February is the one month of the year that many of us associate with our love and romance. We cut out paper hearts for Valentine’s Day cards and wrap up cut flowers for that special person in our lives. But there is another reason to celebrate because February 14th also Oregon’s birthday! Way back in […]
Its June, and that means its time for a new Weed of the Month! We are working with our partners at the Columbia Gorge Cooperative Weed Management Area to promote Scotch Broom (Cytisus scoparius) as our weed-of-the-month for June. Scotch broom was introduced as an ornamental along highway corridors and in western Oregon as a […]
Scotch broom, Scot’s broom, English broom
Cytisus scoparius (syns. Sarothamnus scoparius, Spartium scoparium)
Scotch broom is a fast growing shrub in the Fabaceae (pea) family, characterized by its masses of yellow flowers. It grows upright on young green, 5-angled stems which are hairy. Broom forms dense stands and are shade intolerant. Mature plants can reach 10 feet in height although most plants are typically 3-5 feet tall. Scotch broom is deciduous nitrogen fixing plant. Scotch broom is an invasive plant found in low elevations from British Columbia to California.
4 to 8 feet
Yellow
April to June
It can be confused with the less common Spanish broom, Spanish broom has fewer round stems, very few leaves, and larger yellow flowers.
The areas most infested by Scotch broom are disturbed (logged or burned) sites, grasslands, open forests, and riparian corridors. The plant likes coastal areas and low elevations in dry conditions with plenty of sunshine. Scotch broom flourishes in infertile soil because it is a nitrogen fixing plant which allows it to grow where many plants cannot. Scotch broom likes sandy, acidic and dry soil.
Scotch broom is a pioneer species known to displace native plants and smother tree transplants increasing tree death or slowing growth in the early years. It readily invades disturbed sites, natural areas, dunes, and forestlands. Broom control costs on right-of-ways, public facilities, parkland and private property are in the millions of dollars each year due to its rapid growth and persistent nature. Scotch broom is a prolific seed producer of long-lived (10 years plus) seeds. Broom stands establish persistent soil-seed banks requiring long-term commitment to exhaust. The costs attributed to Scotch broom come from labor and chemical inputs needed to control infestations ($47 million annually) in timberlands and from lost productivity. Pollen production during bloom time also can be quite an allergen source for allergy sufferers.
Europe and North Africa
Oregon Noxious Weed Profile
Washington Noxious Weed Profile
Invasive.org profile
CABI Invasive Species Compendium
Scotch broom, Scot’s broom, English broom
Cytisus scoparius (syns. Sarothamnus scoparius, Spartium scoparium)
Scotch broom is a fast growing shrub in the Fabaceae (pea) family, characterized by its masses of yellow flowers. It grows upright on young green, 5-angled stems which are hairy. Broom forms dense stands and are shade intolerant. Mature plants can reach 10 feet in height although most plants are typically 3-5 feet tall. Scotch broom is deciduous nitrogen fixing plant. Scotch broom is an invasive plant found in low elevations from British Columbia to California.
The leaves of Scotch broom are alternate and compound consisting of three oblong leaflets. Very few leaves on stems. New twigs may only have one leaflet. Leaflets are small 5-20 mm long. The leaflets are dark green and fleshy and serrated along their margin. The underside of the leaflets are covered by flattened, short hairs while the upper surface is smooth.
The flowers are pea-like; upper and lower curved petal have wing petals on each side. Scotch broom flowers are yellow to partially to complete red in color. Small, only 1-2.5 cm. The stamens are fused. Plants flower from April to June.
Fruits develop as seed pods that mature in June-July. Seed pods are flat, 2-5 cm long, smooth with long silky hairs which turn dark brown to black when mature. Seeds are small 2mm, long and shinny, brown to black in color with a whitish appendage (fatty deposit) which attracts ants and some birds. 3-12 seeds found within each pod.
The Scotch broom plants form deep, branched taproots with fine roots associated with nitrogen fixation. New shoots can grow from the crown when plants are cut above the crown.
Scotch broom reproduces by seed. Seeds are dispersed when pods dry, split in half and twist. This action can send seeds up to 3 meters but is often just a short distance from the plant. A variety of ants are attracted to the white seed appendages and disperse the seeds further. Seeds have a hard coating which allows them to survive up to 30 years in the field. Scotch broom produce seed at 2 or 3 years but are in full reproduction at 3-5 years lasting until year 9. Up to 3500 pods can be produced from one adult shrub. Scotch broom lives for 15-20 years.
