A weed may yield a green pesticide that can control a host of plant diseases but is harmless to humans.

In a presentation made at the 236th national meeting of the American Chemical Society in Philadelphia, Pam Marrone, founder of Marrone Organic Innovations of Davis, Calif., described the new pesticide made from an extract of the giant knotweed.

That 12-foot-high goliath, named for the jointed swollen nodes on its stem, invaded the U.S. from Japan years ago and grows along the East Coast and other areas.

The new biopesticide has active compounds that alert plant defenses to combat a range of diseases, including powdery mildew, gray mold and bacterial blight that affect fruits, vegetables, and ornamentals.

The product will be available this October for conventional growers, says Marja Koivunen, director of research and development for Marrone Organic Innovations.

A new formulation has also been developed for organic farmers and will be available in 2009.

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