How to Manage Pests
French broom invading a hillside near Bodega bay, California.
Bridal veil broom.
Scotch broom gall mite.
Brooms are a group of shrubs that were introduced into North America from Europe and North Africa in the mid-1800s. Brooms can be found growing along roadsides, forestlands, coastlines, riparian areas, brushlands, and disturbed areas. Initially introduced as ornamentals, they were later promoted by federal and state agencies for erosion control along roadsides and in mined areas. As a result, five broom species have become naturalized in California and are classified as invasive weeds by many federal, state, and local jurisdictions.
These highly competitive shrubs grow rapidly and form dense stands that both people and wildlife find impenetrable. Their dense stems make regeneration of most other plant species difficult or impossible, and they create a dangerous fire hazard. In addition, as legumes, brooms can fix atmospheric nitrogen, increasing soil fertility and giving a competitive advantage to other non-native weeds that, unlike the local natives, thrive on high nitrogen levels.
The four most common broom species in California are Scotch broom (Cytisus scoparius), French broom (Genista monspessulana), Spanish broom (Spartium junceum), and Portuguese broom (Cytisus striatus).
Although many retailers have stopped selling the species mentioned above, some nurseries still sell these and other brooms, including many hybrids. Residents should avoid planting them as many of these have similar invasive characteristics. Some of the available species include sweet broom (Cytisus x spachianus and Genista racemosa) and multiple Scotch broom hybrids including Burkwood’s broom (Cytisus x burkwoodii), Lilac Time, Moonlight, and Lena to name a few.
The safest approach is to avoid planting any broom species. Several alternate plant species have similar attributes but are not invasive. Contact your county UC Master Gardener office or visit PlantRight.org for a list of recommendations (See RESOURCES).
IDENTIFICATION AND BIOLOGY
Brooms are upright shrubs that grow 3 to 10 feet tall. They generally produce bright yellow, pea-shaped flowers from April to June.
Scotch and Portuguese brooms produce their flowers in the leaf axils, while French and Spanish brooms have flowers at the branch tips. The flowers of French broom are substantially smaller than those of the other three common species. In some areas, Scotch broom flowers can be multicolored, with red or purple spots or petals. Bridal veil broom (Retama monosperma) is a white-flowered broom that has become invasive in parts of Southern California.
Stem shape can be used to distinguish between broom species. Scotch broom has a 5-angled stem (star-shaped when viewed in cross-section), French and Portuguese have an 8- to 10-angled stem, and Spanish broom has a finely ribbed stem, making it nearly round.
Leaf characteristics also identify the species. Spanish broom produces simple leaves, while the other three species have mostly trifoliate leaves. For most species, new leaves produced in spring are often lost during hot, dry summer months or periods of stress, giving the plants their characteristic whisk-broom appearance. Scotch, Portuguese, and Spanish brooms are deciduous while French broom is an evergreen. Table 1 shows identifying features of these four broom species.
All four broom species produce dark colored pods in mid- to late summer that contain shiny greenish-brown seeds. Invasion and spread of brooms are entirely driven by seed dispersal.
The pods ripen during the dry summer months, then explosively eject their seeds several feet away, making a popping noise audible for some distance. All brooms are prolific seed producers, with a single shrub producing as many as 2,000 to 3,500 pods containing up to 20,000 seeds.
Between 30% and 60% of seeds are expected to germinate the first year, with the rest staying dormant and germinating at lower rates in subsequent years. Germination rates vary across species, sites, and years. Under most conditions, the majority of new seedlings die, but even so, the large number of seeds produced by a single plant can result in many seedlings. The seeds have an impervious seed coat, enabling some seeds to remain dormant in the soil for decades and making long-term management difficult.
After germination, growth of seedlings for the first two years can be slow, such that people sometimes do not recognize that they have a broom problem until it is several years along. At that point, or sometimes earlier, growth becomes very rapid—with plants growing as much as 3 or 4 feet in one year. Rapid growth continues for another 3 to 4 years, followed by 6 to 8 years of relatively slow growth. Next is a period of senescence, with more dead woody tissue than green. Plants typically live 12 to 17 years but can survive for as long as a quarter-century.
In established broom stands, seeds often remain dormant until older plants are removed or soil disturbance occurs, at which point a carpet of seedlings will appear. Brooms don’t usually reach flowering maturity until the second or third year of growth, which allows for targeted removal of established shrubs first, followed by seedlings and younger plants thereafter.
|Stems: 5-sided; star-shaped cross section
Leaves: compound, 3 leaflets, deciduous, sometimes single on new twigs
|Stems: 8 to 10 ridges; nearly round cross section.
