Response of Glyphosate-Tolerant Soybean Yield Components to Dicamba Exposure

Abstract

Exposure of soybean to dicamba can result in leaf malformation and sometimes yield loss, but it is unclear how yield components are affected by exposure to low quantities of this herbicide. The objectives were to characterize soybean injury and quantify changes in seed yield and yield components of soybean plants exposed to dicamba, and determine if seed yield loss can be estimated from visual injury ratings. Nine dicamba rates (0, 0.06, 0.23, 0.57, 1.1, 2.3, 4.5, 9.1, and 22.7 g ae ha−1) were applied at three growth stages (V2 – two trifoliates, V5-five trifoliates, or R2-full flowering soybean) to Beck's brand ‘342NRR’ soybean planted near Lafayette, IN, in 2009 and 2010 and near Fowler, IN, in 2009. Visually estimated soybean injury of 20% at the V2, V5, or R2 timing was 0.676 to 0.937 g ha−1dicamba at 14 d after treatment (DAT) and 0.359 to 1.37 g ha−1dicamba at 28 DAT. Seed yield was reduced by 5% from 0.042 to 0.528 g ha−1dicamba and a 10% reduction was caused by 0.169 to 1.1 g ha−1dicamba. The number of seeds m−2, pods m−2, reproductive nodes m−2, and nodes m−2were the most sensitive yield components. Path analysis indicated that dicamba reduced seeds m−2, pods m−2, reproductive nodes m−2, and nodes m−2which were the main causes of seed yield loss from dicamba exposure. The correlation of seed yield loss and visual soybean injury was significant (P < 0.0001) for both the V2 treatment timing (R2= 0.92) and the V5 and R2 treatment timings (R2= 0.91). Early-season injury rating of 8% at the V2 treatment and 2% at the V5 or R2 treatments caused 10% or more yield loss.

Drift of 2,4-D and dicamba applied to soybean at vegetative and reproductive growth stage

“…In contrast, ROBINSON et al (2013b) reported equivalent soybean injury for 2,4-D at rate ranging from 145 and 245g ha -1 . These results are consistent with those reported by GRIFFIN et al 2013; ROBINSON et al, (2013aROBINSON et al, ( , 2013b and SOLOMON & BRADLEY, 2014, who reported that soybean exposure to auxin herbicides drift causes significant more crop injury when applied during vegetative than reproductive stage.…”

“…The degree of injury observed in soybean for 2,4-D and dicamba herbicides were similar to those observed in soybean (GRIFFIN et al, 2013;ROBINSON et al, 2013aROBINSON et al, , 2013bSOLOMON & BRADLEY, 2014). Soybean exhibited the greatest symptoms injury to 2,4-D between 26 and 32% for V 5 and R 2 stages at high rate, respectively ( Figure 1).…”

“…These dicamba rates represented 0.77 and 1.55% of standard herbicide rate of 480g ha -1 , respectively. ROBINSON et al (2013a) reported similar values at 50% of injury, ranging from 1.44 to 4.4g ha -1 when applied in the vegetative stage and from 1.8 to 5.3g ha -1 when applied to reproductive stage.…”

“…Although, 2,4-D exposure to the V 5 soybean stage influenced more than V 2 and R 2 stage (ROBINSON et al, 2013b). Previous research has documented that synthetic auxins herbicides drift onto sensitive soybean can cause many negative effects, such as reduction of seed weight, lower seed quality, lower seed oil and protein concentration, pod malformation and impacts on progeny (ROBINSON et al, 2013a(ROBINSON et al, , 2013bSOLOMON & BRADLEY, 2014;KESOJU et al, 2016;MILLER & NORSWORTH, 2017).…”

Response of glyphosate-resistant soybean to dicamba spray tank contamination during vegetative and reproductive growth stages

“…Yield losses of greater than 18% have been reported due to 1% tank contamination with dicamba in soybean (Derksen 1989;Griffin et al 2013). Robinson et al (2013) found 10% or more yield loss in soybean when exposed to dicamba applied at 22.7 g a.e. ha −1 .…”