Scotch Broom
Cytisus scoparius
Washington State Classification
Class B — Control Required (Designated)
It displaces native and beneficial plants, causing loss of grassland and open forest.
Required control in Region 1 (all western Washington counties)
Quick Reference
Identification
Growth Habit
Scotch broom is a perennial, many-branched, shrub ranging in height from 3 to 10 feet tall.
Leaves
There are few leaves. The upper are simple and the lower are 3 parted. They are deciduous and pointed at both ends. Leaves may fall early in the year, leaving bare green stems.
Flowers
Flowers are typical of those in the pea family. They are bright yellow, about 3/4 inches long and have 5 petals.
Fruit & Seeds
Seed pods are brown-black, legume-like, flattened and have hairy margins with several seeds per pod.
Impact
It displaces native and beneficial plants, causing loss of grassland and open forest. It aggressively spreads to form monocultures, replacing desirable forage grasses and young trees. Seeds are toxic to livestock and horses.
Ecology & Spread
Habitat
Scotch broom can be found on roadsides, pastures, grasslands, open areas and areas of recent soil disturbance. Please click here to see a distribution map of Scotch broom in Washington.
Spread Mechanisms
Reproduction
Scotch broom reproduces by seed. Each seed can remain viable for over 30 years (some estimates are as long as 80 years).
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Control Methods
Mechanical
- Hand pulling and digging up plants are an option for small infestations. Use a tool like a Weed Wrench, Extractigator, or Uprooter to leverage plants out of the ground, along with their roots. Check with your county noxious weed board to see if they have weed wrenches they can loan out. Note that soil disturbance from leveraging out plants may stimulate seed germination. Reduce disturbance as much as possible and control seedlings. Chopping, cutting or mowing is an option for flat areas. Cutting plants close to the ground when they are drought stressed, can provide control on plants with stems wider than 2 inches, but make sure to monitor plants for resprouts and control. Repeated cuttings a year over multiple years may be provide control as well. Combining cutting with an herbicide treatment can also be successful.
Cultural / Prevention
- Reduce weed infestation by handpulling weeds. Careful digging is useful to manage weed populations. However, digging can carry undesirable weed seed to the surface and foster further germination. However, this is very time consuming and frustrating.
Biological Control
- The Scotch broom seed weevil, Exapion fuscirostre, larvae feed on seeds of Scotch broom in developing seed pods. The adults also feed on flowers and the tips of stems, though their damage is not significant. The Scotch broom bruchid, Bruchidius villosus, larvae feed on developing seeds and impact the plant's reproduction. For more information about the biological control of Scotch broom, please visit WSU Extension Integrated Weed Control Project.