GM WATCH COMMENT: The over-reliance on Monsanto's herbicide Roundup (active ingredient, glyphosate), massively encouraged by the growing of Roundup Ready crops, has triggered an explosion in glyphosate-resistant weeds on US farmland.

Attracting particular attention has been glyphosate-resistant Palmer amaranth, or pigweed, which one regional weed specialist has called "a real threat to future cotton production":

"The troublesome weed can quickly grow more than 8 feet tall with a thick stalk and suck valuable nutrients from nearby plants. It can clog a cotton picker, too, making it hard to harvest the crop."
http://www.lobbywatch.org/archive2.asp?arcid=5878

And University of Tennessee weed scientist, Professor Tom Mueller, says the problems are not confined to cotton, "Palmer pigweed that is not killed by glyphosate will cause major yield losses and harvest headaches for soybean, cotton and other row crop producers."
http://www.lobbywatch.org/archive2.asp?arcid=5795

Worse still, as the following article notes, Palmer amaranth/pigweed is just one of a whole series of weeds now proven, or likely, to have developed resistance. The article lists:

horseweed (aka marestail)
lambsquarters
cocklebur
common ragweed
giant ragweed

Some of the resulting problems may be severe. For instance, "Resistant giant ragweed would be a problem comparable to Palmer amaranth in some parts of the country."
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Pigweed not only threat to glyphosate resistance
By Roy Roberson
Farm Press Editorial Staff
Southeast Farm Press, October 19 2006
http://southeastfarmpress.com/news/101906-herbicide-resistance/

Though Palmer amaranth, commonly called Palmer pigweed, is the most pressing weed resistance problem for farmers from the Midwest to the Southeast, it is not the only weed showing resistance to glyphosate.
 
The first glyphosate resistant weed to create problems was horseweed, sometimes called marestail. Horseweed resistance was first found in the Carolinas in 2003, and it continues to be a problem. "Each year we find a little bit more - it is wide-spread all up and down the Coastal Plain of North Carolina," says Alan York, long-time North Carolina State University weed specialist.

In 2006, glyphosate resistant common ragweed was reported in a handful of counties in North Carolina. "High rates of Weathermax uglied-up the terminal, but the ragweed didn't die," York says. He explains that to document resistance, there has to be proof that the resistant trait is heritable.

Giant ragweed is being investigated in Indiana, with distinct signs that it has developed resistance to glyphosate. Resistant giant ragweed would be a problem comparable to Palmer amaranth in some parts of the country.

Common ragweed is not likely to be a big problem for growers in the Carolinas and Virginia, according to York. The biggest problem may be in no-till or reduced-till systems which require a clean field to plant cotton. In these systems the problem is what to use for burn-down. If ragweed is resistant to glyphosate, the options are limited to dicamba, paraquat and 2,4-D.

Researchers in South Carolina have found glyphosate resistant cocklebur, and are in the process of documenting for certain that it is resistant. Clemson researchers are still conducting greenhouse tests, but the evidence is strong that at least one cotton field in South Carolina has glyphosate resistant cocklebur.

Virginia Tech researchers are at a similar place in time in documenting glyphosate resistant lambsquarters. More of a problem in the upper end of the Southeast, lambsquarters, prior to the introduction of Roundup Ready technology, was a constant problem in a number of row crops.

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