Vegetable Insect Pest Updates

Bill Hutchison, Extension Entomologist, University of Minnesota

European corn borer -- ECB trap catches continued to decline this past week, at most south-central and southeastern MN locations, as the first generation flight of the “bivoltine” (2-generation/yr) strain is coming to an end. Degree-day accumulations are now, near normal, for this time of year, indicating that any surviving (significant) larval infestations should be present by the week of the 4th of July. Specifically, this is the time period that most larvae should be 2nd to 3rd instar (approx. ¼” in length), with 3rd instars starting to tunnel into corn stalks, or tassel and ear tissue for early planting dates. NOTE: With first generation ECB, there is a strong correlation between plant height and egg lay. Because of this relationship, the earliest planted (“chest high”) field corn sites at Rosemount, have a 50% whorl-stage infestation (“shot-holing” damage), with 2nd instar larvae present and later planted (“waist-high”) field corn sites have a 7% whorl stage infestation. Any early-planted sweet corn (e.g., Early Vee) should continue to be checked carefully for egg masses of ECB and/or newly hatching larvae.

Courtesy of Marlin Rice, Iowa State University

ECB- Univoltine Strain - - With the decline of the 1st generation flight of the bivoltine strain, we also have the onset of the univoltine flight, for most west-central and some south-central locations. One example of the univoltine flight is shown below for Lamberton, MN, based on data collected by Bruce Potter, Minn. Extension Service.

**For additional Minnesota ECB Flight Summaries, see the BugWeb site “Map” and click on the location of your choice, at: www.mnipm.umn.edu/Bugweb.

Corn earworm-- As expected (in a “normal” year), CEW moths have not yet been recorded in significant numbers (0-1 per week) in southern Minnesota. The major CEW flight does not occur until mid-August. We will continue to monitor selected trap sites throughout the growing season.

Striped Cucumber Beetle -- Striped cucumber beetles remain very active in several southern Minn. Locations. For cucumber squash and pumpkins, action thresholds range from 0.5-1.0 beetles/plant. Primary concerns with SCB include: direct feeding damage on young plants (cotyledon to first true leaf stage) and The transmission of bacterial wilt (Erwinia tracheiphila). With the exception of watermelon, nearly all cucurbit crops are susceptible to bacterial wilt. The only way to control the disease is to provide timely beetle control. See the Midwest Vegetable Production Guide-2000 for control options

Flea Beetles -- Flea beetles remain active in a number of crops including recently planted cabbage. Treatment is recommended if >5% of the plants show feeding damage.

Co-Editors: Bill Hutchison, Department of Entomology, University of Minnesota, hutch002@tc.umn.edu
Jeanne Ciborowski, IPM Program, Minnesota Department of Agriculture, jeanne.ciborowski@state.mn.us
Cindy Tong, Department of Horticulture, University of Minnesota, ctong@extension.umn.edu
Production Editor: Suzanne Wold, Research Specialist, University of Minnesota, woldx018@tc.umn.edu

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Last Revised June 29, 2000.
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