It sounds like a sci-fi movie: American farmers fighting desperately to hold back an onslaught of herbicide-defying "superweeds."
But there's nothing imaginary—or entertaining—about this scenario. Superweeds are all too real, and they have now spread to over 60 million acres of our farmland, wreaking environmental and economic havoc wherever they go.
How did we get into this mess, and how do we fix it? A 2013 UCS briefing paper, The Rise of Superweeds—and What to Do About It, answers these questions.
Roundup: the cure that super-sized the disease
The superweed problem began as a promised solution.
In the 1990s, Monsanto introduced a new line of seeds called "Roundup Ready," which were genetically engineered to be immune to glyphosate, the active ingredient in the company’s patented herbicide, Roundup.
Roundup Ready seeds were expensive, but they were widely adopted because they made weed control easier. And because glyphosate is less toxic than other common herbicides, the Roundup Ready system was hailed as an environmental breakthrough.
But there was a catch: as more and more farmers used more and more Roundup, genes for glyphosate resistance began to spread in weed populations. The growth of resistance was accelerated by a trio of factors:
- Monoculture. Growing the same crop on the same land year after year helps weeds to flourish.
- Overreliance on a single herbicide. When farmers use Roundup exclusively, resistance develops more quickly.
- Neglect of other weed control measures. The convenience of the Roundup Ready system encouraged farmers to abandon a range of practices that had been part of their weed control strategy.
Estimates of actual herbicide use on U.S. soybeans through 2007, as well as future rates forecast by weed scientists. Adapted by permission from Mortensen et al. 2012. (Click for larger version.)
This “perfect storm” of accelerating factors has quickly turned the Roundup resistance problem into a superweed crisis. And because many farmers can no longer rely on glyphosate alone, overall herbicide use in the United States—which Roundup was supposed to help reduce—has instead gone up (see graph at right).
Industry doubles down
The pesticide and seed industry has responded to the superweed crisis with a predictable refrain: let's do it again. A new generation of herbicide-resistant crops is awaiting USDA approval, engineered to tolerate older herbicides, such as 2,4-D and dicamba, in addition to glyphosate.
What's wrong with that?
- 2,4-D and dicamba belong to a chemical class that has been associated with increased rates of diseases, including non-Hodgkins lymphoma.
- They are highly toxic to broadleaf crops, including many of the most common fruit and vegetable crops.
- They are more prone to volatilization (air dispersal) than glyphosate, so their increased use is likely to harm neighboring farms and uncultivated areas.
On top of all these drawbacks is a more fundamental one: weeds that developed glyphosate resistance can develop resistance to the new herbicides as well—and this has already begun to happen. When major weed species develop widespread multi-herbicide resistance, farmers will really be in a bind, because there are no new herbicides coming over the horizon to save the day.
A science-based solution: healthy farms
There's a better way. Farmers can control weeds using practices grounded in the science of agroecology, including crop rotation, cover crops, judicious tillage, the use of manure and compost instead of synthetic fertilizers, and taking advantage of the weed-suppressing chemicals that some crops produce.
Such practices have benefits beyond weed control: they increase soil fertility and water-holding capacity, reduce water pollution and global warming emissions, and make the farm and its surroundings more welcoming to pollinators and other beneficial organisms.
In short, agroecological practices make the farm healthier. And recent research shows that they work.
What we should do
Despite their promise, agroecological practices have been held back by farm policies and research agendas that favor monoculture, as well as a lack of information and technical support for farmers who want to change their methods.
To encourage the adoption of these healthier practices, UCS recommends that Congress and the USDA should take the following actions:
- Fund and implement the Conservation Stewardship Program, which provides support for farmers using sustainable weed control methods.
- Institute new regional programs that encourage farmers to address weed problems through sustainable techniques.
- Support organic farmers and those who want to transition to organic farming with research, certification, cost-sharing, and marketing programs. (Organic farming serves as a "test kitchen" for integrated weed management practices that can be broadly applied to conventional farm systems.)
- Support multidisciplinary research on integrated weed management strategies and educate farmers in their use.
- Bring together scientists, industry, farmers, and public interest groups to formulate plans preventing or containing the development of herbicide-resistant weeds, and make the approval of new herbicide-tolerant crops conditional on the implementation of such plans.
- Fund and carry out long-term research to breed crop varieties and cover crops that compete with and control weeds more effectively.