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Watch For Weeds As You Harvest This Fall

Watch For Weeds As You Harvest This Fall

At a recent field day and seminar at Ames, the topic was development of weed resistance to herbicides and what to do about it. One thing you need to do is watch weeds from combine cab this fall.

As farmers harvest their soybean and corn crops this fall, they should watch for patches of weeds in fields to help them plan and prepare for controlling weeds for next year's crop. Herbicide resistant weeds tend to be concentrated in small patches instead of the weeds being spread over the entire field. That point was made by several weed scientists at mid-September field day sponsored by Bayer Crop Science at Ames, Iowa.

If you think you have a herbicide-resistant weed population in a field, harvest that field last, the weed control specialists advised. Combines do a good job of spreading weed seeds from field to field. Or thoroughly clean out your combine before moving from a field with suspected weed resistance to another field.

A noticeable increase in fields with resistant weeds in Iowa this year

Mike Owen, Iowa State University Extension weed scientist, says there was an increase in the number of reports of herbicide resistant weeds in fields this year in Iowa. There were more reports of fields with weeds showing resistance to glyphosate herbicide. But that's not the only problem. Weed resistance to HPPD herbicides has also been showing up more and more the past few years. "We all need to be concerned about HPPD resistance," says Owen.

Seed corn production fields is where most of the waterhemp resistance to HPPD herbicides has been showing up. However, says Owen, the increasing number of fields with weeds resistant to this herbicide family also includes commercial corn fields. He advises farmers to look at surrounding fields as well, regarding the potential need for managing resistant weeds. At harvest time, combines can spread the seed of herbicide-resistant weeds.

Free training program on management of herbicide resistant weeds

Last week the Weed Science Society of America (WSSA) introduced a free training program designed to educate pesticide applicators, growers, ag chemical retailers, farm consultants and others on herbicide resistance in weeds – a costly problem that threatens crop production across the U.S. and around the globe.

"A significant contributing factor in the evolution of herbicide resistance is the repeated use of a single chemical in the absence of other control methods," says John Soteres, a WSSA member and chairman of the global Herbicide Resistance Action Committee. "It is vital that we have the best possible materials to communicate what we know about resistance and how to manage it in order to preserve crop yields and promote the sustainability of our cropping systems."

WSSA established a task force of weed scientists from universities, industry and private consulting who volunteered to evaluate currently available materials and develop a new, updated training program. Led by Soteres, they spent 18 months pulling together the most current, science-based information available on the causes of herbicide resistance and effective management techniques.

Training program is available as Web-based, PowerPoint slides or video

The result is a peer reviewed, five-module program available as Web-based training, PowerPoint slides or video. WSSA plans to work with grower organizations, government agencies and others to disseminate the materials, with a special emphasis on reaching growers and ag chem retailers. WSSA is also exploring continuing education credits for those who complete the courses. 

"Knowledge is critical," says David Shaw, chairman of WSSA's Herbicide Resistance Education Committee. "When farmers have a better understanding of herbicide resistance and how to manage it, they can adopt proactive programs that delay or mitigate the evolution of herbicide-resistant weeds."

The new herbicide resistance education program initially is available from the WSSA website and from the Pesticide Environmental Stewardship site   Additional sites are to be added soon. A Spanish-language version is actively underway under direction of Enrique Rosales Robles, Ph.D., of INIFAP-Mexico.

Development of the program was supported by the National Corn Growers Association, National Cotton Council and the American Soybean Association. It was funded by WSSA and by the Herbicide Resistance Action Committee, an industry coalition focused on herbicide stewardship.

About the Weed Science Society of America. The Weed Science Society of America, a nonprofit scientific society, was founded in 1956 to encourage and promote the development of knowledge concerning weeds and their impact on the environment. The Weed Science Society of America promotes research, education and extension outreach activities related to weeds, provides science-based information to the public and policy makers, fosters awareness of weeds and their impact on managed and natural ecosystems, and promotes cooperation among weed science organizations across the nation and around the world.  For more information, visit

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