Western Bean Cutworm Scouting Update

July 12, 2010

By Adam Sisson, Corn and Soybean Initiative and Laura Jesse, Plant and Insect Diagnostic Clinic

Western bean cutworm (WBC) moths have been reported in several Iowa counties. The first moth was captured in Adams County, located in the southeast part of the state, on June 16. Iowa State University trap data can be viewed by county. The presence of adult moths in traps indicates only that scouting efforts should begin in an area.

Adult emergence can also be predicted by combining a degree day (DD) model developed in Nebraska with actual trap captures. The DD model is based on the accumulation of DDs (base 50 F) from May 1. Corn field scouting should begin when 1,319 DDs (base 50 F) have accrued, as this is when 25 percent of adult moths have emerged. The following map (Figure 1) displays the accumulated DDs for Iowa.

According to the combined DD and trap capture data, growers should be scouting corn fields now for WBC throughout Iowa.
 

Figure 1. Base 50 F degree days (DD) in Iowa since May 1. Scouting for WBC should begin when 1,319 DDs accumulate. However, when this information is combined with trap capture data, it indicates that corn growers should be scouting throughout the state for WBC. Map courtesy of Iowa Environmental Mesonet, ISU Department of Agronomy.

When scouting corn for WBC, examine 20 successive plants in five different areas of a field. On these plants, check for the presence of eggs or young larvae on the top three to four leaves. (See Figures 2 and 3.) Thresholds, management options and descriptions of WBC are outlined in a previous ICM News article.  

Figure 2. Western bean cutworm eggs
 

Figure 3. Western bean cutworm larvae that have just hatched

 

 

Adam Sisson is a program assistant with responsibilities with the Corn and Soybean Initiative. Sisson can be contacted by email at ajsisson@iastate.edu or by calling 515-294-5899. Laura Jesse is an entomologist with the Iowa State University Extension Plant and Insect Diagnostic Clinic. She can be reached by email at ljesse@iastate.edu or by phone 515-294-5374.

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