciferous weeds, including yellow
rocket, Barbarea vulgaris; shepherds purse, Capsella bursa-pastoris; pepper weed,
Lepidium spp.; and wild mustards, Brassica spp., which serve as important alternate hosts
for the pest, especially in spring before crucifer vegetable crops are planted (Talekar and
Shelton, 1993; Capinera, 2001).
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2.7.1.7 Damage and economic importance of Diamondback moth
Plutella xylostella is a noted defoliator of numerous cruciferous plants in many areas of the
world. In some cases, this insect is considered as the most important limiting factor of
successful production of cruciferous vegetables, particularly in the tropics (Lim, 1992). In
Ethiopia, reported yield loss on cabbage from the pest ranges between 36.1 and 91.2
percent corresponding to 12 to 48.7 tons/ha , respectively (Ayalew, 2006). Total crop
failure is common in seasons of heavy infestation in central rift valley areas (Ayalew and
Ogol, 2006). Most of the chemical control in crucifer production is directed towards
diamondback moth control (Carl, 1992). The global cost of controlling DBM has recently
been estimated between USD 4 and 5 billion (Zalucki et al., 2012). Although such a large
amount of money spent for the control of the pest, the level of control set the expense is
low because of the physiological peculiarity of the insect to acquire resistance to
insecticides very quickly, especially in tropical areas in a desperate attempt to achieve
reasonable control (Talekar and Shelton, 1993). Carl (1992) indicated that over 60% of the
market value of the cabbage crop is spent for the purchase of pesticides in Asian Countries
without considering cost of input including pesticide application. Damage is caused by
larvae feeding on leaves, or by the presence of larvae, which contaminate and lower the
quality of the produce. Although they are small in size relative to other lepidopteran pests
such as cabbage looper, (Trichoplusia ni) and imported cabbageworm, (Pieris rapae)
densities of diamondback moth larvae can reach levels that result in total damage of leaves.
For crops such as broccoli, the presence of larvae in florets can result to the total rejection
of the produce (Capinera, 2001). The pest causes serious economic loss even though proper
economic impact of the pest is difficult to access especially in Africa. It can destroy the
entire cauliflower or cabbage crop (Gujar, 1999). This pest causes an average of 52% loss
to marketable yields of cabbage (Kumar et al., 1983). The perceived yield loss to DBM is
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up to 60% on cabbage in Ghana (Chellaiah and Srinivasan, 1986; Lingappa et al., 2004;
Obeng- Ofori et al., 2007; Fening et al., 2014).
2.7.2 Cabbage aphid, Brevicoryne brassicae (L.)
The cabbage aphids are small, pear- shaped, delicate insects with soft and fragile body
(Kessing and Mau, 1991). It is characterized distinctively from other aphids by its short
cornicles, corned- shaped or triangular cauda with seven to eight curved hairs and white
waxy secretions that cover the aphids and the infested leaves (Elwakil and Mossler, 2013).
The short cornicles and the waxy coating of cabbage aphids help distinguish them from
other aphids that may attack the same host plant (Carter and Sorensen, 2013; Opfer and
McGrath, 2013). Adult aphids may be winged or wingless and are noted to form large
colonies covered with grayish waxy powdery secretions. They vary considerably in colour
from light green, yellow, pink, purple to black or mixed colours. The cabbage aphid is 2.0
to 2.5 mm long and covered with a grayish waxy covering (Carter and Sorensen, 2013) and
may attack the crop at any stage (Elwakil and Mossler, 2013).
2.7.2.1 Biology and ecology
Cabbage aphids have varied life cycle for which they may reproduce in two different ways
(Kessing and Mau, 1991). In the warm climatic zones like Florida and Hawaii, female
aphids give birth to live female nymphs without any mating or egg- laying. Here, only
females are found in the colony. In temperate regions, females are induced to lay eggs after
mating and this condition is temperature dependent where males are produced in response
to a decrease in photoperiod (Blackman and Eastop, 1984). The overwintering stage of
aphids is usually the egg stage. Generations may be overlapping to about 15 generations
during the cropping season (Hines and Hutchison, 2013). In all, the duration of their life
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cycle ranges between 16 to 50 days depending on temperature. Higher temperatures shorten
the life cycle (Kessing and Mau, 1991).
2.7.2.2 Eggs
Eggs are usually produced in the temperate climates and overwinter in plant debris near the
soil surface (Hines and Hutchison, 2013) where as in warm climates only females are found
in the colony, and live female nymphs are produced directly without egg laying (Kessing
and Mau, 1991).
2.7.2.3 Nymphs
In warm climatic condition, eggs are usually not produced but rather the female gives birth
to live female called nymphs. The nymphs are similar in appearance to the adult but slightly
different in terms of their small body size, with less developed caudae and siphunculi. The
nymphal period ranges from seven to ten days. Those that form wings develop and migrate
to new host plants when quality of the plant reduces or when the population is large.
2.7.2.4 Adults
Aphids are pear-shaped soft bodied insects with a posterior pair of tubes called cornicles,
which project backward. Aphids have piercing and sucking mouthparts. Adult cabbage
aphids may be winged and wingless. Wingless adults are about 1/10 inches in length, oval
in shape and grayish-green or grayish-white in colour which is attributed to their waxy
covering (Natwick, 2009; Hines and Hutchison, 2013; Opfer and McGrath, 2013). The
cabbage aphids have about eight dark brown or black spot at the upper part of the abdomen
just below the waxy coat and the spots increase in size toward the posterior end. Unlike the
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wingless females, winged females are smaller in size and do not have any waxy covering
(Natwick, 2009). The wings are short with prominent veins. The winged aphids have
characteristic features that differentiate them from the wingless ones; having a dark brown
head and thorax, dark brown antennae and a yellow abdomen with two dark spots located at
the dorsal anterior segment of the abdomen which later becomes a dark band across the last
abdominal segment (Kessing and Mau, 1991)
2.7.2.5 Economic importance and damage
The cabbage aphid is a destructive pest in all cabbage growing areas (Bhatia and Verma,
1994; Dattu and Dattu, 1995) causing severe loss of yield in cruciferous crops that reduce
their marketability (Liu et al., 1994; Costello and Altieri, 1995). They cause both direct and
indirect damage to cruciferous crops. With their piercing-sucking mouthparts both the
adults and the nymphs cause direct damage to cabbage plant by attaching to the plant
tissues and sucking juices thus, depriving the plant of nutrients (Liu et al., 1994). This
results in curled and twisted leaves and later becomes wilted, distorted or yellowish when
aphid population increases (Kessing and Mau, 1991). Aphids‟ feeding result in curl and
spoon shaped leaves and the damage threshold rely greatly on the time of infestation
(Behdad, 1982). Again aphids feeding may lead to unmarketable head, stunted growth and
eventually death of the plant (Griffin and Williamson, 2012).
The indirect damage includes secretion of honeydew, contamination of harvested produce
and the transmission of viral diseases (Liu et al., 1994). The honeydew produced by
cabbage aphids tends to stimulate the growth of a black sooty mould fungus which
contaminates the crop and reduces its market value (Costello and Altieri, 1995). With even
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low population density, aphids have economic impact on the growth and yield of the crop
(Kessing and Mau, 1991).
2.7.3 Cabbage looper, Trichoplusia ni (Hṳber)
The cabbage looper is one of the most important pests of cabbage. Young larvae initially
are dusky white but become pale green as they commence feeding on foliage (Russel,
1978). Smaller larvae remain on the leaf surface while larger larvae produce larger holes
throughout the leaf (Roland and Martin, 2007). In addition to feeding on the wrapper
leaves, cabbage looper may bore into the developing head. Some defoliation can be
tolerated before head formation but feeding damage and excrement left behind on heads
makes cabbage unmarketable (Infonet-biovision, 2009; Andongma, 2010)
2.7.4 Cabbage webworm, Hellula undalis (F.)
The light brown caterpillars of the cabbage webworm bore into the main veins of leaves of
cabbages and later into the centre of the stems where they then feed (Opfer and McGrath,
2013). This makes the pest difficult to control with pesticides (Obeng- Ofori, 1998). When
webworms attack seedlings and plants, the plants do not survive (Youdeowei, 2002).. In
mature cabbage plant, webworms destroy the heads completely making them unsuitable for
sale (Infonet-biovision, 2009; Andongma, 2010). The main natural enemies of the
webworm are predatory ants and parasitic wasps (Youdeowei, 2002).
2.7.5 Cabbage flea beetle, Phyllotreta spp.
These are minor pests of brassica but are so widespread and common that occasionally they
cause economic damage (Obeng- Ofori, 1998). The main damage is done by the adult
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which feed on seedlings of brassicas (Youdeowei, 2002). They feed mainly on the
cotyledons and the leaves of young plants and produce many small round holes all over the
leaf surface (Obeng- Ofori, 1998). Occasionally, seedlings may be completely destroyed.
The larvae generally live in the soil and feed on the roots (Andongma, 2010).
2.7.6 Variegated grasshopper, Zonocerus variegatus (L.)
This is a pest that has been reported to cause serious damage to cabbage plants in Ghana
(Timbilla et al., 2007). Surveys conducted in 2003, revealed that late instar nymphs and
adults of Z. variegatus cause economic damage to cabbage within a fortnight of attack
(Timbilla, 2006). The damage was observed to primarily occur in cabbage fields close to
hatching sites of both dry and wet season populations of Z. variegatus and up to 26 insects
could be counted per plant. Damage attributed to vegetables including cabbage by Z.
variegatus is documented in Ghana (Timbilla, 1997).
2.8 Management of cabbage pests
Several approaches have been used to manage cabbage pests, but the most common include
the following:
2.8.1 Biological control
Biological control is an alternative to chemical pest control and has the potential to provide
resource - poor farmers‟ low cost natural pest control, to reduce the dependency on
pesticides (Youdeowei, 2002). Biological control can be very effective if control agents are
available. There are over 90 parasitoid species recorded attacking the DBM larvae and
pupae in integrated pest management programmes for commercial cabbage production
(Furlong et al., 2004; Jankowska and Wiech, 2006).
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Parasitoids attack the pest in different developmental stages. It is relevant to determine the
association between biological control agents and specific stages of the pests to improve
biological control strategies (Furlong et al., 2004). A number of natural enemies attack
insect pests of cabbage. In Ghana, the most important parasitoids include Cotesia plutella
(Kurdjumov) (Hymenoptera: Braconidae) and Hockeria sp. (Hymenoptera: Chalcididae)
which attack the DBM, Charops flavipes (Brullé) (Hymenoptera: Ichneumonoidea) which
attack Trichoplusia nii, and the Chelonus sp. and Blepharella sp. attack Spodoptera
littoralis (Boisduval) (Lepidoptera: Noctuidae) (Youdeowei, 2002). Predators such as
brown lacewings, Micromus tasmaniae (Walker) (Neuroptera: Hemerobiidae), several
predacious bugs like Nabis tasmanicus (Strommer), leafhoppers and some dermapterans
feed on the eggs, larvae and pupae of insects and further contribute to mortality (Obeng-
Ofori, 1998). Nuclear polyhedrosis viruses that occur naturally in the field and Bacillus
thuriengiensis (Bt) are also effective against lepidopteran insect pests that attack cabbage
(Roland and Martin, 2007).
