The billion-dollar pest has proven yet again that it is a formidable foe. In late October Corteva Agriscience, the agriculture division of DowDuPont, reported to the Environmental Protection Agency (EPA) the first case of corn rootworm resistance to the Herculex trait. It was found in a Delaware County, Iowa, cornfield.
"This announcement is significant and troublesome given the potential economic implications for corn farmers, so we are watching it closely," said Bob Hemesath, chairman of the National Corn Growers Association (NCGA) Freedom to Operate action team. "With that said, there are protocols in place to deal with resistance. NCGA wants to recognize the extraordinary measures taken by Corteva that are well beyond the steps required by the U.S. Environmental Protection Agency," he added.
The trait, Cry34/Cry35 includes two proteins to control the pest. The Herculex trait was first sold in 2006 by Dow AgroSciences and Pioneer. After 12 years on the market, this is the first documented case of resistance found in a single field. According to NCGA, EPA and Corteva are working with farmers in Delaware County to minimize the spread of resistance.
Resistance indicates a need for continued stewardship and resistance management. It’s important for farmers to follow best management practices with insect pests just as they would with herbicides and weeds. Members of industry have partnered with organizations such as NCGA to create the Take Action initiative, which outlines steps to preserve the usefulness of corn rootworm traits:
- Plant the required refuge. Take into account the product and geography you’re in: corn-growing states’ refuge is 5% in-bag or a 20% structured refuge, and cotton-growing states are 20% in-bag and 50% for a structured refuge.
- Use insect resistance management strategies: rotate crops, use pyramided traits, rotate traits and rotate and use multiple modes of action for insecticide seed treatments, soil-applied insecticides and foliar-applied insecticides.
- Actively to see if control methods are working, and whether there are escapes or possible resistance. Take additional action to control pests when necessary.
“In areas where we’re seeing building population it doesn’t mean you can’t use a double pro, but you will have to add in a soil insecticide to your program,” says Farm Journal Field Agronomist Ken Ferrie, regarding rootworm issues he is seeing in central Illinois. “Keeping an eye on the population and the feeding every year can keep us from a major problem in the fall [dealing] with down corn.”