We have been contacted by several growers and crop advisors regarding heavy feeding on corn ears by Western bean cutworm (WBC). These observations were confirmed during a recent visit to several fields in Northwest Ohio. It was very easy to spot damaged ears, and most, if not all, of these fields showed economic damage. It is quite clear that WBC has become the primary corn ear pest in NW Ohio, and that it will need to be properly managed. Although the damage is already done, now is a good time to see the extent of WBC feeding in your field to help prepare for next year.
Of particular concern was the extent of damage on ears with Cry1F (see figure). Cry1F is also known as the Herculex gene, and is present in a fair number of hybrids, including SmartStax and a few Acremax varieties (for a complete list see this Bt trait table: http://www.msuent.com/assets/pdf/28BtTraitTable2016.pdf). Cry1F includes control of WBC on its label—but it is clear from the figure that this is not control. Based on data from Ohio and other surrounding areas (MI, IN and Ontario), we would highly recommend that growers inspect any fields with Cry1F for WBC damage and to make sure that the Bt gene that you paid for is performing to expectations. Cry1F is one of only two Bt genes that offer control of WBC. Vip3A (commonly known as VIP or Viptera) from Syngenta will still protect against WBC damage and those looking for a transgenic option for WBC control should consider varieties that include this gene. Besides the transgenic options, growers can scout fields in July to observe egg masses and larval hatching. Our WBC trapping and monitoring program for Ohio has shown peak adult flight is July 15-20 resulting larval hatching in late July through early August. Pyrethroid sprays are an option at this time but require treatment before the larva reach the ear or within 7-10 days post-hatching.
Figure 1. WBC feeding on Cry1F ears. WBC damage evident by the damaged ears, holes in the husk, and caterpillar frass. Ear molds are often a secondary result of WBC feeding. The white stick with 2 purple bands shows that Cry1F was indeed present in that particular corn plant.