Weed resistance a global threat
The evolution of herbicide-resistant weeds is not a new issue. But the problem has come to the forefront with widespread use of glyphosate and more difficulties with weeds resistant to the herbicide. A national summit in May identified strategies to address herbicide-resistant weeds where they have emerged and identify steps to act proactively (use best management practices) to preempt further evolution.
About 250 policymakers, farmers, herbicide manufacturers, social scientists, agronomists and weed scientists participated in the summit organized by the National Academy of Sciences in Washington. Charles Arntzen, chairman of the planning committee and an Arizona State University scientist, said the summit grew out of a 2010 report by the National Academy and the National Research Council citing weed resistance as a growing problem and that more research is needed.
A basic question is what happens when thousands of farmers use the same weed control? Many weeds, particularly in the South, have developed resistance. “There is currently no new mode of action in the pipeline to replace glyphosate,” he said.
“We need to focus on all herbicides, not just glyphosate and not just cotton in the South. Resistance has been around a long time — for 50 years,” stated Mike Owen, Iowa State University Extension weed scientist. “All herbicides are at risk. It’s not a glyphosate problem, a triazine problem or an ALS problem. It’s a behavioral problem — the way we use these herbicides. Our production systems have allowed a few weed species to adapt.”
The weeds are there because they’ve adapted to the agri-ecosystem, he said. “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. Herbicides make it possible to farm more acres, but it creates a Darwinian selection process.”
Owen believes the solution is diversity. That is, use multiple modes of action and manage each field separately. A return to tillage and/or cultivation is a possibility. He also says there hasn’t been adequate research to develop new solutions.
“Resistance isn’t new, and it’s not isolated to one product,” added John Soteres, global affairs weed resistance management lead at Monsanto Co. and chairman of the Global Herbicide Resistance Action Committee. “But we do have more knowledge today to manage it and a greater need to diversify products.”
Some companies offer incentives to encourage diversification of herbicide use, including rebates and formulation of lower-cost premixes that have multiple modes of action, reduced handling and a higher certainty of correct application rate.
“The industry, in addition to incentives, is providing more options to manage resistance, including new chemistry, use of biotech, and funding for basic and applied research,” said Soteres. “Using innovative farmer outreach programs is another. Flying Midwest farmers to the Delta to see the impact of weed resistance in that region of the United States is an example.” He added, “We are making progress with the combined efforts of industry and the public sector, but the challenges are significant. Some farmers are evaluating and using other weed control management options such as preplant tillage and cover crops.”
This article published in the July, 2012 edition of WALLACES FARMER.
All rights reserved. Copyright Farm Progress Cos. 2012.