With the release of the dicamba-resistant crop technology and subsequent increase in dicamba off-target movement to non-dicamba-resistant crops, discovering means of mitigating yield loss through studying dicamba injury to soybean and interactions with factors such as irrigation regime and fertilization would prove beneficial. Field experiments were conducted in 2019 in Fayetteville and Colt, Arkansas, to evaluate the effect of irrigation regime to non-dicamba-resistant soybean that was injured by dicamba at a low dose at multiple timings. Another experiment was conducted in Fayetteville in 2019 and 2020 evaluating the impact of nitrogen (N) and potassium (K) fertilization on soybean recovery following injury by dicamba at multiple reproductive stages. Visible injury in both experiments was affected by application timing. Soybean yield components were impacted by dicamba applications within the irrigation regime experiment, and yields were decreased by dicamba applications; however, soybean yield was higher from branches than from the mainstem in dicamba-treated compared to nontreated plants. In the fertilization experiment, soybean treated with a low dose of dicamba that received N fertilization tended to have reduced biomass compared to treatments receiving no fertilizer or K alone, with greatest biomass reduction tending to occur among treatments receiving both N and K. Total grain yield was not affected by either irrigation regime or fertilization. While an increase in yield due to neither irrigation nor fertilization was observed, these results may help improve understanding of the effect of low-dose dicamba on soybean and aid producers making management decisions.

Off-target movement of dicamba has been blamed for damaging millions of hectares of soybean in the United States since registration of the herbicide for use in dicamba-resistant cotton and soybean. Understanding the effect of a low dose of dicamba on non-dicamba-resistant soybean across multiple cultivars, growth stages, and planting dates could help producers better understand the implication of current management practices on yield loss from dicamba in fields where non-dicamba-resistant soybean are grown. A field experiment was conducted in 2019 in Fayetteville and Stuttgart, Arkansas, to evaluate the impact of planting date on response of soybean to a low dose of dicamba. The hypothesis of the planting date experiment was that soybean injury and yield loss will differ depending on planting date and dicamba application timing. Additionally, an experiment was conducted in 2018 and 2019 in Fayetteville to assess whether cultivars differ in sensitivity to dicamba. The hypothesis of the cultivar experiment was that genetic differences of soybean cultivars will allow for differential tolerance to dicamba. In the cultivar experiment, “Eagle DrewSoy” was identified as having enhanced tolerance to dicamba based on reduced injury (47% at R1 and 26% at V3) over both experimental years and locations. Soybean height in this experiment was affected only by application timing. In the planting date experiment, planting after mid-June resulted in reduced yields from dicamba injury. Dicamba exposure reduced yield at the July planting date (61% reduction from nontreated) more severely when compared to dicamba-treated plots of other planting dates (94% average relative yield among other planting dates), indicating that the negative effects of dicamba are increasingly deleterious for soybean planted later in the growing season. Maximum injury manifestation was generally delayed at later planting dates, indicating that dicamba may have been metabolized more slowly.

Off-target movement of glyphosate can be severely injurious to rice (Oryza sativa L.). Glyphosate is routinely mixed with dicamba and applied to crops with resistance to both herbicides, such as glyphosate-and dicamba-resistant corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] cultivars. This research was conducted to evaluate the effects of low rates of glyphosate and glyphosate plus dicamba on rice at multiple application timings. Separate field experiments were conducted and were repeated in 2018 and 2019 near Stuttgart, AR. The first experiment evaluated rice's response to glyphosate alone; a second experiment evaluated responses to glyphosate applied as a mixture with dicamba over several rice growth stages. The rates of glyphosate alone evaluated were 0.023, 0.047, 0.187, and 0.375 oz acid equivalent (ae) acre -1 . Mixtures of glyphosate plus dicamba were evaluated at 0.050 plus 0.025, 0.2 plus 0.1, and 0.8 plus 0.4 oz ae acre -1 , respectively. Visible injury to rice from glyphosate alone was never more than 3%, averaged over application timings. Unique symptomology and greater yield losses were observed for glyphosate mixed with dicamba. There was no reduction in rough rice grain yield after treatment with glyphosate alone. For the glyphosate plus dicamba experiment, no more than 13% injury occurred from any treatment. Rough rice grain yield was reduced by 21% relative to the nontreated control for the highest rate of glyphosate plus dicamba, averaged over application timings. Care should be taken to prevent off-target movement of mixtures of glyphosate plus dicamba to neighboring rice.