Gather Background Information
The first step in an IVM program is to gather information on the biology and habits of the noxious weed.
Scotch broom (Cytisus scoparius), French broom (Genistamonspessulana), and Spanish broom (Spartium junceum) share a similar biology, growth-habit, and life cycle. Since control measures are also similar, they will be considered one group unless otherwise noted.
These three plants are legumes, and are native to the British Isles and to central and southern Europe. They were introduced into California by horticulturists as ornamentals, and by the USDA Soil Conservation Service to prevent erosion and to stabilize soils. Broom is a shrubby perennial characterized by short spiky leaves, yellow flowers, woody stems, and brownish-black pea-like pods that contain several seeds. Unlike French broom, which has many trifoliolate (3-parted) leaves, Scotch and Spanish broom have green, almost leafless branches. Broom has many growth forms; from a low-lying shrub, to a single upright shoot, depending on sunlight and growth conditions. In favorable sites, individual plants can grow over 10 ft. tall with many thin stems (Parker 1994; Hoshovsky 1986).
Broom spreads aggressively into stands of native vegetation, endangering open grasslands and hillsides. Most broom-infested areas create high fire hazards because of the plants’ flammability, fuel load (amount of plant material that will burn), and its frequent location on steep slopes. In forest clearings competition with broom prevents the reforestation of tree seedlings. Broom also changes the nutrient dynamics of the site because of its ability to fix nitrogen (Eldon 1994).
Broom is established along the inland valleys of the Pacific Northwest, from British Columbia to central California. Although it primarily grows west of the Cascades, it has been found on the eastern slopes as well. Its northern limits are probably due to low winter temperatures and the southern limits due to summer drought (Williams 1981; Parker 1994).
Broom can invade pastures, cultivated fields, dry scrubland, native grasslands, dry riverbeds, roadsides, and other travel corridors. Although it does not grow well in forested areas, it can rapidly establish following disturbances such as logging, land clearing, or burning (Williams 1981).
Broom is long-lived and can reproduce from seed or from cuttings. Yellow flowers open in late spring to early summer (March to June), and a second flowering may occur in the fall. During the end of summer, in August and September, brown seeds pods burst open and seeds are shot out into the soil. Broom can produce 2,000 to 3,500 seed pods per bush, each pod containing several seeds. Seeds can also be spread by water, vehicles, birds, and other animals. Years of heavy seed production are generally cyclical and are followed by years of lighter seed production, independent of climate. With their hard coats, seeds form a long-lasting seed bank that can remain viable for over 80 years (if properly stored); however, they do not germinate below a depth of 4 inches (Hoshovsky 1986; Read 1994).
Special Challenges to Management
Broom plants are extremely invasive and grow in almost any sunny site that has been slightly disturbed. Broom has many characteristics of a species adapted to disturbances: it has rapid growth, flower production at a young age (as young as 2 years old), a long life-span (up to 7 years), a long-lasting seedbank, and individuals can resprout from the base.
The movement of unchecked soil for highways in British Columbia has increased the spread of broom into new areas. Once it is established on roadways, seeds can lodge onto tires and be dispersed long distances (Read 1998).
Some questions, such as those below, can only be answered on site.
Set Realistic Goals for Your
The answers to the following questions can help you set realistic objectives and goals.
Reduction - reducing the area covered by a weed, or reducing its dominance. This strategy can also be used against new or established weeds, but it requires more resources and more time than containment.
The "Bradley Method" (see Appendix 2), developed in Australia, is a simple yet innovative strategy for natural areas that combines containment and reduction.
Eradication - completely eliminating the weed from the management area. This strategy usually consumes the greatest amount of time and resources and is applicable mainly to newly-invading weeds that are confined to a limited number of small areas.
Establish Monitoring Programs
When planning a monitoring program, keep in mind the context of your target weed: is it invading or has it already invaded?
Locate and record broom infestations on a map. (Chapter 2 of the University of Northern Iowa IVRM Technical Manual contains a detailed discussion on how to map and inventory vegetation - see Bibliography). Note particularly sensitive areas on the map, such as critical habitat for threatened or endangered species, agricultural production areas, or areas subject to frequent disturbance and thus prone to invasion. Update maps at regular intervals.
Focus monitoring efforts on sites where broom problems are most likely to occur (see Distribution). Encourage public sighting and reporting through an education or incentive program (see Educate Vegetation Management Personnel and the Public).
