Extension Service Garden Hints

Scotch broom is beautiful, but noxious

Scotch broom has been transported throughout the temperate world, where it has few natural enemies to keep it in check. Photo: Lynn Ketchum

McMINNVILLE - This time of year, local hills are scattered with the yellow blooms of Scotch broom. Introduced from Europe as a garden ornamental by early settlers of the Pacific Coast, Scotch broom has spread across nearly 7 million acres of western Oregon and in patches in the central and northeastern parts of the state.

Although it is beautiful, Scotch broom quickly becomes a pest. Wherever it grows, the aggressive broom spreads to form pure stands at the expense of young trees, pasture grasses and native plants, according to Susan Aldrich-Markham, field crops scientist with the Yamhill County office of the Oregon State University Extension Service.

Scotch broom can wreak economic havoc, costing Oregonians an estimated $47 million per year, according to the Oregon Department of Agriculture (ODA). Its invasive habit and economic costs have landed Scotch broom on the State Weed Board's list of noxious weeds, along with its relatives French and Spanish brooms and gorse.

What should you do to control this noxious weed? The OSU Extension Service and ODA's Noxious Weed Program recommend that you learn to identify Scotch broom and the other non-native broom species in the Pacific Northwest that have the potential to become weedy. If you find it on your property:

• Dig it up, including the crown;
• Cut it back to the ground each year before it sets seed;
• Keep an eye out for seedlings each spring and get rid of them, roots and all while they are small. Since Scotch broom seed lasts for years in the soil, vigilance is necessary to prevent reinvasion by new seedlings.

Fall applications of herbicides can be effective, either by spraying the foliage or by spraying just the base of the trunk with a stronger concentration. Another alternative is to cut the plant, then treat each freshly cut stump with herbicide. Herbicide registrations may change, therefore consult your local county office of the OSU Extension Service for recommendations.

Scientists continue to investigate biological control possibilities for Scotch broom and other noxious weeds. ODA has released a species of seed weevil whose larvae feed on the developing Scotch broom seedpods. They can destroy up to about 80 percent of the broom seed inside the pods.

To check to see if these seed weevils are working on your Scotch broom, pop open a mature, brown Scotch broom seedpod. Look for tiny white larvae. Do not spray plants with seed weevils.

Effective Scotch broom control - with or without herbicides - requires follow-up. The area must be retreated if seedlings sprout. Planting something else, such as grass, in the cleared area can provide competition and keep the Scotch broom from re-invading.

For more information on "Scotch Broom," PNW 103, visit our on-line catalog. Our publications and video catalog at: http://extension.oregonstate.edu/catalog/ shows which publications are available on the Web and which can be ordered as printed publications.

By: Peg Herring
Source: Susan Aldrich-Markham, Dan Hilburn

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