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California better place to ward off glyphosate resistance

Whether it is farming or fashions, California is often viewed as the place where it starts.

The latest "trend" in agriculture is weed resistance to herbicides. However, California cannot be blamed for starting this emerging crisis.

Herbicide resistance is nothing new. Resistance to ALS herbicides is not uncommon. What makes the current controversy alarming is that the resistance is being documented in the most widely used herbicide in the U.S., glyphosate.

It is not just widely used, according to University of California farm advisor in Tulare County, Steve Wright, it is the only major herbicide that continues to log increased usage. Wright says use has grown by 700 percent with the introduction of herbicide resistant crops. Contributing to this growth is the falling price of the product as it comes off patent.

Although glyphosate has been around for three decades, it has been only in the past few years with the introduction of Roundup resistant crops that resistance has been an issue.

The list of weeds reported resistant or suspected resistant to glyphosate nationwide is growing from ryegrass to marestail to lambsquarter to Palmer amaranth to ragweed to goosegrass to barnyardgrass and others.

Monsanto, the maker of Roundup, says part of the resistance problem is farmers using less than the recommended rate of the product. Researchers differ on that, citing incidences where repeated, high rates of glyphosate have had no effect on resistant weeds.

Wright told a UCCE grower meeting in Visalia, Calif., recently that 42 percent of the San Joaquin Valley cotton crop was planted to herbicide-resistant varieties. About 30 percent of the state’s corn crop is in RR varieties. And Roundup-resistant alfalfa is expected to be available soon.

Percentages grow

These percentages are expected to continue to grow because herbicide-tolerant crops reduce hand-hoeing and mechanical cultivation. Both are cost factors, but the second is also an environmental issue with the growing regulatory air quality environment.

Roundup Ready crops are more widely planted in the southern U.S. and along with rapid conversion to conservation tillage, glyphosate-resistance is growing. "You can hardly find a cultivator running in the South," Wright said.

Wright said Roundup may be getting a least a partial bad rap in the weed-resistance debate because it is not the herbicide alone that is leading to weed resistance to the herbicide.

Reduced tillage and relying too heavily on glyphosate when other herbicides are available are also factors in spawning resistance.

"It is the change in the weed control system that is causing the problem," believes Wright. "It is not just Roundup. When you take cultivation out of the system; when you take other herbicides out of the system, you get weed shifts and resistance.

"California is in better shape to ward off resistance than any place else," Wright said. Although California farmers have reduced tillage operations, tillage is still part of most farming operations," Wright added herbicides other than glyphosate are used in the many rotation crops in California. These factors contribute to better resistance management, Wright said.


However, that does not mean resistance will not continue to be a concern in California. Wright suggested growers use 2,4-D and Dicamba on broadleaf weed between crops to mitigate resistance to glyphosate.

"Use the Roundup technology on your nastiest fields and when they are cleaned up, go back to conventional weed control systems," he suggested.

The emerging era of Roundup Flex which will allow growers to use the herbicide over the top of cotton until seven days before harvest will also help ward off resistance.

Ignite and Liberty Link cotton also will steer farmers away from Roundup Ready crops and the threat of resistance.

Also, growers who abandoned pre-plant herbicides are returning to these products. "For $6 per acre, growers figure it is worth it to go back for improved weed control and resistance management," he said.

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