Biological control approach has considerable promise, although the widespread and
indiscriminate use of insecticide has frustrated efforts and delayed the establishment of
parasitoids and their beneficial effects (Talekar and Shelton, 1993). Even though biological
control has not been greatly exploited in Ghana, few economic impact studies have
revealed high benefits of biological control in the control of the cassava and mango mealy
bugs (Alene et al., 2005).
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2.8.2 Host plant resistance
This is a technology that represents an attractive control tool to farmers, particularly those
in the urban areas in Ghana (Horna et al., 2007). Crucifer crops differ somewhat in their
susceptibility to attack by insect pests such as diamondback moth. Mustard, turnip, and
kohlrabi are among the more resistant crucifers (Stoner, 1990). Several studies have
surveyed existing germplasm for plant resistance to Lepidoptera including the DBM on
crucifers (Shelton et al., 1988; Dickson et al., 1990; Talekar and Shelton, 1993).
The resistance is chemically based and elicits antibiosis in the larvae, causing levels of
mortality (Eigenbrode and Shelton, 1990). Recent studies indicated that application of s-
ethyldipropylthiocarbamate to normal bloom cabbage changed the leaf surface waxes
similar to those of the genetic glossy type and thereby became resistant to the DBM larvae
(Eigenbrode and Shelton, 1992a; Eigenbrode and Shelton, 1992b). In Europe and India,
rape and brussel sprouts varieties were identified to be resistant to cabbage aphid (Russel,
1978; Pakhraj et al., 2005). Some cultivars of crucifera have also shown to be resistant to
cabbage aphid infestation than others (Singh and Ellis, 1993; Ellis et al., 1998)
2.8.3 Mating disruption using sex pheromones
A number of sex pheromones are available for the management of lepidopteran pests of
vegetables, including cabbage (Badenez-perez et al., 2004). The use of DBM pheromones
has been exploited particularly when used in combination with augmentation or
conservation of natural enemies. Furthermore, sex pheromones and larval frass volatiles
from the diamondback moth, as well as volatile compounds from cabbage, may be used by
these natural enemies to locate their diamondback moth host (Reddy, 2002).
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Pheromone has been used to monitor the DBM populations in the field (Koshihara, 1988).
In Japan, scientists have succeeded in achieving mating disruption in cabbages fields using
high concentrations of pheromone (Nemoto et al., 1992; Ohbayashi et al., 1992). A 1: 1
mixture of (Z) - 11-16: Ald and (Z) - 11-16: OAC, known as KONAGA- CON, is now
commercialized in Japan and collaborative multi- location trials have shown promising
results (Ohbayashi et al., 1992). Gabrys et al., 1997 indicated that the sex pheromone
(4aS,7S, 7aR) - nepetalactone proved to be effective in a laboratory bioassay by increasing
the catches of males of B. brassicae when it was released from glass vials placed above
water traps in crops of autumn brassicas. In addition, larger population of parasitoids of B.
brassicae, Diaretiella rapae, and the more general aphid parasitoid, Praon volucre, were
caught in pheromone traps (Gabrys et al., 1997).
2.8.4 Insecticides
2.8.4.1 Insect growth regulators (IGR’s)
Insect growth regulators (IGRs) slowly kill the insects over a period of few days by
disrupting the normal growth and development of immature insects (Ohbayashi et al.,
1992). IGRs insecticides are comparatively safer to beneficial insects and environment, and
are compatible for use in an integrated pest management system. Novaluron for example
acts as an insecticide mainly by ingestion but has some contact activity (Odhiambo, 2005).
Examples of brand names of some IGRs include Azatin (Azadirachtin 3%), Estar II (S-
Kinoprene) and Preclude (fenoxycarb) (Obeng- Ofori, 1998). They have been used to
control many insects. An example of IGRs used in Ghana is Rimon® (Odhiambo, 2005).
Insect growth regulators and pathogens offer a promising control measure as a viable
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alternative to broad- spectrum insecticides, which often disrupt the control exerted by
natural enemies (Kobayashi et al., 1992).
2.8.4.2 Microbial/ biopesticides
Biopesticides or microbial controls consist of Bacillus thuringiensis (Bt), insect -
consuming fungi such as Beauveria bassiana, Metarhizium anisopliae, and viruses such as
Baculoviruses (Furlong et al., 2004). Bt is a naturally occurring bacterium that produces a
toxin that causes paralysis of a caterpillar‟s digestive tract (Guerena, 2006). A caterpillar
may continue to live for some hours after ingestion, but will not continue to feed. Bt strains
are available in a number of commercial products, under various trade names. Bt degrades
rapidly in sunlight and requires careful timing or repeated applications (Thompson and
Hutchins, 1999; Guerena, 2006). Bt must be ingested in sufficient amounts on the
caterpillar to be effective. Consequently, growers must understand the feeding habits of the
pests, so that proper formulations are used and timing of applications is optimal (Botwe et
al., 2012). Caterpillars in their early stages of development (first and second instars) are
more susceptible to this toxin, whereas, older and bigger worms are harder to kill (Guerena,
2006).
Spinosad is one of such new chemicals which are derived from fermentation broth of soil
actinomycetes, Saccharopolyspora spinosa, containing a naturally occurring mixture of
spinosyn A and spinosyn D. Spinosad have rapid contact and ingestion activity in insects,
causing excitation of the nervous system, leading to cessation of feeding and paralysis
(Thompson and Hutchins, 1999). It is a safer and biodegradable insecticide and has a
known insecticidal property that could be feasible and effective for insect pest management
(Ghosh et al., 2010). Spinosad provides effective control of Lepidopteran, Thysanopteran
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pests and some Coleopteran, Homopteran, Hymenopteran and Orthopteran species (Cherry
et al., 2004). There is no reported phytotoxic activity of spinosad based products.
Degradation of spinosad in the environment occurs mainly by photo - degradation and
microbial degradation (Isman, 2008). Spinosad has relatively low toxicity to mammals and
birds and exhibits wide margin of safety to many beneficial insects (Thompson and
Hutchins, 1999).
2.8.4.3 Synthetic insecticides
Three different classes of insecticides have been used to manage insect pests of cabbage in
Ghana. These include organophosphates, carbamates and pyrethroids (Ntow, et al., 2006;
Andongma, 2010). Insecticides such as lambda - cyhalothrin, deltamethrin, cypermethrin,
dimethoate have been widely used in Ghana for the control of major insect pests of cabbage
(Table 2) (Odhiambo, 2005; Amoako 2010).
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Table 2: Pesticides used to control insect pests on cabbage between 2004 –2008 in Ghana.
Common Name Active Ingredients Type Pre- harvest application intervals
Golan S L Acetamiprid Neonicotinoid 7 days
Deltapaz 2.5 EC Deltamethrin Pyrethroid 7 days
Cypercal 50 EC Cypermethrin Pyrethroid 7 days
Karate 5 EC Lambda cyhalothrin Pyrethroid 7 days
Pyrical 480 EC Chloropyrifos Ethyl Organophosphate 7 days
Orthene 750 sp Acephate Organophosphate 4 days
Pawa 2.5 EC Lambda cyhalothrin Pyrethroid 4 days
Cymethoate Cymethoate Organophosphate 7 days
Dimethoate Dimethoate Organophosphate 15 days
Sumithion Fenitrothion Organophosphate 14 days
Dursban 4 E Chlopyrifos Organophosphate 15 days
Thionex 35 EC Endosulphan Organochlorine 14 days
Cymthox Fenvalerate Pyrethroid 7 days
Thiodan Endosulphan Organochlorine 14 days
Mektin 1.5 EC Abamectin Bio- insecticide 3 days
Confidor 200sl Imidacloprid Neonicotinoids 7 days
Diazol 50 EC Diazion Organophosphate 7 days
Wrecko 2.5 EC Lambda cyhalothrin Pyrethroid 15 days
Endocel Endosulphan Organochlorine 15 days
Lambda Super 2.5 EC Lambda cyhalothrin Pyrethroid 3 days
Attack Emamectin benzoate Bio- insecticide 7 days
Kombat 2.5 EC Lambda cyhalothrin Pyrethroid 3 days
Actellic Pyrimiphosmethyl Pyrethroid 7 days
Polythrine C Cypermethrin + profenetos Pyrethroid 7 days
Rimon 10 EC Novaluron IGRs 7 days
Cocostar Bifenthrin + pyrimiphosmethyl Pyrethroid 7 days
Akate Master Bifenthrin Pyrethroid 7 days
Source: Amoako, 2010.
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2.8.4.4 Sunhalothrin® (Lambda cyhalothrin 2.5% EC)
Sunhalothrin® is a broad spectrum insecticide which has lambda cyhalothrin as its active
ingredient (Odhiambo, 2005; Andongma, 2010). It works by opening the sodium channels
in the neuronal membrane. It affects both the central and peripheral nervous systems of the
insect. It initially stimulates nerves cells to produce repetitive discharge and eventually
causes paralysis (Odhiambo, 2005). Such effects are caused by their effects on the sodium
channels (Ware and Whitacre, 2004). Lambda cyhalothrin is a synthetic pyrethroid
insecticide used for the control of a wide range of pests in a variety of applications
(Amoako, 2010). Lambda cyhalothrin 2.5EC is highly active against a wide range of
species of Lepidoptera, Hemiptera, Diptera and Coleoptera (WHO, 1990). Pests controlled
include caterpillars, aphids, grasshoppers, mealybugs, beetles, etc. (Amoako, 2010). Apart
from agricultural use, lambda cyhalothrin also has public and animal health applications in
which it effectively controls a broad spectrum of insects including cockroaches, flies,
mosquitoes and ticks (Andongma, 2010). It is active as residual spray or inert spray used on
surfaces (WHO, 1957). Farmers in the Accra Metropolis reported that lambda cyhalothrin
was very effective in the control of insect pest complex of cabbage (Odiambo, 2005.)
2.8.5 Cultural practices
Cultural methods of controlling pests are very useful and effective but have not received the
needed attention and support (Stoll, 2003). This is considered important to suppress pest
populations in IPM programmes (Brader, 1979). Some of the classical control methods that
have been tried with some success are intercropping, sprinkler irrigation, trap cropping,
crop rotation and clean cultivation (Talekar and Shelton, 1993). Low DBM populations
have been reported in intercropped cabbage fields (Meyer, 2007). Asare- Bediako et al.,
(2010) also reported that intercropping cabbage with onion, tomatoes and pepper in Ghana
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was as effective as spraying with chlopyrifos. Cabbage - tomato intercropping is reported to
reduce infestation of DBM in the cabbage (Bijlmaker, 2005). The odour from the tomato
intercrop repels the DBM (Minja et al., 2003; Stoll, 2003) or has an oviposition deterring
effect on DBM (Endersby and Morgan, 1991).
