Herbicide-Resistant Weed Plagues Calif.

Aug 10, 9:46 AM EDT

By JULIANA BARBASSA
Associated Press Writer

PARLIER, Calif. (AP) -- Horseweed was once merely a nuisance to farmers - hard to pull out, quick to sprout back after cutting, and capable of towering over tractors.

Now, it's becoming a full-blown nightmare worthy of an agricultural horror flick: scientists in California have found clusters of the weed that are resistant to scores of herbicides, leaving farmers to fight an increasingly formidable and costly foe.

Pete Christensen said he watched his costs soar as the most popular herbicide became increasingly powerless to stop the weeds from choking the grapes on his 75-acre vineyard near Selma.

About five years ago he started noticing that Roundup wasn't withering the weed as usual. Three years later, he had tripled the concentration of the herbicide, and had doubled the applications, but the weeds were growing thicker than ever, rising over his vines and competing with them for water, nutrients and sunshine.