Black Cutworm

Bryan Jensen, IPM Program

WDATCP staff recently reported “light to moderate” black cutworm pheromone trap catches and suggested that cutting of seedling corn could occur by late May in southern Wisconsin. States to our south have also published reports with some catches being described as “intense”. Pheromone traps are an excellent way of monitoring black cutworm migration. Using degree day estimates from the first significant capture we can also predict initial cutting activity. In Wisconsin, we have had cool nights which may affect (reduce?) trap catches but the message is clear that it is time to start scouting emerging corn. Black cutworms prefer to lay eggs in weedy areas, low lying fields and/or in fields with soybean residue. Early instars cause shot-hole feeding in leaves and late instars can cut small corn plants at or below ground level. Late instars may be unable to cut larger corn plants and instead will burrow into the corn plot at, or near the growing point to feed. Above ground symptoms are often described as “dead heart” or “wilted whorl”.

Treatment is suggested if there is more than 5% damaged plants. It would also be a good idea to locate several larvae and determine the average instar for each field. Consult page 63 of A3646, Pest Management is Wisconsin Field Crops-2009 (http://learningstore.uwex.edu/Pest-Management-in-Wisconsin-Field-Crops2009-P155C37.aspx) for a head capsule gauge and instructions. The main point is to consider preventable yield loss. Cutworms in the later stages of larval development will be pupating soon and are unlikely to cause significant economic loss when compared to the cost of insecticide and application fees. Which is why it is important to scout early and catch problems before it is too late.

Of special concern in 2009 are the late plantings. Late planted corn can have significantly more injury because emergence is better timed with the spring migration. Any spring weed growth, especially winter annuals, that occurs before or after tillage can also increase a field’s attractiveness to egg laying females.