Leaves: compound, 3 leaflets, evergreen, usually dense
|Stems: smooth or finely ribbed; round cross section
Leaves: simple, deciduous, sparse
|Stems: 8 to 10 ridges; nearly round cross section
Leaves: compound, 3 leaflets, deciduous, sometimes single on new twigs
|Flowers: single or paired in leaf axils
Petals: yellow or partially red
|Flowers: 4 to 10 in clusters at end of short branches
|Flowers: several in open racemes at branch tips
|Flowers: single or paired in leaf axils
|Seed pods: flattened, only margins hairy||Seed pods: slightly flattened, entirely covered with long hairs||Seed pods: slightly flattened with few, if any, long hairs||Seed pods: slightly inflated, entirely covered with long hairs|
The two primary methods for managing brooms are mechanical removal and treatment with herbicides (weed killers). Broom establishment is through seed dispersal, so maintaining a healthy cover of desirable vegetation and reducing soil disturbance may reduce the potential for broom invasion. Ongoing monitoring for new seedlings is crucial for successful management.
Small infestations can be removed by hand-pulling or mechanical grubbing. A variety of tools can aid in removal, including shovels or picks, chains, or specialized tools such as the Brush Grubber or The Uprooter. It is easiest to remove plants in early spring or late fall when the soil is moist and roots can be dislodged. Grubbing when the soil is dry and hard usually will break off the stems, leaving rootstalks that may resprout. Fortunately, with brooms, fragments of stems do not survive to produce new roots as in some weedy species.
Mowing broom plants gives poor control unless performed repeatedly throughout the growing season. Within a couple months of germination, young plants usually have produced underground rootstocks large enough to recover from a single mowing. Use extreme caution when mowing during spring and summer because of the potential for wildfires. Mowing later in the season also can spread seeds.
Lopping mature plants near the base will provide some control if done when plants are moisture-stressed in late summer, or in late spring following a winter with little rainfall. Lopping at other times can lead to vigorous resprouting.
Under most conditions in California, brush rakes and bulldozers that leave pieces of rootstocks behind do not provide successful control. In some cases, brush removal in late summer, when plants experience moisture stress, can slow their ability to recover. However, using large equipment to clear land may also promote seedling establishment, making follow-up control essential.
Burning alone is generally not an effective method for controlling brooms. Although burning can remove large amounts of debris, it can also increase the broom population, as it removes competitive vegetation and releases nutrients into the soil. A very hot burn will kill seeds, but a cooler burn will stimulate the germination of broom seeds left in the soil.
Cutting the aboveground vegetation of broom and allowing it to dry on site, followed by burning, can effectively control resprouting. Burning is more effective when followed by an herbicide application or subsequent burnings, and then by revegetation with desirable species. It is important to employ a control strategy following a burn, otherwise the broom population in subsequent years may become worse than before.
Grazing can provide control in small areas, if the grazing pressure is high enough to continually suppress growth. Goats and sheep have been shown to feed on resprouting shrubs, including brooms. In horses, however, ingestion of Scotch broom is reported to cause neurologic effects such as excitement and loss of muscle control and balance, as well as digestive and reproductive effects.
In the 1960s, three insects were introduced as biological control agents on brooms—the Scotch broom seed beetle (Bruchidius villosus), the Scotch broom seed weevil (Exapion fuscirostre), and the Scotch broom twig miner moth (Leucoptera spartifoliella). The latter two species are specific to Scotch broom, while the seed beetle also attacks Portuguese broom, Spanish broom, and French broom. Although all three insects are established, none provide significant control.
Recently, a new agent called the Scotch broom gall mite (Aceria genistae) was found in California. Although this small arthropod was not officially released as a biocontrol agent, it has spread across much of Northern California and the Pacific Northwest. Observationally, the mite appears to reduce Scotch broom seed production and at high densities can cause extensive stem dieback and plant mortality. Because brooms are serious problems in many countries, the International Broom Initiative is evaluating other insects and pathogens in their native countries to determine their control potential.
California residents can use postemergence herbicides containing the active ingredients triclopyr and glyphosate for controlling brooms. These herbicides can be used either alone or as a combination of glyphosate with triclopyr or imazapyr.
In areas near rivers or streams, it is important to use the proper formulation of these herbicides. Ester formulations of triclopyr or imazapyr, for example, are not registered for use near water, and most glyphosate formulations cannot be used near water. Depending on the compound, these herbicides can be applied as foliar sprays, cut-stump treatments, or basal bark applications.
