Published on 07/23/03

Scientist warns of resistant weed 'nightmare'

By Brad Haire
University of Georgia

To stay one step ahead of problems in their fields, farmers use many tools to work with and against nature. But relying too heavily on one effective tool now could give nature the upper- hand in the future.

Farmers battle weeds that want to steal valuable nutrients and water from their crops. In the old days this meant long hours digging weeds up with a plow between rows.

But these days farmers rely heavily on herbicides to control weeds, says Stanley Culpepper, a weed agronomist with the University of Georgia Extension Service.

“It’s becoming rare to put a plow in a field,” he said.

Weeds are a major concern for cotton farmers. They can hurt yields and make it difficult or impossible to harvest the cotton lint. Georgia cotton farmers spend over $55 million every year just to control weeds.

Roundup reliant

In recent years, cotton farmers have become increasingly reliant on one mode of attack on these weeds: glyphosate-based herbicides. The herbicide Roundup is the most commonly known of these.

But Roundup can kill cotton plants along with the weeds. New technology over the last decade changed this. Cotton varieties were developed that can stay healthy when sprayed with Roundup. It can be sprayed over the tops of cotton fields killing the weeds, but not the cotton.

It was an economical blessing and a versatile, time-saving, environmentally-benign tool that farmers gladly embraced, said Culpepper.

Roundup-resistant cotton varieties account for about 80 percent of the cotton grown in Georgia this year, according to the U.S. Department of Agriculture.

But just as man can engineer a cotton variety that doesn’t die when sprayed with Roundup, nature can engineer a weed that doesn’t mind glyphosate.

It happens

So could a weed become resistant to a herbicide like Roundup?

“Sure, it could happen,” says Culpepper.

It’s already happened. Roundup-resistant horseweed is being reported in several states, including Tennessee, he said. And other Roundup-resistant weeds have popped up around the world.

Weeds becoming resistant to any means of control has always been a concern to farmers and scientists, Culpepper said. But the risk of resistant weeds increases when farmers become too dependant on one means of control, like their dependance on Roundup.

Georgia has had no reports of Roundup-resistant weeds.

Scary thoughts

But there’s one weed that strikes a little fear in cotton farmers and weed scientists, he said. And that’s Palmer amaranth. It can grow like lightening to about 10 feet high with a stalk about eight inches round.

Many herbicides can’t kill or even bother this weed. But, luckily, Roundup can stop this weed dead in its tracks.

“But if this weed ever became resistant to Roundup, trying to manage it would be a nightmare,” Culpepper said.

Herbicides don’t cause plants to suddenly become mutants, he said. All it takes is one weed plant in a field to be genetically different. Say genetically-resistant to glyphosate.

All the other weed plants in a field are killed when sprayed, but not the resistant one. It makes seed. Next year, there’s a few more resistant plants. If the process is allowed to continue, the offspring of that one resistant weed will cover the field.

Roundup-resistant technology has helped farmers in many ways, Culpepper said. But with new technology often comes new responsibilities. And farmers can’t become too dependant on this technology. They need to be aware of other means of weed control and implement other tools into their Roundup programs.

And they can simply keep an eye on their fields and not give that one resistant weed a chance to make seed.

Brad Haire is the former news editor with the University of Georgia College of Agricultural and Environmental Sciences.