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

Abstract

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 γ‐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.