Corn rootworms lurk in the shadows!

Question: I had some problems with rootworms in first-year corn a few years ago. Since I’ve planted GMO corn with rootworm resistance, I haven’t had a problem. As long as I continue planting GMO corn, can I forget worrying about corn rootworms?

A panel of Certified Crop Advisers provided these answers.

Betsy Bower, agronomist, Ceres Solutions, Terre Haute: The short answer is ‘no.’ There has been some resistance to specific traits documented in Iowa and Illinois following continual use of GMO corn. In these specific cases the same GMO event had been planted year over year and little or no refuge was used as required by law.

That being said if you change up corn rootworm resistance GMO-packages from year to year and follow refuge management guidelines, control of corn rootworms shouldn’t be a problem. There are still very good single-mode-of-action corn rootworm GMO products as well as newer dual-mode-of-action products for corn rootworm available. Both can be found in refuge-in-a-bag products.

Of course we still have traditional soil insecticides that can be applied with the planter in liquid or dry formulations. They are still viable products to control corn rootworm too.

Steve Dlugosz, agronomist, Heartland Co-op, east-central Indiana: Rootworm resistant traits have revolutionized corn rootworm control for many farmers. All farmers are called to be good stewards of these and other traits by adhering to resistance management principles, such as proper use of refuge.

With the recent decline in corn prices, I’ve heard some conversations about saving money on seed cots and moving away from rootworm-traited corn. This makes a grower very vulnerable to a sudden resurgence of rootworm damage. It’s not difficult to recall past devastation of this pest, and the helpless feelings of a farmer looking at acres of lodged corn caused by rootworm feeding during the larval stage. So many roots were destroyed there weren’t enough left to anchor the plants properly. My recommendation is to continue to use this most valuable tool.

Dan Ritter, agronomist, Brodbeck Hybrids, Rensselaer: Don’t worry but continue to monitor corn rootworm levels. It is important to monitor fields for technology efficacy. That means how well it works.

There have been breaks in certain rootworm technologies. Those issues have been in areas of extreme rootworm pressure and with single modes of action. So depending on the rootworm technology you’re using, there may be more or less reason to ‘worry.’

A good scouting program needs to be maintained to monitor all aspects of crop production, including corn rootworm control. If you aren’t using multiple sources of corn rootworm resistance in GMO corn consider doing so in the future. It may be necessary to use multiple sources of resistance to maintain the efficacy of the rootworm technology.

Key points

Don’t forget about corn rootworms, even if GMO traits have delivered good control.

Corn rootworms have already broken through control by one event in specific areas west of Indiana.

The best advice is continuing to scout and monitor each season to make sure you control rootworms