The effect of dicamba on peanut when applied during vegetative growth stages

Authors: BLANCHETT, B - University Of Georgia; GREY, T - University Of Georgia; PROSTKO, E - University Of Georgia; Webster, Theodore

Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2015
Publication Date: 7/1/2015
Citation: Blanchett, B.H., Grey, T.L., Prostko, E.P., Webster, T.M. 2015. The effect of dicamba on peanut when applied during vegetative growth stages. Peanut Science. 42:2, 109-120.

Interpretive Summary: Peanut is an important crop to Georgia and many other southern states of the US. Georgia leads the US with 172,470 ha harvested in 2013 and is commonly grown near cotton and soybean across the southeast. Most cotton and soybean cultivars planted have herbicide resistance technology to aid in weed management, and the increased use of glyphosate and glufosinate herbicides throughout the growing season increased the occurrence of accidental injury to other crops. Peanut injury can occur from herbicide residue remaining in the spray system when it is not properly cleaned prior to the next application in a different crop. Peanut injury can also occur when the herbicide becomes suspended in air, never reaching the target site, then moving onto a sensitive species nearby. Agricultural seed and chemical companies have developed weed management systems that use dicamba on dicamba-resistant crops including cotton and soybean. Dicamba is known to cause significant injury to sensitive broadleaf crops when off-target exposure occurs as a result of tank contamination, herbicide drift, and movement due to volatilization. These studies indicate a significant increase in peanut injury as dicamba rate is increased during peanut vegetative growth stages. Due to the detrimental injury (leaf chlorosis, necrosis, stem epinasty, leaf strapping, stem swelling, and plant stunting) peanut plant growth was reduced or stopped, thus peanut yield decreased as dicamba rate was increased. Peanut injury and yield loss varied highly by location following the preemergence dicamba treatments. Different soil textures and growing environments likely caused peanut to vary in response by location. Generally, dicamba was more injurious when applied closer to beginning bloom (approximately 30 DAP); the first reproductive growth stage (R1). Significant (P < 0.01) correlations between peanut crop injury and yield and between peanut canopy diameter and peanut yield were observed. Dicamba resistant crops will likely have widespread use as weeds with herbicide resistance to other herbicide mechanisms of action continue to increase in importance. These data indicate great care should be taken to prevent dicamba drift, sprayer contamination, and volatilization. Applicators should be aware and follow herbicide label directions and precautions. Due to the sensitivity of peanut to dicamba, growers and applicators should avoid applying dicamba in the proximity of peanut throughout all vegetative growth stages and especially around V3 to V5 and early reproductive growth stages. In the unfortunate situation where peanut injury from accidental dicamba exposure occurs, these data could assist the grower in determining peanut yield loss estimates and a possible plan of action.

Technical 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 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.