Reduction of shoot fly damage in irrigated post-rainy season sorghum by manipulating irrigation

Soil moisture was manipulated to control incidence of Atherigona soccata in irrigated post-rainy season sorghum grown under a rainout shelter and in field conditions in Andhra Pradesh,India, during 1989-90 and 1991-92. After uniform irrigation at sowing, the plants were subjected to water stress at the young seedling stage (7-28 days after emergence) for different lengths of time. Soil water had profound effects on the production of water droplets on the surface of the central whorl leaf of seedlings of sorghum genotypes. Leaf surface wetness, which facilitates movement of the larvae, was more affected in susceptible (CSH 5) than in moderately resistant (IS 1054) genotypes. Oviposition and deadhearts were higher in treatments with full irrigation than in treatments to which less water was applied during the first 3 weeks after seedling emergence. This resulted in higher plant biomass and overall grain yield in the latter treatments. Using insecticides to control the infestation, it was shown that inducing plant stress by reduced soil moisture content during early plant growth gave the same or better control of A. soccata damage and the same or higher grain yield as in insecticide-protected plots with full irrigation