[The Western Producer Jan. 18th, 2013 by Robert Arnason] -- Canadian and American weed scientists want an answer to a provocative question: how will applying more herbicides solve the problem of herbicide resistant weeds in North America? Four Agriculture Canada weed experts and professors from Oregon State and Montana State universities argued in a 2012 paper published in the journal Weed Science that combining new herbicide tolerant genes in genetically modified plants that already contain herbicide tolerant traits is not the answer to the widespread challenge of glyphosate resistance. Last year, the Canadian Food Inspection Agency approved a Dow-Agrosciences technology that stacks 2,4-D tolerance on top of glyphosate tolerance. The company expects to launch its Enlist weed control system for corn in 2013 and soybeans in 2015, pending approval in the United States. Monsanto has developed TruFlex canola, which is expected to serve as a base for future stacked trait technology, and allows for a wider window for glyphosate applications. The company also expects to introduce genetically modified soybean seed next year that combines dicamba tolerance with its existing Roundup Ready technology. Weed scientists have hailed stacked resistance as a key tool to fight gly-phosate resistant weeds, but others, such as Neil Harker of Agriculture Canada in Lacombe, Alta., aren’t buying the arguments. “It’s just another way of delaying the inevitable,” he said. “What you do by stacking technology is you get a reprieve for a few years and then (you) eventually select for multiple resistance.” Instead of relying on technology for a solution, Harker and the authors of the Weed Science paper, including John O’Donovan, Hugh Beckie and Robert Blackshaw of Agriculture Canada, want to set herbicide-frequency reduction targets for major field crops in Canada and the U.S. ${imageDescription} Comment
“If we want to slow resistance to herbicides down … the only real effective way is to use herbicides less,” Harker said. Harker argued in the paper that too many scientists focus on herbicides as the only solution to weed problems. “It is not clear that the weed science discipline should only be looking to herbicides for sustainable weed control solutions, particularly solutions for weed resistance to herbicides,” he wrote. David Mortensen, a professor of weed and applied plant technology at Penn State, agreed that herbicide resistance won’t be resolved through additional technology or the application of more herbicides. “It’s strange that we would solve the problem (of resistance) by inserting more traits that will increase our reliance on herbicides,” he said.
A paper that Mortensen co-published in the American Institute of Biological Sciences last year argued that stacking tolerance genes into crops is a short-term fix to weed resistance. It said growers will adopt the new technology over the next five to 10 years, but weeds and nature will adapt once producers repeatedly apply 2,4-D or dicamba on top of glyphosate.
Bruce Maxwell, a weed science professor at Montana State who co-authored the paper with Mortensen, said diversifying the herbicides that can be used will lead to a more general kind of resistance in weeds. “They (weeds) will be able to deal with any type of herbicide that gets thrown at them, so we get a worse type of resistance.”
Mortensen and Maxwell’s paper said the industry view that developing resistance to two herbicides is ex-tremely unlikely is a flawed perspective based on faulty mathematics. The report said weeds have already developed resistance to dicamba and 2,4-D. The article identified 28 weed species that are resistant to synthetic auxin herbicides such as 2,4-D and dicamba. Given the prevalence of glyphosate resistant weeds in North America, the probability of developing resistance to two modes of action is likely greater than industry estimates, the paper said.
Harker would like producers to adopt an integrated weed management philosophy rather than using more technology and chemicals to cope with herbicide-resistant weeds. That means weed scientists must research alternative methods, such as high crop seeding rates, inter-cropping, weed seed destruction and diverse crop rotations.