Prioritize the sites you will work on. Make a realistic assessment of your weed management resources, keeping in mind the goals of your project and the cost of a follow-up program after any treatments. Without follow-up, your control efforts will be wasted. It is better to thoroughly control a weed at one or two sites than to use up resources to incompletely control the weed at many sites. If the weed is very widespread, try to determine where it poses the most serious economic, social, or environmental problem and concentrate on those areas.
Plan monitoring and treatment efforts to coincide with critical life stages of the weed. To use your resources efficiently, try to include monitoring with other planned activities in the area.
Maintain records of your monitoring activities. Creating standardized forms will make data collection easier and help remind you to gather all the information you need. Forms work best if they include labeled blanks for all pertinent information and allow the user to check or circle rather than having to write words or numbers (See Appendix 3 for some examples of forms).
Include information such as the name(s) of the person(s) collecting the data, the location, and date of monitoring; a qualitative description of the vegetation, such as the names of the plants or types of plants (native vegetation, annual/perennial weeds, trees, etc.) and stage of growth (germinating, flowering, setting seed, etc.); a quantitative description, such as percent cover, plant density, size of the patch, or if possible, the number of plants.
Note special conditions such as unusual weather events and record treatment history, including information on treatment applications (who, when, where, how, cost, difficulties, and successes). This will allow you to evaluate and fine-tune treatments.
Set Treatment Thresholds
Setting treatment thresholds involves prioritizing and balancing treatments with resources. Weeds are treated when populations increase beyond a predetermined level. This level will largely depend on the characteristics of the site and weed. In some cases the level may be no weeds at all, and in other cases the level may be much greater.
Considerations for Setting Priorities
What is the size of the weed population? The opportunity for control is related to the infested area. Small patches can be more easily controlled than large infestations.
What is the level of the threat? Is the broom population changing? Is it in an area where soils are frequently disturbed? Does it threaten cultivated fields, pastures, or rangeland? Is it encroaching on critical habitat for a rare, threatened, or endangered species? Is it displacing the best examples of native communities?
What resources are available? Do you have the resources required for carrying out your goal?
With the advent of herbicides, prevention as a weed management
technique has often been neglected; however, it is a practical, cost-effective,
and extremely important in a weed management program.
General Weed Prevention Measures
(Adapted from Fay et al. 1995).
Plant competition can weaken broom, and in most cases broom must be initially removed using controlled burns or physical methods. If seedlings of native plants cannot grow fast enough to compete with resprouting broom stumps, root crowns may need treatment (cutting, pulling, or herbicide) so that desirable vegetation can establish.
Apply Management Methods
No individual method will control broom in a single treatment; diligence and persistence will be required over a number of years to subdue this weed. The treatment methods described in this section will help you to design an integrated program that will suit the circumstances of your particular situation.
Biological control does not aim to eradicate weeds, but to keep them at low, manageable levels. After their introduction, biocontrol agents can take 5 to 10 years to become established and increase to numbers large enough to reduce the density of the target weed. Once established, effective biological controls provide an inexpensive, long-term, and non-toxic means to control weed populations. Since insects have specific requirements for growing and thriving, it is important to match the insect to the weed management site. Understanding these requirements will help you integrate the insects into other weed control efforts. When you release biocontrols, continue using other control methods on the perimeter of the release site, but avoid using them where they might adversely impact the insect population.
The information provided below is only a summary. For more information consult Biological Control of Weeds in the West (see Bibliography) or contact commercial weed biocontrol insectaries (see Insectaries).
Researchers in New Zealand have introduced the following species against Scotch broom. Bruchidius villosus, a seed beetle, can destroy 50% of the seeds. Arytainilla spariophila, a broom psyllid, is quickly establishing throughout New Zealand, but it is too early to determine the psyllid’s impact on broom. Other possible biocontrol agents against Scotch broom include Gonioctena olivacea (a leaf beetle), Exapion immune (a stem weevil), Chesias legatella (a moth), Agonopterix assimilella (a moth), Sitona regensteinensis (a root weevil), and Polydrusus confluens (a root-feeding beetle) (Hayes 1997).
Studies in New Zealand have identified the fungal pathogens Pleioshaeta setosa on broom and Fusarium tumidum on broom and gorse plants. More studies are necessary before these pathogens can be released, and no attempts have been made to study the effects of these pathogens in the U. S. (Johnston 1995; Hayes 1997).
