By Andy Michel
Our trapping network has started to catch western bean cutworm (WBC) adults, meaning that flight is underway. WBC emergence occurs, for the most part, during July, although it can be extended into August, so we expect our counts to increase. Females lay eggs on corn, and, after hatch, the larvae feed on the tassel, pollen or silk before entering the ear. Late season damage can be quite substantial, as shown in the figure.
Western Bean Cutworm Damage on Corn
From our previous seasons, we have not seen tremendous damage from WBC. Most adults are caught north of US-30, which is about the upper 25% of OH. Additionally, damage reports have centered on extreme northwest and northeast OH, but only a few fields have had economic damage. The extreme rainfalls in June have led to poor or delayed corn development in some areas, or perhaps replants. Females prefer to lay eggs in pre-tassel corn, so any corn that has not tasseled by the 3rd or 4th week of July (which is usually peak flight) is at high risk for WBC infestation.
The best way to control WBC is to scout corn for the presence of egg masses. Egg masses appear in clumps of 25-100, and are first white, then turn purple within 24 hours of hatching. Inspect 20 plants in 5 locations—if 5-8% of the corn has an egg mass, then treatment might be necessary. Bt corn can be a good option, but only varieties with the Cry1F gene or Vip3A will offer control against WBC.