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Can old herbicides save glyphosate?
Posted on May 2nd, 2017 by Dr. Jerry Green in Chemical R&D
An epidemic of glyphosate-resistant weeds is ending the revolutionary impact of glyphosate in glyphosate-tolerant crops. Can using glyphosate with new formulations of herbicides over a half-century old save it?
Glyphosate and glyphosate-tolerant crops had a revolutionary impact on weed management practices in North and South America for the past twenty years. Many growers totally relied on glyphosate for weed control over vast areas of glyphosate-tolerant soybeans, corn, and cotton. It was the solution for managing weeds that were resistant to other herbicides. However it is now the herbicide that needs help; glyphosate can no longer stand alone, and the Roundup Ready® revolution is over.
Mixing Chemicals and Traits
The old herbicide paradigm of discovering your way out of new weed problems is not working. After over 30 years of finding a new commercial herbicide mode-of-action almost every year, the chemical industry has gone over 30 years without finding one, and none are on the horizon for the next decade. Chemical companies solutions to this lack of innovation is to mix and match glyphosate with old and imperfect herbicides. Experts know this approach is a temporary solution, but hope it will be sustainable for long enough, until new chemical and non-chemical weed management technologies become available.
The seed company solution is similar, combining glyphosate traits with traits for other herbicides. The hoped for result is that multiple herbicide-tolerant crops that enable new uses of herbicides with glyphosate will be mainstays of weed management for the next decade. However, without new herbicide modes-of-action, the trait approach is not enough to keep up with the rapid evolution of multiple herbicide-resistant weeds.
The technologies that Monsanto, BASF, Dow, and DuPont are hyping this year are new formulations and less volatile salts of dicamba and 2,4-D herbicides for use in new genetically modified crops. These 50- and 70-year-year old herbicides have a bad track record of off-target movement and injury to non-target organisms, but the companies involved think they have solved these problems with their new formulations and label mandated use restrictions.
Drift and Non-Target Organisms
Both technologies are having serious problems with off-target issues before their first sales. The U.S. EPA approved Dow’s new formulation of 2,4-D and glyphosate with significant restrictions to protect non-target organisms. Then Dow filed a patent application claiming the two herbicides were synergistic. Environmentalists strongly objected that EPA did not consider synergism when they set their non-target organism restrictions. The EPA tried unsuccessfully in court to cancel the registration. Dow withdrew their claim of synergism.
The dicamba-based technologies are having even a worse launch. The USDA approved the sale of dicamba-tolerant seed before the EPA approved the sale of the associated new herbicide formulations. Monsanto had already produced dicamba-tolerant seed and sold it last year. Despite warnings that currently available formulations of dicamba were not approved for use on dicamba-tolerant crops, a large number of growers feeling desperate in their fight against glyphosate-resistant “super weeds” illegally applied dicamba. The resulting widespread drift and injury to non-target organisms were predictable. Very unfortunately, two shooting deaths allegedly resulted when neighbors argued over dicamba drift damage.
Relying so much on old herbicides that already have widespread weed resistance issues to control glyphosate-resistant weeds is not a great situation. However, it will take a long time for all the resistance mechanisms to come together and eliminate the utility of all the mixture possibilities. The new 2,4-D- and dicamba-based technologies will be useful when applied in systematic ways with glyphosate if they perform under commercial conditions as promised, and growers who did not follow directions last year follow label directions this year.
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Dr. Jerry Green
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