Selectivity of post-emergence herbicides in soybean and their efficacy on the control of Conyza spp.

ABSTRACT The management of Conyza spp. is becoming increasingly challenging in soybean, especially post-emergence; therefore, it must be linked to the effectiveness of control with selectivity. This study aimed to evaluate the phytotoxic effects on soybean and the control of Conyza spp. at an advanced phenological stage through different post-emergence herbicides registered for soybean. The experimental design was randomized blocks with plots divided in time with 4 replications, consisting of 14 treatments: cloransulam at three different doses (30, 35, and 40 g a.i. ha-1); fomesafen (250 g a.i. ha-1); imazethapyr (100 g a.i. ha-1); chlorimuron in three different doses (15, 18, and 20 g a.i. ha-1); flumetsulam (108 g a.i. ha-1); lactofen (180 g a.i. ha-1); bentazon (720 g a.i. ha-1); and flumiclorac (60 g a.i. ha-1). All were associated with glyphosate (1080 g a.i. ha-1), in addition to two controls, one weeded and the other without. Visual assessments of phytotoxicity in the soybean crop and weed control were performed at 7, 14, 21, 28, and 35 days after treatment (DAT). Bentazon stood out among all treatments, showing adequate selectivity in soybean, in addition to effective weed control at 14 DAT. No dose of cloransulam or chlorimuron herbicide was effective in controlling Conyza spp. The phenological stage of Conyza spp. and water availability impacted weed control of post-emergence herbicides and selectivity in soybean.