2,4‐Dichlorophenoxyacetic‐n‐methylmethanamine and Haloxyfop‐p‐methyl Interaction: Sequential and Interval Applications to Effectively Control Sourgrass and Fleabane

Sourgrass (Digitaria insularis L.) and fleabane (Conyza spp. L.) constitute a major challenge to weed management in soybean [Glycine max (L.) Merr.] production systems in Brazil, especially when both are resistant to glyphosate and present concurrently. The aim of this study was to evaluate the interaction of haloxyfop-P-methyl [methyl(R)-2{4-{3-chloro-5(trifluoromethyl)-2-pyridyloxy] phenoxy} propanoate] and 2,4-D [2,4-Dichlorophenoxyacetic acid-N-methylmethanamine] to control sourgrass at three to four tillers and flowering stages and 12- to 15-cm fleabane at vegetative stage. The experiments were arranged in a randomized complete block design with four replicates and were conducted twice. Treatments were composed of haloxyfop-P-methyl and 2,4-D applied sequentially at 3-, 6-, and 12-d intervals. Treatments also included an untreated check, haloxyfop-P-methyl, and 2,4-D sequentially (without interval) and stand-alone applications of both herbicides. All treatments across experiments completely controlled fleabane plants, except haloxyfop-P-methyl alone. Haloxyfop-P-methyl applied >= 6 d before 2,4-D controlled flowering and three- to four-tiller sourgrass plants at rates of 50 and 100%, respectively. Based on results of this study, haloxyfop-P-methyl should be applied >= 6 d before 2,4-D in a sequential application structure to control fleabane and sourgrass (three or four tillers) when present concurrently.