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Issue No. 20, Article 3/August 8, 2008

What We Have Heard or Read About Other Insect Pests of Corn and Soybeans

We have learned the following observations from extension entomologists throughout the north-central states and from Kevin Black (insect/plant disease technical manager for Growmark, Bloomington, Illinois).

Bean leaf beetle. Adults from the first generation of bean leaf beetles have emerged throughout most of the Midwest, about 10 days to 2 weeks later than usual, which has been par for the course for most insects this year. Wayne Bailey, extension entomologist at the University of Missouri, indicated that numbers have been fairly large in some areas of Missouri. These beetles will feed on foliage, so the percentage defoliation thresholds are appropriate (20% with allowances for control costs and crop value). Keep in mind, however, that after these beetles complete the first generation, the second generation will begin. Beetles from this second generation will feed on soybean pods.

Southwestern corn borer. Very large numbers of adult southwestern corn borers have been captured in pheromone traps in Illinois and Missouri. Data from traps in southern Illinois ("The Hines Report"), reveal very large numbers of southwestern corn borers captured in Pulaski County during the weeks ending July 22, July 29, and August 5, and in St. Clair County during the week ending August 5. Wayne Bailey, extension entomologist at the University of Missouri, has reported that captures of adult southwestern corn borers have been large in traps in southeastern Missouri. He also received a report of a significantly infested cornfield north of St. Louis. Both corn and sorghum growers and their advisers should scout for egg masses of southwestern corn borers now. Corn hybrids without a Bt trait for caterpillar control may host heavy infestations of this economically important pest.

Spider mites. Although Illinois has experienced very little dry weather this year, dry weather prevails in some areas to the east of Illinois. Consequently, concern about twospotted spider mites in soybeans has increased in those areas. Ron Hammond and Andy Michel, entomologists at Ohio State University, reported finding spider mites in soybeans in the August 4 issue of C.O.R.N. (Crop Observation and Recommendation Network).

Western bean cutworm. Numbers of adults captured in pheromone traps have been relatively larger in 2008 than in previous years in Illinois, Indiana, Michigan, and Wisconsin. According to Chris DiFonzo, extension entomologist at Michigan State University, thousands of acres of corn have been treated with insecticides for control of western bean cutworms. Interestingly, numbers of western bean cutworm moths captured in some areas of Iowa and Nebraska this year have been much lower than numbers captured in previous years. Entomologists throughout the Midwest have also reported that peak moth flight has passed in most areas, so scouting for eggs and small larvae should be underway.

Please keep us apprised of the insect situation in your neck of the woods, and we will share the observations with readers of this newsletters. Thanks to all of you who send area-specific information.--Kevin Steffey

Kevin Steffey

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