Planting of trap crops is one of the cultural methods used for pest management (Metcalf,
1975; Talekar and Shelton, 1993). Indian mustard, Chinese cabbage and radish are good
trap crops for controlling cabbage webworm, flea hopper and mustard aphid when planted
at every 15 rows of cabbage (Infonet-biovision, 2009). Hokkanen (1991) suggests that at
least 35-40 important pest species could likely be controlled with some form of trap
cropping, and yet only a handful of trap crop systems are used regularly in commercial
agriculture. Exploring the potential of new trap crop systems and developing methods that
are acceptable to farmers is an important strategy for increasing the economic and
environmental sustainability of farms (Talekar and Shelton, 1993).
2.9 Use of botanicals and their importance in pest management
Many African countries are rich in plant products that are traditionally used by the rural
inhabitants for medicinal purposes and in some instances as preparations for insect control
(Amoabeng et al., 2013). Certain plant families, particularly Meliaceae, Rutaceae,
Asteraceae, Labiatae, Piperaceae and Annonaceae have been viewed as exceptionally
promising sources of plant-based insecticides (Jacobson, 1989; Isman, 1995). The use of
conventional insecticides has raised some concerns, about their threats to the environment
and development of insecticide resistance in insects (Champ and Cribb, 1985; Halliday et
al., 1988; Barbara, 1993). There is an imperative need for the development of safer,
effective and efficient alternative crop protectants such as botanical insecticides which are
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biodegradable pesticides with greater selectivity (Fening et al., 2013; Amoabeng et al.,
2013). Currently, pest control mechanism is based largely on imported synthetic
insecticides, which are frequently priced beyond easy reach of small farmers, who
constitute a very large proportion of the farming population (Amoabeng et al., 2013).
The role of botanical insecticides in insect pest management and crop protection in Africa
is of much importance due to continual use of effective but „toxic‟ commercial pesticides
(Amoabeng et al., 2013). However, the regulatory environment and public health needs
have created opportunities for the use of safer botanicals, since human and animal health is
now paramount (Fening et al., 2013; Amoabeng et al., 2013). Botanicals have also found
its use in organic food production, both in the field and in controlled environments for
export to developed countries where strict pesticide levels are strictly monitored in
horticultural products before export (Heyde et al., 1984; Kareru et al., 2008). In addition
the greatest benefits from botanicals might be achieved in developing countries, where
human pesticide poisonings are most prevalent (Kareru et al., 2013).
In Africa, extracts of locally available plants have been traditionally used as crop
protectants, when used alone or in mixtures (Table 3). In fact indigenous knowledge and
traditional practice have made valuable contributions to domestic food production in
countries where strict enforcement of pesticide regulations is not applied (Kareru et al.,
2013).
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Table 3: Some plants traditionally used to control crop pests and diseases.
Plant Pests/ Diseases
Neem tree Armyworms, Stem borers, Bollworms, Leaf miners,
Diamondback moth, Caterpillars, Storage pests
(moth), Aphids, Whiteflies, Leaf hoppers, Psyllids,
Scales, Maize tassel, Beetle, Thrips, Weevils and
Flour beetle
Garlic/Onions Caterpillars, Cabbage worms, Aphids
Stinging nettle Caterpillars
Tithonia diversifolia Caterpillars, aphids
Spider weed Aphids
Aloe spp. Ash Storage moths, Storage beetles
Hot pepper Diamondback moth, Stem borers, Bollworms,
Cutworms, weevils, Aphids, Beetles
Tobacco Stem borers, Cutworms, Caterpillars, Grain weevils
Pyrethrum + Mexican marigold Caterpillars, Aphids, bugs, Beetles
Chilies + Mexican marigold
Garlic, Allium sativum + hot pepper,
Capsicum frutescens
goat weed (Ageratum conyzoides) +
Siam
weed (Chromolaena odorata)+
Cinderella weed (Synedrella
nodiflora)+ chili pepper(Capsicum
frutescens)+ tobacco (Nicotiana
tabacum)+ Cassia (Cassia
sophera)+ physic nut (Jatropha
curcas)+ castor oil plant (Ricinus
communis)
and basil (Ocimum gratissimum)
Armyworms, Stem borers, Bollworms, Cutworms,
Leaf miner, Diamondback moth, caterpillars, Aphids
DBM, Aphids, cabbage webworm
DBM, Aphids, cabbage webworm and other insect
pests of cabbage
Source: Mureithi, 2008; Amoabeng et al., 2013; Fening et al., 2013.
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Studies in some Africa countries suggest that extracts of locally available plants can be
effective as crop protectants (Isman, 2008). Among the botanicals used are natural
pyrethrins, the neem extract, Azadirachta indica (A. Juss), Khaya senegalensis against
cotton bollworm (in Benin) and extracts from marigold against bruchid beetles from
cowpeas in storage in Uganda (Kawuki et al., 2005). Shelton and Zhao, (2004) documented
a survey of botanical extracts used as insecticides among farmers within the Victoria Basin.
The study demonstrated that most subsistence farmers use botanical pesticides for pest
management in their farms. Among the plants used were Capsicum frutescens, Tagetes spp,
Nicotiana tabacum, Cypressus spp., Tephrosia vogelii, Azadirachta indica, Musa spp.,
Eucalyptus spp. and Carica papaya.
In Benin, West Africa, the bush mint, Hyptis suaveolens extract has been used for the
control of pink stalk borer, Sesamia calamistis H. (Lepidoptera: Noctuidae) on maize. Also,
botanical insecticides have been tried for the protection of cowpeas in Ghana (Abatania et
al., 2012). Ogunsina et al., (2010) investigated plant extracts from Lantana camara
(Verbenaceae) and African nutmeg (Monodora myristica (Gaerth) against bean weevil
Callosobruchus maculatus (F.) and maize weevil, Sitophilus zeamais Motsch. The overall
results showed that bean weevil was much more susceptible to all the extracts than maize
weevil.
In Ghana, several botanicals such as Azadirachta indica, Ocimum Americana, Capsicum
frutescens, Pleiocapa mutica, Cassia sophera, Pterocarpus erinaceus, Chamaecrista
nigricens, Securidaca longepedunculata, Citrus sinensis, Combretum sp.,Synedrella
nodiflora, Cymbopogon schoenanthus, Chromolaena odorata, Khaya senegalensis,
Vitellaria paradoxa, Lippia multiflora, Mitragyna inermis.etc have been used to protect
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foodstuffs such as vegetables and stored grains against insect pest infestations (Obeng-
Ofori and Ankrah, 2002).
Botanical insecticides contain compounds with properties that repel, deter or disrupt the
growth, feeding or reproductive activities of insect pest on crops (Oparaeke, 2005; Ahmed
et al., 2009; Degri et al., 2012; Degri et al., 2013). Botanical insecticides tend to have
broad spectrum activity, relatively specific in their mode of action, and easy to process and
use at farm levels. They are also safe for higher animals and the environment
(Annonymous, 1991). Botanical insecticides can often be easily produced by farmers and
small-scale industries; the indigenous plant materials are cheaper and hazard free in
comparison to chemical insecticides (Saxena et al., 1980). Plants are rich sources of natural
substances that can be utilized in the development of environmentally safe methods for
insect control (Sadek, 2003). Crude plant extracts often consist of complex mixtures of
active compounds, they may show greater overall bioactivity compared to the individual
constituents (Berenbaum et al., 1991; Chen et al., 1995). The deleterious effects of crude
plant extracts on insects were seen in several ways, including toxicity (Hiremath et al.,
1997) and feeding inhibition (Wheeler and Isman, 2001).
2.10 Common plants used as botanicals
2.10.1 Siam weed, Chromolaena odorata (Asteraceae)
Chromolaena odorata is a Neotropical plant (Plate 3). According to Voigt (1845), C.
odorata was introduced to Calcutta botanical gardens, India in 1845. From its original point
of introduction as an ornamental, it spread throughout Southeastern Asia into parts of
Oceania and into West and Central Africa (Gautier, 1992). It was accidentally introduced to
Nigeria in 1937 (Munniapan and Marutani, 1988). Hall et al., (1972) reported that the weed
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was first discovered in Ghana in 1969 and by 1991 it had colonized about 67% of the total
land area of the country (Braimah and Timbilla, 1991; Timbilla and Braimah, 1996).
Chromolaena odorata contains diverse range of secondary chemicals including flavonoids,
terpenoids and alkanoids (Talapatra et al., 1974; Biller et al., 1994). In China, analysis of
the volatile oil from C. odorata identified 33 components with terpenoid compounds being
the majority (Boeke et al., 2004). The main terpenoid compounds are trans-caryophyllene
(16.22%), A-cardinene (15.53%), a-capaene (11.32%), caryophyllene oxide (9.42%),
germacrene-D (4.86%) and humulene (4.23%). Similar work in Thailand identified 22
constituents (Nisit et al., 2006). Also, phenolic acids (protocatechuic, p-hydroxybenzoic, p-
coumaric, ferulic and vanillic acids) and complex mixtures of lipophilic flavonoid
aglycones (flavanones, flavonols, flavones and chalcones) were found in the crude ethanol
extracts of the leaves of Chromolaena odorata (Toan-Thang et al., 2001). Nisit et al.,
(2006) also investigated the chemical constituents of the leaf extract of C. odorata after
separation and purification. Six flavanoids were obtained including 3,5,4`-trihydroxy -7-
methoxyflavanone; 5,7,3 trihydroxy -5- methoxyflavanone and 3,5,7- tridroxy-
methoxyflavanon.
Biller et al., (1994) reported that C. odorata contains a mixture of pyrrolizidine alkaloids
(PAs) with the major components being rinderine and intermedine, as well as other PAs in
smaller quantities all occurring exclusively as N-Oxides with the highest concentration
occurring in the roots and in the flowers but absent in the leaves.
Caryophyllene and germacrene-D which have been reported to be major constituents in
Lantana camara leaf has been established to possess insecticidal activity against
Dactynotus carthami (Patil et al., 1997), repellent towards bees, mosquitoes and cattle flies
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(Attri and Singh, 1978) and ovipositional effect against Callosobruchus maculatus.
Coumarine a constituent of C. odorata is also well known to possess insecticidal properties.
Plate 3: Siam weed plant (Chromolaena odorata).
2.11 Neem tree (Azadirachta indica A. Juss)
The neem tree, Azadirachta indica A. Juss belongs to the family Meliaceae (Plate 4). It is a
tropical evergreen tree related to mahogany (Tomar and Singh, 2008). The tribe Melieae
consists of two genera Azadirachta and Melia (Rimpi et al., 2010).This tree is native to the
coastal fringe forests of the drier tropical region of East India, Sri Lanka and Burma
(Massaguni and Latip, 2012). It is currently widespread in Pakistan, Myanmar, Thailand,
Malaysia and Indonesia (Tomar and Singh, 2008). The neem tree is undemanding and
grows well on moist, dry, stony, clayey or shallow soils. Therefore, it is able to grow
almost anywhere in the lowland of the tropics (Massaguni and Latip, 2012). However, it
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generally performs best in areas with annual rainfall of 400-1,200 mm (Tomar and Singh,
2008).
