Monitor Corn Fields for Black Cutworms

Bryan Jensen, Integrated Pest Management program, Department of Entomology, UW-Madison

It is early. I get that. It is hard to predict what insects will do. Gosh, that is a lesson I learned a long time ago (and still get several reminders each year!).

DATCP’s latest Wisconsin Pest Bulletin(click here to subscribe) indicates some Wisconsin locations have had an intense flights while other locations a moderate flight. Certainly, those pheromone trap catches are a concern.  Additionally, I am anxious about the timing between black cutworm damage and corn development.  Seedling corn is most susceptible to black cutworm injury.  By the time it reaches V5 the threat of economic damage is reduced if not eliminated.

The way spring planting season is shaping up, a significant portion of our corn acreage may be susceptible to black cutworm damage. That is not a prediction just a cause for concern. The only way to tell for sure is to monitor susceptible fields.

Sometimes it is the occasional insects, like black cutworms, that really catch us by surprise.  We don’t routinely encounter them, and we don’t always think about them during our busy professional life.  This might be a year to keep a watchful eye out.  Fields most likely to see damage, and where I would concentrate initial efforts, are those with early broadleaf weed growth, low lying areas within fields and or where there is significant soybean residue.

Do not assume that if you used an insecticide seed treatment and/or an above ground Bt trait you don’t have to be concerned.  Not all above ground Bt traits provide “control” of black cutworms. Furthermore, both traited corn and seed treatments may not provide adequate control of large larvae.

Don’t consider using a foliar applied insecticide as a preventive treatment.  The reasons not to are longer than I care to mention. Remember, we have had a long history of controlling black cutworms with timely scouting and the use of insecticides if/only when needed.

It can be hard to put to put a “one size fits all” threshold on black cutworm damage.  Typically, when 2-5% of the plants show cutting activity is a time to get concerned.  That threshold range can be affected by price, crop stage and size of larvae.