Sensitivity to sublethal rates of dicamba for selected mid-Atlantic vegetable crops

Abstract

Dicamba is a synthetic auxin herbicide that may be applied over the top of transgenic dicamba-tolerant crops. The increasing prevalence of herbicide-resistant weeds has resulted in increased reliance on dicamba-based herbicides in soybean production systems. Because of the high volatility of dicamba, it is prone to off-target movement, and therefore has been of increased concern regarding dicamba drift onto nearby specialty crops. The present study evaluates twelve mid-Atlantic vegetable crops species for sensitivity to sub-lethal rates of dicamba. 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). Vegetable crop injury was evaluated 4 weeks after treatment using visual rating methods and leaf deformation index (LDI) measurements. Overall, snap bean was the most sensitive crop species with dicamba rates as low as 0.11 g ae ha−1 resulting in significantly higher leaf deformation levels compared to the nontreated control. Other Fabaceae and Solanaceae species also demonstrated high sensitivity to sub-lethal rates of dicamba with rates ranging 0.28 to 0.56 g ae ha−1 causing higher leaf deformation compared to the nontreated control. While cucumber, pumpkin, and summer squash were no or moderately sensitive to dicamba, watermelon showed greater sensitivity with unique symptoms at rates as low as 0.056 g ae ha−1 based on visual evaluation. Within the range of tested dicamba rates, sweet basil, lettuce and kale demonstrated tolerance to dicamba with no injury observed at the maximum rate of 2.24 g ae ha−1.

Influence of growth stage and dicamba rate on eggplant, cucumber, and snap bean tolerance and yield response

“…However, growth or yield were not reduced at the 2.24 g ae ha -1 rate. In a greenhouse screening conducted prior to this study, Wasacz et al (2022) determined that 'Python' was less sensitive to low rates of dicamba than 'Burpless Beauty' cultivar, requiring 1.12 g ae ha -1 and 0.28 g ae ha -1 , respectively, to induce greater leaf deformation than noted for the nontreated control. It is not known why differences in dicamba sensitivity were observed in 'Python' cucumber between the greenhouse and field trials, although abiotic conditions, such as temperature, wind, or humidity, could have influenced the interaction between crop and dicamba.…”

“…Dicamba (XtendiMax®; Bayer Crop Science, St. Louis, MO) was applied at 0.056, 0.11, 0.56, 1.12, 2.24 g ae ha -1 , respectively, corresponding to 1/10,000, 1/5,000, 1/1,000, 1/500, and 1/250 of the maximum recommended label rate (560 g ae ha -1 ) for soybean. These rates were selected based on the lowest rate of dicamba (0.056 g ae ha -1 ) that induced a phytotoxicity response in sensitive soybean plants (Egan and Mortensen 2012) as well as rates previously evaluated in a greenhouse study with these vegetable species (Wasacz et al 2022). Over-the-top applications of dicamba were made using CO 2pressurized backpack sprayers calibrated to deliver 140 L ha -1 at 179 kPa for eggplant, and 187 L ha -1 at 138 kPa for cucumber and snap bean.…”

“…A previous greenhouse study evaluated 12 different vegetable crops in the Cucurbitaceae, Solanaceae, and Fabaceae families for sensitivity to low doses of dicamba (Wasacz et al 2022). Because crop sensitivity to dicamba may differ depending on environmental conditions, the three most sensitive crop species in each botanical family identified in this greenhouse study were selected for further field evaluation at three different locations representative of agronomic and meteorological conditions of the northeastern United States.…”

The consequences of synthetic auxin herbicide on plant-herbivore interactions

“…Most current knowledge of the direct effects of nontarget, synthetic auxin exposure on plants comes from studies of crop plants with a focus on non-transgenic soybean [14,15,44], which like other members of the Fabaceae [45], is highly susceptible to synthetic auxins [46]. In fact, due to its sensitivity, recent landscape level dicamba drift events have been captured using soybean as the 'canary in a coal mine'.…”

Maize genotype selection resistance to fall armyworm (Spodoptera frugiperda J.E. Smith) based on the degree of damaged leaf

“…Screening methods vary widely and one of them uses the leaf injury rating caused by plant pests. Ni 2015) did survey and research to do selection of plants based on the ratings of leaf damage [12][13][14][15]. Seeing the various studies that have been carried out to find and produce FAW-resistant lines, this also encourages this research to obtain FAW-resistant lines and be able to find resistance properties in selected lines through crossbreeding and morphological analysis as planned.…”