Pigweed Poses Challenge to Transformed Herbicide Industry

By Howell Medders, Communication Services, Division of Agriculture - U of A System
Aug. 24, 2007

KEISER, Ark. -- The introduction of transgenic crop varieties, especially those with resistance to Roundup and other glyphosate herbicides, transformed row-crop farming in Arkansas and elsewhere, Ken Smith, a weed scientist with the University of Arkansas Division of Agriculture, said at a field day at the Northeast Research and Extension Center Thursday, Aug. 23.

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However, he added, the agricultural chemical industry was also transformed, with the result that new products that might be needed to solve serious new weed problems are not being developed.

In observance of the 50th anniversary of the center, Division of Agriculture scientists included changes over the past 50 years in presentations about research at the center.

Smith, who is based at the Southeast Research and Extension Center at Monticello, was one of 16 speakers during tours of research plots and an indoor program. State Sen. Steve Bryles of Blytheville gave a luncheon address.

Nearly all of the cotton and soybeans grown in Arkansas are transgenic varieties, which have provided economic and environmental benefits related to less soil cultivation and use of less total chemicals, Smith said. However, some weed species, such as pigweed, are developing resistance to glyphosate and are causing big problems, he said.

Agricultural chemical companies have consolidated and are developing fewer new herbicides that might be needed to control glyphosate-resistant weeds, Smith said. He said only 10 new herbicides were developed over the past 10 years compared to 100 new products developed in the 1980's.

Pigweed, a major weed species in cotton and soybeans, was one of the first to develop resistance to selective herbicides and often required multiple applications of three different chemicals. Transgenic varieties seemed to solve the problem, as glyphosate provided excellent control of pigweed and all other weeds with many fewer applications.

But glyphosate-resistant pigweed has now been found in 17 eastern Arkansas counties, Smith said. Any pigweed plant that grows to maturity after being sprayed with glyphosate may have developed resistance, and seed from such plants quickly increase the resistant population, he said.

"The resistance problem will get worse," Smith said.

Currently, herbicides developed in 1977, Reflex, and 1989, Valor, are being used to control resistant pigweed, Smith said. However, he said he is very concerned that this resilient weed will develop resistance to those herbicides and no alternatives will be available.

Northeast Research and Extension Center Director Fred Bourland said the center was first established in Keiser as the Northeast Branch Station on 655 acres in 1957. The Keiser location was chosen primarily to provide for cotton research on its clay soils, which are typical of many soils found east of Crowley's Ridge. The branch station was an expansion of the Alfalfa Substation established in 1948 nearby at Osceola.

The station was expanded to 766 acres and a resident faculty was appointed when it became the Northeast Research and Extension Center in 1980. It is now one of five regional Division of Agriculture centers with a resident faculty.

In addition to Bourland, who is also a cotton breeder, the resident faculty at NEREC, all with doctoral degrees, includes Glenn Studebaker, entomology; Rob Hogan, agricultural economics; and Daniel Stephenson, agronomy.

Last Updated: 11/27/2007