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Scotch Broom

Scotch Broom

PNW103
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A. Hulting, K. Neff, E. Coombs, G. Miller, L. Miller
Classified as a noxious weed in Washington and Oregon, Scotch Broom has overtaken much of the Pacific Northwest from British Columbia to California. It is especially problematic in disturbed areas such as new housing developments, and will interfere with conifer seedlings and displace native forage species on rangeland. Seeds last up to 60 years in the soil. This instructive weed control guide provides 12 color photographs of the plant at various stages and the areas it tends to invade.
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A bright sign of spring, Scotch broom (Cytisus scoparius) reminds us of its invasive presence each year as many acres of forests, pastures, and rights-of-way burst into golden bloom. Scotch broom is a native of Europe and North Africa, from Great Britain to the Ural Mountains, and from Sweden to the Mediterranean. It was introduced as an ornamental plant in California in the 1850s and later used to prevent erosion and stabilize banks and sand dunes.

Since then, Scotch broom has invaded much of the Pacific Northwest; its range stretches from British Columbia

into central California, and from the coast inland to the Cascade and Sierra Nevada mountains. While not as abundant, it also is present in most counties east of the Cascades in Oregon and Washington. Scotch broom is invading northern Idaho and is sparsely distributed throughout southern Idaho.

A woody, leguminous shrub, Scotch broom establishes quickly in disturbed areas, often outcompeting native plants to form dense, monospecific stands (Figure 1). Scotch broom’s economic impact can be significant; the state of Oregon loses more than $40 million annually in timber revenue and control expenses.

Description

Identification and Biology

Scotch broom is a woody shrub that can grow to 10 feet tall, although the average plant is usually 3 to 5 feet. Plants have sharply angled branches and bright yellow flowers. Plants bloom between March and June, before leaves emerge. Young branches have five ridges, are green and hairy, and are responsible for about half of the plant’s photosynthetic activity.

Branches become smooth and brown as they age. Leaves are small and oblong, often with three leaflets, and develop later in the growing season.Single or paired flowers, clustered in leaf axils, are bright yellow and typical of plants in the Fabaceae family (Figures 2, 3 and 4, page 2). Occasionally plants bearing maroon flowers or bicolor maroon and yellow flower petals are in Scotch broom populations (Figure 5, page 3).

Figure 1: Scotch broom forming a dense thicket in a clearing disturbed by new home construction.
 

Andrew Hulting, Extension weed specialist; Karin Neff, faculty research assistant; Larry Burrill, former Extension weed specialist; all of Oregon State University; Eric Coombs, entomologist, and Glenn Miller, integrated weed management specialist, both of Oregon Department of Agriculture; Robert Parker, Extension weed scientist, Washington State University.

A Pacific Northwest Extension publication

Oregon State University • University of Idaho • Washington State University

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Copyright 2008 Washington State University

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