THE EFFECTS OF FUNGICIDE-INSECTICIDE SEED TREATMENTS ON EMERGENCE, GROWTH AND YIELD OF IRRIGATED COTTON IN THE SUDAN GEZIRA

Fungicide-insecticide seed treatment, particularly with methoxyethylmercuriacetate (MEMA) and dieldrin, often improved emergence, growth and yield of irrigated Egyptian-type cotton (Gossypium barbadense) in the Gezira area of the Sudan. Such treatment reduced post-emergence wilting and death of seedlings resulting from termite attack, and also reduced pre-emergence mortality probably caused primarily by soil insects, but appeared to have little effect on the incidence of termite damage to tap-roots of mature plants at the end of the season. Termite attack tended to be worse in close rotations, and the beneficial effects of fungicide-insecticide seed treatment were greater in three-course than in four-course rotation plots. In one experiment treatment improved growth and yield of cotton plants in the apparent near-absence of insect pests and diseases, this effect perhaps deriving from control of minor root damage caused by soil insects and/or fungi. Certain seed treatments, notably those containing MEMA and gamma-BHC, were slightly phytotoxic, but at the levels applied-0.043% mercury/seed and 0.12-0.24% insecticide/seed-this aspect, although needing further investigation, seems unlikely to be of serious practical significance in the Sudan Gezira where high sowing rates are the rule; any slight phytotoxicity would probably be outweighed by the protective effects of the treatment. Phytotoxicity tended to become more pronounced with increasing number of seeds per sowing hole.