Corn rootworm beetles on corn leaf

Corn rootworm (CRW) is a common economically damaging corn pest, especially in corn-on-corn fields. As larvae, CRW can cause damage to the root tissues and hairs. As the larvae grow and feed, significant root loss can occur, resulting in decreased ability for the plant to capture necessary water and nutrients, and eventually plant lodging can occur. As adults, CRW feed on corn silks and can inhibit proper pollination.

In the Midwest, CRW larvae and/or adults can be found from mid-May through September. Scouting for CRW larvae and CRW beetles should happen throughout the entire season. If you saw significant adult beetle populations this summer, you should take action to prepare a management plan for next season’s crop. After around 2 weeks of feeding on your crop, adult females will return to the soil to lay eggs, which remain buried over the winter months and will hatch in 2023. Soon after, larvae will begin feeding on your young corn crop.

If you grow corn in WI, Agronomy Service Representative Nick Groth considers managing this pest to be one of your top priorities next season, especially if you had issues with your CRW management strategy this year. Groth says that while CRW presence ebbed and flowed in the past, recent years have seen more consistent pressures. In particular, the eastern regions of WI, a heavy dairy-producing area, has seen dramatic increases in pressure this year. If you grow corn-on-corn in these areas, your fields are at an increased risk unless you take action now to help control it.

Map showing the change in CRW beetle counts by district in WI between 2021 and 2022. Source: WI DATCP

In many of the heaviest-hit areas in WI, a single wind event could become a significant problem. CRW feeding can lead to scarred, weak roots and reduced standability, leaving them more vulnerable to these weather-related events. Using a soil-applied insecticide like Force^® 6.5G insecticide can help lead to stronger, more developed root systems and healthier plants that are better prepared to fight off pests and handle increased stress levels.

Here are some helpful tips on how to scout for CRW next season:

• In the V7 to V10 corn growth stage, you can dig roots and put them in a pail of water to float CRW larvae to the surface and see what kind of feeding you have on those roots.
• If you’re looking for corn rootworm beetles, generally the R1 to R3 stage is a very good time to scout. As corn silking begins, setting up yellow sticky traps can help give an idea of how severely your crop is infested.
• If you notice beetles flying around an existing corn crop, that is a clear sign of corn rootworm. It’s important to keep in mind that these beetles are laying eggs and continuing the cycle of infestation.
• One visual symptomology is goose-necking. From this you will see nodal roots eaten off at the ground level.

CRW trial at the Brooklyn, WI, Grow More™ Experience site. Corn with CRW trait with no insecticide application.

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