Azadirachtin (C35H44O16) is a tetranortriterpenoids (limonoids) which is extracted from
Azadirachta plant species. This compound in neem has insecticidal properties such as
antifeedant, repellence, oviposition deterrent, molting inhibition and a growth retardant for
different insects‟ species and arthropods (Rimpi et al., 2010). Although, every part of the
neem tree contains azadirachtin substance, most previous research have shown that the seed
kernels contains higher amount of azadirachtin (Boeke et al., 2004). Azadirachtin in the
neem seed kernel is about 0.1 - 0.5% by weight of the seed. Besides the azadirachtin, neem
also contains more than 20 compounds that are responsible for the characteristics smell of
crushed seeds and neem oil (Massaguni and Latip, 2012).
Plate 4: Fresh neem seeds.
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2.11.1 Importance of neem as botanicals
Extracts of neem are often used to protect stored grains against insects by mixing the grains
and the extract. Boeke et al., (2004) found that the leaf powder, the seed oil and all kinds of
extracts do indeed have a negative effect on seed-eating insects. However, if these plant
parts are used to treat stored seeds against insects, the mammalian consumers of these seeds
especially human beings should not be affected by residues of this treatment (Obeng- Ofori
and Ankrah, 2002). The reason is that neem is reported to be safe for humans and the
environment as it has not been found to possess toxic compound. Yu (2008) found that
neem products are considered safe because the oral LD50 in rats is >5000 mg/kg making it
essentially non- toxic to mammals. The neem leaves and other plant parts are valued for
their therapeutic and medicinal properties and have extensively been used to treat many
ailments in India (Obeng- Ofori and Ankrah, 2002). Many disorders like inflammation,
infections, fever, skin diseases, dental disorders and others have been treated with different
parts of the neem tree (Girish and Shankara, 2008). In addition, neem also exhibits a wide
range of pharmacological activities such as blood sugar lowering properties, anti-
inflammatory, antihyperglycaemic, antiulcer, antimalarial, antifungal, antibacterial,
antiviral, antioxidant, antimutagenic, anticarcinogenic and immunomodulatory (Boeke et
al., 2004).
Among 2,400 plants investigated, neem was rated on top in terms of its pesticidal
properties and was regarded as the most reliable source of eco-friendly biopesticide
(Obeng- Ofori and Ankrah, 2002). The preparation of neem is cheap and highly effective
and thus constitute an important source of pesticide for economically poor farmers
(Massaguni and Latip, 2012; Obeng- Ofori and Ankrah, 2002).
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The increasing amount of research on insect-plant chemical interactions has provided the
potential of utilizing botanicals insecticides in the form of secondary plant metabolites or
allelochemicals (Senthil-Nathan et al., 2009). These naturally occurring biocidal agents
have been shown to be selective, readily biodegradable and safe to human (Obeng- Ofori
and Ankrah, 2002).
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CHAPTER THREE
3.0 MATERIALS AND METHODS
3.1 Study location
The research was conducted at the University of Ghana‟s Forest and Horticultural Crops
Research Centre (FOHCREC), Kade, in the Kwaebibirem district of the Eastern Region.
The Centre is located approximately 120 km North- west of Accra (6o 09N, 0o 55W) (Gray,
1987) and approximately 135.9 m above sea level. It lies within the moist deciduous forest
zone of Ghana and within the wet semi- equatorial climatic region (Ofosu- Budu, 2003).
The climatic condition is representative of a tropical humid forest zone (Dickson and
Benneh, 1995; Ofosu- Budu, 2003).
The area has an annual bimodal rainfall amount ranging between 1200- 1300 mm, and
temperature range of 25- 34oC and monthly actual evapotranspiration of 1200mm/ year
(Christiansen and Awadzi, 2000; Ofosu- Budu, 2003). The relative humidity ranged
between 60 and 80% throughout the year (Dickson and Benneh, 1995). The Centre has
been involved in the promotion of forest and horticultural crops production and protection
since its establishment in 1957 (Ofosu- Budu, 2003).
3.2 Preparation of treatments
The C. odorata crude leaf extracts were prepared along with the neem seed extract as
standard botanical. The reference conventional insecticide, sunhalothrin and the control, tap
water treatments were also prepared prior to application of various treatments.
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3.2.1 Preparation of Chromolaena odorata leaf extracts
Fresh leaves of C. odorata were cut from a field around the Centre and two other suburbs
(Nkwantanang and Okumaning) situated four kilometers from the Centre. The leaf samples
taken from the different localities were mixed and washed with water to remove sand, dust
and chemical contaminants. The leaves were shade-dried for about an hour on a clean
concrete platform to drain off excess water and then ground into coarse powder using
wooden pestle and mortar. To prepare 10g/L of the extract, 10g of the powder was weighed
and then soaked in plastic bucket containing 1 litre of warm water. The resulting solution
was then stirred continuously for 10 minutes and left to stand overnight. Filtration of the
leaf extract was done shortly before application using muslin cloth. The stickiness and
adherence of the plant extract was enhanced by the addition of about three drops each of
natural vegetable oil (0.15 ml per litre) and local soap (alata samina) solution (3% w/v) as
surfactant (Fening, et al., 2014). Similar procedures were used to prepare 20 and 30g/ L of
the extract
3.2.2 Preparation of neem seed extracts
Fresh neem seeds were collected along Winneba- Apam road and dried in the sun for a
week. Before the preparation of the extract, the neem seeds were air-dried at room
temperature, and the shells removed from nuts. The nuts were pounded using a pestle and
mortar to obtain coarse powder which was used for the treatment solution. Crude plant
extracts were prepared by adding 1 litre of distilled water to 50 g weighed plant material to
get desired dose. The solution was left overnight and filtered through fine linen material. A
few drops of local soap solution (Alata samina- 3% w/v) were added to the final extract to
act as a surfactant. The solutions were independently used for the field experiments. The
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neem is being used in this study as a standard botanical to compare with the performance of
Chromolaena odorata, which is the target botanical.
3.3 Field experiment
3.3.1 Nursery establishment
Cabbage seeds (cv. oxylus) were obtained from AGRIMAT Limited shop in Accra. The
seeds were nursed in rows in seed trays and seed boxes raised 1 m above the ground. The
nursery media were made up of sandy loam mixed with carbonated rice husks in a ratio 2:
1. Watering was done manually with watering can. Fertilizer (NPK) was applied to the soil
media as starter solution at a rate of 20g per litre of water. Fungicides (Mancozeb- 20g/L)
were also sprayed on the seedlings to prevent fungal infection during the early stages of
growth.
3.3.2 Land Preparation, field layout and transplanting
The land was manually cleared and later sprayed with herbicide (2, 4- D) before cabbage
seedlings were transplanted onto raised beds. The field layout was done, with each plot or
bed measuring 1.5 m wide x 2.5 m long. A 2 m wide unplanted alley was allowed between
and within each plot or bed to avoid spray drift. The experimental field, which measures 19
m x 11.5 m, were pegged and labeled with three replications, prior to planting. Cabbage
seedlings (cv. oxylus) were transplanted at the 4-5 true leaf stages (about 30 days after
sowing) in a spacing of 0.5 x 0.5 m with each plot containing 24 plants. Replacement and
refilling of weak, diseased or infested seedlings were carried out 2 weeks after
transplanting. A starter solution of N,P,K fertilizer, 20g/L was diluted in water and applied
to each plot. Standard cultural and agronomic practices such as weed control, watering and
earthing-up of soil to improve aeration were employed during the growing period.
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3.4 Experimental design, treatments and agronomic practices
The design was a randomized complete block consisting of six treatments which were
replicated three times.
The treatments were:
T1: Application of 10 g/L crude extract of C. odorata leaves (150g/ 15litres),
T2: Application of 20 g/L crude extract of C. odorata leaves (300g/ 15litres),
T3: Application of 30 g/L crude extract of C. odorata leaves (450g/ 15litres),
T4: Application of 50 g/L Neem seed extract (750g/ 15litres),
T5: Application of Sunhalothrin® (Lambda cyhalothrin)- 2.5ml/ L (37.5ml/ 15litres),
T6: Tap water/ Control.
A 15 litre capacity knapsack sprayer was used to apply each of the treatments at
recommended doses. Application of treatments started two weeks after transplanting of
seedlings. Watering was carried out daily to avoid the withering and dying of seedlings
especially at the early stages of transplanting. Weeds were manually controlled with a hoe
or cutlass at two weekly intervals.
3.5 Data collection, yield and damage assessment
3.5.1 Data collection
Data collection started 14 weeks after transplanting and it was carried out weekly for all the
growing seasons. Data on insect pest population including DBM, aphids, grasshoppers and
other pests and natural enemies were counted and recorded from the middle rows, with the
border plants excluded, which had an average of eight (8) cabbage plants per plot. Cabbage
aphids were much more numerous and difficult to count without disruption, so they were
scored as follows: 0 = absent, 1 = a few scattered individuals, 2 = a few isolated small
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colonies, 3 = several small isolated colonies, 4 = large isolated colonies and 5 =large
continuous colonies (Afun et al., 1991; Fening et al., 2013).
The assessment of the numbers of various insect pest species was done by carefully
examining eight (8) cabbage plants selected; leaf by leaf and turning of leaves as well to
collect any insects from the under-surface of the leaves (Fening et al., 2014). Observations
were conducted in the first week after transplanting before the application of treatments for
both seasons, after which data samplings were taken 3 days after each treatment
application. Data collections were done between 06:00 and 08:00 GMT.
3.5.2 Multiple head formation and head damage assessment
At harvest eight innermost cabbage plants were selected from each treatments plot for
assessment. Head damage index were rated using the modified scale of Dreyer, 1987. Table
4 below shows the description of the scale.
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Table 4: Modified scale of Dreyer (1987) used for damage scoring on cabbage varieties at
Kabete field station, Togo.
Score Description
1 No damage, or few isolated small holes in the outer or lower leaves
2 Many holes but damage limited to outer or lower leaves
3 Considerable damage of the outer or lower leaves and slight damage on the
cabbage head, head marketable with minor leaf removal of outer head leaves
4 Outer or lower leaves completely destroyed, moderate attack of inner leaves,
head marketable after considerable removal of outer head leaves
5 Severe attack on the head (head unmarketable)
Cabbages with multiple or split heads were also counted. The percentage multiple heads
were expressed as:
= Number of multiple heads x 100%
Total number of selected plants
The marketable and un-marketable heads were sorted out in percentages to determine the
consumers‟ acceptability. Percent data were arcsine square root transformed before analysis
using ANOVA.
3.5.3 Yield assessment
At harvest, cabbage heads were used for yield assessment. This was done by harvesting
heads from inner rows of each plot and cleaning them from traces of soil and then weighing
the individual heads on a digital weighing scale at the field. The head weights were
recorded, respectively for each of the eight plants on each plot.
