Biological control is the deliberate introduction of insects, mammals, or other organisms which adversely affect the target weed species. Biological control is generally most effective when used in conjunction with other control techniques.
- Three biological control agents, a beetle (Bruchidius villosus), a seed weevil (Exapion fuscirostre), and a twig miner (Leucoptera spartifoliella), are approved for release and have been established in Oregon and Washington. These agents will not control existing plants, but they can significantly reduce seed production. Contact your local weed authority for more information.
- Goats have been employed in the task of Scotch broom control and removal.
- Only apply herbicides at proper rates and for the site conditions or land usage specified on the label. Follow all label directions and wear recommended personal protective equipment (PPE).
- For control of large infestations, herbicide use may be effective either alone or in combination with mowing. Treated areas should not be mowed until after the herbicide has taken effect and weeds are brown and dead.
- Monitor treated areas for missed and newly germinated plants.
- Choose selective herbicides over non-selective herbicides when applying in a grassy area.
- Minimize the impacts to bees and other pollinators by controlling weeds before they flower. When possible, make herbicide applications in the morning or evening when bees are least active. Avoid spraying pollinators directly.
Specific Herbicide Information
Herbicides are described here by the active ingredient. Many commercial formulations are available containing specific active ingredients. References to product names are for example only. Directions for use may vary between brands.
- A foliar application of triclopyr (Vastlan) is a very effective treatment for Scotch broom. Apply when Scotch broom is actively growing, preferably before flowering. Ensure full coverage of the plant to be effective. Fall treatments of Scotch broom are also effective.
- A combination of triclopyr and 2,4-D (i.e. Crossbow) is also effective.
- Glyphosate (Round-Up) can effectively control Scotch broom when applied to actively growing plants in spring. Glyphosate is non-selective and will kill non-target vegetation such as grass. Treatments with glyphosate should be combined with effective revegetation in treated areas.
- Addition of a surfactant to spray mixes will improve results. Foliage must be thoroughly wetted, although not to the point of runoff. Re-treatment will be necessary to control late-germinating plants.
- Triclopyr and glyphosate can both be used as a cut-stump application. Herbicide is diluted to 50% solution and applied to stumps immediately following cutting.
This BMP does not constitute a formal recommendation. When using herbicides, always consult the label. Please refer to the Pacific Northwest Weed Management Handbook or contact your local weed authority.
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Broom weed seed pod
( Cytisus scoparius)
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.
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.
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.
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.
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