Broom, scotch broom

Scientific name: Cytisus scoparius

Broom in flower

Broom roots

Broom seedling

Broom before flowering

Broom flowers and seed pods

Mature seed pods on broom
  • Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • Almost leafless branched woody shrub up to 3 m tall
  • Stems are green and woody, five ribbed and hairless. New growth has silky hairs on stem margins
  • Produces conspicuous bright golden yellow flowers in spring, followed by explosive pods
  • Flowers are two lipped and pea-like with a long style, 16-25 mm long and sometimes partly red in colour
  • Flowers are either solitary or paired and bloom between September and April
  • Seeds (3 mm long) are enclosed in oblong pods which, when mature, turn from green to brown and burst open explosively to disperse seeds.

Other similar species present in New Zealand

  • Montpellier broom (Genista monspessulana) is similar to broom except that it is more leafy
  • This evergreen shrub has leaves with three leaflets and generally flowers in the colder months
  • Seed pods are 2-3 cm long, contain 3-6 seeds and are very hairy. When seed pods explode they can disperse seeds up to 5 m away from the parent plant
  • While not as common in New Zealand as broom, Montpellier broom is still invasive and competes with native plants.

Origin

  • Native to the Mediterranean, broom has invaded many regions of the world including Australia and New Zealand
  • It has become a serious weed in some regions of New Zealand, forming dense stands and suppressing native plants.

Life cycle

  • Broom is a perennial leguminous shrub which forms dense stands, and can be a threat to biodiversity
  • Almost leafless, the shrub can reach up to 3 m tall, producing paired or solitary golden yellow flowers
  • Broom begins to flower and seed between September and April in its second year
  • Dispersal of seeds is mainly from explosion of pods but seeds may also be dispersed in mud attached to animals or vehicles
  • Seeds are robust, hard and able to withstand transport via river gravels. They can also survive for many years in the soil.

Benefits

  • Flowers provide food for bees, other insects, and small birds
  • Can act as a nurse crop for regenerating bush
  • Broom fixes nitrogen.

Impact on pasture

  • Broom can grow in dense stands which allow it to compete well with other pasture species and native plants. In areas of high broom infestation pasture and native species can be completely suppressed, and wildlife habitats destroyed
  • Broom can also be a fire hazard, especially in drier months or post- herbicide application.

Impact on stock

  • Broom plants and surrounding areas are avoided by stock, reducing the stock carrying capacity of the grazing land.

Grazing management

  • Sheep and goats readily graze broom seedlings which can help reduce establishment of the weed. Intensive grazing of broom seedlings can significantly reduce the number of plants that establish
  • The combination of pasture competition, trampling and grazing can severely reduce seedling numbers.

Pasture species/cultivars and fertiliser application

  • Maintaining a dense, vigorous pasture will help to prevent broom re-infestation
  • Spreading ryegrass and clover with fertiliser can help a pasture to outcompete broom seedlings which establish after burning a mature broom stand.

Burning

  • Burning reduces broom numbers although plants can re-establish from seedlings in bare areas
  • Slashing broom in spring followed by burning in autumn gives more effective control.

Cutting

  • Broom can be ploughed, slashed and pulled with chains towed by bulldozers
  • Cutting can be used in combination with herbicides
  • Cutting is not always possible as broom can grow on inaccessible hillsides and valleys.

Chemical control

  • Chemical control can be used along with cutting for effective control of broom.

ALWAYS READ PRODUCT LABELS BEFORE APPLYING

Active ingredient When to apply Residual effect Grass Damage Clover Damage
metsulfuron-methyl Nov-May Yes Moderate Severe
glyphosate When plant in full leaf No Severe Initially severe but recovery rapid
triclopyr + picloram Spring – early summer Yes No Severe

Consult your farm consultant, industry rep or the New Zealand Agrichemical Manual for more information about chemical control.

Biocontrol

Several insects have been introduced into New Zealand as biological control agents for broom.

Broom psyllid (Arytainilla spartiophila)

  • Native to Europe, this insect was released extensively in the 1990s. Now established at many sites throughout New Zealand, both adults and nymphs suck sap out of new growth in spring
  • The insect produces one generation per year with the adult female laying eggs from late spring to early summer. The following spring, nymphs emerge, developing though five stages and becoming adults by late spring
  • Adults look similar to aphids. They are 2-3 mm long, pale brown and winged.
  • When eggs are laid they are embedded in the stem, protected by a waxy covering
  • Manually spreading the psyllid is beneficial as they only disperse slowly. The best way to do this is to collect nymphs from November-October by cutting infested shoots and carefully placing cut material onto uninfested broom bushes
  • Care must be taken while doing this as psyllids are fragile and spend most of the year immobile. They are also sensitive to herbicides.

Broom seed beetle (Bruchidius villosus)

  • Native to Europe, this beetle was released widely in New Zealand during the 1990s
  • As broom pods begin to form the adult female lays eggs. Larvae then develop inside the seeds and new adults are released when pods mature and burst open. One generation is produced per year
  • Adults are 2-4 mm long, black and roundish. Eggs are smaller than a pinhead, shiny and are laid close to the edge of the pod
  • When larvae emerge they burrow into the soft green seed pods. Pupae develop and are hidden within the seeds
  • In spring, adults can easily be seen on flowers as they feed on pollen
  • Larvae cause the most damage to the plant as they feed on its seeds. Studies show that this insect is capable of destroying 80-90% of an infested plant’s seeds
  • The beetles spread steadily by themselves, although spreading them manually may improve the control of broom
  • The easiest way to do this is to harvest and spread infested pods to other plants when they are blackish-brown and beginning to burst open.

Broom twig miner (Leucoptera spartifoliella)

  • Native to Europe and accidentally introduced in the 1950s, this moth is now common throughout New Zealand
  • Producing one generation per year, adults emerge in early summer, with females laying eggs throughout summer months
  • From early autumn to spring larvae feed on stem tissue, emerging to pupate in mid-late spring
  • Adults are silvery-white tiny moths (3-4mm). They lay white oval eggs on young stems
  • Larvae are translucent. They cause dieback of stems as they feed just under the stem surface. When a large proportion of the plant has been affected bushes grow and flower less. Larvae may also cause the plant to die
  • Large scale outbreaks are common in parts of the South Island. The moth continues to spread successfully throughout the rest of New Zealand, causing severe damage.