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3.6 Cost- benefit Assessment
3.6.1 Costs of treatments
The costs of treatments were recorded in the two field experiments conducted during the
major and minor rainy seasons of 2014. Treatments of crude water extracts of readily
available insecticidal plants (botanicals) were compared with the synthetic insecticide,
lambda cyhalothrin (Sunhalothrin®) and tap water or control. The botanical (siam weed, C.
odorata) used in this study were obtained in the surrounding without purchase but neem
seed, A. indica were obtained at amount of GH¢ 20.00 per bag. The associated costs were
only for labour in the collection, preparation and application of treatment dose. For the
synthetic insecticide, the cost of the product was added to the labour cost of spraying.
Labour cost was based on the existing wage for an unskilled labour at the locality at the
time of study. This was GH¢50.00 per man day. For the purposes of the economic analyses,
values were calculated on a per hectare basis.
In the major season, a man - day of labour was used for collection and preparation of the
botanicals and ensuring that the botanical (siam weed, C. odorata) treatment was prepared
fresh before use. Neem extract preparation had a total of 2 man days of labour in the
collection and preparation. A bag of neem seeds cost was GH¢20.00 and 3bags were used.
There were six sprayings in the major rainy season which costed GH¢50.00/ spray.
Sunhalothrin® was costed at GH¢150.00/ha for six applications at GH¢50.00.
In the minor season, a man day was used for the collection and preparation of each
botanical (siam weed, C. odorata) whilst 2 man days were used for neem extract
preparation. Cost of Sunhalothrin® was GH¢150.00/ha. There were seven sprayings in the
minor rainy season which costed GH¢50.00/ spray. The externalities such as potential
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impacts on the environment, natural enemies, and farm worker and consumer safety
associated with each of the treatments were not considered in the analyses (Amoabeng et
al., 2014).
3.6.2 Assessment of economic benefits
At harvest, plot yields were weighed and recorded. Cabbage heads from each plot were
sorted into marketable and unmarketable based on insect damage and weight of cabbage
head. Individual cabbage head was weighed and sold at the prevailing price on the local
market. Marketable heads were sold at GH¢1.50/ kg (1,500/ ton) and GH¢2.50/ kg (2,500/
ton) for the major and minor seasons, respectively, while unmarketable heads at GH¢0.50/
kg (500/ ton) and GH¢1.00/ kg (1,000/ ton) for both seasons, respectively. Income was
converted to a per hectare basis by extrapolating the plant population of plots based on a
plant spacing of 0.5 m x 0.5 m taking into account unplanted alleys to facilitate movement
within the field. This resulted in a total plant population of 64,000 per hectare, following
the procedures used by Amoabeng et al., 2014.
3.7 Data Analyses
3.7.1 Field experiments
Mean weekly count data for P. xylostella and other pests and natural enemies and the score
data for B. brassicae were computed. All data were subjected to analysis of variance
(ANOVA) using the JMP 10 statistical package. The number of insect counts was
transformed using square root transformation. Treatment means separation was by the
Tukey- Kramer‟s HSD test and the probability of treatment means being significantly
different was set at P < 0.05.
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3.7.2 Economic analysis
Mean head weight per plant, percentage of marketable (undamaged) heads and
unmarketable (damaged) head yield per hectare were subjected to analysis of variance
using JMP. Percentage data were arcsine square root transformed prior to the statistical
analysis. On achieving significant differences (P < 0.05) mean separation was performed
using Tukey- Kramer‟s HSD test.
Formulae for calculating each section in Table 11 and 12
1) Marketable Yield = Percent no. of marketable head x average head weight
(ton/ ha) per treatment per plant
2) Unmarketable Yield = Percent no. of unmarketable head x average head weight
(ton/ ha) per treatment per plant
3) a. Cost of botanical = labour cost of collection + labour cost for spraying per Ha
treatments (GH¢/ Ha) and preparation
b. Cost for synthetic = Cost of product + labour cost for spraying per Ha
insecticide (GH¢/ Ha)
4) Income from marketable = Marketable head x Selling price per tonne
head (GH¢/ Ha) yield
5) Income from unmarketable = Unmarketable head x Selling price per tonne
head (GH¢/ Ha) yield
6) Total income = Income from marketable head + Income from unmarketable head
(GH¢/ Ha) (GH¢/ Ha) (GH¢/ Ha)
7) Net benefit (GH¢/ Ha) = Total income (GH¢/ Ha) – Cost of treatments (GH¢/ Ha)
8) Benefit over control = Income from sprayed – Income of the control treatment
treatments (GH¢/ Ha ) (GH¢/Ha)
9) Cost benefit ratio = Net income of sprayed treatment – Income of control treatment
Total cost of sprayed treatment
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CHAPTER FOUR
4.0 RESULTS
4.1 Insect fauna found on cabbage field during the growing seasons
The cabbage plants attracted a number of insect pests at different stages of the plant growth
due to their nutritive and luxuriant nature. The most abundant insect pests recorded during
the major rainy season were the cabbage aphids and the cabbage webworms, whiles those
in the minor rainy season were the variegated grasshoppers, the aphids and the
diamondback moth (Table 5).
Table 5: Insect pests of cabbage found during the experiments.
Insect pests and arthropods Major season Minor season
1. Cabbage Aphids
2. DBM
3. Cabbage Webworm
4. Variegated grasshopper
5. Whitefly
6. Cabbage flea beetle
7. Cabbage white butterfly
8. Cabbage looper
9. Cotton leafworm
10. Mole cricket
11. Millipede
12. Snail
XXX
N
XX
X
XX
XX
X
X
X
X
X
XX
XXX
XX
N
XX
XX
XX
X
X
X
XX
XX
X
XXX: Uncountable number XX: Many number X: Few number N: Not found.
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4.1.1 Observed damage caused by the major pests on cabbage during the study
period
4.1.1.1 Aphids
Cabbage aphids fed on plant sap and caused leaf cupping outward and inward. Attacked
leaves appeared weak and wrinkled at the under surface. Large colonies of aphids fed on
the underside of leaves (Plate 5), causing leaf curl, leaf discoloration, stunted growth,
yellowing, wilting and death of infested plants. They also secrete sticky honeydew on
which sooty mould grow. In addition, the aphid may transmit viruses which damage the
cabbage plants.
Plate 5: Aphids infestation observed on a cabbage plant during the experiment.
4.1.1.2 DBM, Plutella xylostella
The larvae were the most destructive stage and fed on the underside of the leaf cutting
round holes or more often scratching off the tissue leaving the epidermis of one side
untouched, thus creating a transparent window. In the minor season, high infestations were
observed as compared to the major season which recorded no infestation during the period
of study.
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4.1.1.3 Cabbage Webworm, Hellula undalis
The larvae fed on the growing points (apical meristem) (Plate 6) and the developing leaves
(Plate 7). Larvae of H. undalis were found feeding on cabbage plants and some even cut the
apical meristem of less established plants. Small larvae tunneled into the main stem which
resulted in stunting and deformed plants. Their feeding on cabbage plant led to most
multiple head formation in the major rainy season.
Plate 6: Cabbage webworm attacking the apical meristem of a young cabbage seedling.
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Plate 7: Hellula undalis attacking a developing cabbage leaf.
4.1.1.4 The variegated grasshopper, Z. variegatus
They were found feeding on the cabbage plants 2 days after the transplanting of seedlings.
They chewed all the leaves of most young cabbage plants (Plate 8) and heads and hence
decreased yield. In the dry season, high numbers of grasshoppers were found causing
defoliation throughout the growing period of the crop.
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Plate 8: Leaf damage caused by a variegated grasshopper on cabbage.
4.1.1.5 The African mole cricket
They attacked the stems of the young cabbage in the field. They burrowed into the ground
soil around the plant and made its control very difficult. Other arthropods were also
observed feeding on the cabbage, but their populations were too low to be considered.
These included; the flea beetle, whitefly, snails and the millipedes, and other unidentified
larvae and caterpillars (Plate 9 and 10).
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Plate 9: A millipede causing damage to cabbage.
Plate 10: A snail feeding on the cabbage leaf.
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4.1.1.6 Beneficial insects
However, natural enemies of pests of cabbage such as Diaretiella rapae, Cotesia plutellae,
hoverflies, spiders, lady bird beetles (e.g. Cheilomenes spp.) and other beneficial arthropods
were identified and observed attacking some insect pests.
4.2 Effects of botanicals and conventional insecticides on insect pest populations
Table 6a shows the effect of three levels of siam weed, neem and the conventional
insecticide, sunhalothrin® on the mean number of major insect pests observed in the field
experiment during the major rainy season of 2014. The results indicated that, the three rates
of siam weed extracts were not significantly different from each other (Table 6a). However,
the performance of siam weed extracts were similar to that of neem extract. The three rates
of siam weed and neem extracts also had significantly lower number of aphids than the
conventional insecticide, sunhalothrin®. In addition, siam weed extract applied at 10g/ L
had fewer number of aphids than the control plots. The effect of all the botanicals and the
conventional insecticide, sunhalothrin® were effective in managing the cabbage webworm,
H. undalis. Moreover, they all performed better than the control plots where only water was
sprayed.
Table 6a below shows no significant differences among treatments in the control of
grasshopper, Z. variegatus for the major growing season. However, some botanicals
(Chromolaena odorata- 10 and 20g/L) and the conventional insecticide, sunhalothrin®
showed significantly lower numbers of other pests than the control. Chromolaena odorata
extracts applied at 10 and 20g/L and sunhalothrin® at recommended rate performed better
than the control in controlling other pests such as cabbage flea beetle (Phyllotreta spp.),
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cabbage white butterfly (Pieris rapae), cabbage looper (Trichoplusia nii), and Spodoptera
litorallis.
Table 6a: Mean (±SE) populations of insect pests on cabbage sprayed with botanical and
conventional insecticides and tap water as control, during 2014 major rainy season.
Mean ± SE insect pests/ plant
Treatments B. brassicae H. undalis Z. variegatus Other pests1
10g/L C. odorata 0.67 ± 0.22 c 1.38 ± 0.27 b 1.58 ± 0.26 1.83 ± 0.30 b
20g/L C. odorata 1.58 ± 0.29 bc 1.38 ± 0.28 b 1.29 ± 0.27 2.46 ± 0.31 b
30g/L C. odorata 1.58 ± 0.22 bc 1.79 ± 0.28 b 1.08 ± 0.24 2.63 ± 0.39 ab
50g/ L Neem 1.08 ± 0.28 c 1.13 ± 0.21 b 1.63 ± 0.29 3.04 ± 0.43 ab
Sunhalothrin® 3.33 ± 0.43 a 1.13 ± 0.23 b 1.38 ± 0.26 1.83 ± 0.34 b
Tap water 2.58 ± 0.58 ab 4.0 ± 0.56 a 1.63 ± 0.28 4.08 ± 0.35 a
F- Value 7.44 11.13 0.67 5.56
P <0.0001* <0.0001* 0.647 <0.0001*
Means within a column for each treatment under each dose followed by different letters
differ significantly from each other (P≤ 0.05).
1Other pests: cabbage flea beetle (Phyllotreta spp.), cabbage white butterfly (Pieris
rapae), cabbage looper (Trichoplusia ni), and Cotton leafworm (Spodoptera litorallis).
