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Researchers confirm another glyphosate-resistant weed (17/7/2006)

1.University of Missouri Confirms Glyphosate-Resistant Waterhemp
2.Glyphosate-resistant pigweed could have "a major devastating impact"

EXCERPTS: While all resistant weeds are worrisome, Bradley says resistant tall waterhemp is especially troubling. "Waterhemp is one of Missouri's toughest weed problems," he says. (ITEM 1)

The weed's evolution is rooted in genetically engineered cotton... (ITEM 2)
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1.University of Missouri Confirms Glyphosate-Resistant Waterhemp
Jerilyn Johnson
Farm Futures, 13 July 2006
http://www.farmfutures.com/ME2/dirmod.asp?sid=CD26BEDECA4A4946A1283CC7786AEB5A&nm=News&type=news&mod=News&mid=9A02E3B96F2A415ABC72CB5F516B4C10&tier=3&nid=D8A679E64A404C7F95943BE00364BBDE

University of Missouri researchers have confirmed that tall waterhemp is the sixth glyphosate-resistant weed in the U.S. and the ninth such weed in the world.

Kevin Bradley, a University of Missouri Extension weed scientist, and graduate student Travis Legleiter found that tall waterhemp from a field near the Missouri River in Platte County could survive despite being treated with up to eight times the labeled rate of glyphosate.

Glyphosate is the active ingredient in Roundup herbicide. The fields where resistant waterhemp was found had been in continuous Roundup Ready soybean production since 1996.

Kevin Bradley, University of Missouri weed scientist, explains new waterhemp research trials at the MU Weed Resistance Management Field Day last month near Columbia.

While all resistant weeds are worrisome, Bradley says resistant tall waterhemp is especially troubling. "Waterhemp is one of Missouri's toughest weed problems," he says. "It has developed resistance to a number of other soybean herbicides." That resistance has been known to spread quickly. Waterhemp plants are either male or female, which means females rely on pollen shed from surrounding male plants.

"If the resistant trait is carried in the pollen, which we are fairly confident it is, then you have pollen traveling to fields all around the resistant plants," Bradley adds. Each female waterhemp plant produces hundreds of thousands of seeds, ensuring a ready supply of plants for the following season.

Positive news

Bradley and Legleiter have found good news in their field plots. The glyphosate-resistant waterhemp is killed by a number of popular pre-emergence soybean and corn herbicides. Bradley reported on this strategy at the Weed Resistance Management Field Day June 20 near Columbia, hosted by MU and Monsanto.

The pair plan at least two seasons of examining whether the resistant plants can be brought under control economically in continuous soybeans - using pre-emergence and post-emergence herbicides - or whether it is better for farmers facing resistant weeds to alternate plantings of corn and soybeans. The rotation opens up a wider array of herbicides labeled for use in corn.

The eight other confirmed glyphosate-resistant weeds throughout the world include common ragweed, buckhorn plantain, goosegrass, hairy fleabane, horseweed (a.k.a. marestail), Italian ryegrass, palmer amaranth and rigid ryegrass.
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2.Roundup resistant weed could have "a major devastating impact"
http://www.lobbywatch.org/archive2.asp?arcid=6727

EXCERPTS: The weed's evolution is rooted in genetically engineered cotton - called Roundup-Ready cotton...

"For moderate growers or those that have too much on their plate, it's going to be a major devastating impact" - Stanley Culpepper, a weed expert at the University of Georgia ... Georgia cotton growers fight pigweed Associated Press, July 8 2006 http://www.macon.com/mld/macon/news/politics/14995325.htm

A variety of pigweed resistant to the herbicide Roundup is spreading in Georgia cotton crops, already identified in nearly 50 fields.

The plant - known as Palmer amaranth - is the first resistant weed identified in Georgia, said Stanley Culpepper, a weed expert at the University of Georgia. So far, the weed has popped up in Macon, Dooly and Taylor counties.

The cost of treating weeds increases "drastically" without the luxury of using Roundup, Culpepper said.

"For moderate growers or those that have too much on their plate, it's going to be a major devastating impact," Culpepper said.

UGA agriculture researchers are working on ways to control the weed. So far, the most successful strategy is using a combination of residual herbicides and tilling, Culpepper said.

But residual herbicides are expensive compared to Roundup, which costs about $4.50 per acre to apply compared to the $10-$12 an acre. Farmers also have increased fuel and irrigation costs from the distribution of the herbicides, which require multiple applications.

Pigweed grows 1 to 2 inches per day, flourishes even in a drought and produces an average of half a million seeds. It tolerates many herbicides and easily grows 6 to 8 feet tall.

The weed can't be killed once it reaches a certain height and clogs cotton harvesters.

The weed's evolution is rooted in genetically engineered cotton - called Roundup-Ready cotton - developed a decade ago. The cotton, used by the majority of farmers, allows weeds to be controlled by Roundup without harm to the crop.

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