Effect of time and extent of defoliation on grain yield of maize in relation to Cosmopolitan Armyworm(Mythimna separata(Walker)) damage

Abstract

The effect on grain yield of removing the upper, middle or lower 1/3 of the leaf canopy, singly or in combination, at silking or 2, 4 or 6 wk later, was measured to estimate the grain losses resulting from armyworm caterpillar damage. Complete defoliation at silking produced a 77% reduction in grain yield which lessened with delay in defoliation towards crop maturity. Less severe defoliations resulted in smaller reductions in grain yield and showed the middle and upper leaves to be more important in grain production than the lower leaves. Generally, grain yield was tolerant of post-silking defoliation and yield losses exceeding 20% were recorded only after 2/3 of the leaves were removed and then only when this included the middle 1/3 of the leaves. Returns from insecticide applications to control caterpillars after silking will decrease with crop maturity and controls seem unnecessary unless substantial defoliation appears likely.