A rust disease that occurs naturally offers hope for the biological control of dyer's woad, the attractive but damaging yellow weed that dominates much of Utah's springtime landscape.

Researchers at Utah State University are working to harness the rust, which was first identified 10 years ago near Grace, Idaho. Steve Dewey, USU Extension weed specialist, said the rust appears to have no ill effects on other plants, the environment or humans."It stops seed reproduction, which is dyer's woad's only method of perpetuating itself," Dewey said. "It's systemic, meaning it goes through the entire plant, which increases its chances for success. And it occurs naturally, so fewer tests and quarantines will be required before it becomes commercially available."

Currently, herbicides like 2,4-D are used to spray dyer's woad, but their use is often uneconomical. Dewey sees the rust as a potential way to halt the spread of the pesky weed.

Dyer's woad, a member of the mustard family, was introduced into the United States from Europe during Colonial times and cultivated for use as a blue dye. Synthetic dyes replaced plant dyes, and the woad, left on its own, spread.

Introduced into Utah in about 1917, the weed has since become a serious problem on rangeland and cultivated crops in Utah, Idaho, Nevada and western Wyoming. It's found in isolated areas of Oregon, Montana and California, and is a problem in Yellowstone and Teton national parks.

In Utah, the weed is widespread south to Fish Lake National Forest and the Manti-LaSal range near Moab.

"Distribution and density have increased dramatically since the weed's introduction, and the economic impact is now estimated in the millions of dollars," Dewey said.

The weed is particularly damaging on rangeland that has limited moisture and fertility. It matures early in the year, crowding out other edible range vegetation. Then it dies early in the summer leaving no food for grazing. In addition, the weed's seed pods rot on the ground, exuding a toxin that kills the roots of nearby grasslike weeds.

Dewey said the spread of dyer's woad into many rugged and remote areas makes chemical control extremely difficult or impractical. He said biological control agents may be the only hope for effective control, and the rust pathogen may fulfill that hope.