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Western Bean Cutworm Scouting Update

Western Bean Cutworm Scouting Update

Western bean cutworm is a corn pest and adult moths have already been reported in several counties in Iowa. Here are dates when scouting for this pest should begin in various areas.

Western bean cutworm (WBC) moths have already been reported in the last week or so in several Iowa counties. The first moth of 2011 was captured in Hancock County, located in north central Iowa, on June 17. The moth is the adult form of this pest. The western bean cutworm moth lays the eggs, which eventually hatch to produce the cutworms, which attack corn plants.

The following information on Western Bean Cutworm, a corn pest, is from ISU Extension entomologist Erin Hodgson and colleagues at Iowa State University.

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 east 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.

When should you start scouting for this corn pest in your county?

Adult emergence can also be predicted by using a degree day (DD) model developed in Nebraska. The model is based on accumulation of DDs (base 50 F) from May 1. Sources vary as to when field scouting should begin, at either 25% or 50% adult emergence, which are predicted at 1,319 and 1,422 DDs, respectively. The map displays the predicted dates when 25% and 50% adult emergence should occur based on accumulated and normal DDs. 

Follow these guidelines for 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

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