Selectivity and efficiency of herbicides in weed control on sweet sorghum

Abstract

The lack of registered herbicides for weed control in sweet sorghum has been a limiting production factor. This study aimed at evaluating the selectivity of herbicides in sweet sorghum and weed control efficiency. A randomized blocks design, with four replications, was used. Treatments consisted of sweet sorghum cultivars (BRS 506, BRS 509 and BRS 511) and herbicides applied alone at pre-emergence (atrazine - 1,500 g ha^-1; atrazine + s-metolachlor - 1,665 g ha^-1 + 1,035 g ha^-1; flumioxazin - 50 g ha^-1; s-metolachlor - 1,440 g ha^-1) and post-emergence (tembotrione - 100.8 g ha^-1) and sequentially at pre- and post-emergence (atrazine + s-metolachlor + tembotrione - 1,665 g ha^-1 + 1,035 g ha^-1 + 100.8 g ha^-1; atrazine + tembotrione - 1,500 g ha^-1 + 100.8 g ha^-1; flumioxazin + tembotrione - 50 g ha^-1 + 100.8 g ha^-1), plus two controls, one weeded and one unweeded. The phytotoxicity rate to sorghum was 98.0 %, 98.0 % and 100 % for tembotrione; 100 %, 98.7% and 100 % for flumioxazin + tembotrione; 100 %, 100 % and 100 % for s-metolachlor + atrazine + tembotrione; and 98.7 %, 98.7 % and 99.7 % for atrazine + tembotrione, respectively to the BRS 509, BRS 506 and BRS 511 cultivars. Tembotrione, flumioxazin + tembotrione, atrazine + s-metolachlor + tembotrione and atrazine + tembotrione showed a good control rate of Ipomoea indivisa, Digitaria ciliaris and Urochloa plantaginea, but did not present selectivity to the sorghum cultivars. Atrazine, in general, showed higher selectivity to the yield components of the BRS 509 and BRS 506 cultivars.