Residual effect of imazapyr + imazapic on cotton grown in succession to soybean

Abstract

ABSTRACT The long residual period of pre-emergent herbicides can interfere with successor crops, causing a phenomenon named carryover. This study evaluated the residual effect of imazapyr + imazapic herbicides on cotton crop grown in succession to soybean. The experiment was conducted between September 2016 and March 2017, in a randomized block design with 4 replicates, where the treatments were four doses of imazapyr + imazapic, 75, 150, 225 and 300 g a.i. ha-1, and the control. The analyzed variables were chlorophyll a fluorescence, shoot height, root length and volume, dry shoot mass and root dry mass. The data were submitted to analysis of variance and Tukey’s test, at p ≤ 0.05. The reduction in photosynthetic performance indexes for treatments of 150, 225 and 300 g a.i. ha-1 at 15 days after emergence (DAE) and of 75 g a.i ha-1 at 60 DAE indicated a photoinhibitory effect of these herbicides on plants. However, shoot height, length, volume and root dry mass were not affected in the treatments tested. Therefore, the persistence of the herbicide in the soil was not enough to characterize a carryover effect in cotton 135 days after application (DAA).