Do Glyphosate-Resistant Weeds Pose a Problem for Farmers Using Roundup?

Roundup, a glyphosate-based herbicide

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.

Managing Superweeds

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.

The Solution

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.

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9 thoughts on “Do Glyphosate-Resistant Weeds Pose a Problem for Farmers Using Roundup?”

  1. Is Everyone forgetting about the decades of increase yields , reduced erosion, reduced pesticides, and increased profits for farmers? I DO NOT work for Monsanto but I do think they helped farmers and agriculture (albeit with great profit to themselves). Yes, there is a growing problem with glyphosate resistant weeds and this will need to be addressed but why crucify the company that made the product without any blame going to the people who used it? Hershey knows their products contain sugar and sugar causes obesity if abused. We now have a child obesity problem but nobody is screaming at Hershey. Is Monsanto a better target?

  2. Scott,
    You are right. There was no shortage of voices warning about the potential for development of glyphosate resistant weeds. It was inevitable at some level, but Monsanto is actually right to say that it is manageable. The thing is that it is manageable because of the other companies like DuPont, Dow, Syngenta, BASF and Bayer that have continued to spend the money to discover new herbicides. Biology is always changing and we have to adapt.

    A few mis-statements in the post. Yields of GMO crops are not lower – they are actually higher and more stable – that is why they now qualify for lower crop insurance premiums. Farmers have not completely shifted over to glyphosate anyway. Many still use other herbicides as part of the program both to manage resistance and weed growth very early in the season triggers a growth pattern change in the crop that can be bad if there is drought later. A 100% glyphosate program lets weeds grow for a while.

    Glufosinate resistance has been around as long as roundup resistance, it just hasn’t been as cost effective. There are other forms of herbicide resistance as well, like the non-GMO resistance to ALS inhibitors.

    Give farmers some credit. They understand this situation pretty well and are demonstrably innovative.

  3. Scott and Steve are wrong, GM crops do NOT increase yield. The only two traits introduced to any extent are herbicide- and insect-resistance. The Union of Concerned Scientists has shown this, see

    And they’ve increased herbicide use by 383 million lbs. in the 13 years from 1996 to 2008. That’s offset only a little by 64 million lbs. less insecticides thanks to the Bt crops. Overall impact, 318 million lbs. MORE pesticides thanks to GM crops. The people who deny this and say the opposite are paid to spread misinformation by the biotech companies. See

    Monsanto deserves a huge share of the blame for the Roundup-resistant weed epidemic. The company assured farmers they could use Roundup over and over on Roundup Ready crops without resistance developing. They basically misled farmers to sell as many GM seeds and as much Roundup as possible prior to patent expiration on Roundup in 2000. An Iowa weed scientist adopted Monsanto into his Herbicide Hall of Shame for misleading farmers in this way. See

    Steve is wrong about “new herbicides.” There are practically no new herbicides in the pipeline. What DuPont, Bayer, Monsanto and Dow ARE doing is engineer crops for resistance to older, more toxic herbicides. Worst ones in this category are Dow’s 2,4-D tolerant soybeans and corn. 2,4-D was part of Agent Orange used in the Vietnam War. That’s right, Dow wants to spray hefty doses of 1/2 of Agent Orange on millions of acres. That’s not all. Monsanto has dicamba-resisant soybeans – dicamba is a close chlorinated relative to 2,4-D. Check out USDA’s website for EIGHT pesticide-promoting GM crops awaiting approval at Biotechnology = pesticide treadmill, in overdrive.

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