Table 6b below showed that the botanicals had significantly lower number of aphids than
the conventional insecticide, sunhalothrin® and the control in the minor growing season.
However, there were no significant differences among all treatments in the control of P.
xylostella, Z. variegatus and other pests.
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Table 6b: Mean (±SE) populations of insect pests on cabbage sprayed with botanical and
conventional insecticides and tap water as control during 2014 minor rainy season
Mean ± SE insect pests/ plant
Treatments B. brassicae P. xylostella Z. variegatus Other pests1
10g/L C. odorata 1.83 ± 0.22 b 4.50 ± 0.73 3.33 ± 0.48 1.67 ± 0.35
20g/L C. odorata 1.21 ± 0.25 b 3.13 ± 0.69 2.96 ± 0.43 0.88 ± 0.19
30g/L C. odorata 1.58 ± 0.32b 3.79 ± 0.64 3.08 ± 0.51 1.13 ± 0.25
50g/ L Neem 1.46 ± 0.26 b 3.08 ± 0.54 3.33 ± 0.50 1.13 ± 0.31
Sunhalothrin® 3.96 ± 0.64 a 4.13 ± 0.09 3.17 ± 0.50 1.46 ± 0.30
Tap water 3.75 ± 0.62 a 5.08 ± 1.01 4.46 ± 0.71 1.96 ± 0.32
F- Value 7.61 1.02 1.06 1.67
P <0.0001* 0.4094 0.3831 0.1456
Means within a column for each treatment under each dose followed by different letters
differ significantly from each other (P≤ 0.05).
1Other pests: cabbage flea beetle (Phyllotreta spp.), cabbage white butterfly (Pieris
rapae), cabbage looper (Trichoplusia ni), cabbage webworm (Hellula undalis) and Cotton
leafworm (Spodoptera litorallis).
4.3 Effects of treatments on natural enemies
The results showed that there were no significant differences in the numbers of D. rapae, C.
plutellae and hoverflies when the various treatments were applied. However, 20g/ L of C.
odorata and neem had significantly high number of spiders compared to the other
treatments. Also, for other natural enemies such as ladybird beetle (Cheilomenes lunata),
earwigs, red ants (Oecophylla sp.) and mason wasp sampled, 20g/ L C. odorata treated
plots had significantly high populations than that of sunhalothrin® (Table 7a).
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Table 7a: Mean (±SE) numbers of natural enemies of pests of cabbage sprayed with
botanical and conventional insecticides during 2014 minor rainy season.
Mean ± SE natural enemies/ plant
Treatments D. rapae C. plutellae Spider Hoverfly Other N.E1
10g/L C. odorata 1.67 ± 0.64 1.58 ± 0.62 2.33 ± 0.41 ab 1.0 ± 0.35 1.25 ± 0.8 ab
20g/L C. odorata 2.38 ± 0.78 1.83 ± 0.50 2.58 ± 0.43 a 1.08 ± 0.22 1.50 ± 0.26 a
30g/L C. odorata 1.0 ± 0.43 0.83 ± 0.39 1.92 ± 0.40 ab 0.58 ± 0.25 0.42 ± 0.20 ab
50g/ L neem 1.13 ± 0.45 1.25 ± 0.34 2.67 ± 0.41 a 1.17 ± 0.35 1.13 ± 0.24 abc
Sunhalothrin® 2.29 ± 0.97 1.88 ± 0.53 0.83 ± 0.21 b 0.42 ± 0.15 0.29 ± 0.11 c
Tap water 2.5 ± 0.86 2.21 ± 0.58 1.96 ± 0.31ab 1.25 ± 0.38 0.67 ± 0.20 abc
F- Value 0.84 0.95 3.22 1.27 4.82
P 0.5213 0.4536 0.0088* 0.2792 0.0004*
Means within a column for each treatment under each dose followed by different letters
differ significantly from each other (P≤ 0.05).
1Other natural enemies: ladybird beetle (Cheilomenes lunata), earwigs, red ants
(Oecophylla sp.) and mason wasp
Table 7b shows the mean numbers of natural enemies sampled on the various treatment
plots in the major rainy season. The result showed that 20g/L C. odorata had the highest
number of D. rapae as compared to 30g/L C. odorata, neem and sunhalothrin®. The result
again showed that, 20g/L C. odorata, neem and the tapwater (control) had the highest
number of other natural enemies such as ladybird beetle (Cheilomenes lunata), Earwigs,
Red ants (Oecophylla sp.) and Mason wasp as compared to the plots treated with the
conventional insecticide, sunhalothrin®. Meanwhile, the results showed that there were no
significant differences among all treatments in the number of spiders and hoverflies
sampled (Table 7b).
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Table 7b: Mean (±SE) numbers of natural enemies of pests of cabbage sprayed with
botanical and conventional insecticides during 2014 major rainy season.
Mean ± SE natural enemies/ plant
Treatments D. rapae Spider Hoverfly Other N.E1
10g/L C. odorata 1.88 ± 0.57 ab 2.13 ± 0.30 0.63 ± 0.25 2.29 ± 0.42 ab
20g/L C. odorata 3.75 ± 0.63 a 2.00 ± 0.26 0.04 ± 0.05 3.50 ± 0.56 a
30g/L C. odorata 0.83 ± 0.21 b 1.63 ± 0.38 0.08 ± 0.09 2.83 ± 0.42 ab
50g/ L Neem 1.25 ± 0.38 b 2.08 ± 0.28 0.17 ± 0.09 3.50 ± 0.51 a
Sunhalothrin® 2.33 ± 0.75 b 1.17 ± 1.22 0.46 ± 0.24 1.46 ± 0.26 b
Tap water 2.29 ± 0.57 ab 2.00 ± 0.32 0.54 ± 0.29 3.38 ± 0.31 a
F- Value 3.51 1.55 1.68 3.65
P 0.0051* 0.1781 0.1433 0.004*
Means within a column for each treatment under each dose followed by different letters
differ significantly from each other (P≤ 0.005).
1Other natural enemies: ladybird beetle (Cheilomenes lunata), earwigs, red ants
(Oecophylla sp.) and mason wasp
4.4 Effects of treatments on cabbage head damage
Head damage were as a result of insects‟ holes in/or on cabbage leaves; which were mainly
caused by DBM, cabbage webworms, the variegated grasshoppers and the millipedes in the
growing seasons. There were no significant differences in the head damage among the
treatments in the major season (Table 8). On the other hand, there was significant
difference in the mean head damage among treatments in the minor rainy season. Cabbage
heads from tap water or control plots had the highest head damage as compared to neem
seed extract which had the lowest damage.
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Table 8: Mean (±S.E) scores for head damage during 2014 major and minor seasons.
Mean ± SE head damage/ plant
Treatment Major rainy season Minor rainy season
10g/L C. odorata 3.17 ± 0.33 a 2.5 ± 0.28 ab
20g/L C. odorata 3.21 ± 0.29 a 2.96 ± 0.30 ab
30g/L C. odorata 3.13 ± 0.37 a 2.79 ± 0.32 ab
50g/ L Neem 1.96 ± 0.25 a 1.83 ± 0.27 b
Sunhalothrin® 3.04 ± 0.35 a 2.75 ± 0.27 ab
Tap water 3.04 ± 0.31 a 3.38 ± 0.31 a
F- Value 2.20 3.03
P 0.0575 0.0126*
Means within a column for each treatment under each dose followed by different letter
differ significantly from each other.
4.5 Effects of treatments on cabbage multiple head formation
Figure 1 shows the mean percent of multiple heads formed in the treatment plots during the
two growing seasons. Tap water and 30g/L C. odorata treated plots had significantly high
percentages of multiple heads formed in the major rainy season. Whiles, plots sprayed with
10 and 20g/L C. odorata and sunhalothrin® had significantly lower percentages of multiple
head formed, with 50g/L neem having the least mean percent of multiple heads formed in
the major season (Table 9). However, there were no significant differences in the percent
mean of multiple heads formed during the minor season (Table 10).
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Figure 1: Effects of treatments on cabbage multiple heads formation during 2014 major and
minor cropping seasons.
4.6 Effects of treatments on marketability of cabbage
Figures 2 and 3 shows the mean cabbage head or marketable yield acceptability compared
to the unmarketable cabbage heads per plots as affected by the various treatments. In both
seasons, the neem extract treated plots had the highest mean yield of marketable heads (ton/
ha) compared to the cabbage heads of the other treatments. There were no significant
differences in the mean yields of marketable heads among the other sprayed treatments for
both growing seasons, but differed from those of the tapwater treated plots. Also, there
were no significant differences in the mean yield of unmarketable heads in all treatment
plots for both major and minor seasons.
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Figure 2: Effects of the various treatments on the mean yield of cabbage head marketability
in the major season.
Figure 3: Effects of the various treatments on the mean yield of cabbage head marketability
in the minor season.
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4.7 Effects of treatments on weight of cabbage head
The gnawing, chewing and sucking activities of different insect pests on the leaves and
heads of cabbage significantly reduced the mean weight of cabbage heads harvested during
the growing periods (Table 9 and 10). Even though, there were significant differences
among treatments in the major and minor rainy seasons, 2014 (Table 9 and 10), with Neem
seed extract treated plots recording the highest mean weight for both major and minor rainy
seasons of the year. The mean head weight differences among the three levels of C.
odorata, Sunhalothrin® and tap water for both growing seasons were not significant. The
mean yield of cabbages treated with C. odorata at 10 and 20g/L were significantly higher
than that of tapwater.
Table 9: Mean (± S.E) number of multiple heads, weight of cabbage heads and yield of
cabbage under different spray treatments during 2014 major rainy season.
Mean ± SE:
Treatments # of cabbage with Weight per Total yield of
multiple heads (%) cabbage head (kg) cabbage (ton/ ha)
10g/L C. odorata 3.13 ± 1.14 ab 0.21 ± 0.05b 8.37 ± 1.83 b
20g/L C. odorata 2.08 ± 0.95 ab 0.26 ± 0.05b 10.50 ± 2.19 b
30g/L C. odorata 6.25 ± 1.30 a 0.24 ± 0.05b 9.67 ± 1.95 b
50g/ L Neem 1.56 ± 0.87 b 0.52 ± 0.06a 20.75 ± 2.39 a
Sunhalothrin® 2.60 ± 1.07 ab 0.24 ± 0.05b 9.43 ± 1.88 b
Tap water 6.25 ± 1.29 a 0.20 ± 0.05b 3.30 ± 0.58 b
F- Value 3.44 4.93 8.96
P 0.0059* 0.0004* <0.0001*
Means within a column for each treatment under each dose followed by different letters
differ significantly from each other (P≤ 0.005).
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Table 10: Mean (± S.E) number of multiple heads, weight of cabbage heads and yield of
cabbage under different spray treatments during 2014 minor rainy season.
