David Owens, Extension Entomologist, owensd@udel.edu
Corn
Begin scouting for Japanese beetle defoliation and for brown stink bugs. NCSU thresholds for stink bugs are 10 or more bugs per 100 plants at V14-VT. Please note that stink bug thresholds more than double once plants begin silking, which means timing an insecticide to coincide with a fungicide leaves a lot of damage potential on the table IF stink bugs are at an economic threshold. In this case, it pays to scout fields, particularly those adjacent to winter wheat.
Soybean
Scout seedling double crop soybean fields for defoliation. Last year a field near Bridgeville was almost completely defoliated by Asiatic garden beetle. Other typical defoliators are present including bean leaf beetle, bean leafroller, and green cloverworm. Be on the lookout for spider mites moving into fields from field edges. Due to dry weather with limited rain in the forecast, it may be advisable to treat soybean at lower levels of defoliation (20% vs 30%) in fields that are not irrigated.
Alfalfa
Continue scouting alfalfa for potato leafhopper. We looked at two fields at the end of last week, one had very high counts of potato leafhopper while the second did not have any. Thresholds can be found https://www.udel.edu/content/dam/udelImages/canr/pdfs/extension/sustainable-agriculture/pest-management/Insect_Control_in_Alfalfa_-2023.pdf. Note that thresholds are low for short alfalfa and the table maxes out for alfalfa that is greater than 12 inches.