Black Cutworm Threat Remains Real

Larvae emerging form record catches.

Published on: May 23, 2011

It's now official. More black cutworm moths have been caught in 2011 than in the past several years, through 2006. Purdue University entomologists Christian Krupke and John Obermeyer say the record catch, which spiked to an unprecedented level in mid-April, is likely the result of all the storm activity in April, which brought moths northward into Indiana from the Gulf States.

Just 10 days ago, the catch was again above catch levels compared to 2006 and afterwards. With corn being planted in some locations, the threat of damage becomes real.

Here are some points the entomologists want you to remember as you decide what to do about the black cutworm threat.

Scout- Their number one recommendation is still to scout, use the Purdue University Corn & Soybean Field Guide for guidance on identification of black cutworm vs. other species, and be prepared to apply an emergency foliar insecticide if conditions warrant treatment.

Monitor temperatures- It takes 300 heat units total accumulation for black cutworm larvae to reach the size that they can begin feeding on corn plants. As of May 15, that threshold was reached in parts of southern Indiana, but was still a ways off in northern Indiana.

Watch for early signs- Black cutworm generally starts out as feeding on the leaves when the larvae first begin to feed. That's because they are small. As they grow larger, they can cut plants.

Know your hybrid- Do you have a hybrid resistant to black cutworm damage? If you're not sure, now would be a good time to call your seedsman and find out.

Check entire field- Windshield scouting won't do the trick on this one. Black cutworms tend to be heaviest in pressure where there was lots of green vegetation, and sometimes in low areas of fields. Just because you don't see any symptoms along the outside rows doesn't mean that the black cutworms aren't at work somewhere else in the field.

Beware 'preventive' insecticides- Some people have been convinced to apply a foliar insecticide with their burndown herbicide application in anticipation of black cutworms. The problem with this approach, entomologists say, is that these are contact herbicides. Once they land on the soil, they begin to break down. While some claims of control for several weeks have been bantered about in coffeeshop environments, the entomologists say the smart money is on 7 to 10 day control at best. Depending on how larvae emerge and corn plants develop, that may or may not do any good. It's also a shotgun approach which puts an insecticide into the environment, whether it's actually needed or not.