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.

Abstract Residual herbicides remain the primary tool for efficient weed control in cucurbit crops because of the lack of crop tolerance to many POST herbicide options. Field experiments were conducted in New Jersey in 2018 and 2019 to determine weed control efficacy and tolerance of direct-seeded cucumber ‘Python‘ and summer squash ’Gold Prize‘ to S-metolachlor applied at 0.7 or 1.4 kg ai ha-1 at planting (PRE) or when crops reached the 2nd to 3rd leaf stage (EPOST). Regardless of applied rate, S-metolachlor PRE or EPOST provided 96 to 100% control 3 wk after planting (WAP) of smooth pigweed, large crabgrass, and giant foxtail. S-metolachlor PRE significantly improved American black nightshade and carpetweed control 3 WAP with respect to bensulide, and smooth pigweed with respect to clomazone + ethalfluralin. Summer squash showed excellent tolerance, regardless of S-metolachlor rate or timing of application, with stunting not exceeding 17% 4 WAP and 3% 7 WAP at the 1.4 kg ha-1 rate. Marketable yield decreased by 15% with S-metolachlor PRE or POST at 1.4 kg ha-1 with respect to clomazone + ethalfluralin, a reduction not noted when comparing to bensulide or the handweeded control. Marketable fruit number per plant and individual fruit weight were not affected by Smetolachlor applications. Conversely, cucumber was more sensitive to S-metolachlor than summer squash with 30% seedling emergence reduction and 36 to 43% stunting 4 WAP when S-metolachlor was applied PRE at 1.4 kg ha-1. EPOST application resulted in 15 to 26% cucumber injury 1 wk after treatment (WAT). Marketable yield declined by 21 and 39% with the 0.7 and 1.4 kg ha-1 rates of S-metolachlor, respectively, compared to clomazone + ethalfluralin. Therefore, S-metolachlor may be a novel alternative to already labeled residual herbicides for summer squash but would cause unacceptable injury and yield reduction for supporting its registration on cucumber.

Following the introduction of dicamba-resistant (DR) soybean in 2017, concerns regarding dicamba off-target movement (OTM) onto sensitive crops, including vegetables, has increased. Field trials were conducted in New Jersey, New York, and Delaware to evaluate cucumber (‘Python’), eggplant (‘Santana’), and snap bean (‘Caprice’ and ‘Huntington’) injury and yield response to simulated dicamba drift rates. Crops were exposed to dicamba applied at 0, 0.056, 0.11, 0.56, 1.12, 2.24 g ae ha-1, representing 0, 1/10,000, 1/5,000, 1/1,000, 1/500, and 1/250 of the maximum soybean recommended label rate (560 g ae ha-1), respectively. Dicamba was applied either at the early vegetative (V2) or early reproductive (R1) stages. Minimal to no injury, vine growth reduction or yield loss was noted for cucumber. Dicamba was more injurious to eggplant with up to 22% to 35% injury 2 WAT at rate ≥ 1.12 g ae ha-1; however, only the highest dicamba rate caused 27% reduction of the commercial yield compared to the nontreated control. Eggplant also showed greater sensitivity when dicamba exposure occurred at the R1 than at theV2 stage. Snap bean was the most sensitive crop investigated in this study. Injury 2 WAT was greater for Caprice with dicamba ≥ 0.56 g ae ha-1 applied at V2 compared to R1 stage, whereas similar difference occurred as low as 0.056 g ae ha-1 for Huntington. Compared to the nontreated control, reduction in plant height and biomass accumulation occurred for both cultivars at dicamba rate ≥ 0.56 g ae ha-1. Dicamba applied at 1.12 g ae ha-1 or greater resulted in 30% yield loss for Caprice whereas Huntington yield dropped 52% to 93% with dicamba ≥ 0.56 g ae ha-1. Caprice bean yield was not influenced by dicamba timing of application. Conversely, Huntington bean yield decreased by 8% following application at R1 compared to V2 stage.

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.

Cover crops included in a crop rotation can help increase nitrogen (N) availability to subsequent crops, raise soil organic matter, and suppress emergence and growth of various weed species. However, weed suppression by cover crops has mostly been investigated shortly after cover crop termination and not over a longer period spanning into the next cropping season. The effects of sunn hemp (Crotalaria juncea) and sorghum-sudangrass (Sorghum ×drummondi) planted the previous year on N availability before transplanting of late summer cabbage (Brassica oleracea), weed germination and growth, and cabbage yield was examined in field studies conducted in 2018 and 2019 at Pittstown, NJ. Results established that there was little evidence for a functional difference in soil N availability for fall cabbage production because of previous cover crop type. Heavy rainfall events both years may have caused major losses of available N that might otherwise be expected to come from N mineralization of residues of legume cover crop like sunn hemp. During the cover crop season, smooth pigweed (Amaranthus hybridus) and common lambsquarters (Chenopodium album) dry biomass was 77% and 82% lower, respectively, in sorghum-sudangrass compared with sunn hemp plots. The subsequent season following sorghum-sudangrass cover crop, dry biomass of broadleaf weeds was lower by 74% and 56% in June and July, respectively, compared with preceding sunn hemp. Smooth pigweed, common lambsquarters, and hairy galinsoga (Galinsoga quadriradiata) were the weed species most consistently affected by preceding sorghum-sudangrass cover crop with biomass decreased by up to 80%, 78%, and 64%, respectively. Thus, it appears that sorghum-sudangrass can provide suppression of some broadleaf species over a relatively long period and is indicative of sorghum-sudangrass allelopathic activity. On the contrary, density and biomass of grassy weeds as well as commercial yield of transplanted cabbage were unaffected by the preceding cover crop. These results suggest that sorghum-sudangrass cover crop could be integrated to transplanted cole crop rotation for providing weed suppression benefits without altering crop yield in New Jersey organic vegetable cropping systems.