Vollmer, Kurt M.Lynn M. SosnoskieVanGessel, Mark J.Besançon, Thierry E.2024-06-042024-06-042024-06-01Vollmer, Kurt M., Lynn M. Sosnoskie, Mark J. VanGessel, and Thierry E. Besançon. "Varietal Tolerance of Cucurbitaceous Crops with S-metolachlor Applied Postemergence", HortTechnology 34, 3 (2024): 388-395, https://doi.org/10.21273/HORTTECH05420-241943-7714https://udspace.udel.edu/handle/19716/34446This article was originally published in HortTechnology. The version of record is available at: https://doi.org/10.21273/HORTTECH05420-24. © American Society for Horticultural Science 2024Cucurbit crops comprise ∼25% of the vegetable acreage in the mid-Atlantic and Northeastern United States. However, options for postemergence weed control in these crops are limited. Overlapping herbicides is a technique that involves sequential applications of soil-applied residual herbicides to lengthen herbicidal activity before the first herbicide dissipates. Residual herbicides such as S-metolachlor will not control emerged weeds, but weed control efficacy may be extended if these herbicides are applied after crop emergence, but before weed emergence occurs. Currently S-metolachlor is not labeled for broadcast applications over cucurbit crops. Greenhouse studies were conducted to evaluate pumpkin, cucumber, and summer squash variety response to varying S-metolachlor rates. S-metolachlor was applied at 1.42 and 2.85 lb/acre at the two-leaf stage of pumpkin and 0.71, 1.42, 2.85, and 5.7 lb/acre at the two-leaf stage of cucumber and summer squash. Cucumber showed a greater response to S-metolachlor with up to 67% injury observed at 5.70 lb/acre. S-metolachlor applications to pumpkin and summer squash resulted in less than 6% injury, regardless of application rate or crop variety. S-metolachlor applied at 2.85 lb/acre reduced pumpkin and cucumber dry weight 6% and 19%, respectively, but did not reduce squash dry weight. S-metolachlor reduced cucumber dry weight 78% for all varieties. Pumpkin varieties ‘Munchkin’ and ‘Baby Bear’ exhibited a 23% difference in dry weight, but no other differences were observed among other varieties because of S-metolachlor applications. Summer squash varieties ‘Respect’ and ‘Golden Glory’ exhibited a 31% difference in dry weight, but no other differences were observed among other varieties. Results show that pumpkin and summer squash demonstrated good crop safety when S-metolachlor was applied as a broadcast treatment after crop emergence. However, caution should be urged when applying this herbicide to cucumber.en-USAttribution-NonCommercial-NoDerivatives 4.0 InternationalCucumis maximusCucumis sativusCucurbita pepoCucurbita pepo subsp. pepoherbicideinjuryArticle