WBCW, expanding its range eastward from the western Corn Belt, is a new pest to be aware of within the corn ear pest complex (corn earworm, European corn borer).
Western Bean Cutworm- One to Watch
Eileen Cullen, Extension Entomologist, UW Entomology Department
Western bean cutworm (WBCW) moth flights were monitored using pheromone traps during the 2006 growing season (July and August) by WI DATCP and cooperators, including UW Extension. Results are available on a regional map maintained by Iowa State University, “Western Bean Cutworm Monitoring Network” http://www.ent.iastate.edu/trap/westernbeancutworm/.
WBCW, expanding its range eastward from the western Corn Belt, is a new pest to be aware of within the corn ear pest complex (corn earworm, European corn borer). Larvae feed on pollen, silks, and kernels. Unlike corn earworms, WBCW are not cannibalistic and multiple larvae can infest one ear. WBCW enter the ear through silk channels, or chewing a hole into the husk. Larvae feed on kernels until approximately mid-September and can injure the tip, base and sides of the ear.
In contrast to corn earworms, WBCW has one generation per year and DOES have the potential to overwinter in the upper Midwest. Larvae feed on kernels until approximately mid-September. At the last larval stage (5th instar), WBCW chews an exit hole in the husk, drops and burrows underneath the soil to overwinter. In spring WBCW pupate, and moths emerge in July.
WBCW moth and larval identification, feeding damage, scouting procedures, economic thresholds, insecticide spray timing, Bt corn hybrid option, and continued pheromone trap monitoring network records will be covered in upcoming UW Extension winter meetings and 2007 growing season newsletters. This article serves as an update on 2006 pheromone trap records.
The map below (ISU, 2006) illustrates pheromone trap catch results for the 40 reporting Wisconsin counties. Blue counties are traps reporting, but no moths captured; red counties registered 1-100 moths; and purple counties 100 to 500 moths. (White counties are those where no trap is present/recording). The map represents WBCW moth detections in Wisconsin and regionally up to 4 August 2006.
Traps cannot be used to predict which fields should be sprayed; rather, they can indicate those areas that have significant moth flights and where fields should be scouted (Pope and Rice, 2006). Flight activity of WBCW moths has ended for the 2006 season, as Wisconsin pheromone traps captured very few moths for three successive weeks, and trap counts show that peak flight was registered in early August (WI DATCP, 2006).
Frequency of WBCW moth captures has increased in Wisconsin over the last two years. Reports of corn ear damage by WBCW are, at this point, still scattered and relatively rare. This is likely due to the fact that large populations of overwintering larvae have not established in WI yet; and the fact that growers and consultants are not yet accustomed to comparing WBCW larvae and ear damage with the usual suspects (European corn borer, and corn earworm). Increased frequency of WBCW moth detections indicate the potential for increased overwintering larval survival; and potentially, a new corn ear pest to contend with. How serious a pest this will be for Wisconsin remains to be seen and will be watched by researchers, Extension, growers and consultants alike.
The picture above (Photo Credit: Marlin Rice, Iowa State University) shows a WBCW larva feeding on kernels. Additional photos of in-field damage in 2006 are presented in an article by University of Illinois Field Crop Extension Entomologist, Dr. Kevin Steffey (Pest Management and Crop Development Bulletin, No. 21, August 18, 2006). To view images, click directly on the link http://www.ipm.uiuc.edu/bulletin/article.php?id=615; or go the Bulletin’s home page http://www.ipm.uiuc.edu/bulletin/ and click on Issue 21, August 18, 2006.