Response of Soybeans to Foliage Losses in South Carolina1

Abstract

Defoliations of 17, 33, 50, and 67% were made during periods of insect activity on soybeans at midbloom, pod-set, pod-fill, and on a continued basis from midbloom to pod-set. Foliage losses of 33% at bloom did not result in significant yield losses in any of 10 tests; 67% defoliation at pod-set, or on a continued basis from bloom to pod-set caused greatest losses; and 17% defoliation did not cause significant losses at any stage of growth or on a continued basis. Yield losses from defoliations at pod-fill were intermediate between those at bloom and pod-set. Yield reductions were generally accompanied by reductions in seed weight and protein content and increases in oil content. Seed germination was not affected. Although results were not affected significantly by date of planting and by use of irrigation or different varieties, there was a tendency toward generally lower yields at high production levels in the ‘Hampton’ variety after severe defoliations (50 and 67%) at bloom and pod-fill. It was concluded that foliage losses of 17 or 33% allowed additional light penetration to lower leaves, resulting in compensation by increased photosynthate production in these leaves.