University of Illinois

No. 16/July 11, 1997

Flights of Corn Earworm Adults Have Been Heavy in Some Areas

Rick Weinzierl, Extension entomologist on campus, reported a couple of weeks ago that the numbers of corn earworm adults captured in traps were extremely large in southwestern Illinois (100 to 400 per night). Flights elsewhere were very light (0 to 1 or 2 per night in east-central Illinois), light (3 to 6 per night at Dixon Springs), low to moderate (6 to 10 per night near LaSalle-Peru, and 3 to 5 per night near Belvidere), to heavy (46 per night in one trap in central Illinois, and 20 to 100 per night in western Illinois). Although this news is a bit old, I thought you might want to keep corn earworms in the back of your mind. Field corn rarely is economically damaged by corn earworm larvae, but their presence can increase the incidence of ear rots. It should also be interesting to watch for the presence of corn earworm larvae in Bt-cornfields. Bt-corn does not provide outright control of corn earworms, but research indicates that it "messes up" their development. Other research indicates that the incidence of aflatoxin associated with corn earworm injury is reduced in Btcorn hybrids.

Producers of seed corn and sweet corn always are concerned about corn earworms. To place the previously mentioned moth counts in perspective, the guideline for protecting seed corn is to treat if 10 or more moths are captured in a pheromone trap for several consecutive nights. However, only fields silking and/or pollinating during this time would be candidates for treatment. This information was taken from Seed Corn Pest Management Manual for the Midwest, published by Purdue University. Rick Weinzierl offers the following treatment guideline for corn earworms in sweet corn: Earworm sprays should begin within 1 or 2 days after first silk whenever moth counts consistently are more than 2 to 3 per night. Spray intervals should be based upon moth counts and temperatures–as short as every 2 days when moth counts exceed 50 to 100 per night and temperatures are in the 90s; as long as every 4 to 5 days when moth counts are under 10 and daily highs are in the 70s. Just one more caterpillar to think about!
Kevin Steffey, Extension Entomology, (217)333-6652