By Adam Sisson, Corn and Soybean Initiative; Laura Jesse, Plant and Insect Diagnostic Clinic; and Erin Hodgson, Department of Entomology
Western bean cutworm (WBC) moths have been reported in several Iowa counties. The first moth of 2011 was captured in Hancock County, located in north central Iowa, on June 17.
Trap data by participating counties can be viewed at the North Central (NC) ipmPIPE Web page. Click on a highlighted county to see the number of recorded moths in that county. If captures occur on consecutive days and moth numbers are increasing, this is the signal to begin scouting. Tama County, located in central Iowa, experienced this on June 24, but to date there has not been any increasing trap catches in the rest of the state. The presence of adult moths in traps indicates only that scouting efforts should begin in an area.
Adult emergence can also be predicted by using a degree day (DD) model developed in Nebraska. The DD model is based on the accumulation of DDs (base 50 F) from May 1. Sources vary as to when field scouting should begin, at either 25 or 50 percent adult emergence, which are predicted at 1,319 and 1,422 DDs, respectively. The following map (Figure 1) displays the predicted dates when 25 and 50 percent adult emergence should occur based on accumulated and normal DDs.
Figure 1. Iowa climate divisions showing predicted 25 and 50 percent emergence of adult western bean cutworm moths. However, there was also a flight recorded in Tama County on the June 24.
Scouting for western bean cutworm
When scouting 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 (Figures 2, 3) on the top three to four leaves. Thresholds, management options and descriptions of WBC are outlined in a previous ICM News article, Use Treatment Thresholds For Western Bean Cutworm.
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 email@example.com or by calling 515-294-5899. Laura Jesse is an entomologist with the Iowa State University Extension Plant and Insect Diagnostic Clinic; contact at firstname.lastname@example.org or by phone 515-294-5374. Erin Hodgson is an assistant professor of entomology with extension and research responsibilities; contact at email@example.com or phone 515-294-2847.
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