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European corn borer degree day model: July 6

Last fall I wrote an article summarizing an annual UMN Extension European corn borer survey organized by Extension entomologist Dr. Bill Hutchison and IPM Specialist Bruce Potter.  Some of the results of this survey and the implications for planting non-Bt corn hybrids were discussed in this article.

Lab results regarding the European corn borer strain that is prevalent in the counties I surveyed (Clay, Becker, Mahnomen, Norman, Polk, Clearwater, Red Lake, Pennington, Marshall, Kittson and Roseau) confirmed that all of the borer larvae I collected in 2019 turned out to be the univoltine strain.  This is important information from a corn borer management perspective as those that plant non-Bt hybrids would like to best target their scouting efforts and insecticide applications because insecticides are largely ineffective once larvae have made their way into the stalk.

The following information discussing both univoltine and bivoltine European corn borer strains was written by UMN Extension IPM post-doc Dr. Anthony Hanson.

In addition to the "traditional" bivoltine (two-generation/yr) strain of ECB, the univoltine strain has become more common in southern Minn., as well as continuing as the dominant strain in northwest MN and in ND. In southern MN, this strain is typically most active from late June to late July. Of interest, the univoltine strain has maintained a presence in southern MN for at least the past 20 years, albeit at low numbers (as estimated by annual black-light trap moth data). Beginning with the 2018 growing season, we are providing Degree-day (DD) model updates, and 7-day forecasts for univoltine moth flight timing, to assist growers, processors and agronomists in scheduling scouting plans and IPM decision-making. The modified DD model is based on a lower (50 degrees) and upper threshold (86 degrees), and January 1st as the start date; this is similar to the original model developed by Hoard & Weiss (1995) at NDSU, and reviewed by Phil Glogoza via the NDSU Extension publication. Degree-days were calculated from current and 7-day forecast daily temperature data provided by the U.S.A. National Phenology Network.

Figure 1. Forecast European corn borer degree days for July 6, 2020 (source: Anthony Hanson). 

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