Alert: Corn Earworms off to an Unusually Early Start

Eileen Cullen, Field Crops Extension Entomologist

Corn earworm moth flights have been high for the past three weeks in Wisconsin, as well as IL, IN and IA. During the last week in June, WI DATCP pest survey reported high average nightly pheromone trap catches ranging from 2 to 30 moths at locations including Cashton, Janesville, Lancaster, Manitowoc, Tomah and Sparta.

Trap captures from one of UW Extension Monroe County Agricultural Agent Bill Halfman’s pheromone traps and one of Bryan Jensen’s (UW IPM Program) Columbia County traps registered over 100 moths in less than a week in June. 

Egg deposition is expected to be intense at this time and fields should be watched closely for evidence of larval feeding. The eggs produced by this early flight of moths hatch in 2 to 6 days. For weekly updates on Corn Earworm flights, visit the WI DATCP Pest Bulletin http://pestbulletin.wi.gov/ and click on Trapping Networks.

Corn earworm moth

Typically, we see these high levels of Corn Earworm flights closer to sweet corn silking.

Any corn (field and sweet corn) in late whorl to early tassel stages should be checked carefully. Corn earworm is capable of defoliation damage to vegetative whorl stage corn if larval populations are high (see Field Corn Recommendations below).  Processing sweet corn growers and canners should set pheromone traps, take counts, and be prepared to manage the insect as sweet corn silking occurs (see links to Sweet Corn Recommendations below).

 Corn earworm larvae (note green and light brown/pink color forms).

Field Corn Recommendations

See the recent article by Kevin Steffey, University of Illinois Extension Entomologist. As Kevin wrote:  Historically impact of corn earworms in field corn has not been important; their feeding on corn ears does not often translate to economic loss for field corn.  Additionally, trying to control larvae before they enter the ear is difficult. However, corn earworm larvae are capable of defoliation in vegetative corn. This year, given the late planting and slow crop development, there is potential for noticeable leaf-feeding injury caused by corn earworm larvae.  Feeding by small larvae will result in pinholes in corn leaves; feeding by larger larvae may result in more significant defoliation. In the southern United States, entomologists who deal with whorl-feeding corn earworm larvae recommend control may be warranted if 50% of the whorls are infested. (Steffey, 2008. The Bulletin, No. 13, Article 4, June 20, 2008). For the complete article visit http://www.ipm.uiuc.edu/bulletin/article.php?id=963

Sweet Corn Recommendations

For sweet corn recommendations, visit the VegEdge, ZEA-MAP site for recent newsletter articles, and corn earworm migration forecasts; http://www.vegedge.umn.edu/ZeaMap/zeamap.htm , and a recent article by Rick Weinzierl, University of Illinois; http://www.ipm.uiuc.edu/ifvn/volume14/frveg1408.html#veg