Round Up Rebels: The Rise of the Superweed

Round Up use on Round Up ready crops has led to resistant weeds.

Overuse of Round Up on GM crops like this cotton have led to Round Up-resistant weeds.

No, this isn’t a story about a new Cheech and Chong movie. What I’m referring to are herbicide-resistant weeds. And in particular, weeds resistant to the herbicide every Green loves to hate, Round Up (or glyphosate).

I got to thinking about this because of a recent story aired by NPR on the rise of Round Up-resistant weeds. These things are getting to be a real pain for farmers growing crops genetically modified to be resistant to the herbicide Round Up (see the video below).

Many anti-GMO folks were worried about this happening. They were concerned about something called horizontal gene transfer where an added gene moves from one plant to another. They were worried this Round Up-ready weed would then go on to become a dangerous pest.

They were only partly right. The weeds are indeed resistant to Round Up but they aren’t Round Up ready. None of the weeds tested so far managed to get a hold of the added gene; it stayed put in the GM plants.

Instead, these weeds became resistant the old-fashioned way: through natural selection. This is the same thing that makes bugs resistant to pesticides and cancers resistant to chemotherapy.

This Pigweed didn't need outside
genes to be resistant to Round Up.
It pulled it off all on its own.

There were always a few individuals in the weed species that happened to be resistant to Round Up. Spraying lots of Round Up killed all the sensitive weeds leaving the resistant ones behind. These resistant ones were the only ones that went on to have seedlings so they essentially founded a new population. Now this species of weed is mostly Round Up resistant.


But again, not because of horizontal gene transfer. These weeds managed to become resistant in other ways.

Round Up works by binding to a specific enzyme and keeping it from working. One way some of the weeds became resistant was to make lots of extra enzyme. The excess enzyme sopped up the Round Up leaving enough behind to do their job.

Another way to become resistant is to neutralize most of the Round Up. One way plants have managed this is by shuttling the herbicide to vacuoles where it is harmless.

And there are other ways that I won’t go into. But none of them involve a gene traveling from crop to weed.

So this is really just an everyday story about the ongoing battle between pest and farmer, doctor and disease and not one about the dangers of GM crops. If you overuse a pesticide, antibiotic, antiviral, medicine, etc., nature will find a way to get around it.

Still, some anti-GMO folks should be a bit happy. Some people opposed these particular GM crops because they were worried about the safety of Round Up. Having weeds resistant to Round Up means that a whole lot less will get used.

Of course this doesn’t help at all if you are against GM crops because they are GM. There are plenty of new GM crops in the pipeline, meaning more and more of them will probably be planted in the future. But at least there will be less Round Up sprayed (if that is what bothers you).

Definitely a hot topic in the farming world

More Information:

Facts About Glyphosate-Resistant Weeds

Vacuolar Glyphosate-Sequestration Correlates with Glyphosate Resistance in Ryegrass (Lolium spp.) from Australia, South America, and Europe: A 31P NMR Investigation

Weed species shifts in glyphosate-resistant crops