Issue No. 13, Article 4/June 20, 2008
Captures of Corn Earworm Adults Are Worth Noting
Several people who trap for corn earworm adults in the Midwest have reported very large numbers thus far in 2008, numbers that are larger than usual at this time of year. Ron Hines (FS seed agronomist, southern region, Growmark) has noted captures of more than 100 adults during a couple of recent weeks in the traps located in Pulaski and St. Clair counties, and captures in the trap in Marion County have been notable. Entomologists at Purdue University and the University of Kentucky also have reported captures of large numbers of corn earworm moths this spring.
We have largely ignored the potential impact of corn earworms that infest field corn; their feeding on corn ears does not often translate into economic loss. Besides, trying to control the larvae before they enter the ears is very difficult. However, voracious corn earworm larvae are capable of considerable defoliation if they find themselves in cornfields still in vegetative stages of growth. Given the late planting and slow development of corn this year, there is potential for noticeable leaf-feeding injury caused by corn earworm larvae. Feeding by small corn earworm larvae will result in pinholes in the corn leaves; feeding by larger larvae may result in considerable defoliation. In the southern United States, entomologists who regularly deal with whorl-feeding corn earworm larvae recommend that control may be warranted if 50% of the whorls are infested.
With crop conditions and prices being what they are, use good judgment when making decisions about managing corn earworm larvae feeding on corn leaves. A threshold of 50% infested whorls may seem extravagant with corn at $6 or $7 per bushel, but keep in mind that defoliation of corn often looks worse than it truly is in economic terms. We'll keep you apprised of developments if we begin to receive reports of corn earworms (or other Lepidoptera, for that matter) in corn whorls.--Kevin Steffey