Published Wednesday, November 12, 2003
Weeds that defy one of world's most popular herbicides have spread quickly across Central Valley nut orchards in recent years -- an early warning to farmers worldwide who rely on Roundup for weed control on tens of millions of acres.
Although the number of Roundup-resistant weeds remains small, scientists closely watch the cases in California and several Eastern states. The interest is driven by the massive volumes of Roundup applied to crops that are genetically engineered to withstand blasts of Roundup.
The threat is significant enough that Tom Lanini, a weed ecologist and researcher at the University of California, Davis, is warning orchardists this fall that overuse of Roundup could compromise the effectiveness of a relatively safe chemical that kills a wide range of weeds.
Herbicide resistance occurs when plants survive herbicide sprays that typically would kill them, then spread seeds that also are more likely to survive the chemical. Widespread continuous reliance on a single herbicide speeds the spread of resistant plants.
Lanini said Roundup resistance in ryegrass was isolated to a few orchards near Chico when he discovered it in the late 1990s.
Now, however, he estimates that resistant weeds dot 5,000 acres -- just a fraction of the state's 800,000 acres of almonds and walnuts but enough to make Roundup resistance a feature of Lanini's talks at this fall's growers' meetings.
His alternative ideas include deploying flocks of geese, which eat grass but won't hurt almond trees, or using mechanical means to kill weeds.
"Roundup is used so frequently in these orchards," said Lanini. "Basically, what they are doing is selecting out everything but the resistant population, (which) may just be one or two plants initially, but after a while you have a whole population of plants that are resistant."
The problem isn't news to Colusa County farmer Gerry Rominger, who has killed weeds with glyphosate -- best known by the brand name Roundup -- since its introduction by St. Louis-based Monsanto in 1974.
Increasingly, Roundup doesn't kill ryegrass under Rominger's almond trees, where weeds steal irrigation water and force him to hire extra help to rake nuts from the grassy tangle.
"I am concerned about it in the long term," he said. "In certain places (ryegrass) seems to be very stubborn, very difficult to control with the normal application rate."
The potential for Roundup resistance is gaining increased attention worldwide with the rapid adoption of crops that are genetically engineered to withstand Roundup. The vast majority of those seeds use Monsanto's technology, which allows farmers to spray Roundup on crops to kill the weeds without hurting cultivated plants.
Farmers planted herbicide-resistant crops on an estimated 120 million acres worldwide in 2002, raising concerns that overreliance on Roundup would lead to the evolution of resistant weeds in corn, soybeans, canola and cotton. Researchers from Mississippi to Maryland have reported Roundup-resistant horseweed in field crops.
At Monsanto, continued efficacy of its flagship herbicide is a priority, though the company downplays the potential for widespread problems given that Roundup has been used for three decades, and there's still only a handful of resistant weeds.
Monsanto sold $1.8 billion of Roundup and other glyphosate-based herbicides in 2002, down sharply from 2001, according to the company's annual report. Company officials on Tuesday told investors that the company's strategic priorities involved "managing the decline of the Roundup business," caused partly by competition from competing glyphosate products.
Roundup remains effective for more than 100 weeds, "far more than any other herbicide on the market," said Monsanto spokeswoman Shannon Troughton.
She said Monsanto tracks resistance closely and helps farmers find other chemicals where needed. "Clearly it is something that is manageable and being managed," she said.
Chemical companies and farm advisers also are urging farmers to alternate other herbicides with Roundup before they see problems.
"Mix it up a little bit," said Rob Kiss, field supervisor for Sacramento-based almond giant Blue Diamond. "That may slow down the resistance process."
Resistance to a wide array of herbicides has grown dramatically in the last two decades, in the worst cases lowering land values when farmers run out of weed-controlling chemicals. It's a worldwide problem, but the United States has far more resistant weed populations than any other country.
Ian Heap, chairman of the herbicide-resistant plant committee for the Weed Science Society of America, said U.S. growers need to be careful with one of their most effective chemical tools.
"The total domination of glyphosate in Roundup Ready crops means that we are now relying on one herbicide, and we believe we are going to see more and more herbicide resistance to glyphosate," he said.
Heap said it might take more than 15 years to determine whether Roundup resistance will become a major problem.
To date, most herbicide resistance has been solved by the introduction of new chemicals. However, experts say that Roundup is so cheap and dominant that companies are developing very few replacements.
Heap said that in recent decades most top agriculture universities had active research programs focused on assessing the effectiveness of herbicides that companies wanted to make commercially.
"Researchers are finding that there aren't many new herbicides out there to screen anymore because companies have essentially lost interest," he said.
About the Writer The Bee's Mike Lee can be reached at (916) 321-1102 or mflee@sacbee.com.
Increase in worldwide herbicide resistance [36k GIF]