For the last two days, I have received lots of calls and emails about significant black cutworm damage in southern and central Iowa. The predicted cutting dates for black cutworm larvae are pretty close to our degree-day map published on 5 May. Mark Carlton, ISU Field Agronomist in SW Iowa, had a client with fields approaching 7% infestation. That density is clearly above a treatment threshold and was treated with an insecticide to protect yield. Mark Licht, ISU Field Agronomist in central Iowa, suspected black cutworm damage in this young corn plant (and I agree).
It is important to scout for larvae and damage through the V5 stage, especially after weeds or nearby grasses have been killed. Remember, if larvae found in the field are smaller than ¾ inch, then a threshold of 2 to 3 percent wilted or cut plants indicates an insecticide application is warranted.