Pyrithiobac-sodium : atividade residual sobre plantas daninhas e seletividade da mistura com amonio-glufosinate em algodoeiro transgênico Liberty Link®

Abstract

This study aimed to evaluate the effect of residual activity of pyrithiobac-sodium in the control of important weeds of cotton crop, as well as the selectivity of this herbicide in association with ammonium-glufosinate to transgenic variety cotton LL® (Liberty Link). From the results generated in the experiments, the following conclusions: the biotype of B. pilosa demonstrated no sensitivity to pyrithiobac-sodium applied to the soil showing a possible resistance to ALS herbicide inhibitors. Growth of Euphorbia heterophylla resistant to ALS herbicide inhibitors was restricted by the residual activity of pyrithiobac-sodium in soil, although there was no death of plants. Residual activity of pyrithiobac-sodium caused restriction to the vegetative growth of other species evaluated. The residual activity pyrithiobac-sodium in soil decreases with time; the first application time provided lower levels of control for the species in this study. Increased doses of pyrithiobac-sodium provides longer residual control of this herbicide in soil. The species that demonstrated high sensibility to the residual activity of pyrithiobacsodium were, in descending order: N. physaloides, A. tenella, S. americanum, S. latifolia, A. lividus, A. hybridus, C. benghalensis, soja RR®, I. grandifolia, E. heterophylla and T. procumbens. The transgenic cotton LL® was tolerant to ammoniumglufosinate and crop yield decreases were not found after use of up to 1500 g ha-1 of this product, divided in three applications. The mixture of pyrithiobac-sodium with ammonium-glufosinate was found to be selective to the cotton only for one postemergence application.