MN Fruit & Vegetable IPM News - Vol. 4, No. 3

Despite the accumulation of 432 degree days through May 21^st, black light captures of European Corn Borer (ECB) have been slow to develop. Most likely, the primary cause is the low night time temperatures we have experienced across the state over the last week. Because of variable and cool weather, ECB emergence is typically erratic during the 1^st flight. For example, a bi-modal pattern of emergence will be observed when periods of cold or rainy nights occur between warm, favorable nights for moth flight. We are currently at about 432 degree-days (degree-days > 50F), which is near the beginning of the first flight (graph, below). To date we have not caught any ECB moths in the black light trap at Rosemount (Dakota Co.). We hope to provide some additional summaries on ECB regional population dynamics as the year progresses.

Peak flight 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 at least 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 major magnet for early infestations. All light-trap cooperators should have their traps up and running for the year.

Reminder: View and bookmark the Moth Flight web page to track the 2007 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).

Sweet corn growers, particularly in south-central and west-central MN, should continue to be aware of the "UCB" (Univoltine strain of Corn Borer). 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 (1 gen/yr) strain is dominant, or becoming more common. With the univoltine strain, the flight comes out 2-3 weeks later than the first flight of the bivoltine (i.e., late June to late July). In south-central MN, where both strains occur, this can create an insect management nightmare, where sweet corn and other crops can essentially be vulnerable to larval infestations throughout the summer. As the summer progresses, we will keep you abreast of significant flights of the Univoltine strain of ECB.

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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, 2007 by woldx018@umn.edu
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