Resistant Weeds Are on the Rise

A pre-emergent herbicide with multiple effective modes of action is the answer many growers are seeking.
Weeds pose no competition for this clean field of young soybeans in Boone, Iowa.
Weeds pose no competition for this clean field of young soybeans in Boone, Iowa.
Resistant weeds are an increasing problem in corn and soybean fields across the Midwest. Research indicates that giant ragweed, morningglory, marestail, Palmer amaranth and waterhemp are among the most difficult-to-control weeds, robbing growers of yields, time and money.

Recent reports indicate that some of these weeds, including waterhemp and Palmer amaranth, are developing resistance to PPO herbicides in soybean fields, leading to weedy fields in both corn and soybeans. Weedy soybean fields in 2015 can lead to weedy cornfields in 2016. It’s no surprise that four out of five growers are actively seeking new products, primarily to achieve better weed control.*

Get Weeds Before They Emerge

All hope isn’t lost when it comes to defeating tough weeds. They’re most difficult to control after they emerge, so experts agree that a pre-emergent herbicide application is the best approach.

“Weed resistance is a growing problem across the Midwest,” says Gordon Vail, Ph.D., technical product lead at Syngenta. “Growers who had a weed-control problem in 2015 are likely to have even bigger weed issues in 2016, unless they use a robust herbicide with multiple effective active ingredients. Even in financially difficult years when commodity prices are low, growers cannot afford to cut corners with herbicides and must use a full rate for optimal weed control.”

Not all herbicides are created equally as multiple factors—including soil absorption, soil composition and water solubility—influence herbicide effectiveness.

“A dependable herbicide begins with strong active ingredients that work well across different environments and soil types,” says Vail. “Many herbicides often rely on a single active ingredient, which can be negatively impacted but changing environmental conditions.”

Bud Sanken, a grower in Hutchinson, Minnesota, explains that weed resistance developed on his farm over time. “It’s the broadleaf weeds that give me the most trouble, like lambsquarters, waterhemp and giant ragweed,” he says. “We wanted a product that would take us to the next level.”

Multiple, Effective Modes of Action Are Key

Syngenta Agronomy Service Representative Dean Grossnickle, who lives in Iowa, says that growers can expect in the future to rely more on herbicides with multiple modes of action. “Glyphosate-resistant waterhemp is among the most difficult weeds to control in Iowa,” he says. “Multiple effective modes of action with overlapping residual control are becoming more important each year as more weeds are becoming resistant to different chemicals.”

Grossnickle explains that if there are two active ingredients with two different modes of action in a herbicide, but weeds are already resistant to one of those active ingredients, then growers can expect to drive selection pressure to resistance for the remaining active ingredient. “Once the weeds are resistant to that last herbicide, that will lead to a weedy field,” he says. “It’s important to have effective, rather than simply multiple, active ingredients.”

Sanken began using Acuron® corn herbicide from Syngenta in 2015. “I’ve seen great control against resistant weeds and plan to use Acuron again in the future,” he says.

Powered by four active ingredients, including bicyclopyrone, and three modes of action, Acuron delivers broad-spectrum control of the toughest weeds in corn without the use of glyphosate. “Built-in resistance management in Acuron allows growers to have the best opportunity at clean fields for a successful 2016 season,” says Grossnickle.

*2014 Syngenta market research.