When using herbicides, be sure to prevent them from getting on desirable plants. Because glyphosate is a nonselective compound, it will damage or kill other vegetation. Triclopyr is a broadleaf herbicide that will not injure grasses but will damage or kill other broadleaf plants.
Home gardeners and professional applicators should always wear appropriate protective equipment as stated on the herbicide label.
Foliar Sprays. Herbicides applied to the canopy of broom are often applied when the plants are actively growing from April to July. In mild climates where young broom stems can stay green year-round, late fall and winter applications can also be effective.
Herbicides can be applied as foliar sprays using one of two methods. The first is “spray-to-wet,” where all leaves and stems should glisten following an application. Coverage, however, should not be to the point of runoff. Spray-to-wet applications are made using a backpack or hand sprayer with a flat fan or adjustable spray nozzle. The other foliar method is a low-volume technique called a “drizzle” application, using a spray gun fitted with an orifice disk.
Rather than spraying the entire canopy as in a spray-to-wet treatment, a drizzle application is made to the canopy using an intermittent pattern. It is important to note that the two foliar techniques use the same amount of herbicide active ingredient on a given plant but within different total volumes of water. In a spray-to-wet application, total spray volume can range from 20 to 100 gallons per acre, while the total volume using the drizzle technique will be between 2 and 5 gallons per acre.
The drizzle application is useful for managing plants in areas that are difficult to access. The drizzle nozzle will reach a target plant 15 to 20 feet away, while a flat fan nozzle may only reach plants 2 to 3 feet away. Because of larger spray droplets, the drizzle method also minimizes herbicide drift. The lower volume of water used also reduces sprayer refilling requirements and total weight, potentially reducing applicator fatigue.
For spray-to-wet applications, products containing at least 41% glyphosate as the active ingredient can provide good to excellent control of brooms when applied at 2.5 ounces of product per gallon of water (2% of the total solution). Some products available for use in the home landscape with this concentration of active ingredient are Roundup Pro, FarmWorks Grass & Weed Killer 41% Glyphosate Concentrate, RM43 Total Vegetation Control, Compare-N-Save Grass & Weed Killer Concentrate, and Remuda Full Strength.
Glyphosate products that have a lower concentration of active ingredient, such as Roundup Concentrate (18% active ingredient), will require about 6 ounces of product per gallon of water (4.7% of the total solution) for effective control.
Triclopyr is available in either ester or amine formulations. Triclopyr ester is more effective on brooms, since this formulation is more easily absorbed into the foliage and stems. Products containing a minimum of 61% active ingredient of triclopyr ester can provide good to excellent control when applied at 1 to 1.25 ounces of product per gallon of water (0.75% to 1.5% of the total solution). One such product with this concentration is Brushtox Brush Killer with Triclopyr. Other less concentrated formulations, such as Crossbow, are also available.
Mixing triclopyr ester with commercially available seed oils can offer better penetration. One available product is Hasten-EA modified vegetable oil concentrate. Mix this at 1.25 ounces of product per gallon of herbicide solution (1% of the total solution).
Amine formulations of triclopyr include Bayer BioAdvanced Brush Killer Plus, Ortho GroundClear Poison Ivy & Tough Brush Killer1, and Monterey Brush & Vine Control.
For drizzle applications (low volume, as per product labels), products containing at least 41% glyphosate can provide good to excellent control of brooms when applied at 13 ounces of product per gallon of water (10% of the total solution).
Triclopyr ester can also be applied using the drizzle method. Products containing 61% active ingredient should be applied using 13 ounces of product (10% of the total solution) and 13 ounces of seed oil (10% of the total solution) per gallon of water.
Since drizzle applications use more concentrated herbicide solutions, one gallon of herbicide solution may adequately treat up to one-half acre of densely populated broom.
When air temperatures are higher than 80°F, it is better to use glyphosate or the amine formulation of triclopyr, since triclopyr ester is subject to vaporization.
Cut-Stump Application. Cut-stump treatments can be done throughout the year. Immediately after cutting, apply the herbicide to the cut surface with a paint brush, spray bottle, or plastic squeeze bottle. Delaying application will result in poor control, because the cut surface will quickly dry, preventing movement of the chemical into the plant.
For small stumps, completely cover the cut surface. For large stumps, it is only necessary to wet the outer ring of wood next to and including the bark. For small-stemmed shrubs, cut the stems with loppers or clippers and paint or sponge the herbicide solution onto each cut end.
