On Jan. 18, 2023, Bruce Potter, University of Minnesota Extension IPM specialist and Dr. Anthony Hanson, UMN Extension IPM educator joined UMN Extension crops educator Ryan Miller for a wide-ranging discussion of European corn borer. This was the second episode of the 2023 Strategic Farming: Let’s talk crops! webinars in this series. 

In recent years, UMN Extension entomologists, specialists and educators have conducted a European corn borer survey in Minnesota, continuing a tradition that began in 1963 by the Minnesota Department of Agriculture. This survey serves multiple purposes, including improving our understanding of: 1) whether ECB Bt traits are still effective, 2) how Bt hybrids affect ECB population dynamics in fields planted to hybrids with and without ECB Bt traits, 3) the footprint of different ECB biotypes (univoltine=single generation per year; bivoltine=two generations per year; or a combination).  Briefly, 10 plants in each of two corn fields sampled randomly and two fields that are known to be growing nonBt corn per county are surveyed for ECB feeding injury; those plants with injury are dissected to count the number of larvae and measure tunnel length, which is  related to yield loss. 

ECB population densities hit a peak of nearly 400 borers per 100 plants surveyed in 1995, the year before genetically modified hybrids expressing a Bt protein specific to ECB were available to plant. On average fewer than 2 borers per 100 plants have been found in the survey since that time. Says Hanson, “In 1995, you’re looking at more than 300 larvae per one hundred plants surveyed in southern Minnesota. As the surveys continued into recent years it was hard to find borers across the state, oftentimes just one or two per field.”

While there is no substitution for scouting one’s own corn fields for ECB injury symptoms, by and large the recent results of these surveys point to several conclusions: 1) overall the Bt trait is resulting in area-wide suppression of ECB populations even in fields not planted to Bt corn, 2) the ECB Bt trait is still effective against ECB larvae. Scouting is recommended for those that plant non-Bt corn, as there is a narrow window between when larvae emerge from their eggs and when they begin boring into the stalk, where insecticides can no longer reach the larvae. Scouting of Bt fields is also recommended to quickly identify any Bt trait failures. ECB populations that have evolved resistance to the ECB Bt trait have been identified in eastern Canada, making scouting for resistance management important. 

In addition to ECB feeding injury and larvae, UMN Extension personnel are also examining corn plants for both signs of the tar spot fungus, a pathogen capable of causing significant yield losses in Minnesota corn, and stalk rot.

For those that missed this session, it is now available to view on YouTube at https://youtu.be/_R9Hbb7M5lA. For more information and to register to attend other weekly session through the end of March, visit z.umn.edu/strategic-farming.