On Feb. 26, Dr. Fei Yang, UMN Corn Extension entomologist, joined UMN Extension Crops Educator Dr. Anthony Hanson for a discussion on corn insect pests. Dr. Yang provided an update on the current challenges Minnesota faces with these pests and shared insights from his research on corn insect pest management. This was the eighth episode of the 2025 Strategic Farming: Let’s Talk Crops! webinar series, which will continue through March.

Two primary corn rootworm species including western (WCR) and northern (NCR) species continue to cause significant injury to corn in Minnesota. These pests share similar life cycles, with adults laying eggs in late summer that overwinter and hatch from late May to June. The larval stage is particularly damaging, as it can severely damage roots, impeding water and nutrient uptake, leading to corn lodging and increased susceptibility to diseases like crown rot. Adults also feed on tassels and silks, reducing pollination and increasing the risk of ear mold.

Effective management strategies for corn rootworms include Bt corn, crop rotation and insecticides. Bt corn with multiple proteins targets rootworms through different modes of action, reducing the risk of resistance. Insecticides can be applied as soil treatments, seed treatments or foliar sprays, but Bt corn remains the most effective tool, especially when combined with other practices.

Resistance to Bt proteins, particularly Cry3 and Cry34/35, has been observed in WCR populations across Minnesota, including Yellow Medicine, Brown, Mower and Redwood counties. While NCR resistance is less common, cases have been found in North Dakota and Meeker County, Minnesota. Despite these challenges, Bt corn remains a key management tool. The WCR exhibits rotation resistance by laying eggs in non-corn fields, allowing larvae to hatch when corn is planted again, while NCR shows rotation resistance through extended diapause, enabling eggs to survive longer before hatching. A 2021-2024 Minnesota study using yellow sticky traps found crop rotation to be effective in managing corn rootworm populations. However, in 2024, first-year corn fields in Minnesota experienced WCR injury, raising concerns about the spread of rotation-resistant WCR variants.

Dr. Yang’s research on insecticides found that increasing concentrations of pyrethroids and other insecticides did not significantly reduce rootworm damage. However, combining organophosphates with pyrethroids proved to be effective. Additionally, Dr. Yang found that Bt corn controlled rootworms effectively, even without seed treatments. In cases of Bt resistance, higher concentrations of neonicotinoid seed treatments, including thiamethoxam or clothianidin, may provide added protection.

European corn borer (ECB) larvae, which cause stalk breakage and ear drop, have been effectively controlled by Bt corn with Cry1 and Cry2 proteins for over 28 years. However, resistance to Cry1F was first detected in Canada in 2018, and in 2023, ECB resistance to Bt corn was reported in Connecticut. ECB’s mobility increases the risk of resistant populations spreading across regions. In 2024, ECB damage was observed in Clearwater County, and larvae from this area were collected for resistance analysis. Dr. Yang’s research found low resistance to Cry1 proteins but high resistance to Cry2Ab2. While resistance remains low overall, the spread of resistant ECB populations is a growing concern, though Cry1 proteins continue to provide effective control.

In 2024, two new pests were identified in Minnesota: the corn leafhopper and cornsilk fly. The corn leafhopper, discovered on the University of Minnesota campus in St. Paul, can transmit pathogens that cause stunting and red leaves. The cornsilk fly, which primarily affects sweet corn, was found in Rosemount. While these pests are not currently a major concern, they will be closely monitored moving forward.

For those that missed this session, it is now available to view at: z.umn.edu/StrategicFarmingRecordings.

For more information and to register to attend other weekly session through the end of March, visit z.umn.edu/strategic-farming.