Palmer Pigweed Taking Over Cotton Fields, Financially Hurting Farmers

Al Tompkins

Poynter Online, August 12 2009
http://www.poynter.org/column.asp?id=2&aid=168248

Palmer Pigweed, a common weed found in cotton and soybean fields, was once fairly easy to control. Such fields, however, are now infested with the weed, which has become resistant to the herbicide that farmers typically use to kill it.

The problem, which is adding to farmers’ financial woes, started in Georgia in 2005 and later spread to Tennessee, Kentucky, South Carolina and other states. http://www.reuters.com/article/pressRelease/idUS216887+05-Mar-2008+PRN200803 05

The Memphis Commercial Appeal in Memphis, Tenn., said:

“In Arkansas alone, the weed has invaded some 750,000 acres of crops, including half the 250,000 acres of cotton. In Tennessee, nearly 500,000 acres have some degree of infestation, with the counties bordering the Mississippi River hardest hit.

“The infestation is cutting farmers’ cotton yields by up to one-third and in some cases doubling or tripling their weed-control costs.

“Reminiscent of the premechanized, preherbicide days when cotton was a labor-intensive operation, growers have resorted to hiring chopping crews. They’re made up of laborers who generally are paid about $7.50 an hour to manually cut the weeds.” This isn’t just a cotton-growers problem. Every year farmers, gardeners, etc., collectively use 100 million pounds of the herbicide Roundup, which goes by the chemical name glyphosate. The chemical is often used to control weeds in lawns and fence rows. http://www.commercialappeal.com/news/2009/aug/09/the-perfect-weed/

The Commercial Appeal went on to explain more about why weed is such a threat:

“It’s so prevalent that cotton, soybeans and other plants have been genetically engineered to withstand it, allowing farmers to spray the chemical quickly and easily to kill weeds without worrying about harming crops.

” ‘I think this threatens our way of farming more than anything I’ve seen in the 30-plus years I’ve worked in agriculture,’ said Ken Smith, weed scientist with the University of Arkansas’ division of agriculture.

“In fact, some officials draw parallels between the pigweed resistance problem and the effects of the boll weevil infestation of cotton fields in the early 20th century.

“What makes the weed such a formidable threat is its rapid growth rate — more than an inch per day — and the proliferation that results from a single plant producing 50,000-100,000 seeds.” http://www.commercialappeal.com/news/2009/aug/09/the-perfect-weed/

Herbicide resistant pigweed dominates farmers’ concerns at University of Arkansas research field day

University of Arkansas, August 11 2009 [shortened]
http://www.seedquest.com/News/releases/2009/august/27121.htm

KEISER, Arkansas, USA – Farmers, agricultural consultants and county agents who turned out for a field day at the University of Arkansas System Division of Agriculture’s Northeast Research and Extension Center all had at least one question in common: what to do about herbicide resistant pigweed?

Ken Smith, extension weed scientist at the Division of Agriculture’s Southeast Research and Extension Center in Monticello, said that eight years ago, morning glory was the problem weed on every grower’s mind. Today, “herbicide-resistant pigweed has choked out the morning glory,” he said.

Smith discusses the problem and management of herbicide resistant pigweed in a Division of Agriculture Web video: http://aaes.uark.edu/nerec_video.html

The growing problem is glyphosate resistant Palmer amaranth, known best to farmers as Roundup resistant pigweed. First confirmed in Mississippi County in 2005, Smith said, the problematic weed has spread to most of the counties in eastern Arkansas.

Research technician Ryan Doherty said glyphosate resistant pigweed has been confirmed in 21 counties throughout the state. A research location has been established to study control programs in a field situation. Research on those plots is revealing the nature of the resistance and helping to develop management strategies.

Doherty said the most resistant pigweed population identified by division scientists was found in Lincoln County.

“The farmer had already put two 22-ounce applications of Roundup on that field before he called us,” Doherty said. “We put on another 44-ounce application of Roundup and it didn’t hurt it at all.”

Even another application of 128 ounces of Roundup did not kill the pigweed biotype found in that field. Doherty said all those plants probably came from a single female plant.

Smith said division scientists confirmed this month that there are two distinct patterns of distribution in Arkansas from pigweed plants with two different mechanisms of tolerance. In one pattern, called segregated, the herbicide resistant plants are scattered throughout the field randomly among plants that are not resistant. Spraying these fields with glyphosate kills about 80 percent of the pigweed. The remaining plants are scattered randomly throughout the field. Smith cautioned that resistance is creeping up in these pigweed populations; 80 percent may be killed this year, but next year it may be only 70 percent.

Smith calls the second pattern non-segregated. In these fields, the resistant plants are clustered tightly together and glyphosate herbicide does not kill any of them. “All the offspring of these plants have high levels of resistance,” he said.

“hen you see these,” Smith advised, “Do whatever you have to do to take them out.”

Smith said Division of Agriculture scientists had devised a number of strategies to control glyphosate resistant pigweed, most involving a combination of different herbicides beginning with a preplant application. Roundup is still a valuable weed control product, he said, because it controls more than 100 other weeds. But it will have to be part of a new program for weed control.

“There is no prescription that works in every cotton or soybean field,” Smith said. “But in any program, soil residual herbicides are going to be essential for controlling these pests.”

Smith said farmers should overlap soil residual applications to keep them on the field all the time. He recommended scouting for pigweed at the same time growers would be scouting for insects. Catching and killing pigweed before it matures and goes to seed is important in controlling the spread of the weed.

Agricultural economist Bob Stark said glyphosate resistant Palmer amaranth is the main economic concern among all herbicide resistant weeds.