ABSTRACT
Attack by Helicoverpa armigera remains the major constraint to increased productivity of cotton in Tanzania. For optimal yield, six preventive sprays of chemical insecticides are required during flowering for control of this pest. However, the abolition of subsidies on chemical insecticides/fertilizers and devaluation of the currency (brought about by an on going structural adjustment programme), increased production costs have led to a decline in profitability. VIn light of this new economic environment, on station and on farm trials were carried out between 1994 and 1997, to evaluate the utility of threshold based spraying and plant based insecticides for optimal management of H. armigera. The study showed that spraying on a threshold of 50% damaged buds, reduced spraying frequency from six to three sprays without significantly reducing yield. Similarly, 17% v/v extracts from Tephrosia vogelii, Jatropha curcas, Azadirachta indica and Derris eliptica applied by Micron ULVA + in 10 litres of water/ha, were comparable to either endosulfan applied at 625 or cypermethrin at 45 g a.i ha-1 for control of the bollworm. Botanical insecticides gave 17 to 65 % less yield than conventional pesticides but an average of 38% more than the unsprayed control.

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