Syngenta USA recommends overlapping residual herbicides for season-long waterhemp management

Due to the expanding threat of resistant waterhemp, Syngenta urges corn and soybean growers to prepare a management strategy that includes overlapping residual herbicides with multiple, effective modes of action (MOAs) for the upcoming growing season. 

Waterhemp, a small-seeded broadleaf weed, is one of the most common weeds found in corn and soybean fields. According to Purdue University, it can grow as much as 1 inch per day and up to 4 to 5 feet in height, with some weeds reaching up to 12 feet. Producing as many as one million seeds per plant, waterhemp pollen can travel one-half mile or more, and because of the cross-pollination that occurs, resistance spreads.

"The driver weed across most of Illinois is waterhemp," said Aaron Hager, Extension weed specialist at the University of Illinois. "Twenty-five years ago, you couldn’t find two people in Illinois who knew what waterhemp was. Have farmers learned about it now? They sure have. Biology has forced them to learn about driver weeds to understand how to control them."

Joe Wuerffel, Ph.D., research and development scientist at Syngenta, explained that waterhemp is known to germinate as early as March and continue through August. Because of this, it’s imperative to implement a herbicide strategy to control waterhemp and manage future resistance. Overlapping residuals are recommended to improve yields and keep fields weed-free for longer.

“Herbicide resistance in waterhemp is very widespread,” Wuerffel said. “We’ve seen its resistance to six different unique MOAs. We pretty much assume that if you have a waterhemp plant in a field, it’s probably ALS-resistant.”

According to Wuerffel, growers can control waterhemp and protect yields by using multiple, effective MOAs that provide residual control and a start-clean, stay-clean approach to weed control. Acuron® corn herbicide has four active ingredients and three effective MOAs. Its atrazine-free counterpart, Acuron Flexi corn herbicide, has three active ingredients and two effective MOAs. Both contain the active ingredient bicyclopyrone, which provides improved, more consistent waterhemp control.

“Our biggest problem now is with waterhemp, not because it’s such a tough weed, but because it’s so prolific and it’s building a little resistance,” said Glenn Beller, a grower in Lindsay, Nebraska. “Acuron has pretty much kept the waterhemp at bay.”

Syngenta also offers an effective soybean weed control program that starts with pre-emergence, long-lasting residual control from Boundary® 6.5 EC or BroadAxe® XC herbicides. In addition, a post-emergence application of Flexstar® GT 3.5 is an effective herbicide for control when applied to 2- to 4-inch waterhemp.

“Waterhemp grows so fast and it’s gained so much resistance that there really isn’t anything to stop it once it’s over 3 to 4 inches tall,” said Brian Ellison, a grower in Belleville, Illinois. “The residual component in Flexstar GT 3.5 holds them down.”

Decades of research and development have put Syngenta at the forefront of introducing herbicides with extended residual control to help fight resistance. The Syngenta Resistance Fighter® program provides education, local recommendations, and a comprehensive herbicide portfolio to help growers and retailers effectively manage resistant weeds in their area.