Scotch (Scot’s) Broom is Noxious Weed

— from Judy Jackson, Coordinator,
San Juan County Noxious Weed Control Program ––

On behalf of the San Juan County Noxious Weed Control Board, tremendous thanks go to Bill Buchan for his on-going efforts in removing Scotch broom from Orcas roadsides.

The roadsides and meadows throughout the county are bedecked with the bright chrome yellow flowers of Scotch broom (Cytisus scoparius). For many years, broom was widely planted throughout the northwest as a soil stabilizer and ornamental landscape plant. Its success, however, has been its undoing. It has naturalized in a wide variety of habitats including pastures, meadows, open forests, roadsides and seasonally dry washes.

As the seeds are easily spread by animals (including ants), mowers, logging machinery, land clearing activities, and soil transport, broom has become the most prominent invasive weed in our county, crowding out native plants and preventing the regeneration of native trees such as Garry oak and bigleaf maples and creating a fire hazard. As a nitrogen fixer, broom successfully out-competes most native shrubs that have evolved in our nitrogen-poor soils.

The broom invasion has become so severe that the Washington State Department of Agriculture has banned the sale and importation of the species (including all of the many cultivars), and the State Noxious Weed Control Board has designated it as a Class B noxious weed. In San Juan County, the County Noxious Weed Control Board has mandated the species for control.

Control can be achieved by uprooting the plants with a weed wrench, cutting them at the base before the seed pods ripen, or by the use of herbicides. In areas of high conservation value such Garry oak woodlands, cutting the mature plants at ground level has proven to be the most effective technique, as it minimizes regrowth and soil disturbance, thus bringing fewer seeds to the surface where they can germinate. Cutting to the ground is most effective when the shrubs are more than ¾-inch in butt diameter (average thumb’s thickness), and are drought stressed and their energy is sapped by flower production, but before the seeds are ripe.

In disturbed areas of lower conservation value such as roadsides, a combination of cutting and pulling is effective. During the wetter winter and spring months when the soil is moist, seedlings may be pulled by hand. Larger plants can be tackled with a weed wrench. When using this tool, care must be taken to minimize soil disturbance and trampling of native or other desirable vegetation. Later in summer and early fall when the soil is drier, cutting becomes more effective and less damaging to the environment.

Herbicides containing glyphosate or triclopyr can be effective when used carefully, depending on the location. Using a foam brush, immediately dab a minute amount of undiluted herbicide on a freshly cut stub. San Juan County regulations prohibit the use of herbicides on County rights-of-way. Always follow the label instructions when using any herbicide. The label is law.

Prevention of seed production is critical in any weed control project. Removal of plants before they set seed, either by cutting or pulling, is the first step. In order to slow the spread of broom always remove isolated plants first, and then work from the margins of an infestation towards the center. In all cases, the follow-up treatment on a yearly basis is essential. Seed life for Scotch broom may be up to 80 years, and young plants can start to produce seed in their second year.

Weed wrenches are available for loan from the following sources:

• Orcas and Shaw–Noxious Weed Control Program at the Eastsound Senior Center;
• San Juan–Land Bank, Public Works or the National Park Service;
• Lopez–Public Works and Land Bank.

For more information on Scotch broom or other noxious weeds, contact the San Juan County Noxious Weed Control Program at 376-3499.