Revenge of the Weeds: developing resistance to multiple herbicides [View all]

[enough]

A fairly long, detailed article in The Scientist.

http://the-scientist.com/2012/05/20/revenge-of-the-weeds/

It’s a story suited for a Hollywood horror film, yet it’s also a tenet of evolutionary biology. Introduce a toxin to a system, and you inevitably select for resistant survivors. These few individuals gain a reproductive advantage and multiply; sometimes they can’t be stopped with even the most potent chemicals. For years, this general plot line made headlines in the fields of antibiotic resistance and cancer research. More recently, plants have become a common protagonist. Weeds around the world are developing resistance to glyphosate—one of the most common herbicides on the market—and like bacteria and tumor cells, many plants can also withstand multiple other toxins, each with unique molecular targets.

long snip>

If the situation wasn’t bad enough already, it appears to be snowballing. Weeds in nine different countries have independently developed resistance to multiple modes of action. Some stubborn survivors can now survive most of the chemicals used by farmers, and the infestations are spreading.

Last year, for example, farmers in Iowa reported infestations of waterhemp in their corn and soy fields. The weed has now encroached on 500 acres, and continues to survive treatments of glyphosate and six additional chemicals. The case is a rare example of a weed developing resistance to three chemical classes, each with a unique molecular target. Even more impressive, a biotype of Rigid Ryegrass growing in Victoria, Australia, is now resistant to four chemical classes. Only about 10 acres are impacted so far, but the weeds are predicted to spread.

Despite the seemingly small odds of a plant evolving resistance to multiple herbicides, the dramatic increase in glyphosate-resistant weeds, which now infest more than 17 million acres nationwide, has made this possibility exponentially more likely. “We don’t need a single plant to undergo two unlikely adaptations—we just need one event to happen in a biotype that already has glyphosate resistance,” says Mortensen.

snip>