Impact of Exposure to 2,4-D and Dicamba on Peanut Injury and Yield

The potential widespread adoption of cotton and soybean varieties with 2,4-D and dicamba resistance traits in the southeastern US will increase the risk of accidental exposure of peanut to these herbicides because of drift or application errors. When such accidents occur, growers must decide between continuing the crop and terminating it. In order to make this decision, growers need to estimate the potential yield reduction caused by 2,4-D or dicamba. Dose-response studies were conducted under field conditions in Citra and Jay, FL in 2012 and 2013 to determine peanut injury and yield reduction after exposure to 70, 140, 280, 560, and 1120 g ae ha(-1) of 2,4-D or to 35, 70, 140, 280, and 560 g ae ha(-1) of dicamba at 21 and 42 d after planting (DAP). Only herbicide by rate interactions were significant (P < 0.04). Dicamba caused 2 to 5 times higher peanut injury and 0.5 to 2 times higher yield reductions than 2,4-D. Injury ranged from 0 to 35 % when peanut plants were treated with 2,4-D and from 20 to 78 % with dicamba. The maximum yield reduction was 41 % with 1,120 g ha(-1) of 2,4-D and 65% with 560 g ha(-1) of dicamba. Linear regression indicated that the intercept for yield reduction was 12% for 2,4-D and 23% for dicamba, and there was a 2.5 % and 7.7% increase in yield reduction per additional 100 g ha(-1), respectively. Although high variability was observed for the different variables, there was a positive correlation between injury and peanut yield reduction (P < 0.0001) with Pearson's Rho values ranging from 0.45 to 0.59 for 2,4-D and from 0.27 to 0.55 for dicamba, suggesting that growers can use injury data to make rough projections of yield reduction and decide if they continue their crop, especially when injury is evident.