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.