Pest Profile: Common Waterhemp

Resistant to as many as five modes of action, waterhemp is a force to be reckoned with.

Nothing gives growers a sinking feeling quite like the sight of waterhemp (Amaranthus tuberculatus) in a glyphosate-treated field. Twenty years ago, the weed was barely recognized by most growers, but in large areas of the U.S. today, the weed is resistant to as many as five separate herbicide modes of action, with confirmed reports of four in a single plant. Especially in the Midwest, few miss the telltale signs of this pest—and for good reason. According to WeedSOFT®, a computer module developed by university weed scientists, a single uncontrolled waterhemp plant per square yard can reduce yields by 7.5 bu/A.

Twenty years ago, waterhemp was barely recognized by most growers, but in large areas of the U.S. today, the weed is resistant to as many as five separate herbicide modes of action, with confirmed reports of four in a single plant.

Back to Square One

Some of the solutions to the rise of herbicide-resistant waterhemp can be frustratingly time-consuming. Plus, few of these tactics still work for growers facing resistant waterhemp. These include pulling the plants by hand and cultivation.

Most producers continue to use herbicides in a carefully planned rotation. The University of Minnesota Extension recommends varying modes of action and hitting waterhemp with both pre- and post-emergence herbicides because a plant that survives one herbicide is less likely to survive the second as well. This approach dictates that growers keep a sharp eye out for the occasional escaped weed. By scouting fields 10 to 14 days after application, growers can determine whether bad timing, misapplication, later weed flushes, poor weather or resistance is to blame.



A single uncontrolled waterhemp plant per square yard of corn is estimated to reduce yields by 7.5 bu/A.


Eliminating Waterhemp Early

Some corn producers get ahead of waterhemp early in the season by implementing pre-emergence herbicide programs. In corn, this can make a significant impact. According to the Purdue University Extension, allowing waterhemp to exceed six inches in height reduces corn yields by 15 percent.

Effective at controlling waterhemp resistant to glyphosate, PPO and triazine herbicides, Corvus corn herbicide features CSI safener technology, making it safe to use as a pre or early post.

Corvus® corn herbicide from Bayer supports growers in their weed management programs by offering broad-spectrum control of labeled grass and broadleaf weeds, including resistant ones like waterhemp, for the full season. Using two modes of action, Corvus also offers a built-in anti-resistance strategy. Each of its two active ingredients attack a weed’s ability to process sunlight for fuel, but in different ways, making it harder for the weed to develop resistance.

Growers who rely on Corvus have noted that they like the season-long control they can achieve in a single pass. A full rate of Corvus delivers rapid burndown to eliminate early weeds, long-lasting residual to prevent new weeds and rain reactivation to control late weeds. As weeds like waterhemp continue to evolve resistant biotypes, growers increasingly need the flexibility of products like Corvus to combat the threat to their corn yields.

Works Cited

  • Gunsolus, Jeffrey. "Glyphosate-Resistant Weeds Confirmed in Minnesota." Minnesota Crop News 05 May 2008: n. pag. Web. 29 Jul 2011. www.extension.umn.edu.
  • Nordby, Dawn. "Biology and Management of Waterhemp." Purdue Extension. N.p., Nov 2007. Web. 1 Aug 2011. www.ces.purdue.edu.
  • "Yield Loss from Resistant Weeds - Waterhemp."Resistance Fighter. Syngenta, n.d. Web. 29 Jul 2011. resistancefighter.com.

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