For triclopyr ester products containing 61% active ingredient, use 1 part product and 4 parts water. For triclopyr products containing 8% amine, such as Ortho Poison Ivy Tough Brush Killer1 use undiluted.
Glyphosate can also be used as a cut-stump application. If using a product containing 18% glyphosate, make a 1:1 solution of the product and water or use undiluted. For products that contain 41% glyphosate, use 1 part product and 3 parts water.
Basal Bark Application. Concentrated formulations of triclopyr ester can be applied to the trunks of broom using a backpack sprayer, spray bottle or wick applicator. Thoroughly cover a 6-inch band around the basal trunk of the shrub. Basal bark applications can be made almost any time of the year, even after leaves have senesced. For triclopyr ester products with 61% active ingredient, the application ratio is 13 ounces of product (10% of the total solution) and 25 ounces of seed oil (20% of the total solution) per gallon of water.
Glyphosate and the amine formulation of triclopyr provide poor control using this technique.
After implementing a control technique, it is important to monitor the area for regrowth. One application of an herbicide does not always completely control brooms. Watch treated areas closely for at least a year and retreat as necessary.
UC Master Gardeners. (Accessed June 8, 2020).
The PlantRight Program. plantright.org/ (Accessed June 8, 2020).
Bossard C, Randall J, Hoshovsky MC. 2000. Invasive Plants of California’s Wildlands. Berkeley: University of California Press. (Accessed June 8, 2020).
DiTomaso JM, Healy EA. 2007. Weeds of California and Other Western States. UC ANR Publication 3488. Oakland, CA.
DiTomaso JM, Kyser GB, et al. 2013. Weed Control in Natural Areas in the Western United States. Davis: University of California Weed Research and Information Center. (Accessed June 8, 2020).
Hoshovsky MC. 1986. Element Stewardship Abstract for Spartium junceum (Spanish Broom). (PDF) Arlington: The Nature Conservancy. (Accessed June 8, 2020).
Oneto SR, Kyser GB, DiTomaso JM. 2010. Efficacy of Mechanical and Herbicide Control Methods for Scotch Broom (Cytisus scoparius) and Cost Analysis of Chemical Control Options. Journal of Invasive Plant Science and Management 3:421-428.
Parker IM. 2000. Invasion dynamics of Cytisus scoparius: A matrix model approach. Ecological Applications 10(3):726-743
Parker IM. 2001. Safe site and seed limitation in Cytisus scoparius: Invasibility, Disturbance, and the Role of Cryptogams in a Glacial Outwash Prairie. Biological Invasions 3(4): 323-332.
Pest Notes: Brooms
UC ANR Publication 74147
AUTHORS: Scott R. Oneto, UC Cooperative Extension, Joseph M. DiTomaso, Plant Sciences, UC Davis, and Guy B. Kyser, Plant Sciences, UC Davis.
TECHNICAL EDITOR: K Windbiel-Rojas
ANR ASSOCIATE EDITOR: AM Sutherland
EDITOR: B Messenger-Sikes
Produced by University of California Statewide IPM Program
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Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2020 The Regents of the University of California. All rights reserved.
BMP: SCOTCH BROOM (Cytisus scoparius)
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 is shade intolerant. Mature plants can reach 10 feet in height although most plants are typically 3-5 feet tall. Scotch broom is a 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 shiny, 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 produces seed at 2 or 3 years but is 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.
- Grows rapidly and forms dense stands.
- Out-competes native plants by shading out and by changing soil fertility.
- Prevents reforestation by out-competing conifer seedlings.
- Dramatically increases the hazard and intensity of fires
- Displaces native plants and wildlife.
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 a 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.
State of Oregon:
The management of invasive weeds is best served through a process known as Integrated Pest Management (IPM). IPM is a weed management methodology that utilizes:
- Management thresholds to determine when and if to initiate control,
- The ecology and life history characteristics of the targeted invasive weed,
- Site-specific conditions and land use considerations to inform management practices,
- The effectiveness and efficiency of various control methods.
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 it is labor intensive. Seedling and small shrubs can be hand pulled between January and May. Pulling when the soil is moist will make it 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 a 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 a 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 seed bank. 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 the 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.
Before you Start:
- Before purchasing any herbicide product it is important to read the label. The label is the Law. Carefully review all parts of the label even if you have used the product before. Select a product that is most appropriate for your site. If you have questions, ask your vendor before purchasing a product.
- When selecting herbicides always use a product appropriately labeled for your site. Follow label recommendations and restrictions at all times. If any information provided here contradicts the label, the label takes precedence. Always follow the label!
