This spring, we have had several reports of fields with high numbers of grubs from field agronomists in central Iowa. There are multiple species of white grubs in Iowa, including the Japanese beetle. Recent warm temperatures are accelerating insect development, and with forecasted temperatures, Japanese beetle emergence could begin in southern Iowa counties this week (Figure 1). Japanese beetle adults will begin emergence when approximately 1,030 growing degree days (GDD; base 50°F) have accumulated since January 1 and will continue emerging until 2,150 GDD have accumulated.
Iowa State University
Dean, Ashley and Hodgson, Erin W., "Japanese Beetle Adult Emergence Beginning in Southern Iowa" (2021). Integrated Crop Management News. 2696.
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