The evolution of herbicide resistant weeds is not a new issue in agriculture. But the problem has come to the forefront recently with increased use of glyphosate and more and more problems with weeds resistant to the herbicide. That's why a national summit was held in Washington, D.C. on May 9 to identify strategies to address resistance where it has emerged and identify steps to proactively take steps (best management practices) to preempt further evolution.
More than 250 policymakers, producers, herbicide manufacturers, social scientists, agronomists and weed scientists participated in the summit at The George Washington University in Washington, D.C.
Charles Arntzen, Arizona State University, explained the summit grew out of a 2010 report by the National Academy of Science and National Research Council that indicated weed resistance was a growing problem and that more research was needed. A basic question, he noted, was "what happens when tens of thousands of farmer use the same weed control?" He added that there is currently no new mode of action in the pipeline to replace glyphosate. "In the past, when we ran into a problem the industry came forward with a solution, but we are at the end of solutions."
"We need to focus on all herbicides, not just glyphosate. All herbicides are a risk," added Mike Owen, Iowa State University professor of agronomy. He said, "It's not a glyphosate problem, a triazine problem, or an ALS problem. It's the way we use these herbicides." He explained the weeds are there because they have adapted to the agri-ecosystem. "Even a few escapes can increase substantially over two or three years and the next generation will be even more resistant. Seed dormancy is key - once a weed is established, it will only get worse."
Owen believes the solution is diversity - use multiple modes of action and manage each field separately. A return to tillage and/or cultivation is a possibility.
"Australia has had claim to the title of No. 1 in the world in weed resistance," noted Michael Walsh, University of Western Australia. "The U.S. is closing in fast on that title." In Australia the problem started in 1970 when sheep and wool prices dropped and farmers shifted from sheep production to crop production. The primary forage had been Lolium (rye grass). But growers switched to wheat with no tillage, no crop rotation, no diversity of herbicides and low rates of application.
Eventually, Lolium became resistant to herbicides. The Australians tried a number of options with some success, including harvesting crop residue with weeds and removing them from the field. But in the end, weed resistance problems and laws forcing farmers to adopt new technologies caused many farmers to give up. "Weed resistance played a major role in the reduction of farmers in southern Australia, especially young farmers who didn't want to deal with the laws, etc."
Best management practices
David Shaw, Mississippi State University, offered a list of best management practices to combat weed resistance.
- Understand the biology of weeds.
- Use a diversified approach toward weed control focused on preventing weed seed production, and reduce the number of weed seeds in the soil.
- Plant weed-free seed.
- Use multiple herbicides with multiple modes of action.
In fact, that was the overall theme of the conference - several speakers advocated using multiple modes of action to fight weed resistance to herbicides. In addition, speakers noted growers will have to have a mindset and behavorial change. One speaker referred to "Roundup Ready Babies." A whole generation has learned to farm with Roundup -- with the idea there is no need for cultivation
Impediments to change
One of the solutions offered at the conference was to include cultivation in the weed management system. Dave Miller, an Iowa farmer, stated, "Conservation compliance is one of the impediments to change. My conservation plan dictates no-till. I don't own a cultivator. I don't own a sprayer. There are so many regulations and liabilities that I hire that done."
He added, "I get a lot pressure not to use atrazine because of water quality issues."
Several speakers indicated a "return to steel" is not the answer. Farmers are used to the labor savings, etc. of not having to till or cultivate.
"On an optimistic note, Dale Shaner, a plant physiologist with the USDA Agricultural Research Service, noted, "Farmers and the industry will adapt. We will find a new herbicide. It may be out there already. It just may take a while for it to see the light of day."
At the end of the day, the bottom line seemed to be - in the near term farmers will need to consider diversifying their weed management programs to preempt and/or control weed resistance to herbicides. As more than one speaker noted, "you may not have weed resistance yet, but you will." In the long run, there is optimism that new modes of action will be brought to market to overcome the weed resistance issue
Look for more on his summit in future issues of your Farm Progress publication.