By Scout Nelson
Corn rootworm hatch is reaching critical levels across Minnesota this June, especially in southern and central regions. Experts from the University of Minnesota urge farmers to begin scouting as soon as possible to detect larvae and protect corn roots from feeding damage.
Corn rootworm egg hatch is temperature-driven, tracked by growing degree days (GDDs) with a base temperature of 52°F. Peak hatch typically occurs between 684 and 767 accumulated GDDs. Recent reports confirm that southwestern Minnesota has already reached this range, and other regions will follow within one to two weeks.
Two species of rootworm, western and northern, are common pests in Minnesota. Both complete one generation per year and rely solely on corn roots for development. Larvae feed for 4–6 weeks, and later instars can severely damage roots, leading to poor water uptake, nutrient loss, and crop lodging. Root injury can also lead to diseases like crown rot.
In 2024, a new variant of the western corn rootworm was found laying eggs in crops like soybeans and alfalfa. This discovery means first-year corn can now be at risk too. Northern corn rootworm, more common in northern areas, has eggs that survive multiple winters due to extended diapause.
Scouting is essential in the next few weeks. The float test helps detect larvae: place corn roots in water, and larvae—white with a dark head and tail—will float up. Four weeks after peak hatch, use the 0 to 3 Node Injury Scale from Iowa State University to assess root damage. A rating above 0.50 is unacceptable for hybrids with Bt or RNAi traits.
Timely scouting ensures better pest control and helps protect future yields.
Photo Credit: university-of-minnesota
Categories: Minnesota, Crops, Corn