Superweeds

May 8, 2010

I’ve written here several times about the development of antibiotic resistant bacteria, such as methicillin resistant Staphylococcus aureus, owing to the well-intentioned but indiscriminate use of antibiotics and other anti-microbial agents.  Using these agents creates selection pressure for the evolution of resistant organisms, and overuse accelerates it.

There is no reason to suspect that this general principle applies only to microbes, of course, and an article in the New York Times reports that the extensive agricultural use of a popular weed killer, glyphosate, sold by Monsanto under the trade name Roundup, has led to a similar sort of problem.   Roundup was originally developed and patented by Monsanto, and its use really took off when the company introduced seed varieties of corn, cotton, and soybeans that had been genetically modified to resist the herbicide.

Sales took off in the late 1990s, after Monsanto created its brand of Roundup Ready crops that were genetically modified to tolerate the chemical, allowing farmers to spray their fields to kill the weeds while leaving the crop unharmed. Today, Roundup Ready crops account for about 90 percent of the soybeans and 70 percent of the corn and cotton grown in the United States.

Roundup was eagerly adopted by farmers because it is fairly safe to use, killed a wide variety of weeds, and breaks down relatively quickly in the environment.

However, the law of unintended consequences has still not been repealed; as one might have expected, widespread use of Roundup created selection pressure for the evolution of resistant weed species.

Just as the heavy use of antibiotics contributed to the rise of drug-resistant supergerms, American farmers’ near-ubiquitous use of the weedkiller Roundup has led to the rapid growth of tenacious new superweeds.

This has forced farmers to return to some methods, such as frequent plowing, that they had abandoned, as well as the use of more toxic weedkillers.  These changes can bring along adverse environmental impacts of their own.

Monsanto, Bayer, and other agricultural chemical companies are now exploring the use of herbicide combinations, and the development of crop varieties resistant to other, older herbicides, in order to keep the problem of resistant weeds manageable.  Still, this is another reminder that these large, uncontrolled experiments have a habit of producing some rather undesirable consequences.


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