Feature Article: Vegetable Insect Summary

Bill Hutchison and Eric Burkness, Dept. of Entomology, University of Minnesota, St. Paul

Insect Outbreaks: The year 2001 was an interesting year with regard to unique insect outbreaks in vegetable crops. Minnesota growers and processors experienced an onslaught of new and unusual pest situations. A few examples include:

Black cutworm in sweet corn (June 8th)
Alfalfa caterpillar in peas (June 29th)
False chinch bug in potato, lettuce (June 29th)
Checkered white butterfly in cabbage (August 3rd)
Potato leafhopper in snap beans (July 13th)

Sweet corn, Corn borer and corn earworm: In addition to the unusual, we also had our usual barrage of European corn borer (ECB) and corn earworm (CEW). As indicated by each figure, MN growers experienced significant insect pressure in mid- and late-season sweet corn plantings. Untreated check plots in our 2001 trials ranged from 60-90% of the ears infested with CEW and ECB larvae, respectively. Even with ECB, we experienced the unusual phenomenon of what appeared to be the first occurrence of the univoltine ECB strain (one, July generation/yr) at the Rosemount (East Central MN), in addition to the usual bivoltine strain. When this overlap occurs, we essentially have a continuous ECB flight throughout summer (see ECB graph; Rosemount). Consequently, we estimated that approximately 30% of the larvae in some of our treated plots (Aug. 20th harvest date) were likely due to the univoltine strain, that we were not accounting for in our spray timing decisions. These data also affirm that only 20-30 ECB moths/night (what we had for the July flight) will create an economically damaging infestation.

A final unique aspect for ECB this year, is evidence of a 3rd generation flight, in early-mid September (e.g., Rosemount, Blue Earth). The additional heat unit accumulations from late July-mid August probably permitted enough time for a 3rd flight to develop (i.e., note the beginning of the 2nd flight=last week of July). The presence of a 3rd flight is beneficial in that most larvae hatching from late-season egg masses will not survive the winter-thus removing larvae from local populations.

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

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Last Revised September 13, 2001.
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