- Protect yourself. Always wear the recommended protective clothing identified on your label and shower after use.
- When applying herbicides use spot spray techniques whenever possible to avoid harming non-target plants.
- Do not apply during windy or breezy conditions that may result in drift to non-target plants
- Avoid spraying near water. Hand-pull in these areas, to protect aquatic and riparian plants and wildlife.
- Avoid exposure to pets, pollinators, and wildlife. Remove animals from treatment areas to avoid exposure to herbicides. Follow the reentry instructions on your herbicide label and keep pets out of the area until the herbicides have dried. Avoid spraying when insects and animals are active. Avoid spraying blooming plants to minimize any effects to bees and pollinators.
- Be sure to store any chemicals, out of the reach of children and pets to keep your family safe.
- Product labels and formulations change regularly. Check the Pacific Northwest Weed Management Handbook and the label for current control recommendations.
The mention of any brand name product is not, and should not be construed as an endorsement for that product. They are included here only for educational purposes. Suggested rates are generalized by active ingredient. Specific rates will vary between products. Be sure to review the label before application and use the recommended label rate at all times.
Product Names: Accord, Aquamaster, Rodeo, Roundup, XRT II, and various others
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
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 broadleaf 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)
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 selective and will not harm grasses, but may damage desirable broadleaf 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 the label for specific warnings and recommendations.
Product Names: Arsenal, Habitat, Stalker, Chopper, Polaris
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 the 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
Broadcast: 2 pints/acre (non-cropland) or 1 qt/acre (rangeland) 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.
Scotch Broom Control: Getting Rid Of Scotch Broom Shrub From The Yard
Though sometimes attractive in the landscape, the scotch broom shrub (Cytisus scoparius) is a noxious weed in the northwestern U.S. and responsible for the loss of a good deal of that areas’ timber income due to crowding out native species. Scotch broom control is difficult and often time-consuming, but worth the effort to get rid of scotch broom in the yard and forest.
Scotch broom shrub was introduced as a landscape ornamental as early as the 1800’s, then used extensively for erosion control in public landscapes, such as roadside plantings, but quickly became a nuisance. Once established, it is difficult to kill scotch broom.
Scotch Boom Identification
Scotch broom is a deciduous shrub that can be found on the edges of wooded areas and in open fields. It is an aggressively invasive plant that will grow thickly rather quickly.
Scotch boom has tear-shaped leaves that grow in groups of three and mostly bright yellow flowers with occasional purple and red flowers mixed in. The flowers grow in clusters along the length of the stems. When in flower, the entire bush appears to be yellow.
After flowering, scotch broom will produce several dozen large pods that contain hard brown seeds.
Reasons to Kill Scotch Broom
Effects of scotch broom shrub include competition with native forest plants. In addition, the scotch broom shrub produces soil conditions which encourage growth of other non-native weeds, choking out native foliage.
Wildlife find the shrub unpalatable and may be driven from a habitat overtaken by the scotch broom. Preserving native habitats is an important reason to get rid of scotch broom.
Information on Scotch Broom Control
Scotch broom control may be mechanical, shearing to the ground by hand, or with machinery. Mechanical scotch broom control requires repeated shearing with a chainsaw or trimmer. The roots form a dense and returning mass so this may have to be done repeatedly to kill the plant.
Root removal is often best carefully done by hand in the home landscape. Make sure you get all of the roots, as partial removal of roots will it to come back instead of fully getting rid of scotch broom.
Controlling scotch broom in the home landscape may be best accomplished by continual shearing during the driest seasons. Be mindful of new sprouts, which will quickly establish themselves and remove these as they appear.
Spread mainly by prolific seed production and dispersal, it is difficult to kill scotch broom in the long term because of the seeds. The hard-coated seeds remain viable for as long as 80 years.
Mechanical removal with large tillers and plows often does not work well with controlling scotch broom, and encourages re-growth. Scotch broom shrubs most often overtake areas where soil had been disturbed, as by tilling. Broad spectrum herbicide control is somewhat successful, but must be applied before flowers emerge.
Biological controls, such as a species of seed weevil, are under experimentation and found to be successful at reducing seed spread in Oregon. Larvae of the weevil enter seedpods and are estimated to eat 80% of the seed before they can disperse. Check inside seed pods before treating with chemicals. Larvae should not be destroyed, as they appear to be the best resource for controlling scotch broom invasions.
Note: Although broom plants produce attractive, sweet-pea like blooms, they have become highly invasive in many areas. It is important to check with your local extension office before adding the plant or its relatives to your landscape to see if allowable in your area.