By Scout Nelson
Corn rootworm (CRW) adults are beginning to emerge in cornfields across southern Minnesota, marking an important time for growers to monitor insect activity. Researchers recently observed western corn rootworm (WCR) and northern corn rootworm (NCR) adults in research plots at the University of Minnesota Rosemount Research and Outreach Center. Only a small number of beetles have appeared so far, and their light color shows they are newly emerged adults.
Dr. Yucheng Wang, University of Minnesota Postdoc Researcher, and Dr. Fei Yang, University of Minnesota Extension corn entomologist, reported that soil temperature is the main factor controlling corn rootworm development. Adult emergence usually begins after soil growing degree days reach 1,300 to 1,500 with a 52°F base temperature. Southern Minnesota has already reached this level, while central and northern areas are expected to reach it within the next one to two weeks.
Adult emergence usually starts in late June and may continue into mid-August, depending on weather and local conditions. The emergence period normally lasts four to eight weeks. Western corn rootworm adults generally appear before northern corn rootworm adults. Male beetles also emerge earlier than females, allowing time for mating once female beetles become active.
After emerging, adult beetles feed on corn pollen, fresh silks, leaves, and exposed kernels. Female beetles begin laying eggs about two weeks after emergence. Most eggs are placed in the soil of cornfields, where they remain through winter before hatching the following growing season.
Growers are encouraged to begin scouting fields now, especially those with continuous corn production or previous rootworm problems. Fields showing root pruning or lodged plants should receive extra attention. Whole plant counts and yellow sticky traps can help measure beetle populations and estimate the risk for future infestations.
Researchers are also asking producers to assist with monitoring efforts. Farmers who notice heavy corn rootworm infestations, especially in corn with Bt traits, are encouraged to volunteer insect samples for testing. The University of Minnesota will evaluate the insects for Bt resistance and provide growers with individual reports to support future management decisions.
Photo Credit: pexels-pixabay
Categories: Minnesota, Crops, Corn