Black Cutworm Early Season Threat to Corn

Corn farmers should pay attention to the spring migration of the black cutworm. The moths wing their way into the Midwest every year.

The black cutworm rides the southerlies north into the Corn Belt. The female moths look for farm fields lush and green mostly with weeds. Winter annuals are the favored nesting ground says University of Illinois Extension Entomologist Mike Gray.

Quote Summary - They go into those fields and lay eggs. They lay eggs on those weeds. Eventually, once the fields are planted with corn, many of the surviving black cutworm larvae will move off the weed hosts onto corn seedlings. Corn fields in the one-to-four-leaf stage are very susceptible to cutting.

If those cuts are made below the growing point of the corn plant, then it dies. Most of the cutting, says Mike Gray, takes place over night or occasionally on a very overcast dark cloudy day.

Quote Summary - Growers are encouraged to look for early signs of black cutworm activity. This would be small pin hole areas on leaves that have been removed by the caterpillars in their one to three instar stage. Once they caterpillar reaches the fourth larval instar stage it can begin to cut plants.

Many insecticides can be used as rescue treatments if needed to combat the black cutworm. Most Bt corn is also capable of protecting the crop, but not in equal measure.

Quote Summary - Not all Bt hybrids offer the same level of protection when it comes to black cutworms. Some are quite good, but finding that trait can be confusing. I encourage growers to use the Handy Bt Trait table put out annually by Michigan State University. Search Google for “Handy Bt Trait Table ”. It is very informative and identifies if the hybrid chosen offers black cutworm protection.

If the hybrid chosen does not protect against the black cutworm, then the farmer will clearly, urges Gray, need to pay much more attention to the lifecycle of the insect and potentially gear-up for rescue treatments as needed.