Feature Article: Vegetable Pest Alerts

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

ECB moths (l - female, r - male) (Photo courtesy of Marlin Rice, Iowa State University)	The 2nd generation flight of European corn borer (ECB) is well underway at Rosemount (Dakota Co., MN); moth catches increased to 30/night on July 30th, 90/night on July 31st, then declined to 12/night on Aug. 1st (see Figure 1, below). It is too early to tell if we are at the peak of the ECB flight for the bivoltine strain; the peak can occur between 1700 and 2000 degree-days (50F base).

Moth catches of corn earworm (CEW) throughout MN (CEW Pheromone Traps) continue to remain light, as of Aug. 1st. As indicated in previous years, CEW catch for southern and central Minnesota typically takes off in mid-August, with a major increase anytime around Aug. 25th. Thus, any sweet corn still tasseling/silking at this time will be highly attractive to egg-lay by CEW. Not surprisingly, the highest CEW trap catches, that we are currently aware of, are still south of the MN/WI border. Jim Chenhall (Syngenta), Lone Tree, IA (southeast of Iowa City), reported a gradual increase this past week, from 9 to 55/night (7/30/01). We can usually detect a gradual increase in moth catch from south to north, as the successive flights continue to move north. Within MN, from south to north, CEW captures should start picking up in the next 2 weeks. For the most recent information on ECB and CEW trap catches (for MN locations), view the respective maps at the BugWeb site) http://www.mnipm.umn.edu/Bugweb/ More information for the new CEW network will be provided next week.

Corn leaf aphid (CLA) numbers continue to remain fairly high (e.g. >100 aphids/plant) at Rosemount, in sweet corn still in the early to late-tassel stages. However, many aphid colonies are also “crashing” due to various natural enemies, including the aphid-specific fungi. In addition, some pyrethroids are known to “flair” aphid infestations (typically used for ECB and CEW control). Thus, treatment decisions are for CLA in sweet corn are not well developed for processing or fresh-market sweet corn. Research is underway to look at various seed treatments, in combination with foliar sprays, for potential CLA control. At this time, the only clear recommendation is for fresh-market growers, where CLA may be heavy on the ears, near harvest. In this situation, one Malathion treatment before harvest (spray must be at least 5 or more days before harvest (pre-harvest interval=5 days)) may be necessary to control the aphid, and maintain the “insect-free” corn-on-the-cob ear quality some customers demand.

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, ctong@umn.edu
Production Editor: Suzanne Wold, Graduate Research Assistant, University of Minnesota, woldx018@umn.edu

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Last Revised August 2, 2001.
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