Scotch broom [Cytisus scoparius (L.) Link][SAOSC][CalEPPC: A-1][CDFA list: C] Photographs
French broom [Genista monspessulana (L.) L. Johnson][ CalEPPC: A-1][CDFA list: C] Photographs
Spanish broom [Spartium junceum L.][CalEPPC: B] Photographs
SYNONYMS: Relationships between the genera of brooms are complex and weakly differentiated. Consequently, many species have been shuffled back and forth between genera several times.
GENERAL DESCRIPTION: Shrubs to 3 m tall, with green stems and yellow pea-like flowers. Refer to the Brooms table for a quick comparison of distinguishing characteristics. The brooms were originally introduced as landscape ornamentals. Scotch and Spanish broom were also extensively planted along highways in some areas to prevent soil erosion in the early half of 1900’s. Brooms have escaped cultivation and have aggressively invaded many natural areas. Scotch and French broom often form dense stands that displace native vegetation and wildlife. Infestations in forested areas increase fire hazard and on rangeland, diminish usability. Flowers and seeds of brooms contain quinolizidine alkaloids and can be toxic to humans and livestock when ingested. Foliage may be mildly toxic and is unpalatable to most livestock, except goats. Scotch and Spanish broom are used medicinally in Europe. However, Scotch broom is considered to be an unsafe herb by the U.S. Food and Drug Administration.
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SEEDLINGS: No descriptions available.
MATURE PLANT: Stems erect, dense, green. Leaves alternate (to sub-opposite in Spanish broom).
ROOTS and UNDERGROUND STRUCTURES: Taproots deep, branched, associated with nitrogen-fixing bacteria. Nitrogen-fixation occurs year round where winters are mild. Roots do not produce new shoots, but plants cut above the crown can grow new shoots, especially during the rainy season.
FLOWERS: Pea-like, usually bright yellow. Stamen filaments fused. Insect-pollinated. Mostly out-crossing.
FRUITS and SEEDS: Seeds have a small cream-colored to yellowish appendage (strophiole) at the attachment scar (hilum).
POSTSENESCENCE CHARACTERISTICS: Plants tolerate frost, but typically die-back after severe cold winter conditions. Some branch death can occur during seasonal drought. Natural decline and senescence occurs over a period of years. Symptoms of decline in Scotch broom include an increase in the ratio of woody to green plant material, a thinning of stems, and a decrease in pod production. Eventually old plants die and topple over, opening the canopy for seedling establishment.
HABITAT: Colonize open disturbed sites, such as logged or burned sites, roadsides, and pastures, and can invade +/- undisturbed grasslands, coastal scrub, oak woodlands, and open forests. Do not tolerate heavy shade, but can tolerate minimal shade along the edges of forest canopies. Drought-resistant.
.DISTRIBUTION: Common.
PROPAGATION/PHENOLOGY: Reproduce by seed. Pods typically burst apart into spiral halves, ejecting seeds a short distance from the parent plant. Seeds disperse to greater distances with water, soil movement, vehicle tires, human activities, and animals. Seeds are hard-coated and long-lived under field conditions. Brooms can re-sprout from the crown when cut above.
MANAGEMENT FAVORING/DISCOURAGING SURVIVAL: Established infestations are difficult to eliminate because large, long-lived seedbanks typically accumulate. Minimizing soil disturbances, monitoring, and manually pulling young plants when discovered can help prevent new infestations. Machines and tools used to remove stands may inadvertently transport seed to uninfested sites. Cutting Scotch broom shrubs to ground level at the end of the dry season can help reduce re-sprouting from the crown. Planting native shrubs and trees within and around broom stands can eventually help to minimize infestations by shading. Goats confined to a small area can help control stands of young shrubs or young re-growth from cut shrubs. Prescribed burns can eliminate above ground growth, but do not prevent re-sprouting from the crown and may stimulate a flush of seed germination.
SIMILAR SPECIES: There are several other brooms with yellow or white flowers that have naturalized locally in some areas. The most important of these are Portuguese broom [Cytisus striatus (Hill) Rothm.][CalEPPC: A-1] and bridal broom [Retama monosperma (L.) Boiss. = Genista monosperma Lam.][CalEPPC: red alert]. Portuguese broom is yellow-flowered and is often confused with Scotch broom. Unlike Scotch broom, Portuguese broom has stems that are 8-10-angled, pubescent calyxes, and slightly inflated pods that are densely covered with white hairs. Portuguese broom occurs in the San Francisco Bay region, South Coast, and Peninsular Ranges, to 300 m (1000 ft). Introduced from Spain and Portugal. Bridal broom is easily distinguished from other brooms by having white flowers with purple calyxes and nearly round pods that contain 1 or 2 seeds. Pods do not open to release the seed(s). Bridal broom was first discovered at Fallbrook Naval Weapons Station in San Diego County. Introduced from Spain and North Africa. Portuguese and bridal brooms are expected to expand range. Unlike brooms, gorse [Ulex europea L.] has thorny stems.
CONTROL METHODS:
Mechanical: The weed wrench is one of the most effective techniques for the complete removal of French broom Scotch broom, and other brooms. The wrench locks on to the base of the stem and leverage is used to remove the entire plant. The wrench was specifically designed for complete broom removal to prevent any resprouting. The weed wrench is effective on many trees and shrubs up to a 2.5 inches in diameter. Some soil disturbance will occur with removal, which may favor new seedlings or deeply bury seeds in the soil. However, the disturbance is minimal and the technique can be employed even on steep slopes. Generally, a flush of broom seedlings may occur directly beneath the previously canopied area, which will need to be controlled. Mowing or cutting the shrubs may prevent seed production. However, resprouts will need to be managed.
Biological: There are currently no registered biological agents for use on French broom or gorse. However, the gorse weevil (Apion ulicis) was accidentally introduced into California in 1953 from France. The weevil feeds on seeds, spines, and leaves of the gorse plant, but has had limited success for control. There are two approved insects for Scotch broom, a stem miner (Leucoptera spartifoliella) and a seed beetle (Apion fusciostre). However, both insects have had limited success in California. Intensive goat grazing has been used to control brooms and gorse. Goats are most effective in controlling regrowth following initial control strategies. Goat grazing may be difficult if you are trying to reestablish natives during the control process since goats will also likely browse the native plants.
Chemical: For brooms and gorse, glyphosate applied as a 2-3% v/v foliar spray has been an effective treatment. Triclopyr applied as a 25% basal bark application in an oil carrier is also effective. Some resprouting may occur with these treatments and follow-up management will be necessary for future flushes of seedlings.
Prescribed fire: Brooms and gorse are highly flammable. Fire has been used to eliminate large impenetrable thickets and prepare areas for easier follow up treatments. Fire stimulates seed germination and large flushes of seedlings may be expected following burning. Fire appears more effective in controlling resprouts when there is adequate grasses to carry the fire.