Mean ± SE:
Treatments # of cabbage with Weight per Total yield of
multiple heads (%) cabbage head (kg) cabbage (ton/ ha)
10g/L C. odorata 3.65 ± 1.18 a 0.25 ± 0.03 b 10.04 ± 1.08 b
20g/L C. odorata 2.60 ± 1.05 a 0.25 ± 0.04 b 10.13 ± 1.60 b
30g/L C. odorata 5.73 ± 1.29 a 0.24 ± 0.03 b 9.56 ± 1.31 bc
50g/ L Neem 3.13 ± 1.14 a 0.47 ± 0.06 a 18.80 ± 2.45 a
Sunhalothrin® 4.69 ± 1.25 a 0.22 ± 0.03 b 8.99 ± 1.17 bc
Tap water 5.73 ± 1.30 a 0.17 ± 0.03 b 3.49 ± 0.62 c
F- Value 1.20 7.14 10.82
P 0.3106 <0.0001* <0.0001*
Means within a column for each treatment under each dose followed by different letters
differ significantly from each other (P≤ 0.005).
4.8 Economics of cabbage production
4.8.1 Yield and income
All the botanical treatments and the synthetic insecticide, sunhalothrin® in both growing
seasons were financially profitable compared to the tap water or control treatment. Treated
plots other than the control (untreated plots) had higher marketable head yields which
resulted in income that exceeded the cost of production for the major rainy season whiles in
the minor season, higher prices of marketable heads resulted in high income (Tables 12 and
11, respectiviely). There were differences in the total cost of treatments between the major
and minor rainy seasons because there was one spray more in the minor season than in the
major rainy season.
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4.8.2 Cost: benefit ratio
In the minor rainy season, the 10 and 20g/ L C. odorata had better cost and benefit ratio as
compared to 30g/L C. odorata as shown in Table 11 below. Also, neem had the best cost:
benefit ratio of 1: 67.3 as compared with the sunhalothrin which had the lowest ratio of 1:
19.8 during the study period (Table 11). In the major rainy season, neem sprayed plots
showed economic viability over the tap water control and had a ratio of 1:50.6. The other
botanicals (Siam weed, C. odorata) had better cost and benefit ratios as compared to the
conventional plots which gave the ratio of 1: 18.8 (Table 12).
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Table 11: Evaluation of cost and benefit in managing cabbage pests with crude water extracts of Siam weed, neem and conventional insecticide,
Sunhalothrin® during 2014 minor rainy season.
Treatment Mean total Marketable Unmarketable Cost of Income from Income from Total Income Net benefit Benefit Cost:
yield per Head Yield head yield treatment Mktable head Unmktable head (GH/ ha) (GHC/ha) over Benefit
plant (ton/ha) (ton/ha) (ton/ha) (GHC/ha) (GHC/ha) (GHC/ha) Ctrl. ratio
10g/L 10.04 ± 1.08 6.01 ± 1.04 4.02 ± 0.42 400.00 15,025 4,020 19,045 18,645 12,635 1:31.6
C. odorata
20g/L 10.13 ± 1.60 8.04 ± 1.02 2.10 ± 0.44 400.00 20,100 2,100 22,200 21,800 15,790 1:39.5
C. odorata
30g/L 9.56 ± 1.31 6.07 ± 1.12 3.45 ± 0.45 400.00 15,175 3,450 18,625 18,225 12,215 1:30.5
C. odorata
50g/L Neem 18.80 ± 2.45 15.06 ± 1.95 3.20 ± 0.58 510.00 37,650 3,200 40,850 40,340 34,330 1:67.3
Sunhalothrin 8.99 ± 1.17 4.54 ± 1.07 4.02 ± 0.55 450.00 11,350 4,020 15,370 14,920 8,910 1:19.8
Tap water 3.49 ± 0.62 1.74 ± 0.42 1.66 ± 0.48 0.0 4,350 1,660 6,010 6,010 0 -
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Table 12: Evaluation of cost and benefit of managing cabbage pests with crude water extracts of Siam weed, neem and conventional insecticide,
Sunhalothrin® during 2014 major rainy season
Treatment Mean total Marketable Unmarketable Cost of Income from Income from Total Income Net benefit Benefit Cost:
yield per Head Yield head yield treatment Mktable head Unmktable head (GH/ ha) (GHC/ha) over Benefit
plant (ton/ ha) (ton/ ha) (ton/ha) (GHC/ha) (GHC/ha) (GHC/ha) Ctrl. ratio
10g/L 8.37 ± 1.83 7.05 ± 1.02 1.32 ± 0.60 350.00 10,575 660 11,235 10,885 7,785 1:22.2
C. odorata
20g/L 10.50 ± 2.19 8.32 ± 1.61 2.15 ± 0.65 350.00 12,480 1,075 13,555 13,205 10,105 1:28.9
C. odorata
30g/L 9.67 ± 1.95 6.31 ± 1.19 3.22 ± 0.81 350.00 9,465 1,610 11,075 10,725 7,625 1:21.8
C. odorata
50g/L Neem 20.75 ± 2.29 16.45 ± 1.25 4.33 ± 1.05 460.00 24,675 2,165 26,840 26,380 23,280 1:50.6
Sunhalothrin 9.43 ± 1.88 7.17 ± 1.05 2.55 ± 0.95 450.00 10,755 1,275 12,030 11,580 8,480 1:18.8
Tap water 3.30 ± 0.58 1.65 ± 0.45 1.25 ± 0.55 0.0 2,475 625 3,100 3,100 0 -
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CHAPTER FIVE
5.0 DISCUSSIONS
5.1 Effects of the treatments on insects population
The findings from this research have demonstrated that, the production of cabbage in the
moist deciduous agro-ecological zone can be affected by numerous insect pests among such
are cabbage aphids (B. brassicae), DBM (P. xylostella), cabbage webworm (H. undalis),
grasshopper (Z. variegatus), cabbage flea beetle (Phyllotreta spp.), cabbage white butterfly
(Pieris rapae), cabbage looper (Trichoplusia ni), Cotton leafworm (Spodoptera litoralis)
and other arthropods.
Insect pests sampled on the cabbage field in the major season were slightly lower compared
to those that were present in the minor season (Table 5). The results showed that the
presence and abundance of the insect pests differed during the two seasons and this could be
attributed to seasonal and climatic differences. Also, surprisingly diamondback moth, P.
xylostella was not found on the treatment plots during the major season. The reasons may be
attributed to the dominance of the natural enemies such as predators and parasites that feed
on them and natural elements such as rainfall, which washes off the eggs, larvae, pupae and
the adults from the plant to the soil where they are destroyed during the period.
However, population of aphids, B. brassicae, was dominant throughout both seasons and
was reduced as a result of the application of the treatment with siam weed and neem seed
extracts. This was especially observed in the 10g/L C. odorata and neem seed extracts plots
in both the minor and the major seasons. This reduction was due to the toxic effect of the
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plants. Botanicals and plant - based insecticides have been noted for their larvicidal effects
(Sanda et al., 2006; Ogendo et al., 2008; Agboka et al., 2009). The effectiveness of siam
weed and neem seed extracts in the study were generally better as compared to the
conventional insecticide in the control of aphid. This may be due the fact that B. brassicae
may gradually be developing resistance to the conventional insecticides (Fening et al. 2013).
The performance of the plant extracts in reducing the population of B. brassicae indicates
their usefulness in controlling insect pests when incorporated into Integrated Pest
Management (IPM). The efficacy of the botanical treatments against B. brassicae is
supported by the findings of previous studies on this insect pest. For instance, the extracts of
Azadirachta indica and Melia azedarach have been successfully used to control infestations
of cabbage aphids (Rando et al., 2011 and Kibrom et al., 2012).
Also, the 10 and 20g/L C. odorata performed better as compared to the 30g/L C. odorata in
the control of other pests such as T. ni, P. rapae, S. littorallis and Phyllotreta spp. Other
herbivores species found on both botanical and conventional treated plots did not differ
significantly among the various treatments. Plutella xylostella was dominant during the
minor season on the treatment plots. Moreover, there was no significant difference in their
level of infestations. Cabbage webworm, H. undalis was dominant during the major rainy
season due to favourable weather conditions. The variegated grasshopper, Z. variegatus and
other arthropod pests were also found in both seasons but were more destructive in the
minor rainy season. According to the findings of Ayalew (2006), yield losses of cabbage
may be due to insect pest and vary depending on the season and severity of pest infestation.
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Monoculture enhanced pest infestation on cabbage by lepidopterous insects and aphids since
it created conducive environment for particular insect pest to flourish (Kumar, 1986).
5.2 Effects of treatments on natural enemies population
High incidence of natural enemies per plot is dependent upon the number of insect pests
present, the toxicity of the treatments and the vigorous growth and succulence of the plant.
Ideally, insecticides used in controlling insect pests should either have less impact on natural
enemies or promote their build- up. The number of parasitoids and predators observed on the
cabbage treated plot was somewhat not different from that of the control. In the minor rainy
season, D. rapae and C. plutellae showed no significant difference due to less toxicity of the
treatments on the beneficial insects. For instance, neem products have been proved to be
harmless to beneficial insects and environmentally friendly (Borror et al., 1992).
However, the 20g/ L C. odorata treated plots in the major season performed better in
ensuring the survival of D. rapae than the 30g/L C. odorata treated plot, and also more other
natural enemies such as ladybird beetle (Cheilomenes lunata), earwigs, red ants (Oecophylla
sp.) and mson wasp than the conventional insecticide, sunhalothrin in both the major and
minor seasons during the study. The effectiveness of 20g/ L C. odorata may be attributed to
its low toxicity of the treatment on the beneficial insects, hence making them available and
thereby promoting high level parasitism and predation (Charleston, 2004).
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5.3 Effects of treatments on cabbage head damage
Cabbage is prone to insect pest attack and the tendency to produce healthy and quality
cabbage heads with low insecticide residue to meet consumers demand has been a problem
yet to be solved. A study conducted in the South Western Ontario in Canada concluded that
attack by insect pests alone contributed significantly to yield loss of cabbage by 50%
(Tolman et al., 2004). Meanwhile, DBM which is a cosmopolitan pest of crucifers cause a
significant yield loss of 20- 100% and up to 60% on cabbage in India and Ghana,
respectively (Chellaiah and Srinivasan, 1986; Lingappa et al., 2004; Obeng- Ofori et al.,
2007; Fening et al., 2013). In the study, it was observed that the three rates of C. odorata,
neem and sunhalothrin® were most active against insect pests causing damage to cabbage
heads as compared with control plot in the minor season. Fening et al., 2011, however,
revealed that the use of plant extracts in IPM provides added advantage over the use of
synthetic insecticide; as, they are not persistent in the environment, readily available,
affordable and easily made.
5.4 Effects of treatments on multiple heads formation
Higher significant percentages of multiple heads were formed on untreated plots as
compared to treated plots. These findings indicated that cabbage cannot be cultivated
without making an attempt to control insect pests because like other crucifers, they contain
mustard oil and glucosides (Gupta and Thorsteinson, 1960) which make them more
susceptible to insect pest attack especially cabbage webworm, H. unadalis.
