Investigations on insecticidal seed dressings, soil treatments and foliar sprays for the control of Melanagromyza phaseoli (Tryon) in Ceylon

Abstract

Three methods of chemical control of Melanagromyza phaseoli (Tryon) on bean (Phaseolus) have been investigated, these comprising seed and soil treatments and spraying of the foliage.Organophosphorus and chlorinated hydrocarbon insecticides have been tested, chiefly as seed soaks, in the control of the pest. Applied in this way, the former gave poor protection, whereas the chlorinated hydrocarbons, especially the cyclodiene compounds, aldrin, dieldrin, endrin and chlordane, gave adequate protection. Reduction of the period of soaking led to better germination of treated seed. When seed-borne diseases were present, soaking in water or insecticidal solution enhanced their incidence. Bean varieties varied in their response to soaking in water or the insecticidal fluids used, the germination of most varieties being adversely affected. Endrin 20 per cent, emulsifiable concentrate (E.C.) used at a dilution of 1:250 as a soak for six hours or at a dilution of 1:125 for three hours or 1:50 for momentary dipping or up to an hour's soaking, gave good germination and protection from M. phaseoli with the climbing bean variety Kentucky Wonder but reduced very considerably the germination of several other varieties.Where soil was treated with various insecticides for control of M. phaseoli. pre-sowing treatment was more effective in protecting the bean plant from this seedling pest than treatment given after seedling emergence. Soil treatment with endrin did not induce phytotoxic symptoms in those varieties that were adversely affected when the seeds were soaked in emulsified solutions of endrin.Foliar spraying with DDT 18 per cent. E.C. at one fl. oz. per gal., endrin 20 per cent. E.C. at 0·5 fl. oz. per gal. or parathion 46 per cent. E.C. at 2 ml. per gal. at weekly intervals up to the time of flowering was very effective in controlling M. phaseoli.The efficient control of the pest obtained with pre-sowing treatment of soil or seed suggests that the insecticides concerned may have been acting systemically. Laboratory studies on the life-cycle of the pest in plants derived from treated and untreated seed show that endrin (which was the only insecticide studied in detail in this way) has a larvicidal effect when used as a pre-sowing treatment.