The billion-dollar pest has proven yet again it is a formidable foe. In late September, Corteva Agriscience, 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 field in Delaware County, Iowa.
The field with damage was reported in 2017, and Corteva Agriscience has been testing the insect populations to confirm resistance ever since, says Ryan Myers, Corteva Agriscience corn category lead for Pioneer. “[However] in 2018 we had no additional
customer calls from Delaware County.”
The Cry34/Cry35 Herculex trait includes two proteins to control corn rootworm. Herculex was first sold in 2006 by Dow AgroSciences and Pioneer. After more than a decade, this is the first field-documented case of resistance that required reporting to the EPA. Corteva Agriscience and EPA are working with farmers in Delaware County to minimize the spread of resistance.
“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.”
Western corn rootworm, the specific resistant variant, is actually better to work with in the lab because the populations are easier to breed and test. Certain populations of western corn rootworm have adapted to lay eggs in soybean fields so they hatch in corn the following year.
“This is something we prepared for; right from the time we launched we knew resistance was a likely outcome over time,” says Nick Storer, Corteva Agriscience global regulatory efficacy lead for seeds. “The uncertainty is how long it will take and how widespread it will be, so we’re not surprised to find a single field with resistance after 12 years. If anything, we could have seen more problems if we hadn’t taken proactive management [measures].”
There is only one field that had resistance, and it’s being managed. Overall, the trait is highly effective, Storer says. “It’s just a reminder a single tactic over multiple years leads to problems, so we encourage farmers to have a multi-year strategy to better manage rootworm.”
Resistance indicates a need for continued stewardship and management. It’s important farmers follow best management practices with insects just as they would with weeds. Farmers who saw greater populations of corn rootworm this past season should prepare for next season.
“In areas where we’re seeing building population, it doesn’t mean you can’t use [an above-ground only trait package], but you will have to add a soil insecticide to your program,” says Farm Journal Field Agronomist Ken Ferrie, regarding rootworm issues he’s seen in central Illinois. “Keep an eye on the population levels, and the feeding can keep us from a major problem in the fall with down corn.”
Maximize Rootworm Traits
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 your geography. The refuge requirement in corn-growing states is 5% in-bag or a 20% structured; in cotton-growing states, it’s 20% in-bag and 50% structured.
- Use insect resistance management strategies. These include rotating crops, stacking traits and multiple modes of action for insecticide seed treatments and soil- and foliar-applied insecticides.
- Scout. Get out into your fields to see if control methods are working and if there are escapes or possible resistance. Take additional action to control pests when necessary.