Sensitivity of Grape and Tomato to Micro-rates of Dicamba-based Herbicides

There is Agro-climatic concern that the widespread use of dicamba-based herbicides in Dicamba-Tolerant (DT) soybeans can result in un-intended drift onto non-DT crops in nearby field due to windy conditions and volatility. New dicamba-based products such as Engenia® and XtendiMax® with Vapor Grip technology were developed to reduce volatility, however, they are not completely volatile-free. A study was conducted to evaluate the sensitivity of pot-grown grape and tomato to six micro-rates of three dicamba-based products (Clarity®, Engenia® and XtendiMax®) in 2016 and 2017, at Haskell Ag Lab, Concord (42.37oN, 96.68oW), NE, USA. The tested dicamba formulations negatively impacted growth of grape and tomato as measured by vine length and plant height respectively, as well as by plant biomass. About 2% of the label rate was high enough to cause 50% injury and reduction in vine length or plant height. For example, a dose of 6.54 to 9.13 g ae ha-1 and 3.98 to 5.35 g ae ha-1 caused 50% injury in grape and tomato respectively, at 21 DAT. At 50% injury and vine reduction threshold, grape appeared more sensitive to XtendiMax® than Clarity® and Engenia®. For instance, a dose of 1.83 g ae ha-1 of XtendiMax® was required to cause 50% reduction in vine length (~49 cm) compared to significantly higher dose of 5.64 and 7.59 g ae ha-1 required for Clarity® and Engenia®, respectively. However, in tomato, there was no significant difference in sensitivity to all three products. In general, the present study showed that grape and tomato were very sensitive to micro-rates of all three dicamba products, irrespective of the of the new dicamba technology that reduces volatility. Hence, efforts should be made to avoid drift of dicamba onto these crops.