Control of hairy fleabane in sequential and pre-emergence applications in soybean crops

ABSTRACT The control of Conyza spp. can be conducted at different times in the soybean crop. This study aimed to evaluate the efficiency of controlling Conyza spp. by positioning herbicides at different times and their selectivity in the soybean crop. The experiment was conducted under field conditions in a randomized block design with four replications. A first application of 2.4-D + glyphosate (975 + 1500 g of active ingredient [a.i.] ha-1) was conducted, followed by the following treatments: glufosinate (500 g i.a. ha-1), diquat (400 g a.i. ha-1), and saflufenacil + glyphosate (50 + 1500 g a.i. ha-1 ) and a third application of the pre-emergents flumioxazin + imazethapyr (60 + 127 g i. a. ha-1), sulfentrazone + diuron (210 + 420 g a.i. ha-1), diclosulam (35 g a.i. ha-1), and s-metolaclhor (1440 g a.i. ha-1), in addition to the control treatment. High percentages of control were obtained with saflufenacil + glyphosate and diquat. Glufosinate provided satisfactory control seven days after the treatment (DAT) application, with regrowth throughout the evaluations, except when diclosulam was applied. The pre-emergent herbicides reduced the emergence of Conyza spp. resulting in 0.25 plants m-2 when flumioxazin + imazethapyr was applied at 28 DAT. Regardless of the treatment, the soybean crop had no significant phytotoxicity. The management of Conyza spp. with the positioning of herbicides at different times proved to be more efficient when the sequential use of diquat and/or saflufenacil + glyphosate and flumioxazin + imazethapyr in pre-emergence was carried out.