Oregon Tries to Sweep Out Scotch Broom

Driving around the corner of a logging road, botanist Jeanne Klein got a rude shock.

The golden yellow patch of Scotch broom where she had released a precious new bug was gone, ripped out by a U.S. Bureau of Land Management road crew that failed to recognize it as one of just a dozen sites where a new biological agent was set loose to control Oregon’s most noxious weed.

“I released them right about here,” said the BLM botanist, standing in the raw earth at the side of the gravel road. “I chose this site because there were no timber sales planned in here.”

Chalk up another win for Scotch broom.

A symbol of the Plantagenet kings in its native Europe, the shrub with the brilliant golden blossoms came to Oregon in the late 1880s as an ornamental. Nurseries still sell it for landscaping.

But in timber plantations, pasture, meadows and power line right-of-ways, the shrub is a scourge, causing $47 million a year in damage. That puts it at the top of the list among noxious weeds in Oregon.

The greatest impacts are in timber plantations, where Scotch broom crowds out new seedlings. Along streams, it elbows aside native plants. In pastures and meadows, it chokes out grasses. Along power lines, it creates a fire hazard and makes the ground impassable.

Despite volunteers ripping it out of the ground with root wrenches, road crews grubbing it out with backhoes and timber crews hacking and spraying it with herbicides, Scotch broom has spread to 16 million of the some 20 million acres of western Oregon.

The march of Scotch broom could make a horror movie. The pods fling the seeds up to 35 feet, where they can lie dormant for 60 years, just waiting for a road crew to come along and rip up the ground, creating the disturbed soil conditions that trigger the seeds to sprout.

Mowing doesn’t work unless the plant is dried out by drought. Root-wrenching is effective but too laborious to make much of a dent in the current stands.

Enter a pair of lowly insects, which love nothing more than to munch on Scotch broom seeds. Like a fussy child, they will eat nothing else, a key factor in winning approval as a biological control.

In 1983, the Oregon Department of Agriculture turned loose the first batch of a weevil--known to scientists as Apion fuscirostre--west of Salem.

Native to Europe, the bugs are harvested from broom on the East Coast, where they are well established, by whacking the bushes with a tennis racket and catching the bugs in a tarp. The adults lay their eggs on the seedpods, and the larvae eat up to 80% of the seeds on a bush. But that still leaves lots of seeds.

Now a new bug has been added to the fight. It is a tiny hairy beetle known as Bruchidius villosus, also a European native.

“We’re hoping that between the two of them we can control most of the seeds,” said Tim Butler, a field operations manager for Oregon’s agriculture department.

Biological controls will never wipe out Scotch broom. The best hope is that they will make it just another member of the plant community, rather than a rampaging new arrival.

But the search is expensive. Approval of a new bug can take $10 million and 20 years of research.

Butler had Bruchidius villosus for only 12 sites this year, and the 250 individuals that Klein released above Hubbard Creek represented the only site in Douglas County.

Klein walked across the road to some surviving Scotch broom and shook the branches over a blue tarp, hoping to see some of her bugs. About 100 would need to survive to start a viable population. Several Apion fuscirostre fell out, and perhaps one of the Bruchidius.

“This could be one,” she said, reaching for the bug just as the wind blew it away. “Whoops. That was encouraging to at least think I had one for a moment.”