Issue No. 13, Article 4/June 22, 2007
Western Corn Rootworm Adults Abundant in Many Corn Fields
As reported in last week's Bulletin (issue no. 12, June 15, 2007), emergence of western corn rootworm adults is well underway across much of southern and central Illinois. In many corn fields, a range of corn rootworm life stages can now be found, including second and third instars, pupae, and adults. We should anticipate more leaf feeding this season in corn fields because of the early adult emergence and the overall unavailability of pollen or silk tissue at this point. We've had early emergence of western corn rootworm adults in the past, most often in conjunction with a hot, dry spring. A review of some articles written for the Bulletin in 1988 revealed that western corn rootworm adults were observed on corn in Champaign County on June 20. The first sightings of adults this year correspond very well to the 1988 season. Let's hope that most other comparisons between 1988 and 2007 end here.
Western corn rootworm adult, Piatt County, June 20, 2007.
On June 18, we made some observations in our standard corn rootworm efficacy trial located south of Urbana and noted that plants in many treatments were under considerable stress due to root damage and lack of moisture. Several of the root systems that we examined had numerous corn rootworm larvae.
Bt (right) and non-Bt (left) plots, corn rootworm trial, Urbana, Illinois, June 18, 2007.
Severely stressed plants in corn rootworm trial, Urbana, Illinois, June 18, 2007.
Over the next week to 10 days, rainfall will need to occur in order for some root regeneration to begin. We also observed striking differences between the Bt and non-Bt plots. Plants in the Bt plots were faring much better and had considerably less leaf rolling than the non-Bt treatments. Because of the very dry soil conditions in Urbana throughout May and June, the soil insecticides are facing a significant performance challenge. We look forward to sharing the results of our root evaluations in July. As requested last week, please share your observations with us regarding your perceptions of corn rootworm product performance this season.--Mike Gray and Kevin Steffey