MN Fruit & Vegetable IPM News - Vol. 5, No. 3

Despite the long-term global warming trend, the brisk winter of 2007—2008 seems to also be influencing our cool spring. Although there is a possibility of “summer-like” temperatures returning to southern Minnesota, our current degree-day models for the European Corn Borer (ECB), show very low accumulations as of May 19^th, of only 164 DDs (> 50F threshold), for Rosemount, MN. For the same date in 2007, we had reached approximately 430 DDs. We are approximately 210 degree days from catching the 1st European corn borer (ECB) in the black light trap. In a typical year, this would mean about another 2 weeks before the 1^st ECB begin flying (assuming we accumulate about 10-15 degree days per day) or sometime shortly after June 1^st. Even as heat accumulations begin to pick up, low night-time temperatures or rainfall events will often limit moth trap catch during the first-generation flight. Also, because of variable and cool weather, ECB emergence is typically erratic. A bi-modal pattern of emergence will be observed when periods of cold or rainy nights occur between warm, favorable nights for moth flight. As noted in the graph below, we are still near the start of the first flight. To date we have not caught any ECB moths in the black light trap at Rosemount (Dakota Co.). We will provide some additional summaries on ECB population dynamics and forecasts as the year progresses.

Peak flight of the first generation of the bivoltine strain (2 generations/year) occurs at 50% "Cumulative Moth Capture" (see 0.5 on graph), which is approximately 600 degree-days. Please review the ECB forecast graph, for expected emergence, and follow upcoming issues of the newsletter for ECB and degree-day updates. As temperatures warm and ECB activity increases, all early-planted sweet corn, with extended leaf height of approximately 17" and/or corn in the early green tassel stage will be most attractive for egg-lay. These fields should be watched closely. Because relatively few fields of field corn will likely be attractive for egg-lay, the early planted sweet corn is often a “magnet” for early infestations.

The good news, is that as in recent years, our “forecast” for the bivoltine strain of ECB, is that the 1^st generation flight for most of southern Minnesota, should remain “below-average,” in large part due to the continued use and market penetration of several Bt corn hybrids planted for field corn production in Minnesota, and surrounding Midwest states. Most of the data supporting this trend, comes from the annual ECB fall survey (larvae) conducted by the Minnesota Department of Agriculture (MDA). We will provide more information about these trends in future articles of this year’s newsletter.

Reminders: All light-trap cooperators should have their traps up and running for the year. View and bookmark the Moth Flight web page to track the 2008 ECB and Corn Earworm flights this summer (http://www.vegedge.umn.edu/moth.htm).
You may also want to bookmark the Wisconsin Web Site which provides daily updates on ECB Degree-day accumulations (http://www.soils.wisc.edu/wimnext/corn/euroborer.html).

Univoltine strain of ECB: Sweet corn growers, particularly in south-central and west-central MN, should continue to be aware of the Univoltine strain of ECB. The model presented in this article applies only to growing regions where the dominant strain is the "bivoltine" (2-generation/year) ECB ecotype. However, during the past 10 years, we have also observed a continued increase in univoltine activity (same ECB species, but single generation/year) in southern Minnesota, spreading eastward across the lower third of the state. In 2002, we observed a significant univoltine flight at Rosemount. In many areas of southern Minnesota (as in northwestern MN), the univoltine strain is dominant, or becoming more common. With the univoltine strain, the flight comes out 2-3 weeks later (i.e., late June to late July), compared to the first flight of the bivoltine. In south-central MN, where both strains occur, this can create a pest management nightmare, where sweet corn and other crops are essentially vulnerable to larval infestations throughout the summer. As the summer progresses, please watch the light trap fight data, provided here, to stay abreast of significant flights of both strains of ECB throughout southern Minnesota.

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ACKNOWLEDGEMENTS

Co-Editors: Bill Hutchison (hutch002@umn.edu), Department of Entomology, University of Minnesota, Jeanne Ciborowski, Minnesota Department of Agriculture, Ag. Resources Management and Development Division, and Suzanne Wold-Burkness (woldx018@umn.edu), Department of Entomology, University of Minnesota

The Newsletter is published weekly from May through August, cooperatively, by the Minnesota Department of Agriculture (MDA) and the University of Minnesota (U of MN). Reports are posted on the U of MN and MDA web sites on Fridays. If you have suggestions and/or comments, please send your contributions by 4 p.m., Wednesday to Jeanne Ciborowski, 651-201-6217, jeanne.ciborowski@state.mn.us , MDA, 625 Robert St. North, St. Paul, MN 55155. You can access the Newsletter at the U of MN web site in htm format at: www.vegedge.umn.edu/MNFruit&VegNews/mnindex.htm and at the MDA web site in pdf format at: www.mda.state.mn.us/plants/pestmanagement/ipm/ipmnews.htm

Partial funding for this publication is provided through partnership agreements with the Minnesota Fruit and Vegetable Growers Association (MFVGA) and the United States Department of Agriculture – Risk Management Agency (RMA). These institutions are equal opportunity providers.

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 manufacturer directions.

Last Revised May, 2008 by woldx018@umn.edu
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