TROUBLE BREWING. Small waterhemp plants emerging within soybean fields are well on their way to yield-robbing stands that continue to germinate throughout the growing season. Season-long competition from waterhemp has been shown to reduce soybean yields by as much as 44%. (Photo Courtesy of Dr. Kevin Bradley, University of Missouri)

Waterhemp Continues Foiling Chemical Control

The discovery of waterhemp that is tolerant to a seventh class of herbicide action means growers have to double down on weed management by including cultural and mechanical controls to fight resistance.

As farmers across the Corn Belt were wrapping up the 2019 harvest, the buzz among corn and soybean producers centered on reports from Illinois that the tough-to-control weed, waterhemp, had shown resistance to yet another class of chemical weed control — those in Group 15.

“Herbicides are grouped into classes based on their mechanism of action (MOA), or the specific target within a plant that’s vulnerable to the compound’s attacks,” says Aaron Hager, University of Illinois weed scientist. “Because of various regulations and biological and agronomic realities, a limited number of herbicide MOAs can be used on any given crop and the suite of weeds that accompanies it.

“Historically, about nine herbicides have been useful for waterhemp — and now the weed appears to be resistant to at least seven of those,” he explains.

To date, waterhemp is documented resistant to the following herbicide classes:

  • ALS inhibitors (Group 2)
  • Synthetic auxins/growth regulators (Group 4)
  • Photosystem II inhibitors (Group 5)
  • EPSP synthase inhibitors (Group 9)
  • PPO inhibitors (Group 14)
  • Fatty acid synthesis inhibitors (Group 15)
  • HPPD inhibitors (Group 27)

Hager’s associate in reporting the latest development, and head of Crop Sciences at Illinois, Adam Davis, says in some areas, growers are only one or two MOAs away from completely losing chemical control of waterhemp and other multiple-herbicide-resistant weeds. “There are no new herbicide MOAs coming out. There haven’t been for 30 years,” he adds.

“We don’t want to panic growers, but they need to…

To view the content, please subscribe or login.
 Premium content is for our Digital-only and Premium subscribers. A Print-only subscription doesn't qualify. Please purchase/upgrade a subscription with the Digital product to get access to all No-Till Farmer content and archives online. Learn more about the different versions and what is included.

Dan crummett 0618

Dan Crummett

Dan Crummett has more than 35 years in regional and national agricultural journalism including editing state farm magazines, web-based machinery reporting and has an interest in no-till and conservation tillage. He holds B.S. and M.S. degrees from Oklahoma State Univ.

Top Articles

Current Issue


No-Till Farmer

Get full access NOW to the most comprehensive, powerful and easy-to-use online resource for no-tillage practices. Just one good idea will pay for your subscription hundreds of times over.

Subscribe Now

View More

Must Read Free Eguides

Download these helpful knowledge building tools

View More
Top Directory Listings