Black Cutworm Feeding on Bt Corn Technology
Eileen Cullen, Extension Entomologist
Reports of black cutworm feeding (chewing holes in leaves) and cut plants are coming, with two calls this week. Late planted corn is still smaller than V4-V5 making it vulnerable to cutting as black cutworm larvae reach the cutting stage. Please see the May 5, 2011 WCM article Black Cutworm Damage Potential for Corn to review information on scouting, thresholds, treatment, and fields that are likely candidates for black cutworm.
As noted in that article, heavy spring moth flights and pheromone trap catches in WI and surrounding states indicated potential for black cutworm larval feeding in June. I provided a link in that article to recent research (reviewed by Mike Gray, Entomologist, Univ. of Illinois in The Bulletin) that sheds light on what we can expect of Bt corn (Cry 1F protein in the research) and one insecticidal seed treatment (clothianidin), Black Cutworms, Bt Corn, and Insecticidal Seed Treatments: Recent Research Developments.
In Wisconsin, I’ve had one report this week from Bill Stangel, CCA, Soil Solutions Consulting, of black cutworm feeding holes, cut plants, and confirmed larval ID in SmartStax corn in a Dodge Co. field. These are large larvae 0.5 inch or larger and small corn plants, smaller than V4/V5. Clearly, black cutworm populations this year are feeding through some Bt technologies that list black cutworm on the spectrum of control or suppression. Reports to date relate to the Cry 1F protein (Herculex and SmartStax products).
A good article on this observation was also posted this week by entomologists Christian Krupke and John Obermeyer, Purdue University in their Pest & Crop newsletter. The have several similar reports from growers and consultants that larger larvae, > 0.5 inch, are not controlled by Bt proteins expressed in Herculex and SmartStax. Likewise seed-applied insecticides may not provide complete control under heavy infestations. You can read their report here: Cutworms Chewing Through Technology.
With larger black cutworm larvae active, and corn is still in the vulnerable stage, don’t overlook scouting of Bt corn fields. It is worth checking to see if a rescue treatment is required as evidenced by recent reports covered in this article.