Impact of Pre-Emergence Weed Management Using Pendimethalin (456 g/L EC) And Oxadiargyl (400 g/L SC) on the Growth, Development and Minimum Residue Levels in Two Onion (Allium cepa L.) Varieties
Date
2019-07
Authors
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Journal ISSN
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Publisher
University Of Ghana
Abstract
Two field experiments were conducted at the University Ghana farm, Legon from September, 2018 to March 2019 to evaluate the impact of two herbicides( Oxadiargyl (400 g/L SC) and Pendimethalin 456 g/LEC) on weed management, soil microbial populations, growth and yield of two onion varieties (Dayo and Bawku red) as well as their residual effects on succeeding crops. The study also assessed the cost benefit of using the herbicides compared to hand weeding. The first experiment was laid out in a split plot design in RCBD with four replications and with herbicides treatments as the main plot and onion varieties as the sub plot. A reconnaissance survey was conducted to identify weed species including broadleaves, grasses and sedges in the experimental area prior to land preparation. Oxadiargyl 400g/L SC) applied at 0.5 L/ha (Manufacturer’s recommended rate), and 0.4 L/ha, Pendimethalin 456 g/L EC) applied at 1.25 L/ha (manufacturers recommended rate) and1.00 L/ha and Hand weeding (control) were the main plot treatment while Dayo and Bawku Red (onion varieties) were the sub plot treatments. Data collected were percentage crop establishment, number of days to weed emergence, number of weeds, weed biomass, soil pH, soil microbial population, plant height, number of leaves, leaf length, leaf diameter, plant chlorophyll content, days to bulbing, stem girth, days to physiological maturity, average bulb weight, average bulb diameter, average bulb length, yield and residual levels of herbicides in bulbs. Data were analyzed using analysis of variance and the least significant difference test (P< 0.05) was used to separate the means where there were significant differences. Oxadiargyl treatments led to a significant (P< 0.05) longer number of days to weed emergence compared to Pendimethalin treatments which were also longer than hand weeding. Hand weeding produced the highest weed biomass than all the herbicide treatments. The pH of the soil was affected by weed management methods. Pendimethalin 1.25L/ha resulted in the highest number of soil microbial population. For all treatments, Dayo established better than Bawku red. Dayo at Pendimethalin 1.25L/ha treatment produced the highest plant height. Pendimethalin 1.25L/ha treatments led to the highest number of leaves of onion plant. Pendimethalin 1.00L/ha led to the longest length of onion plant and largest leaf diameter than all the other treatments. Dayo with Pendimethalin (1.00L/ha) treatment resulted in higher leaf chlorophyll content throughout the growth period of the onion plant. Herbicide treatments had a positive effect on chlorophyll content of onion plants. Pendimethalin (1.00L/ha) led the largest stem girth of onion plants. Dayo with Pendimethalin (1.00L/ha) led to the highest plant biomass throughout the growth of the plant. Bawku Red with Oxadiargyl treatments led to the early bulbing of onion plants. Bawku Red with Oxadiargyl treatments also led to earliest maturity of onion plants. Bawku Red with Oxadiargyl (0.4L/ha) led to the largest diameter of onion bulbs. Herbicide treatments showed positive effect on bulb diameter. Pendimethalin (1.00L/ha) with Dayo onion variety showed the largest bulb length compared to other treatments. Bawku red with Oxadiargyl (0.4L/ha) led to the highest bulb weight of onion. Pendimethalin (1.00L/ha) with Bawku red led to the highest onion yield in tons per hectare with Dayo at hand weeding recording the lowest yield. Pendimethalin (1.00L/ha) resulted in the highest marketable yield of onion whiles. Dayo at hand weeding showed the lowest marketable yield. While no traces of Pendimethalin were observed in the onion bulbs, traces of Oxadiargyl (0.05 to 0.9) above the recommended maximum residue limit set by the European Union (0.01) were recorded in onion bulbs from plots treated with the two rates of the herbicide. It was more cost effective to use Pendimethalin at both rates in both varieties than hand weeding and Oxadiargyl. Cowpea bioassay revealed that there were no traces of Pendimethalin in the soil as it did not affect germination growth negatively. On the other hand, cowpea sown on Oxadiargyl treated plots died just after emergence indicating possible of Oxadiargyl.
Description
MPhil. Crop Science (Agronomy)
Keywords
Weed Management, Pendimethalin (456 g/L EC), Oxadiargyl (400 g/L SC), Onion (Allium cepa L.)