In this issue:

Sweet Corn Pest Update

*NOTE: the next issue of this newsletter may not be published until August 2nd. For continued moth flight updates (twice per week), please refer to the VegEdge Home Page. CLICK on the left-margin entry entitled: “Weekly Moth Catch Data”

Sweet Corn Pest Update

Bill Hutchison, Patrick O’Rourke & Eric Burkness, Department of Entomology, University of Minnesota, St. Paul

European corn borer - The univoltine (single generation per year) strain of ECB is now underway throughout southern Minnesota (see ECB Graph). By July 4th, most locations had exceeded 1100 degree-days (>50F), indicating the end of the 1st generation flight of the bivoltine ECB. Thus, since July 4th, most moths collected are likely to be univoltine. Previous research has shown that flights >20 moths/night are capable of producing enough eggs to create 25-40% larval infestations in untreated sweet corn. The light trap at St. James caught over 200 moths on the night of July 8th. Recent nighttime temperatures and high humidity have been conducive for maximum ECB mating and egg-lay. Growers with Bt sweet corn will see continued control of the univoltine flight throughout the year. For all non-Bt sweet corn, refer to management recommendations below.

Corn earworm - As indicated last week, the CEW flight is underway and the moth catch continues to be active this week (see CEW Graph). The highest moth catch continues to be observed at Blue Earth and Owatonna. As indicated by a fresh-market grower near Austin, MN (see photo on left), a small CEW infestation is now present in some early-planted tasseling corn (10-15% of plants infested).

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NBSP

Western bean cutworm - WBC catches have fortunately been low, to date, in Minnesota. However, the catch increased this past week in NW Iowa, to >100 moths/night at one site. For WBC, this catch is still very low. Based on work by Dr. Gary Hein, Univ. of Nebraska (Western NE), and colleagues in Idaho, significant egg-lay does not begin until cumulative moth catch exceeds 1500-2000 moths/trap. A new research project on WBC in Minnesota, is now underway, via funding from the USDA Specialty Crops Legislation, via the Minn. Dept. of Agriculture and the Midwest Food Processors Association. Until we have further recommendations for WBC in Minnesota sweet corn, we are recommending an Idaho-based threshold of 2-3% of the plants with WBC egg masses, from tassel through silk. WBC egg masses usually include about 20 eggs and have a distinctive purple color, unique from ECB.

Western Bean Cutworm larva (photo courtesy of Marlin Rice, Iowa State University)

Management Implications - Given the high univoltine ECB flight, and the high CEW flights at several key southern MN production areas, a spray program should now be underway for any sweet corn in the green-tassel (e.g., 25-50% tassels visible), or later reproductive stages. Because of the CEW pressure, spray intervals should be every 5-6 days, depending on temperature (see July 1st issue of newsletter). If inclement weather is anticipated, applicators should strive for a 5-day interval in the event future sprays are delayed 1-2 days. Given the necessary spray timing for ECB and CEW, any WBC larvae should also be controlled as well.

Organic Control Options - Growers should be using Dipel or Pyrethrum-based sprays (check with organic certification group for final approval of specific pyrethrum products). Spray interval should not be more than 5 days. Note that Dipel is generally compatible with Trichogramma parasitic wasps released for ECB or CEW eggs. However, one would still want to be sure the spray has dried before releasing new parasites. Pyrethrum-based products will cause significant Trichogramma mortality.

Special Thanks to All of the Moth Trap Cooperators for 2002 Who Make this Information Possible for Timely Delivery to the Processing and Fresh Market Industry

We appreciate the continued funding for this effort by the Midwest Food Processors Association, Madison, Wisconsin.

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 Assistant, University of Minnesota, woldx018@tc.umn.edu

Disclaimer
Reference to products in this publication is not intended to be an endorsement to the exclusion of others which may have similar uses. Any person using products listed in this publication assumes full responsibility for their use in accordance with current directions of the manufacturer

Last Revised July 11, 2002.
The University, including the Minnesota Extension Service, is an equal opportunity educator and employer.©2002 Minnesota Extension Service, University of Minnesota. All rights reserved. Contact copyright@extension.umn.edu for information on reproduction or use of this material.