California Agriculture journal reports on resistant weeds

The July-September 2008 issue of California Agriculture journal includes a science brief and a research article documenting increasing resistance to the common weed killer glyphosate in California weeds. The most common brand name for the herbicide is RoundUp.

In 2005, UC weed researchers Anil Shrestha and Kurt Hembree notified the media that they had confirmed glyphosate resistance in horseweed. In 2007, a news release by Stephanie Klunk of the UC Integrated Pest Management program reported on glyphosate resistance in hairy fleabane.

The California Agriculture science brief says at least 14 glyphosate-resistant weed species have been reported, threatening the loss of the herbicide.

"Because of its (glyphosate's) ease of use, environmental safety and effective control of weeds, it is important to maintain the viability of glyphosate in California," Shrestha is quoted in the brief. It says experts suggest using a variety of weed control tactics, not glyphosate alone, to reduce resistant weeds.

The research article details research by Shrestha, Hembree and USDA research agronomist Bradley Hanson that confirmed the hairy fleabane resistance.

Hairy fleabane that survived glyphosate applications.

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