E-mail this article to
yourself or a friend.
Enter address:


Weeds seen more resistant to herbicide

(Sunday, Sept. 14, 2003 -- CropChoice news) -- Emily Gersema, AP: WASHINGTON - Increased findings that weeds are developing resistance to Roundup, the world's most popular herbicide, have some scientists urging new planting practices. The product's manufacturer says the problem is being overblown.

Roundup, whose generic name is glyphosate, has been on the market for more than 30 years. It long has been a favorite of farmers, home gardeners and golf course greenskeepers because of its effectiveness in killing weeds.

It allows growers to cut back on tilling, a more labor-intensive and expensive method of controlling weeds, and does not pollute the environment.

"Roundup Ready" crops, which have been genetically altered to tolerate the chemical, now cover much of the nation's farmland since their development in the late 1990s. They allow farmers to spray the glyphosate herbicides widely without harming crops.

The Agriculture Department estimates that 80 percent of the 73 million acres of soybeans in the United States are Roundup Ready soybeans, and Roundup Ready cotton accounts for more than 30 percent of the 12 million acres planted. The corn variety, still new to the market, covers 11 percent of 70 million acres.

"Farmers are planting too many Roundup Ready crops," said Stephen Powles, an expert on weed resistance at the University of Western Australia.

The herbicide is vital for food production systems in the United States and in many other parts of the world, Powles said. Should weed resistance become widespread, he said, "I think the problem will become a crisis."

In 1996, Australia was the first to note that weed resistance to glyphosate was developing in rigid ryegrass found in a few grain and sorghum fields. Five years later, South Africa reported seeing the resilient rigid ryegrass had infested a few hundred acres of vineyards.

In 2000, University of Delaware scientists reported to the Weed Science Society of America, which tracks farm chemical resistance, that in some soybean fields, mare's tail was resisting glyphosate. Since then, resistant mare's tail has been reported in other states - Indiana, Kentucky, Maryland, New Jersey, Ohio, Arkansas, Mississippi and Tennessee.

Far more worrisome are cases in Iowa, Illinois and Missouri, where glyphosate is becoming ineffective on abundant weeds such as velvet leaf and water hemp.

Allan Felsot, an environmental toxicologist at Washington State University, said weeds naturally develop resistance to a pesticide and dismissed the idea they might be picking up a resistant gene from Roundup Ready soybeans, corn or cotton.

"Any time you have a place where you're using a strictly singular herbicide, you may end up with some resistance in some cases," he said.

Nonetheless, some scientists want farmers to alter their planting practices to assure that Roundup and competing brand names of glyphosate maintain their effectiveness as a herbicide in the future. The Australian Powles advocates cutting back on plantings of Roundup Ready crops.

Mark VanGessel, a weed scientist at the University of Delaware, advocates a more moderate course. He suggested that farmers rotate their Roundup Ready crops with conventional varieties.

"My gut reaction is that we do need to limit the use of glyphosate-resistant crops," VanGessel said. "That doesn't necessarily mean don't develop them or don't use them altogether, but instead use a planned approach so to not use the glyphosate-resistant crops year in and year out."

Monsanto Co., which markets Roundup Ready crops in addition to the herbicide, said the problem is not nearly that severe.

"Most of the situations that we're dealing with, we're dealing with very small acres," said Greg Elmore, a soybean technical manager at Monsanto. "We're not talking about a whole county. In some cases, we have one field only."

Regardless, farmers could turn to tilling and a combination of other chemicals besides glyphosate, he said.

Monsanto's competitor, Syngenta, agrees with VanGessel that farmers should rotate planting of Roundup Ready corn and soybeans with conventional crops. Syngenta makes its own glyphosate spray, Touchdown.

"We really feel like the problem is real and the problem is growing," said Sherry Ford, a Syngenta spokeswoman. "Just like with antibiotics, an overreliance on one type of solution is going to eventually make that solution ineffective."


Weed Resistance: http://www.farmassist.com/resistance
Weed Survey: http://www.weedscience.org/in.asp