Pesticide use Pattern and Insecticide Residue Levels in Tomato (Lycopersicum Esculentum Mill.) in Some Selected Production Systems in Ghana

Abstract

A survey of 120 tomato farmers under two production systems was carried out at Tono and Vea in the Upper East region, Derma and Techimentia in the Tano district of the Brong Ahafo region to assess farmers’ knowledge of insect pest problems, production systems and pest management practices with emphasis on pesticide use patterns. Residue levels of Lindane, Endosulfan and Chlorpyrifos insecticides in harvested tomato fruits from Derma, Techimentia, Tono and Vea areas were determined by Gas Chromatography and compared with FAO/WHO MRLS’s The major insect pests of tomato were the fruitborers Helicoverpa armigera (Hubner) and the variegated grasshopper Zonocerus variegatus (L). Pests such as aphids Aphids gossypii Glover, mirids Nesidiocoris tenuis Reuter, whiteflies Bemisia tabaci Genn. and Africanmole cricket Gryllotalpa africana were identified but it was obvious that fanners lacked knowledge on aspects of pest biology, damage and management. Yield losses perceived by farmers to be caused by pests ranged from 5% - 40%. In the Tano district, traditional tomato varieties such as Power, Reno, Yokohama and Italy were cropped from uncertified seed source. About 84.6% of tomato farmers in the Upper East region cropped certified, exotic and high yielding varieties. Farmers did not practice integrated pest management. Highly hazardous insecticides recommended for the control of cocoa and cotton pests were used on tomatoes. These included Deltaphos 262 EC (Deltamethrin and Triazophos), Cypercal P 186 EC (Cypermethrin and Profenefos), Decis D 312 EC (Deltamethrin and Chlorpyrifos methyl), Polythrin 336 EC (Cypermethrin and Chlorpyrifos methyl), K D (Lamda-cyhalothrin and Chlorpyrifos methyl), Thiodan 50 EC (Endosulfan), Thiodan 35 EC/ULV (Endosulfan) and “Gammalin” 20 EC (Landane). About 23.1% and 13.3% of the insecticides used by farmers in the Brong Ahafo and Upper East regions respectively were organochlorines. Fungicides such as Topsin (Thiophanate methyl), Benlate (Benomyl), Ridomil (Metalaxyl), Dithane (Mancozeb) and the Copper base products were applied more in the Brong Ahafo region. In most cases, contact and systemic fungicides were not used to control specific diseases, but for luxuriant vegetative growth and cosmetic value. The average frequency of application was 10-12 and 4 - 6 times of cocktail of pesticides in the Brong Ahafo and Upper East regions, respectively based on calendar spraying at 3 - 7 days intervals. Studies into residue levels of Lindane, Endosulfan and Chlorpyrifos insecticides applied on tomato revealed that fruits sampled from Tano district had residue levels of Lindane ranging from 0.005 mg/kg to 0.712 mg/kg. Residue levels of Alpha endosulfan ranged from 0.014 mg/kg to 0.126 mg/kg. The residues of both insecticides were below Maximum Residue Limits (MRLs’) recommended by FAO/WHO. Chlorpyrifos residues analysed in tomatoes from Upper East region ranged from 0.019 mg/kg to 0.937 mg/kg. About 25% of tomato samples analysed had residue levels exceeding FAO/WHO MRL’s check for Chlorpyrifos at 0.5 mg/kg (FAO/WHO, 1993). The findings underscore the need for routine monitoring of pesticide residue levels and improved practice of pesticide use to ensure food safety