Abstract
The development of dicamba-resistant cotton and soybean cultivars has created great concern about the potential off-target movement of dicamba onto sensitive broadleaf crops. Peanut is often grown in close proximity to cotton and soybean. Therefore, field studies were conducted during 2012 and 2013 at Plains, Ty Ty, and Attapulgus, GA to evaluate peanut response to dicamba rates 35, 70, 140, 280, and 560 g ae ha-1 applied at preemergence (PRE), 10, 20, or 30 d after planting (DAP) corresponding to PRE, V2, V3, and V5 peanut growth stages, respectively. Nontreated controls were included for comparison. Location by rate (P < 0.0002) and location by treatment timing (P < 0.004) interactions were significant. As dicamba rate increased peanut injury and yield loss increased. There was variation in peanut response by location after PRE treatments. Plains peanut was injured less among locations, possibly due to the Greenville soil there having higher organic matter and clay contents at 3.8 and 30%, respectively. Soil texture and other environmental factors can affect the extent of injury that occurs to peanut from dicamba exposure. When dicamba was applied at the V5 peanut growth stage, peanut was at 25% bloom, so a reduction in yield occurred, in part, from injury during that sensitive growth stage and from peanut having less time to recover before harvest. Dicamba at 35 g ha-1 applied to V5 peanut in Attapulgus had 33% injury, 42% canopy diameter stunting, and 45% yield loss as compared to the NTC. Linear regression and log-logistic regression models were used to evaluate peanut yield and injury data. There were significant correlations between peanut injury at 20 DAT and peanut yield as % NTC, injury and canopy diameter at 20 DAT as % NTC, and canopy diameter and yield (P < 0.01), with correlation coefficients of -0.57 to -0.96, -0.69 to -0.91, and 0.37 to 0.87, respectively. Growers and extension agents will be able to use peanut injury estimate and canopy diameter data to make improved predictions of potential peanut yield loss where off-target movement of dicamba or sprayer contamination occurred.