Yield response of pumpkin and winter squash to simulated cucumber beetle (Coleoptera: Chrysomelidae) feeding injury.

Field studies were conducted to characterize the yield responses of pumpkin, Cucurbita pepo L., and wintersquash, Cucurbita maxima Duch., to simulated striped cucumber beetle, Acalymma vittatum (F.), feeding damage. Preliminary studies in pumpkin ('Spookie') were conducted in 1993, and more complete studies in 1994 and 1995 in pumpkin (Spookie), and in 1995 and 1996 in winter squash ('Waltham'). Plants were artificially injured 1 time at the cotyledon, 1st, 2nd, or 3rd true leaf stages by clipping specified percentages of leaf area from all leaves on the plant. Treatments consisted of a control treatment with no simulated injury and 4 levels of simulated injury. Pumpkin treatments were 10, 20, 40, and 80% leaf area removal in 1993 and 1994 and 20, 40, 60, and 80% in 1995. Winter squash treatments were 20, 40, 60, and 80% leaf area removal in 1995, and 10, 20, 40, and 80% in 1996. In 1993, 5 wk after planting, mean leaf, stem, and total dry weight were significantly lower on pumpkin plants subjected to > or = 20% simulated leaf injury regardless of the growth stage when the injury occurred. Injury at the 3rd leaf stage resulted in a significant reduction in the mean leaf and total dry weight of plant, across all levels of injury. At 2-3 wk before crop maturity, fruit weight and number of fruit per plant were significantly lower with 80% leaf area removal. In 1994 and 1995, and when pumpkins were grown to full maturity and apparently able to compensate for the simulated damage, neither number nor weight of marketable fruit per plant were affected significantly by simulated injury at any stage of development nor level of simulated injury. In contrast, > or = 20% and 80% leaf area removal to winter squash resulted in significant reductions in the weight of marketable fruit and/or number of marketable fruit, in 1995 and 1996, respectively. The results of this study indicate that pumpkins can tolerate relatively high levels of simulated defoliation, whereas winter squash is less tolerant. Variable results across years in winter squash may indicate an interaction between injury and plant stress caused by abiotic factors such as soil moisture availability.