AVALIAÇÃO DE DESFOLHAMENTOS CONTÍNUOS E SEQÜENCIAIS, SIMULANDO DANO DE PRAGAS EM SOJA SOBRE O CULTIVAR BRS

Abstract

The objective of this research was to evaluate the effect of both continuous and sequential defoliation on soybean BRS 66 yield. The treatments were evaluated during the vegetative and reproductive stages by using the injury leveis recommended for the management of soybean defoliating pests. The study was conducted at the Univer- sity of Passo Fundo, in Passo Fundo-RS, from December 1999 to May 2000. The experimental design was complete randomized blocks with six treatments and four replications. The following treatments were tested: (i) 33% of continuous defoliation at stages V4 to V9 and of (ii) 17 and (iii) 33% at stages RI to R4 (1-tHR & CAVINES, 1977, stage); sequential defoliation of (iv) 33+17% and (v) 17+33% from stages V4 to V9 and from stages RI and R4; and (vi) control (no defoliation). Independent of the defoliation levei applied and the fenologic growth stage, the treatments did not de- crease the grain yield per area and per plant. The sequential defoliation of 17%+33% increased the number of grains and the normal pods per plant. However, this treatment decreased the grain weight. This latter effect was also observed with the sequential defoliation of 33%+17% and the continuous of 33% (reproductive stage). The sequential defoliations of 33+17% or 17+33% at the vegetative and reproductive stages, respectively, are more indicated for the control of leaf- feeding insects for the soybean variety BRS 66.