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5.5 Effects of treatments on marketability of cabbage
Marketable cabbage heads harvested from the treated plots were significantly higher as
compared to that from control plots which had significantly higher mean weight of
unmarketable heads for both major and minor seasons. This may result from the treatments
offering some level of protection against the key pests of cabbage. Neem treated plots in
both seasons recorded the highest significant mean marketable heads compared to the other
treatment plots. This might be as a result of the numerous effects of the neem extract on the
crop pests through their repellency effect, antifeedant effect by preventing insects from
laying eggs or as inhibitors by interfering with insect life cycle (Kareru et al., 2013).
5.6 Effects of treatments on weight of cabbage head
The significant performance of the cabbage heads among the various treatments during the
major and minor rainy seasons respectively were attributed to the treatment effects.
However, other factors may have accounted for the yield performance, such as the existing
insect pest pressure, land use history, crop resilience, soil fertility and prevailing climatic
conditions (Fening et al., 2014). High yield of cabbage head was recorded on treated plots
against that of control plot with Neem seed extract treated plots recording the highest mean
weight of cabbage heads due its insecticidal ability. This result confirms the findings of
Landis et al., (2000), that acqueous neem seed extracts (ANSE) applied at 50- 70 g/L
provided good protection against collard insect pests and increased dry matter content
significantly.
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5.7 Cost: benefit ratio
Cost: benefit ratio is an indicator of the relative economic performance of the treatments
(Aziz et al., 2012, Amoabeng et al., 2014). A ratio of more than one indicates the economic
viability of the treatment. Economic analysis, however, is useful because besides the spray
type applied: all other input costs were constant for all treatments (Amoabeng et al., 2014).
The cost: benefit ratio, the total income and the benefit obtained from each treatment is
greatly influenced by the price of the commodity. The results in the study show that the cost:
benefit ratios in the minor rainy were slightly higher for treatments as compared to that of
the major rainy season. This may be attributed to the price of cabbage heads which was
higher (50%) in the minor season harvest than the major season yield.
In the study, cabbage heads from plots sprayed with the conventional, sunhalothrin® and
those from the botanical plots were sold for the same price. If cabbage heads from plots
protected with botanicals were sold for premium price, then, there would be corresponding
increases in the economic benefit. In the developed countries where human health is of
paramount importance, there are premium prices for food commodities that do not have
pesticide contamination and health- conscious consumers eagerly patronize (Njoroge and
Manu, 1999; Amoabeng et al., 2014).
However, in Ghana, food commodities including vegetables such as cabbage on the market
are not currently identified as organic and conventional. Organic food producers in
developing countries should raise awareness of the benefits of pesticide- free food
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commodities to obtain the deserved prices for their commodities and subsequently obtain
higher benefit and also have access to export commodities to the US and EU markets
(Njoroge and Manu, 1999; Amoabeng et al., 2014).
The study has shown that the 10g/L and 20g/L of C.odorata extracts were effective in the
management of insect pests, less detrimental to natural enemies and also economical to use
than the higher rate, 30g/L C. odorata extracts. This finding has therefore offered a remedy
to Amoabeng et al., (2013) who applied C. odorata extract at 30g/L and was effective in the
control of insect pests but was more detrimental to the survival of natural enemies. Thus, C.
odorata applied at 10- 20g/L of water and also neem at 50g/L are recommended for use by
small scale cabbage farmers (especially those in organic farming systems) to ensure food
and environmental safety (Fening, 2013).
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CHAPTER SIX
6.0 SUMMARY AND CONCLUSION
The awareness regarding food safety has increased the demand for organically produced
food. Globally, the non-pesticide management (NPM) of crops is becoming popular among
vegetable farmers since it endeavours to keep the control of insect pests and crop cultivation
costs to a minimum and avoid dependency on manufactured inputs by utilizing plant
materials that are readily available to farmers. The study has demonstrated that there is some
potential for the use of lower rates of C. odorata extracts at 10- 20g/ L and neem seed
extract to control some of the major pests of cabbage and conveniently maintain ecological
balance with their natural enemies on cabbage plants and also have increase in yield. The
advantage of using the Siam weed and neem extract is that they are cheap and easy to
prepare especially the siam weed. However, further work is required to fine- tune its
extraction so that optimum amount of the active ingredient could be obtained.
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APPENDICES
Appendix 1: ANOVA for the effects of botanicals and conventional insecticides on
insect pest population
ANOVA for B. brassicae in the major season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 116.55556 23.3111 7.4379 <.0001*
Reps. 2 27.76389 13.8819 4.4293
Error 136 426.23611 3.1341
C. Total 143 570.55556
ANOVA for H. undalis in the major season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 146.70139 29.3403 11.1348 <.0001*
REPS 2 2.09722 1.0486 0.3980
Error 136 358.36111 2.6350
C. Total 143 507.15972
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ANOVA for Z.variegatus in the major season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 5.80556 1.16111 0.6699 0.6470
REPS 2 1.76389 0.88194 0.5088
Error 136 235.73611 1.73335
C. Total 143 243.30556
ANOVA for other pests in the major season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 85.89583 17.1792 5.5556 0.0001*
REPS 2 0.50000 0.2500 0.0808
Error 136 420.54167 3.0922
C. Total 143 506.93750
ANOVA for B. brassicae in the minor season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 179.61806 35.9236 7.6087 <.0001*
Reps. 2 0.43056 0.2153 0.0456
Error 136 642.11111 4.7214
C. Total 143 822.15972
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ANOVA for P. xylostella in the minor season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 73.7847 14.7569 1.0183 0.4094
REP. 2 6.0139 3.0069 0.2075
Error 136 1970.8611 14.4916
C. Total 143 2050.6597
ANOVA for Z. variegatus in the minor season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 35.47222 7.0944 1.0642 0.3831
Reps 2 26.09722 13.0486 1.9573
Error 136 906.65278 6.6666
C. Total 143 968.22222
ANOVA for other pests in the minor season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 17.20139 3.44028 1.6716 0.1456
Reps. 2 8.22222 4.11111 1.9975
Error 136 279.90278 2.05811
C. Total 143 305.32639
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Appendix 2: ANOVA for the Effects of the treatments on the natural enemies
ANOVA for D. rapae in the minor season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 52.1181 10.4236 0.8432 0.5213
Reps. 2 7.3889 3.6944 0.2989
Error 136 1681.1528 12.3614
C. Total 143 1740.6597
ANOVA for C. plutellae in the minor season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 29.05556 5.81111 0.9459 0.4536
Reps. 2 6.09722 3.04861 0.4963
Error 136 835.48611 6.14328
C. Total 143 870.63889
ANOVA for spiders in the minor season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 54.03472 10.8069 3.2241 0.0088*
Reps. 2 2.76389 1.3819 0.4123
Error 136 455.86111 3.3519
C. Total 143 512.65972
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ANOVA for hoverfly in the minor season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 13.66667 2.73333 1.2729 0.2792
Reps. 2 3.29167 1.64583 0.7664
Error 136 292.04167 2.14737
C. Total 143 309.00000
ANOVA for other natural enemies in the minor season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 28.50000 5.70000 4.8224 0.0004*
Reps. 2 4.50000 2.25000 1.9036
Error 136 160.75000 1.18199
C. Total 143 193.75000
ANOVA for D. rapae in the major season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 124.3056 24.8611 3.5115 0.0051*
REPS 2 64.3889 32.1944 4.5473
Error 136 962.8611 7.0799
C. Total 143 1151.5556
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ANOVA for spiders in the major season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 16.58333 3.31667 1.5512 0.1781
REPS 2 2.62500 1.31250 0.6138
Error 136 290.79167 2.13817
C. Total 143 310.00000
ANOVA for hoverflyin the major season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 7.63889 1.52778 1.6809 0.1433
REPS 2 6.05556 3.02778 3.3312
Error 136 123.61111 0.90891
C. Total 143 137.30556
ANOVA for other natural enemiesin the minor season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 80.78472 16.1569 3.6469 0.0040*
REPS 2 19.34722 9.6736 2.1835
Error 136 602.52778 4.4304
C. Total 143 702.65972
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Appendix 3: ANOVA for the effects of treatments on cabbage head damage:
In the major season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 27.36806 5.4736 2.2033 0.0575
Reps. 2 22.93056 11.4653 4.6151
Error 136 337.86111 2.4843
C. Total 143 388.15972
In the minor season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 31.78472 6.35694 3.0314 0.0126*
Reps. 2 3.18056 1.59028 0.7584
Error 136 285.19444 2.09702
C. Total 143 320.15972
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Appendix 4: ANOVA for the effects of treatment on multiple head formation:
In the major season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 520.8333 104.167 3.4376 0.0059*
Reps. 2 6.5104 3.255 0.1074 0.8982
Error 136 4121.0937 30.302
C. Total 143 4648.4375
In the minor season
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 213.7587 42.7517 1.2041 0.3106
Reps. 2 8.6806 4.3403 0.1222 0.8850
Error 136 4828.5590 35.5041
C. Total 143 5050.9983
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Appendix 5: ANOVA for the effects of treatments on marketable and unmarketable
cabbage heads.
ANOVA for marketable cabbage head in the major season.
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 1.690834 0.338167 5.2857 0.0002*
Reps. 2 0.851391 0.425695 6.6539
Error 136 8.700891 0.063977
C. Total 143 11.243115
ANOVA for unmarketable cabbage head in the major season.
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 0.0837557 0.016751 1.3854 0.2336
Reps. 2 0.0255045 0.012752 1.0547
Error 136 1.6444347 0.012091
C. Total 143 1.7536949
ANOVA for marketable cabbage head in the minor season.
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 1.5734765 0.314695 6.8949 <.0001*
Reps. 2 0.1956544 0.097827 2.1434
Error 136 6.2072698 0.045642
C. Total 143 7.9764007
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ANOVA for unmarketable cabbage head in the minor season.
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 0.02573852 0.005148 1.3404 0.2510
Reps. 2 0.00675464 0.003377 0.8794
Error 136 0.52228495 0.003840
C. Total 143 0.55477811
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Appendix 6: ANOVA for the effects of treatments on weight and total yield of cabbage
head .
ANOVA for cabbage head weight in the major rainy season.
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 1.560578 0.312116 4.9331 0.0004*
Reps. 2 0.821725 0.410863 6.4938
Error 136 8.604686 0.063270
C. Total 143 10.986989
ANOVA for total cabbage yield in ton/ ha for the major season.
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS
5
3915.072
783.014
8.9610
<.0001*
Reps. 2 678.858 339.429 3.8845 0.0229*
Error 136 11883.781 87.381
C. Total 143 16477.711
ANOVA for cabbage head weight in the minor rainy season.
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 1.2974452 0.259489 7.1369 <.0001*
Reps. 2 0.1485852 0.074293 2.0433
Error 136 4.9447981 0.036359
C. Total 143 6.3908285
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ANOVA for total cabbage yield in ton/ ha for the minor season.
Source DF Sum of
Squares
Mean Square F Ratio Prob > F
TREATMENTS 5 2900.048 580.010 10.8147 <.0001*
Reps. 2 160.505 80.252 1.4964 0.2276
Error 136 7293.887 53.632
C. Total 143 10354.439
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