Here comes another season of western bean cutworm trapping! Western bean cutworms (WBC) emerge as adults from late June until August, with peak flight usually occurring the 3rd week of July. After mating, they lay eggs in corn, and the developing larvae may eventually enter the ear to cause significant ear damage. While our trap catches have increased slightly over the past few years, we have been noticing an increase in damage, some of which may be economic. WBC prefers to lay eggs in pre-tassel corn—so any corn that does not develop tassels over the next 2 weeks is at high risk for western bean cutworm infestation. We have a lot of late planted corn, so good scouting is important!
Egg masses are the most important stage to scout corn. Eggs are laid on the upper surface of the top 1-3 most leaves, especially those still in the vertical position. Egg masses are usually in clumps of 25-100, start out white, then, within 24 hours of egg hatch turn dark purple. After hatching, the larvae will feed on the tassel and pollen before entering the ear. Once they enter the ear, they are mostly protected from insecticides, so spraying, if necessary should occur after egg hatch. Thresholds are based on inspecting 20 plants in 5 locations, and if 5-8% of the corn has egg masses, treatment is necessary. Many insecticides have efficacy against WBC. Furthermore, Bt products with Cry1F or Viptera will provide control; however we have noticed a fair amount of feeding with Cry1F in our trials. While it may protect against economic losses, these fields should be scouted as well. Further information can be found in our fact sheet (http://ohioline.osu.edu/factsheet/ENT-40) and a free article in the Journal of Integrated Pest Management (http://jipm.oxfordjournals.org/content/1/1/A1).