Pratap Devkota, Weed Scientist, UF/IFAS West Florida Research and Education Center, Jay, FL
In the Florida Panhandle, peanut is the major crop that is grown in close proximity to cotton and soybeans. As such, there is potential for peanut plants to be exposed to dicamba applied on neighboring dicamba tolerant cotton or soybean fields. Dicamba is also commonly applied tank-mixed with glyphosate to increase the weed control spectrum. The peanut injury response can be severe when it is exposed to tank-mix of dicamba plus glyphosate. Research was conducted at West Florida Research and Education Center, Jay, Florida to evaluate the peanut response after exposure to a tank-mix of XtendiMax plus Roundup PowerMax (i.e. dicamba plus glyphosate) herbicide. The research evaluated peanut response when exposed at different growth stages, and at various rates of XtendiMax plus Roundup PowerMax. The summary results on the peanut injury and yield loss response from dicamba plus glyphosate exposure are presented in the table below.
Response on peanut injury and yield:
Peanut exposed to XtendiMax plus Roundup PowerMax at 25 days after planting (i.e., at vegetative growth stage) showed greater injury compared to exposure at 50 or 75 days after planting (i.e., at pegging and pod development stages). Similar response was observed for peanut yield, where yield loss was greater when peanut was exposed to XtendiMax plus Roundup PowerMax at an earlier stage than the later growth stages. These results suggests that XtendiMax plus Roundup PowerMax drift occurrences on peanut early in the growing season (i.e., vegetative growth stage) could be more severe than drift that occurrs later in the growing seaon (i.e., pod formation and development stages).
Peanut injury response is highly dependent on the exposure amount of XtendiMax plus Roundup PowerMax herbicide. Tank-mixes of XtendiMax plus Roundup PowerMax at less than 1/128 times the labeled rate caused minimal peanut injury and yield loss. However, exposure to the rate above 1/32 times caused significant peanut injury and yield loss. Likewise, the higher injury after exposure also translated into higher yield loss at the end of the season.
This research suggests that in the event of XtendiMax plus Roundup PowerMax drift (or similar dicamba plus glyphosate products), assessment of peanut injury within 1 to 2 weeks afterwards is critical. This timely assessment can be informative for predicting later season crop growth response. Likewise, accounting for the timing of the drift (particularly if it occurs early in the growing season) could be useful in estimating potential yield losses.