Scotch broom

(Cytisus scoparius)

 

Invasive implications

Scotch broom is native to the Mediterranean areas of Europe. It was intentionally introduced to B.C. in 1850 by Captain Walter Grant who planted broom at his farm on Vancouver Island. Regrettably, few realized the invasiveness of this perennial as it quickly spread up the east coast of Vancouver Island before invading the Gulf Islands and mainland. Humans encouraged its continued spread as highway departments planted Scotch broom as a bank stabilizer because of its deep root structure and rapid growth. Nowadays, Scotch broom can be spotted with its brilliant yellow flowers in open areas such as roadsides, power lines, and natural meadows. This weed is a strong competitor with various native plants including those within declining Garry oak ecosystems as well as newly planted coniferous forests. It competes with native species for available light, moisture and nutrients, especially on disturbed sites. So far there are no known natural predators for this weed, therefore allowing it to spread throughout southern B.C. and other parts of North America. It does particularly well in recently disturbed areas, and for this reason it continues to increase in areas of Vancouver Island and the Lower Mainland where land development is intensive. Despite these detriments, Scotch broom is quite spectacular with its striking array of bright yellow flowers in spring.

 

Identification

Spring

Summer

Winter

  •  Scotch broom flowers in May until early June

  •  mature plants grow up to 3m

 

  •  bears over wintering buds above the ground surface

Leaves

Stem

Flower

 

 

 

  •  small and alternate
  •  three leaflets near the base of the stem (4-8mm long)
  •  sometimes has few or no leaves
  •  new stems are green and strongly angled (left)
  •  become woody and grey as plant matures (right)
  •  deep taproot
  •  bright yellow, sometimes red or purplish-tinged
  •  seed pods black when mature with 5-9 seeds (see pictures below)

 

 

Similar Plants

Scotch Broom has several close relatives including Gorse (Ulex europaeus) and Spanish Broom (Spartium junceum L.). The possession of large spines distinguishes Gorse (see WeedsBC) from Scotch broom.

   

Key Features

Cytisus scoparius is a deciduous, perennial shrub that grows up to 3m tall. It begins to reproduce when it is approximately three years old and usually lives from 10-15 years. After flowering, it forms black seed pods, carrying an average of 5-9 seeds that disperse after the pods audibly 'pop' open! Scotch broom is known as a 'prolific seed producer' with up to 18,000 seeds per plant which spread by wind, small animals, water and humans. These seeds are protected with a seed coat that can delay germinating for over 30 years. As mentioned, it has yellow flowers (sometimes white or red) that attract large bees to deliver its pollen. Scotch broom is adapted to tolerate drought conditions with its deep taproot, reduced leaf area, photosynthetically active stems, and a thick wax coating to prevent water loss. It prefers open sites because it is generally shade intolerant, thriving in dry to very dry soils. This plant also tends to acidify surrounding soil, preventing other species from establishing. 

Seed Pods

 

Control Measures

Scotch broom is difficult to control due to longevity of seed banks, profuse seed production, tolerance to drought, long life span, and lack of natural enemies. Using mechanical control such as uprooting often triggers the germination of seeds in the ground that could be decades old! Subsequently, control efforts must be sustained until the seed banks are essentially depleted. Despite these overwhelming odds, stewardship groups on Vancouver Island have managed to gain significant ground on some monocultures of Scotch broom through cutting and hand pulling. Their success is marked by the reestablishment of native wildflowers at various sites. As this invader is shade intolerant, planting native species after removal will likely assist in control through covering exposed soils to prevent seed germination. Besides mechanical control, some studies are focusing on the use of chemical spot treatment. Not all chemicals are effective, however; for example 2, 4-D is usually more effective than Roundup. As for biological control agents, the Oregon Department of Agriculture recently released a seed weevil (Apion fuscirostre) that has shown promising results with significant seed damage. There is also some hope that fungal agents could be used as a future control method.

 

Non Chemical Control

  Hand pulling/cutting Machinery Mulch
How Smaller plants can be pulled by hand while larger plants can be cut using laupers or saws. Cut the stem right down to the ground. Use machinery such as power tools, bulldozers and backhoes to uproot or crush plant. Surround desirable plants with canvass moss or landscape fabric to prevent broom from competing
When When plant is flowering and before seed sets. Cutting is effective during periods of moisture stress When plant is flowering and before seed sets. At same time as planting exposed area
Duration

 

Several years until no new growth is detected, may re-grow from cutting Should only be performed once to minimize soil disturbance. Until desired plant is established and broom poses little threat
Pros/Cons Is cost-effective, fairly unobtrusive but labour intensive. May cause excessive soil disturbance May be feasible option for low conservation value land such as roadsides otherwise this may  harm sensitive habitat with excessive soil disturbance. This is an effective yet costly and labour intensive form of control

 

Non Chemical Control

  Burning Grazing
How Can be used to remove flowering stalks. La Manchia goats were effective grazers on a small plot on southern Vancouver Island.
When When plant is flowering. Before plant has set seed.
Duration

 

If done properly, this should only be performed once. Several years until no new growth is detected
Pros/Cons Cost effective but will germinate seeds in soil with  light to moderate burns, allowing colonies to reestablish. Also creates smoke pollution. Efficient control in areas that have become a monoculture and where practicable.

 

 

Chemical Control

 

Spot Application

How Cut back stems to ground level. Immediately apply a 25% solution of Roundup or 2,4-D and diesel oil to the cross section of the stem.
When In the fall when leaves are translocating to rhizomes is most effective time.
Duration Twice per year, may need to repeat over two years
Pros/Cons This technique benefits from being very selective and effective. May not be feasible for large areas.

 

Control Warnings:

Disposal - Make sure to properly discard all plant pieces in thick plastic bags and transport them to a sanitary landfill site or incinerator. Composting is not an appropriate means of disposal as this may result in further distribution. Remember that humans can actually spread invasive plants by taking seeds from one place to another on clothing, tires, equipment, etc.

Chemicals - The recommended method for Scotch broom control (i.e. applying to a cut stem) at least allows a specific application to the weed versus the surrounding environment. Although some chemicals are approved for control of invasive plants, extreme caution must be taken as many pesticides are harmful to humans. Permits may be required for chemical use and buffer zones exist beside waterways to protect fish and wildlife. Chemical control is not a long-term solution and therefore should be part of a finite plan and applied sparingly. Please see the following web sites for further information: Provincial: MWLAP Pest Information  Federal: Pest Management Regulatory Agency

 

Additional Resources