Crop tolerance and yield response of select mid-Atlantic vegetables to sub-lethal dicamba rates
Creators: name: Wasacz, Maggie Helen
Publisher: name: No Publisher Supplied
Year: 2022

description: In 2017, transgenic dicamba-resistant soybeans and cotton became available to American farmers to help combat glyphosate-resistant weeds, such as Palmer amaranth. With this technology, dicamba products can be applied preplant in no-till production systems and over the top of resistant crops during the growing season. Because dicamba has a tendency to move off-target during and after application, concern for dicamba drift injury has increased for growers, applicators, and manufacturers. The objective of this research was to determine the relative sensitivities of several economically important vegetable crops of the mid-Atlantic United States to sub-lethal rates of dicamba. The first experiment was conducted over two years under greenhouse conditions to evaluate a novel method of measuring dicamba-caused leaf deformation without rater bias. Potted vegetable plants were treated with several sublethal dicamba rates and evaluated visually. Additionally, the leaf deformation index (LDI) was calculated by dividing the projected area of the affected leaves in their natural configuration, by the projected area of the same flattened leaf. This method objectively quantified the amount of leaf deformation and the results of a log-logistic analysis determined that the LDI method detected leaf deformation more precisely than visual deformation ratings. The second experiment was conducted in a greenhouse over two years to evaluate different vegetable crop species to sub-lethal dicamba rates. Soybean, snap bean, lima bean, tomato, eggplant, bell pepper, cucumber, summer squash, watermelon, pumpkin, sweet basil, lettuce, and kale were grown in the greenhouse and exposed to dicamba at 0, 0.056, 0.11, 0.28, 0.56, 1.12, 2.24 g ae ha⁻¹, which is respectively 0, 1/10,000, 1/5,000, 1/2,000, 1/1,000, 1/500, and 1/250 of the maximum recommended label rate for soybean application (560 g ae ha⁻¹). Plant foliage was evaluated weekly up to 4 weeks after treatment using visual rating methods and leaf deformation index (LDI) measurements. The data suggested that Fabaceae and Solanaceae species were highly sensitive, with sub-lethal rates of dicamba with rates ranging 0.11 to 0.56 g ae ha⁻¹ causing significantly higher leaf deformation compared to the nontreated control. Cucurbitaceae crops had varied sensitivity between crops and cultivars, while basil, lettuce and kale had no observable injury at any rate in the study. The third experiment was conducted over two years and three field locations. Snap bean, cucumber, and eggplant were grown in the field and dicamba was applied at 0, 0.056, 0.11, 0.56, 1.12, 2.24 g ae ha⁻¹, which is respectively 0, 1/10,000, 1/5,000, 1/1,000, 1/500, and 1/250 of the maximum recommended label rate for soybean application (560 g ae ha⁻¹) at the early vegetative and early bloom stages. Visual evaluations, height measurements, and yield data were measured for each plot. Cucumber resulted in no detectable visual injury and no significant yield or vine length differences at any rate or application timing. Eggplant demonstrated significantly higher visual injury at rates 0.56 g ae ha⁻¹ and above compared to the nontreated control, but resulted in no detectable yield differences at any rate or time. Sub-lethal dicamba rates caused high visual injury and yield reduction at both locations. When averaged across application timings, ‘Caprice’ snap bean yield was reduced to 63% of the nontreated control yield (3510 g ha⁻¹) when 2.24 g ha⁻¹ of dicamba was applied in New Jersey. In New York, dicamba at 2.24 g ha⁻¹ reduced ‘Huntington’ snap bean yield 85% and 96% when applied at the vegetative and reproductive stages, respectively, compared to untreated plants.