David Owens, Extension Entomologist, owensd@udel.edu
Alfalfa
Scout alfalfa for potato leafhopper. Our Insect management guide has a dynamic threshold table incorporated, accounting for plant size and value of hay, and control cost. If your fields are experiencing drought stress, it may be better to treat at lower leafhopper numbers. Alfalfa insect control can be found at: https://www.udel.edu/content/dam/udelImages/canr/pdfs/extension/sustainable-agriculture/pest-management/Insect_Control_in_Alfalfa_-2023.pdf.
Corn
Continue scouting late planted corn for cutworm. Thresholds at V2-V3 are 5% cut plants with larvae present.
Soybean
Many full season bean fields will receive a herbicide application in the near future. It may be tempting to tank-mix a cheap pyrethroid to ‘keep the field clean.’ However, over the last several years, we installed large strip trials with the help of several cooperators (and funding through Northeast SARE and USDA/NIFA) and monitored them over the remaining season. In only one of more than 15 site years did herbivore populations reach a point where a treatment was considered, and no significant yield differences were obtained between treated and untreated strips. In the vast majority of cases, save the money and leave the insecticide out.
You may notice large numbers of thrips on soybean leaves causing a silvery scarring. In the vast majority of cases, this is cosmetic. There is some thought in some extension literature that drought stressed beans may benefit if thrips numbers are greater than 8-10 per leaf, but other states advise that thrips have never been associated with a yield response. Full season bean fields can withstand greater than 40% defoliation before yield impacts are observed.