Corn Rootworms

Bryan Jensen, UW Extension and IPM Program

Northern and Western corn rootworm beetles are emerging and larval feeding is starting to peak. Monitoring root damage over the next few weeks and scouting for beetles in continuous corn will provide useful information for the 2018 growing season.

Digging and evaluating corn roots for damage will tell you several things including:

1. How well your rootworm control practice(s) worked

2. If you had problems with rotation resistance western corn rootworms on first year corn

3. Confirm if Bt resistance might be present

Corn roots may be evaluated for damage starting the end of July and likely can be accomplished throughout the month of August. However, the optimal time period is late July through early August. The main drawback of waiting is that root regeneration may mask injury if you wait too long.

Scouting for corn rootworm beetles is often overlooked but provides valuable information that can be used to diversify management practices. Rotating to a crop other than corn continues to be a viable, if not preferred management practice. However, it does not always fit in every producer’s strategy. If rotation is not an option, whole plant beetle counts taken during the egg laying period (early/mid-August to early September) will provide valuable, field-specific data. Monitoring beetles has never been fun or easy. However, DATCP’s Pest Survey Bulletin indicates low beetle pressure over the past few years which indicates to me, that beetle monitoring will provide useful information to your clientele. Using this data will help you recommend management strategies (Bt hybrids, soil applied insecticides on conventional hybrids and seed treatments) which are the best match for each individual field. Diversifying management strategies will reduce the reliance on Bt CRW hybrids and slow resistance while maintaining economic control. This video will provide basic information needed to monitor beetles.