Goats and sheep graze of the tops of young plants, preventing plant development, seed formation, and gradually depleting root reserves. Grazing, or other management methods, must continue until the seed bank is eliminated. Broom is slightly toxic and somewhat unpalatable to most livestock. Eldon (1994) suggests grazing before flowering when broom is more palatable and less toxic to herbivores. Goats and sheep cost less to use than mechanical and chemical control methods, they can negotiate slopes too steep to manage with machines, and they do not pose the environmental risks of herbicides.
If confined, Angora and Spanish goats will feed on broom. Since goats trample or browse virtually any vegetation within a fenced area, any desirable trees or shrubs can be protected with light-weight flexible fencing reinforced with electrified wire. Goats are most cost-effective when used to clear one- to four-year-old regrowth rather than the initial clearing of dense, mature stands. When faced with mature brush, goats defoliate twigs and strip off bark, but do not touch the plant’s main branches, which are too tough to eat (Daar 1983).
In addition to their value for weed control, sheep can also be used for income from the sale of their wool. It is possible, however, that seed re-introduction may occur from sheep droppings. Grazing by animals may also cause soil disturbances.
Chickens scratch and peck out weed seeds and potentially
reduce the seed bank in an area up to one acre. They effectively destroy
most, if not all weed seeds that pass through their digestive system. Chickens
are best used in areas that have been cleared of mature broom stands (Parker
1994; Robbins et al. 1942).
When beginning a hand removal project, flag the treated areas so they can be identified for follow-up in subsequent seasons. It is easiest to work in relatively small areas of infestation. When faced with dense and/or extensive stands of broom, it is best to divide them into grids (with flags, stakes, etc.) so that workers can thoroughly weed smaller areas before moving onto the next grid. The grid system also facilitates dividing work activities between those pulling and those removing the debris.
Cut stems close to the ground under maximum drought conditions to reduce its ability to resprout. The effectiveness of cutting depends on stem diameter, time of cut, and the age of the plant. For scotch broom, its ability to resprout declines with age. Cutting plants low during dry months (late July and August usually after flowering) can kill broom, whereas cutting prior to flowering, although effective in preventing another seed crop, may result in resprouts and little mortality. Avoid cutting shrubs during the rainy season (December to March) when resprouting is highest. When resources are limited, Read (1998) suggests concentrating efforts on larger, mature, seed-producing broom first, before spending time on younger plants (Bossard 1994; Read 1994).
Repeated burning has been used to control broom in Marin County, California. Broom stems were cut in the fall and burned in the spring when weather conditions were more favorable. The cut debris was left on the site to provide fuel for the burn. After the initial burn, sterile plants were planted to prevent broom re-establishment and to provide the necessary fuel source for subsequent burns. Even though these plants provided a small, patchy amount of fuel, the following burn killed broom seedlings and resprouts, and also stimulated native vegetation that is adapted to fire. At present it is unclear how many subsequent burns are required to deplete the long-lasting seed bank; however, Boyd has seen dramatic reductions of broom densities after 3 burns. Like many weed species, long-term treatments are necessary (Sigg 1997; Boyd 1996 and 1997).
A flame thrower or a weed burner device can be used as a spot treatment to heat-girdle the lower stems of broom. A flame thrower has a nozzle similar to a welding torch and is fueled by a portable propane tank. This technique can be used in sensitive areas or at sites with inefficient fuel loads.
In IVM programs, herbicides are considered transition tools that enable the manager to suppress weeds and replace them with desirable, competitive vegetation. Thus, it is important to select the least-toxic, low-residual herbicide that is effective against the target weed, and to apply them in a judicious manner.
The following links discuss the primary considerations when using herbicides: Use Herbicides Properly, Herbicide Information Resources, Criteria for Selecting an Herbicide, and Application Methods.
Applying herbicide when the broom is most susceptible and preferably before seeds are produced is critical for the effectiveness of the treatment. Broom is more susceptible to chemicals when young. Translocating chemicals are best applied when plants are actively growing, in full leaf, and when soils are moist (Read 1994).
Vegetation Management Personnel
and the Public
Evaluate the Vegetation Management Program
Abdallah, M.M.G., R.A. Jones, and A.S. Wl-Beltagy. 1989. An efficient method to overcome seed dormancy in Scotch broom (Cytisus scoparius). Environmental and Exp. Bot. 29(4): 499-505.
Andres, L.A. 1979. Biological control - Will it solve the problem? Fremontia 7(3): 9-11.
Archibald, G. 1996. A French broom control method. CalEPPC News 4(3): 4-6.
