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Glyphosate resistance has gone global

The well-documented problems farmers in the Southeast are having with several weed species that have developed resistance to glyphosate are part of a world-wide and ongoing problem discussed by scientists from North and South America and Europe at a recent Syngenta-sponsored Media Summit.

Interviews conducted with 400 farmers, split into the southern and northern U.S., revealed some startling information about the reality and perception of herbicide resistance in the U.S. Criteria for farmers interviewed was to grow more than 250 acres of corn and/or more than 500 acres of cotton.

Of the farms surveyed in the South, 83 percent use Roundup Ready technology. Of these growers, 42 percent use only glyphosate for weed control. Average use of Roundup Ready technology in the South was 4.4 years.

In the South, 39 percent of growers reported having glyphosate resistant weeds. Of these growers nearly 25 percent indicated 100 percent of their acreage has glyphosate resistant weeds. Nationwide, less than 5 percent of farmers surveyed indicated they would reduce use of Roundup Ready technology to solve their resistance problems.

Southern farmers who do not have resistance problems on their farms indicate they expect glyphosate resistance would cost them an extra $15-16 per acre for weed control and 7-8 percent yield loss.

Perhaps the most the stunning information coming from the Syngenta-sponsored survey is that over half (53 percent) of southern farmers surveyed believe new products will solve the problem.

Mark Swinney, who heads Syngenta’s product development program in the United Kingdom, contends that is not likely in the near future. Spinney noted that in Europe, growers have lost 47 herbicides to a lack of re-registration since the inception of Roundup Ready technology.

Industry-wide, he says, there has been a decrease in research and development spending by agri-chemical companies by 17 percent. Even if the mythical magic bullet is found to control weeds that are currently resistant to glyphosate, the time from discovery to market is roughly 10 years.

At the 2005 Beltwide Cotton Conference, Allen York, widely regarded as the dean of southern weed scientists, warned cotton growers that there would be no silver bullet to combat weed control. He also indicated herbicide resistant Palmer pigweed may be a bigger threat to southern cotton production in the 21st century than the boll weevil was in the 20th century.

Spinney says there are 183 weeds worldwide with scientific documentation of resistance to herbicides. While most are manageable with current herbicides, some like water hemp and its cousin Palmer amaranth are not because of their ability to develop resistance to multiple modes of action.

The magic bullet scientists are seeking is a herbicide that contains: a new mode of action, broad utility, ability to pass regulatory hurdles, safe for crops, address current resistance issues and justify the cost of development.

Currently, only 11 companies worldwide are seeking such a product. By comparison, in 1985, 35 companies were actively pursuing new herbicides.

Though growers in the Southeast contend the situation couldn’t get much worse with pigweed now resistant to both ALS and glyphosate-based herbicides, it could get much worse, and the problem is by no means limited to the U.S.

In South America, Ribas Vidal, professor of weed science at the University of Rio Grande du Sol in central Brazil, says four provinces in the northern part of Argentina documented cases of glyphosate resistant johnsongrass in 2006. Already, Vidal says, researchers in Brazil have found suspect cases of resistance in johnsongrass in soybean fields there.

A huge problem in Brazil, and one that will likely become bigger in parts of the U.S. is wild poinsettia. This weed has shown multiple herbicide resistance, including glyphosate resistance and is a problem on over 40 million acres in Brazil.

In the U.S., Bill Johnson, an associate professor of weed science, first started fighting glyphosate resistance problems in 2003 when resistant horsenettle or marestail started showing up in Indiana. Though a problem, Johnson contends this weed is only a minor nuisance compared to what is on the horizon.

In the Midwest, he says waterhemp has emerged as one of the most problematic weeds in soybeans. Multiple resistance to triazine and ALS chemistry has been well documented. Now, to a lesser degree the weed has shown resistance to glyphosate. Johnson, speaking at the Syngenta-sponsored Media Summit, showed some dramatic pictures of lambsquarters and giant ragweed, both of which have shown resistance to glyphosate. Another long-time Weed Scientist, Ken Smith, from the University of Arkansas, says agricultural production systems in his state and throughout the upper Delta region are built around glyphosate. Widespread resistance, he contends, would be most devastating in cotton, because there are no alternatives that most cotton farmers can afford. Soybeans, he says, is a close second, only because there are limited alternatives to glyphosate.

Smith says the use of Roundup Ready technology has created a tremendous increase in acreage among farmers who previously farmed 2,000 acres or more. By 2006, he estimates 30 percent of farms over 2,000 acres got bigger. The concept of farming more acreage with less equipment is based on glyphosate, and more so than any time in history, time is money for these growers.

The Arkansas weed scientist concurred with others on the panel that horsenettle resistance got some growers attention, but is basically a manageable problem. In 2005, Arkansas weed scientists found a 500 acre farm with pigweed that showed signs of glyphosate resistance.

Further greenhouse studies in 2006 leave little doubt the problem is there. The question, he says, is how fast will it spread?


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