Soybean response to dicamba exposure in furrow irrigation

Abstract

AbstractSensitive crop exposure to residual dicamba in irrigation is a potential hazard in regions with overlapping use of transgenic dicamba‐resistant crops and on‐farm water storage–tailwater recovery (OFWS‐TWR) systems. This field study examined non–dicamba‐resistant soybean [Glycine max (L.) Merr.] for response to a dicamba dose gradient (7.6–630 g ae ha−1) in a furrow irrigation system. In a second study, growth stage and application timing effects were explored, with dicamba applied at 160 g ae ha−1 in entirety to V3 or R1 soybean or split across exposure events. Plant injury 14 and 28 d after treatment (DAT) increased with dose, with significant injury at 160–630 g ae ha−1. Plant injury 28 DAT was higher after split exposure compared with single exposure. Height and yield reduction occurred at 160–630 g ae ha−1 and in plants treated at reproductive growth stages. Regression models associated yield loss of 10, 20, and 30%, with effective doses of 19, 43, and 110 g ae ha−1, respectively, and plant injury 14 DAT of ∼10, ∼25, and ∼40%, respectively. Dicamba doses in irrigation that elicited equivalent response to foliar exposure were up to an order of magnitude higher, suggesting soybean plants are less sensitive to root uptake of dicamba. Alternately, dissipation in the environment may reduce total uptake. Off‐target dicamba exposure in irrigation will likely result in yield loss if tailwater dicamba concentrations exceeding ∼0.20 mg L−1 in 30.8 ha‐mm irrigation. This high residual concentration would likely only occur in OFWS‐TWR systems under “worst‐case scenario” conditions.