NOTE: Christopher Preston, the Australian weed specialist featured here during a tour of in Arkansas, is an ardent GM supporter, yet even he can't deny the total unsustainability of the kind of farming practices Roundup Ready crops have encouraged:

"Farmers here have used Roundup Ready cropping with glyphosate as the only herbicide while pulling back on tillage. In that system, the only thing that's really controlling the weed is glyphosate. Do that for a decade and you'll have problems."
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Arkansas fields of glyphosate-resistant pigweed
By David Bennett
Farm Press, Sep 25 2008 [shortened]
http://deltafarmpress.com/cotton/resistant-pigweed-0925/

As Roundup Ready crops have come to dominate Mid-South agriculture, so have glyphosate-resistant genes come to increasingly dominate a handful of problem Mid-South weeds. Currently, Palmer amaranth, a pigweed, tops the list of worries.

It was mostly that weed, along with the cropping systems and treatments around it that Christopher Preston, an Australian, was in Arkansas to tour in late August. Preston, a weed specialist and associate professor at the University of Adelaide, made the trip at the invitation of the University of Arkansas.

Preston is "well-known and entirely respected in the world for his work in weed resistance issues," said Bob Scott, Arkansas Extension weed specialist and Delta Farm Press contributor. "We hope he can provide some insights into what's happening here that can lead to things that'll help our growers."

After a trip through Arkansas row-crop land, Preston recently spoke with Delta Farm Press from Fayetteville. Among his comments:

Your initial impressions of the Arkansas weed situation?

"In terms of glyphosate-resistance, Palmer amaranth is clearly the worst issue farmers will have to deal with. And that's out of all the weeds that have so far gained some sort of resistance. That's simply because there's so much of it and the control options are reasonably, although not totally, limited.

"The worst case I've seen of the problem was the original infestation in Georgia. I visited there in 2005 and that situation had been allowed to get out of control.

"What I've seen in Arkansas is a really good attempt to control the problem once it had arisen. It hasn't been totally successful, but at least a farmer can put a combine through his soybeans."

On resistance issues in Australia”¦

..."The most important parallel is where we saw the glyphosate-resistant ryegrass ”” and where it still occurs there - are situations where the only thing being used to control the weed is glyphosate. The producers aren't using tillage, not using other herbicides. Only glyphosate is used.

"Well, do that for 10 years, or so, and you'll end up with glyphosate resistance as we saw with ryegrass.

"That parallel is almost identical with the U.S. pigweed. Farmers here have used Roundup Ready cropping with glyphosate as the only herbicide while pulling back on tillage. In that system, the only thing that's really controlling the weed is glyphosate. Do that for a decade and you'll have problems."