By Ken Roseboro
Published: April 4, 2012
Category: GM Food Environmental Risks
The dramatic rise of weeds resistant to glyphosate, the main ingredient in Monsanto’s Roundup herbicide, is leading biotechnology companies to develop more genetically modified crops that are tolerant to older, more toxic herbicides such as 2,4-D and Dicamba.
In a paper published recently in BioScience, David Mortensen, professor of weed ecology at Penn State, and fellow researchers criticized this “single tactic” approach of herbicide-tolerant GM crops to control weeds. The paper says the approach will dramatically increase herbicide use and threaten environmental quality, create even more herbicide resistant “superweeds,” and encourage continued neglect of public research and extension investment in integrated weed management approaches in favor of chemical company profit-driven GMO approaches.
In 2010, Mortensen told a US House Oversight Committee that the government should restrict the use of herbicide-tolerant GM crops and impose a tax on GM seeds to fund research and educational programs for farmers.
Ken Roseboro, editor of The Organic & Non-GMO Report, recently interviewed Mortensen.
What were the key findings of your paper published in BioScience?
Dave Mortensen: There are three parts to the paper. In the first part we outlined the problems with genetically modified herbicide-tolerant crops. The over-reliance on glyphosate herbicide, coupled with vast acreage of glyphosate-tolerant GM crops, including most recently Roundup Ready alfalfa and sugar beets, has created intense selection pressure for the evolution of glyphosate resistant weeds.
In the second part of the paper we discuss how the biotechnology companies are reacting to this weed resistance problem by introducing more genes into crops that will facilitate more herbicides to control weeds. The companies are using GM methods to ramp up herbicide use. This industry-led solution is causing a transgene-herbicide treadmill that will result in a doubling or tripling of herbicide use in corn, soybeans, and cotton.
The companies are saying that the way to manage resistant weeds is to use multiple herbicides and more GM crops. We know from past experience that a silver bullet approach will not solve complicated weed problems.
We do understand why farmers would use the glyphosate and glyphosate-resistant crop package. It is simple and relatively cheap, but we have to think about the long-term consequences.
In the last part of the paper we discuss practical approaches for integrated weed management. These approaches, such as cover cropping, go in a different direction than what biotech companies want to go.
How many weed species are now resistant to glyphosate?
DM: Twenty-one, and 75 percent of those have been documented since 2005, despite company-sponsored research stating that the resistance would not occur.
How many millions of agricultural acres are affected by glyphosate-resistant weeds?
DM: I believe there are 15 million acres of land affected with glyphosate resistant weeds. There are a number of projections by biotech companies that the number of affected acres could hit 20 or 30 million in the next few years.
You talk about a transgene-facilitated herbicide treadmill. Please tell me more about this.
DM: The biotechnology companies’ reaction to the weed resistance problem is to develop more herbicide-tolerant GM crops that will encourage more herbicide use to control weeds. The companies are creating a genetic modification treadmill similar to the pesticide treadmill experienced in the mid-20th century, when companies produced increasingly more toxic substances to manage pests resistant to pesticides. This continual insertion of more genes into crops is not a sustainable solution to herbicide resistance.
Another aspect that is disturbing is that the original justification for developing the herbicide-tolerant GM crops was that we would move away from older, less environmentally benign herbicides. Specifically, several companies are actively developing crops that can resist glyphosate, 2,4-D and Dicamba herbicides. Such genetic manipulation makes it possible to use herbicides on these crops that previously would have killed or injured them. What is more troubling is that 2,4-D and Dicamba are older and less environmentally friendly.
Will weeds becoming resistant to these other herbicides?
DM: Yes, weeds will eventually evolve combined resistance to Dicamba, 2,4-D and glyphosate. Globally, there are already many examples of weeds simultaneously resistant to two or more herbicides.
What are some other problems with 2,4-D and Dicamba?
DM: Increased use of 2,4-D and Dicamba applied over the growing corn and soybean means much more of these herbicides will be applied at a time of year when many sensitive crops like tomato and grapes are most vulnerable to injury. Such injury results when these herbicides move from the targeted field during or following an application.
Overuse of herbicides may increase chances that farmers will use the herbicide during inappropriate weather conditions, leading to herbicides drifting from the targeted area and killing or harming other non-target plants and crops.
I recently saw a database on pesticide spray drift complaints. These happen when a farmer applies herbicides and they blow into adjacent fields or gardens and damage that crop or garden. In the most recent years, the most frequent complaints involved 2,4-D, Dicamba, and glyphosate. What’s worrying is that farmers aren’t even using much 2,4-D and Dicamba now, but they will be with GM crops being ramped up for marketing in the next few years.
The harm to non-target plants (from pesticide drift) is likely to amplify greatly with the use of these older compounds.
You recommend integrated weed management as a solution to the weed resistance problem. What are the practices involved in this?
DM: Planting cover crops, rotating crops, and using mechanical weed control methods, as well as targeted, judicious use of herbicides.
Cover crops such as winter rye, hairy vetch, crimson or red clover can be planted in early fall following annual cash crops, or seeded in early spring. These crops add a smothering effect and keep weed seeds from emerging.
In the Northeast, there are now incentives to encourage farmers to adopt cover crops to enhance water quality in the Chesapeake Bay. I recently heard a talk by John Lundgren (an entomologist with US Department of Agriculture’s Agricultural Research Service) who said that cover cropping can significantly reduce pest pressure and insecticide use.
Unfortunately we have an agricultural industry that doesn’t want to encourage cover cropping because it goes in the opposite direction of where they want to go with GM crops and herbicides.
© Copyright The Organic & Non-GMO Report, April 2012