The areas most infested by Scotch broom are disturbed sites, grasslands, open forests, and riparian corridors. The plant likes coastal areas and low elevations in dry conditions with plenty of sunshine. Scotch broom flourishes in infertile soil because it is a nitrogen fixing plant which allows it to grow where many plants fail to flourish. Scotch broom likes sandy, acidic and dry soil.
The original introduction of Scotch broom to Oregon is believed to have occurred between 1875 and 1899 (Christy et al., 2009). The plant is native to Europe and North Africa and was commonly introduced by European settlers to remind them of their home but quickly escaped cultivation. It was also used to stabilize soil especially along roadways before the realization of its invasive characteristics. Due to its showy flowers, Scotch broom was commonly produced in the horticultural trade where many varieties have been developed.
Scotch broom can be found throughout Clackamas County. It is very widespread and directly impacts properties throughout the county. As an ubiquitous weed this is not a species that is actively surveyed and the mapped distributions do not represent the full extent of the Scotch broom population in Clackamas County.
The management of invasive weeds is best served through a process know as Integrated Pest Management (IPM). IPM is a weed management methodology that utilizes:
An IPM based strategy ensures the maximum effectiveness of treatment measures. IPM strategies typically use more than one management method to target one or more susceptible life stages. It is adaptive to site conditions in the field and to the response of a plant to management. The utilization of multiple management tools also inherently reduces the use of herbicides in a management plan. The IPM process ultimately provides a framework for the establishment of Best Management Practices (BMP) which outlines the best approach for controlling a weed particular infestation.
The control of Scotch broom can be a difficult task. The long lived seeds, long growing season, aggressive roots, thick stands and the ability to resprout from young stumps or root crowns make Scotch broom difficult to control .
Manual removal of Scotch broom can be an effective control option especially for smaller infestations, but its is labor intensive. Seedling and small shrubs can be hand pulled between January and May. Pulling when the soil is moist will make is easier to remove the roots and put less strain on the worker. All plants and roots need to be removed to reduce regrowth. Continual manual removal, every year pulling the next generation, is one of the most effective controls for Scotch broom. A weed wrench, shovel or hoe can be used to assist with root removal.
While manual removal can be an effective treatment, it can cause heavy soil disturbances on site. Soil disturbance can bring broom seeds deep in the soil to the surface creating a new generation of growth.
For old established stands, cut Scotch broom between ground level and three inches using loppers or a saw during the dry season (July to August). Try to cut before seed pods mature to limit spread.
Cutting alone during the right time can be a useful management tool to prevent seeding. Young Scotch broom plants will resprout following cutting from above the root crowns. Older plants generally will not resprout following a cutting. Large stands of resprouting plants following cutting are best controlled with a targeted herbicide application.
Large infestations of Scotch broom can be removed through mowing. Like cutting, brush mowing alone won’t kill the broom. Mowing should be done between flowering and seed maturity and must be repeated at regular intervals to exhaust plant. Mowing is not a very effective control by itself, however when used in conjunction with herbicide application it can be very effective.
Mowing equipment can transport seeds if not cleaned before leaving site and if plants are cut during seed production.
Burning can be an effective tool to remove debris, but it will not eliminate Scotch broom. Other management such as crown removal or herbicide application is required to achieve control. The available fuels in dense broom stands can also be substantial, so care needs to be taken to keep fire contained. As such fire is generally not a recommended control measure. You should check with your local Fire District or the Oregon Department of Forestry for rules and recommendations.
Grazing by goats is a potential method for controlling Scotch broom. Unfortunately, broom plants can be toxic to both humans and livestock which limits other grazing activity. Goats confined to a small area will eat the resprouting Scotch broom after treatment.
Chemical control is an effective tool to control large stands of Scotch broom. Continued treatment and monitoring will be required due to the copious number of seedlings emerging from the seedbank. Scotch broom is susceptible to several systemic herbicides. Plants should not be mowed or cut after application for a minimum of two weeks to allow herbicide to reach the roots. Scotch broom flowers can hinder herbicide application by not allowing the chemical to reach other areas of the plant. Large treated/dead stands of brooms are a fire hazard and need to be monitored and removed if necessary.
Product Names: Accord, Aquamaster, Rodeo, Roundup, XRT II, and various others
Rate:
Spot treat: use 1.5% to 2% v/v solutions.
