Ground Game

Controlling insects in corn crops is like trying to solve a crossword puzzle. Sometimes the answers aren’t as simple as they might seem, especially when it comes to managing corn rootworm (CRW).

“We’ve seen a steady increase in CRW pressure in this area over the past six or seven years,” says Andy Muff, grower and Syngenta Seed Advisor^™ from Ventura, Iowa. “In several fields, the CRW pressure was so severe

in 2013 that 10 to 12 beetles would crawl out of nearly every corn ear.”

Rootworms are estimated to cost U.S. corn growers more than $1 billion annually. Most of the damage occurs underground, where rootworm larvae feed on developing corn roots. Light to moderate rootworm damage can be easy to miss, but it still hurts yields. “CRW chew on the tiny root hairs during the seedling stage,” says Mike Missman, a Syngenta Seed Advisor from Woden, Iowa. “By the time you notice anything is wrong, the damage has been done.”

Crops with moderate to severe damage may be stunted. The CRW larvae prune the root of the corn, reducing the water and nutrient uptake of the plant. Plants weakened by rootworm damage may also lodge, leading to problems at harvest. “So much of the ‘factory’ of the plant is underground in the roots,” Muff says. “You can’t fix CRW damage once it’s done.”

Missman is concerned about the trend he's seeing of farmers growing conventional corn in his area. While CRW hasn’t been a major problem locally, he knows it’s easy to get complacent and lulled into a false sense of security.

“Conventional corn is cheaper to plant than seed with the rootworm trait, but some of the conventional corn growers don’t plan to use insecticide either,” Missman says. “We could be setting ourselves up for trouble.”

Getting to the Root of the Issue

While CRW pressure can vary from year to year, it remains an ongoing challenge. “CRW has been around for decades and is not going to go away,” says Miloud Araba, Ph.D., Syngenta technical product lead for commercial traits. “CRW adapts to different environments, and there’s no one-size-fits-all solution.”

Even fields with no history of CRW issues may be susceptible. Entomologists at Purdue University have found that rootworm beetles can readily move between fields and may cause damage in locations other than

"So much of the ‘factory’ of the plant is underground in the roots. You can’t fix CRW damage once it’s done."

where they emerged. Beetles may also move into corn and/or soybean fields that have an abundance of pollen-producing weeds, such as volunteer corn, ragweed or foxtail.

Effective CRW management requires the integration of multiple control measures, as opposed to a single strategy, says Araba, who encourages an integrated pest-management approach. This starts with scouting. Muff checks fields at several key times during the growing season, starting in late June or early July when corn is close to tasseling. He conducts a float test to check for CRW larvae.

“I fill a bucket half-full of water, do a root dig and submerge the roots in the water for about five minutes,” Muff says. “Any larvae will float to the surface.” Adding salt to the water in the bucket helps CRW larvae float to the top.

Muff returns to the field three to four weeks later to check for adult beetle emergence in the corn. He comes back in early fall to conduct another root dig to see if there has been more root feeding.

“If we don’t find much during any of these three inspections, I know CRW pressure is low,” Muff says. “If any of the tests show moderate to high infestation, it’s time to take action.”

Syngenta recommends the following strategies if growers expect CRW to be a problem:

• Take a multiyear, whole-farm approach. Effective, long-term CRW management requires a three- to five-year plan. “Know the CRW history of your fields and develop a long-term management plan,” Araba says. “Also, reassess your plan every year, since CRW pressure can change from year to year.”
• Rotate to a non-host crop when there is an option. This is the first option for breaking the CRW cycle but may not be practical in some areas. In those cases, rotating to a non-host crop every third or

  

  fourth year, rather than every second year, might be a better option, Araba says. In Missman’s area of Iowa, for example, growers have been successful with a three-year corn/one-year soybean rotation plan.
• Integrate multiple measures of control. Effective CRW management requires a multipronged approach. In fields with severe CRW pressure, where 10 to 12 beetles were coming out of nearly every ear of corn, Muff encouraged the growers to use tillage in the fall to bury cornstalk residue and create a less hospitable environment for CRW. Then he helped the growers develop a long-term plan that incorporated the right combination of seed traits and/or insecticides for their needs.
• Use trait stacks with multiple CRW traits. Syngenta offers options, including hybrids with built-in CRW control with the Agrisure^® traits portfolio, which offers best-in-class insect control to protect quality and yield. Agrisure Duracade^® trait stacks combine the Agrisure Duracade trait, the newest mode of action against CRW, with the Agrisure RW trait, a proven mode of action for CRW. Agrisure Duracade attacks CRW unlike anything else on the market by expressing a unique protein that binds differently in the gut of the corn rootworm, making it a critical tool in any CRW management program.
  “Agrisure Duracade is tremendous,” Muff says. “One USDA study has shown that it reduces adult corn rootworm beetle emergence by 99.97 percent because it kills the larvae. When you reduce the ‘breeding stock,’ you start winning the battle against CRW.” In addition to the Agrisure Duracade 5122 E-Z Refuge^® and Agrisure Duracade 5222 E-Z Refuge trait stacks, the Agrisure traits portfolio offers another dual-mode-of-action trait stack for CRW control, Agrisure 3122 E-Z Refuge, as well as technologies containing a single CRW trait: Agrisure Viptera^® 3111 and Agrisure 3000GT. These corn rootworm trait stack packages also give growers the opportunity to rotate traits, thus providing another important means to effectively manage corn rootworm.
• Apply a soil insecticide. Force^® soil-applied insecticide, when used in combination with hybrids containing single- or multiple-CRW trait combinations, increases yields by an average of more than 10 bushels per acre, as demonstrated by hundreds of field trials.1 The same research shows Force also protects yield of hybrids without CRW traits. “When used at the full rate, Force provides long-residual control,” Missman says. “It works very well, plus a pyrethroid like Force has excellent crop safety regardless of which herbicide you use.”
• Consider a foliar insecticide. To minimize egg laying from adult CRW females and facilitate proper pollination by preventing silk clipping later in the season, consider applying Warrior II with Zeon Technology^® foliar insecticide.

Using the right mix of technologies is key to controlling CRW and managing resistance for the long run. “CRW will continue to adapt, so it’s vital to balance CRW control, yield protection and resistance management,” Araba says. “Syngenta Seed Advisors and resellers are ready to help growers find this balance to protect the durability of CRW traits and their crop’s yield potential.”

CRW Management Recommendations

Want more information on developing the right corn rootworm (CRW) plan? Visit the Syngenta CRW management guide that provides management recommendations tailored to your fields. The online tool provides management recommendations, from trait stacks to insecticides and seed treatments. “Use this handy resource as a guide, and also work with your Syngenta Seed Advisor or reseller to help develop a customized CRW plan,” Araba says.

1Average yield increase of 10.42 bu/A based on 326 Syngenta field trials.