Agronomic Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Alfalfa
Potato leafhoppers are active in low numbers. I visited a field earlier this week with an average of 2-3 leafhoppers per 15 sweeps, and did not see nymphs. The field was also at a stage where it could be cut any time. However, if you have recently cut alfalfa, pay attention for leafhopper. Cutting will remove eggs, kill most nymphs, and discourage adults from staying in the field, but be sure to scout for them! Once hopperburn symptoms are visible, damage has already occurred. You can find more information, including dynamic thresholds and cultural control tactics here: https://www.udel.edu/content/dam/udelImages/canr/pdfs/extension/sustainable-agriculture/pest-management/Insect_Control_in_Alfalfa_-2020_-_David_Owens.pdf.

Corn
Corn should be outgrowing slug injury by now. Wireworm and white grub feeding symptoms are evident now. Be sure to scout for stink bugs. As mentioned in last week’s WCU, North Carolina has recently revised thresholds for pre-tassel corn down significantly. Be sure to also scout for cutworm and armyworm damage. A foliar spray may be advised if upon scouting, you see 3% of cut plants or 10% of plants with recent feeding (small holes in rows on leaves) for small corn. Between 2-4 leaf corn, the threshold is a little higher: 5% cut plants with active larvae. Pyrethroids are the go-to materials.

Soybean
Recent warm, dry weather has helped curb some slug activity, especially in fields in which vertical or turbo tillage was used. Bean leaf beetle activity has increased, although I am not aware of any economic infestations. Seedling defoliation thresholds are pretty high, 40% defoliation with 2 beetles per plant.