Cut stump: 25% v/v (up to 50% can reduce resprouting)
Time: Foliar application in late summer or early fall. Cut stump application again in late summer to early fall, immediately after cutting.
Comments: Re-treatment may be required to achieve effective control. Glyphosate is not selective and will harm grasses. Use care when working around desirable plants to avoid damage. Leaves should be sprayed until wet but not dripping to achieve good control. Cut stems horizontally at or near ground level and immediately apply herbicide.
Product Names: Garlon 4 (triclopyr ester), Garlon 3A, Element 3A (triclopyr amine), Pathfinder II
Rate:
Broadcast: Triclopyr ester- 2 – 3 qts/acre (1 – 1.5 at ae/acre), Triclopyr amine- 3 – 4 qts/acre (1.125 – 1.5 qt ae/acre)
Spot treat: Triclopyr ester use 0.75% to 1% v/v solution, Triclopyr amine use 1% – 1.5% v/v solution plus 0.25% – 0.5% v/v surfactant
Basal Bark: Triclopyr ester- use 20% v/v solution ethylated crop oil and water
Cut stump: Triclopyr amine-50% in water
Time: Apply post emergence when plants are growing rapidly in the spring and again in the fall. Applications should be made before a killing frost.
Comments: Re-treatment may be required to achieve effective control. Triclopyr is selective and will not harm grasses but will harm desirable broad leaf plants, trees, and shrubs. Use care when working around desirable plants to avoid damage. Leaves should be sprayed until wet but not dripping to achieve good control. Triclopyr ester formulations may volatilize under warm temperatures.
Product Names: Crossbow (Triclopyr + 2, 4D)
Rate:
Spot treat: 0.5% to 1.5% v/v solution
Time: Apply post emergence when plants are growing rapidly in the spring and again in the fall. Applications should be made before a killing frost.
Comments: Re-treatment may be required to achieve effective control. Triclopyr + 2, 4D is a selective and will harm grasses, but may damage desirable broad leaf plants, trees, and shrubs. Use care when working around desirable plants to avoid damage. Leaves should be sprayed until wet but not dripping to achieve good control. Check label for specific warnings and recommendations.
Product Names: Arsenal, Habitat, Stalker, Chopper, Polaris
Rate:
Spot treat: 1 to 2% v/v solution plus 0.25 to 0.5% surfactant v/v
Cut stump: 20% v/v solution in water plus 20% ethylated crop oil
Basal bark: 20% v/v solution in water plus 20% ethylated crop oil
Time: Apply post emergence in late summer to early fall when plant is growing rapidly. Best when used in late summer to early fall.
Comments: Imazapyr is a soil residual herbicide and may result in bare ground around plants after treatment.
Product Names: Tordon 22K
Rate:
Broadcast: 2 pints/acre (non-cropland) or 1 qt/acre (range land) plus 0.25 to 0.5% v/v surfactant
Time: Apply post emergence in spring and again in fall when plants are growing rapidly at or beyond early to full bloom stage.
Comments: Picloram can cause long term soil activity and should not be used around trees because of root uptake. Use care when working around desirable plants to avoid damage. Leaves should be sprayed until wet but not dripping to achieve good control. Restricted herbicide: not registered in California.
There are several insects which feed on the seeds and leaves of Scotch broom. Scotch broom bruchid (Bruchidius villosus), Scotch broom seed weevils (Exapion fuscirostre or Aprion fuscirostre), twig mining moth (Leucoptera sartifolilella), Eriophyid gall mite (Aceria genistae) and the shoot tip leaf moth (Agonopterix nervosa) are known to damage the Scotch broom plants. These bugs will not eradicate an infestation, they have poor to fair effectiveness controlling a stand and any results might not be seen for up to 7 years.
Scotch broom plants that have not gone to seed are able to be disposed of in regular household trash cans or in yard debris containers. Cut plants can be left on site but can be a fire hazard. Scotch broom plants that have gone to seed should be left on site to minimize the spread of the seeds, or piled on tarps and bagged before being moved off site. Plant debris can also be burned on site with appropriate safety measures and permits. You should check with your local Fire District or the Oregon Department of Forestry for rules and recommendations.
Diligence is the most important aspect for controlling Scotch broom. New broom plants will germinate from the seed bank living in the soil even after years following treatments and soil disturbances, so repeated follow-up is required.
