Feature Article: Corn Earworm and European Corn Borer, Take Off!

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

European corn borer (ECB) trap catches continue to remain strong at Rosemount over the past 5 days (130/night at Rosemount, Dakota Co.), and have increased at other locations, including Le Sueur (100/night) and Blue Earth, MN. Given our current heat unit accumulation at Rosemount, we should be (hopefully) close to the peak for this 2nd flight (generation) of ECB. To put this flight into better perspective, our IPM crew at Rosemount confirmed today (Aug. 8th) a high oviposition rate, with 11/20 plants (55%) with egg masses. However, several plants had more than one egg mass, for a total of 17 egg masses/20 plants (untreated check plots; corn in the late-tassel, early silk stage). This is clearly a SIGNIFICANT flight; well over the threshold of 4% of plants with egg masses. The good news is that just a few had hatched, about 25% are black-headed (will hatch soon), and 70% are freshly-laid (white). Thus, growers still have time to treat susceptible sweet corn in the area. See the July 20th issue, for the latest efficacy results for synthetic pyrethroids (both ECB and CEW). Also refer to the 2001 Midwest Vegetable Production Guide, for label information, at: http://www.entm.purdue.edu/Entomology/ext/targets/ID/index2001.htm

Corn Earworm Alert! In the meantime, if you do not have ECB, get ready for the Corn Earworm (CEW). CEW moth catches in pheromone traps REALLY took off in the past 5 days, first in IOWA, and now in southern (Blue Earth) and south-central (Le Sueur) MN. Trap catches at most Twin City Fresh Market areas remained low (<6/night) as of Aug. 8th, but moth counts went over 15/night at Rosemount (Dakota Co.) on Aug. 9th. CEW moth counts could be much higher in the next few days. As noted earlier, our late-season flights are due to new CEW migrations from the southern states (including TX and KS, as field corn in those areas begins to senesce). To give you an idea of what might come our way, Jim Chenhall (Syngenta) reported the trap in Lone Tree, IA (southeast IA) catching approx. 354 Aug. 6 and another 350 on Aug. 7th. We will continue to update our CEW graphs at the VegEdge site (http://www.vegedge.umn.edu/CEWTRAPS/CEW2001.htm ), as quickly as possible. Also continue to check the NEW CEW Pheromone Trap Network at the BUGWEB site, for new updates, at: http://www.mnipm.umn.edu/bugweb/bugbase/earwormnetwork/earmainmenu.htm (click on “FIND a SITE”, and look at either the Iowa OR MN maps).

Note threshold: the action (spray) threshold for CEW catch in pheromone traps is only 10 moths/night for 2 consecutive nights (when fresh silks are present).

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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 August 9, 2001.
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