Studies of the application of insecticides on cotton in Zambia

Abstract

The status of insect pest management on small farms in Zambia was investigated by interviewing the farmers.Field trials evaluated the timing of insecticide sprays, methods of spray application and the effect of different swath widths using the 'Electrodyn' sprayer.Farmers were aware of the insect pests, their status and the losses they caused, so all of them applied insecticide on their cotton crops. They did not scout their crops for insect pests properly due to the lack of training and help from extension staff. The role of biological control and weed control in cotton insect pest management was unknown to most of the cotton farmers. The majority of farme)'s had knapsack sprayers as these were more versatile and easily available. Some farmers reported problems due to water supply, diluting the insecticides, and the heavy weight of equipment. Farmers who used 'Electrodyn' sprayers appreciated their effectiveness, light weight and the elimination of water. Farmers wanted 'Electrodyn' sprayers to be more versatile so that they could apply pesticides on other crops.Many farmers were aware of the use of ULV spinning disc sprayers and the knapsack sprayers fitted with a tail boom but these were not available in their areas. They were generally not aware of fitting 2 nozzles on a lance,using an ox-drawn or tractor-mounted sprayer. Twenty percent of the farmers had suffered from mild symptoms of insecticide poisoning. Protective clothing was not available in most areas and the important safety precautions during spraying were unknown to most of them. Only about half of the farmers had attended a training course or demonstrations, and at these there was very little emphasis on insect pest management of cotton.The farmers expressed an urgent need for more training, particularly on insect pest scouting and the application of insecticides on cotton.In field trials an economic threshold for He!iothis, a key pest of cotton in Zambia, was 0.50 eggs per plant, when 3 to 4 sprays gave yields similar to 5 routine sprays. Heliothis infestation generally increased during the 10th week after germination coinciding with flowering of cotton so farmers could avoid the first or second spray in most seasons. Similar yields of seed cotton were obtained when cypermethrin (30 g. a.i./ha) and lambda cyhalothrin (12 g. a.i./ha) were applied with an 'Electrodyn', knapsack and ULV sprayers. The yields were also similar when charged and partially discharged spray droplets were applied with 'Electrodyn' sprayers.There is an urgent need to modify the currently recommended fixed schedule of 5 sprays of pyrethroids in Zambia and to emphasise the scouting of Heliothis eggs and other major pests to improve timing of sprays which should lead to the reduced application of insecticides using the improved application techniques appropriate to small scale cotton farmers.