Strategic Farming: Let's talk crops focused on corn insect pests

Although European corn borer (ECB) populations dropped dramatically after widespread adoption of Bt-corn hybrids, the discovery of Bt-resistant populations reminds us to not let our guard down on this pest. Corn rootworm (CRW) is another major corn pest in Minnesota where resistance to Bt traits has led to management challenges. ECB and CRW were the topic of discussion on the March 13th, Strategic Farming: Let’s Talk Crops program with Dr. Fei Yang, Extension Entomologist with University of Minnesota Extension.

European corn borer (ECB) European corn borer, specifically the larva, caused significant yield losses and economic damage throughout the U.S. Corn Belt prior to the introduction of Bt hybrids. Injury from ECB can lead to stalk breakage, ear droppage, stalk rots, ear rots, mycotoxins, and ultimately yield losses. Control was particularly challenged in MN by the existence of two biotypes, the univoltine biotype, which has only one generation in a year, and the multivoltine biotype, which has at least two generations each year.

Because ECB larvae burrow into the stalks and ears of corn, timing an insecticide application for effective control is challenging. Transgenic Bt corn replaced the use of insecticides for ECB control in many fields, providing excellent control of ECB for almost 27 years in the U.S. ECB resistance to the Bt technology Practical resistance in ECB to Bt corn (Cry1F) was first found in four fields in Nova Scotia, Canada in 2018. Since then, practical resistance to Cry1F and other Bt proteins has been documented to widely expand in other locations in Canada, and in 2023 practical resistance in ECB to Bt sweet corn (Cry1A.105 + Cry2Ab2) was found in the U.S. in Connecticut. Although resistance in ECB to Bt corn is still rare in the U.S., insect resistance to Bt proteins poses a significant threat to the long-term sustainability of this technology.

The close proximity of the Canadian populations to MN is concerning as ECB moths can migrate long distances. Monitoring for resistance, use of a high dose/refuge strategy, and pyramiding or stacking traits in hybrids have been effective so far at fending off and slowing down resistance.

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