Northwest Iowa Extension Crop and Pest Information by Todd Vagts ISU Extension Crops Specialist Counties Served:  Carroll, Calhoun, Crawford, Ida, Monona, Pocahontas and Sac.
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Western Bean Cutworm

Northwest IA
Degree-Day and Trap Catch Information

The following chart shows the progression of accumulated degree-days (base 50) for 4 locations in central and northwest Iowa.  The chart also projects accumulated degree-days for the next 7-days according to forecasted temperatures from the "Weather Channel".

Information from the University of NE (NebGuide G98-1359-A) indicates that 25, 50 and 75 percent moth emergence occurs at 1319, 1422 and 1536 degree-days respectively.

Degree Day Accumulation

Scouting Recommendations from Ronald C. Seymour (Extension Educator in Adams County) and Gary Hein (Extension Entomologist Panhandle REC)
... Even though field scouting for western bean cutworm in field corn should begin when the first moths are caught, control decisions should be made shortly after the moth flight peaks. The moth flight usually peaks between July 10 and July 24. 

When scouting for western bean cutworms in corn, check 20 plants in at least five areas of each field. Look for eggs on the top surface of the upper most leaf or look for larvae in the tassel. If 8% of field corn plants, 5% of seed corn plants or 5% of popcorn plants have egg masses or larvae, consider applying an insecticide.  

Western bean cutworm moths prefer to lay eggs in corn plants that are in the late whorl stage compared to those that have completely tasseled. Pay particular attention to later planted fields or those with uneven development. Western bean cutworm eggs that hatch when corn plants are in the whorl stage of growth have a high rate of survival. The larvae are well protected in the whorl or tassel.  

If an insecticide treatment is warranted in corn fields, it should be made when 95% of the plants in a field have tasseled. This timing of the application increases the chance that the worms will be exposed to the insecticide resulting in better control.

Trap Catch Data
(Excel Spreadsheet)