Large populations of sweetpotato whiteflies (Bemisia tabaci) have become more regular occurrences during the fall months in parts of the southeastern United States. Large populations of sweetpotato whiteflies have resulted in a significant increase in the incidence of sweetpotato whitefly-transmitted viruses, particularly the cucurbit leaf crumple virus (CuLCrV), which has the potential to cause complete yield loss of fall-planted yellow squash and zucchini (Cucurbita pepo). This study evaluated commercial cultivars of yellow squash and zucchini for resistance against CuLCrV and estimated the yield and fruit quality under environmental conditions during the fall growing season in the southeastern United States. A factorial experimental design was conducted with nine yellow squash and 11 zucchini cultivars during Fall 2017, Fall 2018, and Fall 2019 in Tifton, GA. In situ weather stations monitored the weather conditions during growing seasons, and yellow pest monitor cards monitored the sweetpotato whitefly populations in 2018 and 2019. During all growing seasons, yellow squash and zucchini plants were rated weekly for the severity of CuLCrV. Harvests were conducted 12 times during each season, and fruit were graded as fancy, medium, and culls. Rainfall distribution directly affected the sweetpotato whitefly populations during the production year. In 2018, frequent rainfall events created field conditions that reduced the sweetpotato whitefly populations compared with those during 2017 and 2019. The severity of CuLCrV negatively impacted both the yield and quality of fruit of yellow squash and zucchini, and no resistant commercial cultivars of yellow squash or zucchini were identified. Nonetheless, the yellow squash cultivars Lioness, Gold Prize, and Grand Prize, and the zucchini cultivars SV6009YG and SV0914YG had the highest yields when subjected to the highest sweetpotato whitefly populations during the study.
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