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
[Spartium junceum L.][CalEPPC: B] Photographs
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 1900s. 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
Stems erect, dense, green. Leaves alternate (to sub-opposite in
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.
usually bright yellow. Stamen filaments fused. Insect-pollinated.
and SEEDS: Seeds have a small cream-colored to yellowish appendage
(strophiole) at the attachment scar (hilum).
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.
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.
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.
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.
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.
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