French Broom
Genista monspessulana
Washington State Classification
Class A — Eradication Required Statewide
This invasive shrub is a noxious weed on the west coast.
Quick Reference
Identification
Growth Habit
French broom is a taprooted shrub that has fine roots associated with nitrogen-fixing bacteria.
Leaves
Leaves are alternate and compound, with three leaflets. Leaflets are oblong, variable in size with most 0.4 to 0.8 inches (10-20 mm) long. Upper and lower surface is sparsely to densely covered with appressed short, silvery hairs.
Flowers
Flowers are yellow, pea-shaped and around 0.35 to 0.47 inches (9-12 mm). Flowers are typically in head-like racemes (clusters) of 4-10 flowers at the ends of short axillary branchlets.
Fruit & Seeds
The seed pods (legumes) are brown at maturity and slightly flattened, 0.4 to 1.2 inches (1-3 cm) long, and densely covered with appressed, silky, silvery to reddish gold hairs. Pods have 3-8 seeds per pod on average.
Impact
This invasive shrub is a noxious weed on the west coast. It can form infestations that outcompete native and forage plants, interfere with reforestation efforts and aid the spread of wildfires into tree canopy layers. With high seed production, established infestations are difficult to eradicate.
Ecology & Spread
Habitat
French broom grows in open, disturbed sites including, roadsides and pastures. It can also be found in less disturbed to undisturbed sites such as grasslands, coastal scrub, oak woodlands, riparian areas and open forests. In Washington only one escaped population has been found on the UW campus in Seattle. Please click here to see a county level distribution map for French broom in Washington.
Spread Mechanisms
Reproduction
French broom spreads by seeds and can produce over 8,000 seeds a year. French broom roots do not produce new shoots but plants can resprout when cut, frozen or burned above the crown.
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Control Methods
Mechanical
- Genista monspessulana can be effectively pulled with weed wrenches. Flaming--using a torch that is hot but does not have a flame--to quickly pass over plants, can be an effective method to control seedlings. Applying a layer of wood chip mulch can also decrease the germination of seedlings. These techniques can be used after adult plants have been removed.
Biological Control
- A seed beetle, Bruchidius villosus, which is used on was found to attack Genista monspessulana in the Eugene area in Oregon. Since French broom is a Class A noxious weed, this biological control would not be used in Washington since eradication is required. Using goats for grazing can be an option.