Evaluating the impact of insecticide timing and varietal resistance on melonworm (Diaphania hyalinata) in Arkansas pumpkins

Melonworm, Diaphania hyalinata, is often the most damaging insect pest of pumpkins in Arkansas. Adult melonworm moths migrate to the Midsouth every year from tropical areas of the U.S. as early as August. Melonworm larvae defoliate cucurbits and burrow into pumpkin rinds and under handles. Although significant yield loss from melonworm has been observed recently, no previous research has established effective integrated pest management (IPM) tools for the Midsouth region. The objective of this study was to develop IPM tools to sustainably manage melonworm in the Midsouth. We evaluated varietal resistance of four major Cucurbita species used for Fall market pumpkins and sought to establish best management practices for melonworm management using insecticides. We evaluated varietal resistance of eight pumpkin cultivars in four major Cucurbita species: Cucurbita pepo, Cucurbita maxima, Cucurbita moschata, and Cucurbita mixta. Additionally, we compared scouting and calendar-based applications of conventional (pyrethroid and diamide) and organic (Bt) insecticides on ‘Magic Lantern’. C. pepo exhibited significantly more damaged fruit than C. moschata, at 35% and 10% damaged fruit, respectively. While large levels of variation occurred within varieties, no feeding damage was observed on ‘Fairytale’ and under 10% on ‘Jarrahdale’. All varieties of C. pepo exhibited over 20% damaged fruit. No differences in damaged fruit were observed for pesticide treatments. Weekly Bt applications and one or two applications of a diamide effectively suppressed melonworm. However, higher melonworm infestation density is likely necessary to differentiate pesticide treatments from untreated pumpkins. More research is necessary to establish IPM tools for growers.