Archibald, G. 1996. French broom seedbank depletion: a micro-experiment on summer die-off. CalEPPC News 4(1): 10.
Bossard, C.C. 1991. The role of habitat disturbance, seed predation and ant dispersal on establishment of the exotic shrub Cytisus scoparius in California. The American Midland Naturalist 126(1): 1-13.
Bossard, C.C. 1993. Seed germination in the exotic shrub Cytisus scoparius (Scotch Broom) in California. Madrono 40(1) : 47-61.
Bossard, C.C. and M. Rejmanek. 1994. Herbivory, growth, seed production, and resprouting of an exotic invasive shrub. Biological Conservation 67: 193-200.
Boyd, D. 1997. Pers. Comm. California Department of Parks and Recreation, 1455-A East Francisco Blvd., San Rafael, CA 94901.
Boyd, D. 1996. Use of fire to control French broom. Proceedings California Exotic Pest Plant Council Symposium '95: 9-12.
Comings, A. 1994. Fighting invaders with bare hands. Fremontia 22(3): 30-31.
Daar, S. 1983. Using goats for brush control. The IPM Practitioner 5(4):4-5.
Dewey, S.A. and J.M. Torell. 1991 What is a noxious weed? In: James et al., Noxious Range Weeds. Westview Press, Boulder, CO.
Fay, P.K., T.D. Whitson, S.A. Dewey, and R. Sheley, eds. 1995. 1995-1996 Montana-Utah-Wyoming Weed Management Handbook. Coop. Ext. Serv., Montana State University, Bozeman, MT. 245 pp.
Fuller, T.C., and G.D. Barbe. 1985. The Bradley method of eliminating exotic plants from natural reserves. Fremontia 13(2): 24-25.
Gillespie, P. 1991. Woody weed control in the Dandenong Ranges National Park. Plant Protection Quarterly 6(3): 130-131.
Hayes, L. 1997. Personal e-mail (Nov. 21, 1997).
Hoshovsky, M. 1995. Element Stewardship Abstract.for Broom spp. The Nature Conservancy, 785 Market St. 3rd floor, San Francisco, CA.
Jacobs, J.S., R.L. Sheley, and B.D. Maxwell. 1997. Yellow starthistle population dynamics model. Colorado Weed Management Association 1997 Annual Conference Proc. Granby, CO 80446-1910.
Johnson, D.R., K.L. Wyse and K.J. Jones. 1996. Controlling weeds with phytopathogenic bacteria. Weed Technology 10:621-624.
Lacey, C.A., et al. 1988. Bounty programs—an effective weed management tool. Weed Technology 2:196-197.
Maxwell, B. " YST software." Personal e-mail (9 Feb 1998).
McClintock, E. 1979. The weedy brooms-where did they come from? Fremontia 6(4): 15-17.
Montllor, C.B., et al. 1995. Regional defferences in the distribution of the pyralid moth Uresiphita reversalis (Guenee) on french broom, an introduced weed. Pan-Pacific Entomologist 71(2): 92-104.
Mountjoy, J.H. 1979. Broom-A threat to native plants. Fremontia 6(4): 10-15.
Ness, T, 1989. New invention uproots woody plants. Restoration & Management Notes 7(2) : 77-78.
Norris, R.F. 1985. Why control weeds? Fremontia 13(2): 10-12.
Pearson, W. 1998. Pers. Comm. County Weed Extension Agent. Stillwater County, Columbus, Montana.
Pemberton, R.W. 1985. Naturalized weeds and the prospects for their biological control in California. Fremontia 13(2): 3-9.
Petterle, S. 1990. As assessment of broom control methods. Marin Open Space Dis. Landscape Architecture. and Water Man. 13 pp.
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Robbins, W.W., A.S. Crafts, and R.N. Raynor. 1942. Weed Control: A Textbook and Manual. McGraw-Hill Book Co. Inc. New York, NY.
Smith, J.M.B. 1994. The changing ecological impact of broom (Cytisus scoparius) at Barrington Tops, New South Wales. Plant Protection Quarterly 9(1): 6-11.
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Syrett, P. and H.M. Harman. 1995. Leucopter spartifoliella Hubner as a biological control agent for broom in New Zealand. Plant Protection Quarterly 10(2): 75-78.
University of Northern Iowa. 1993. Integrated Roadside Vegetation Management Technical Manual. Produced by the Roadside Management Program. To obtain, call Kirk Henderson at 319-273-2813.
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