Sweet Corn Insect Pest Update

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

The second generation flight of the European corn borer (ECB) continued to remain "average" to moderate this past week in southern Minnesota. Although total catch at key locations (see graph below) remains <100/night, we have had ideal weather conditions for mating and egg-lay. Warm, calm nights with ample humidity (and dew on plants for adult feeding) all lead to maximum mating and subsequent egg-lay. Thus, all corn in the row-tassel to early silk stages is highly attractive for egg-lay and larval survival. All corn in these stages, as well as crops such as snap beans and peppers that are in fruiting stages, should be protected with insecticide. Any growers who have initially been using Penncap-M for ECB control in sweet corn, should now be using one of the pyrethroids (Ambush, Baythroid, Capture, Pounce or Warrior) to provide both ECB and CEW control (see article below). Also note: Asana works well for CEW control, but do not use this product for ECB. For both ECB and CEW, timing of the first spray is most critical (i.e., at row tassel to first silk). With the pyrethroids, timing of the 2nd and 3rd applications should be spaced 6-10 days apart, depending on temperature. Once the corn is 7-10 days to harvest, additional sprays are unnecessary for processing sweet corn, and possibly for fresh-market sweet corn (depending on customer preferences). If the spray program has been timely, the only larvae that can possibly still hatch and be present at harvest, will be early instars (mostly 1st instar; <1/8th to <1/4th inch).

Corn earworm (CEW) has also reached much higher numbers this past week in the most south-central region of the state, such as Blue Earth. The new CEW graph (this issue) provides CEW trap catch data for the same locations as we provide for ECB. The CEW moth flight is still low in the Twin Cities sweet corn growing areas (< 5 moths/night). Again, for the "cities" area, the CEW flight does not really take off until late August. Once CEW moth counts exceed 10 moths/night, sweet corn in the early tassel to silking stages will also be attractive for egg-lay, and should be protected with one of the pyrethroid insecticides. All of the pyrethroids labeled for sweet corn are effective on CEW, including Ambush, Asana, Baythroid, Capture, Pounce and Warrior.

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 August 10, 2000.
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