Do glyphosate-resistant weeds pose a problem for farmers using Roundup? Monsanto used to answer that question with a resounding “No!” Nowadays, it’s more of a weaker “no”, but with a few caveats.
Glyphosate was invented in 1970 by a scientist working at Monsanto and entered the pesticide market as Roundup in 1976. The first glyphosate-resistant weeds showed up in 1996, the same year that Monsanto released its Roundup Ready soybean. In 1997, Roundup Ready canola and cotton were introduced, followed in 1998 by Roundup Ready corn.
Why Do Farmers Buy Roundup Ready Crops?
The big selling point of the Roundup Ready variety of GM crops has been lower pesticide usage, increased usage of no-till farming methods (a method used by both conventional and organic farmers), and a claim by Monsanto that Roundup becomes inert in the soil. Furthering the use of glyphosate is the expiration of Monsanto’s patent on it, meaning that it can be made by other companies, lowering the price of the pesticide significantly.
But by 2000, some agriculturally-significant weeds had become glyphosate-resistant. Now, in 2010, about 10% of the farmland used for GM crops has been infested by glyphosate-resistant weeds and the number of these weeds is increasing rapidly.
How Do Weeds Become Glyphosate-Resistant?
Glyphosate kills plants by being absorbed into the leaves and inhibiting an enzyme involved in growth, thus it can only be sprayed on plants that have sprouted. Glufosinate, another broadleafed weedkiller, interferes with the production of a certain amino acid and prevents ammonia detoxification by the plant. Some other herbicides kill by inhibiting an enzyme involved in germination, while still others bind to certain proteins and starve a plant.
A plant becomes resistant to a specific herbicide when it has a genetic mutation that enables it to survive a spraying. Herbicides don’t cause mutations to occur in the weeds. An individual weed will have a genetic trait that will keep it alive after a spraying and it will pass on this trait to other individuals in its species through its seeds or pollen.
Spraying Roundup on a field reduces competition for resources, leaving only the GM crop and the glyphosate-resistant weed. Weeds are weeds because they can out-compete a crop for nutrients and water. The Roundup Ready crop doesn’t stand a chance.
This week, the New York Times ran a story on “superweeds”, referencing the glyphosate-resistant weed varieties. A Monsanto spokesperson is quoted in the article as saying, “It’s a serious issue, but it’s manageable.”
Of course it’s manageable. Conventional farmers can always return to the old ways (pre-GMO) of doing things. Farmers can add more herbicides to their arsenal, although many glyphosate-resistant weeds are already resistant of other herbicides. Using other herbicides will also increase the risk of injury to the crop. Farmers can go back to tilling the soil, increasing erosion and the runoff into the watershed of herbicides, pesticides, fungicides, insecticides, and chemical fertilizers. Farmers can dig these weeds up by hand, increasing labor costs. These are the methods being recommended to farmers by agricultural extension advisors.
Why Buy GM Crops?
But then why would anyone buy GM crops for planting? GM seed is more expensive and has a lower yield rate than seeds bred through conventional methods. Fighting glyphosate-resistant weeds makes Roundup Ready crops even less competitive.
What is Monsanto’s solution? Monsanto and Syngenta are both developing GM crops resistant to glyphosate and glufosinate, enabling farmers to limit the addition of herbicides to their arsenal to just one. Syngenta’s LibertyLink (glufosinate-resistant) GM soybeans came on the market in 2009.
The first agriculturally-significant glufosinate-resistant weeds were also discovered in 2009.