Noxious Weed IVM Guide Contents
Broom, Canada Thistle, Gorse, Knapweeds, Leafy Spurge, Purple Loosestrife,
Purple Starthistle, Smooth Cordgrass, Tansy Ragwort, Yellow Starthistle
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IVM Technical Bulletin

This technical bulletin has been prepared as a resource for vegetation managers seeking practical information on effective, environmentally sound methods for managing noxious weeds (see Appendix 1). This bulletin provides information on how to set up an integrated vegetation management program.

Because no single tactic can solve a current weed problem or prevent future infestations, managers are encouraged to combine several treatment methods into an integrated weed management program tailored to the site and resources available. In addition, a noxious weed management program will benefit from communication and cooperation among the many individuals and agencies involved in management of the problem.

Integrated Vegetation Management

The management method for noxious weeds described in this bulletin is known as Integrated Vegetation Management (IVM). This approach is defined as follows:

Integrated Vegetation Management is a decision-making and management process (See IVM Flowchart below) that uses knowledge from a broad base of expertise, a combination of treatment methods, and a monitoring and evaluation system to achieve vegetation management goals. The objective of the IVM process is to achieve effective, long-term weed prevention and management compatible with both the legal mandate to control noxious weeds and the needs of humans, animals, plants, and environmental resources at and beyond the treatment site.

IVM programs contain the following principle components:

The IVM process considers factors from the entire system in which the noxious weed problem is occurring in order to find practical, effective solutions. The goal is to keep noxious weed populations low enough to prevent unacceptable spread, damage, or annoyance, and to encourage desirable vegetation to permanently replace the weeds.

Treatment occurs only when monitoring indicates thresholds have been reached and treatment is necessary. Several methods are selected from educational, biological, cultural, manual, mechanical, and least-toxic chemical control tactics, and then integrated into a treatment program. IVM emphasizes revegetation with desirable plant species as well as other actions that will prevent future weed infestations.

Successful implementation of IVM programs require:

When applied appropriately, the IVM process results in improved management, lower cost, greater ease of maintenance, and lower environmental impacts from control activities.

Gathering Background Information

It is important to know as much as possible about the weed you are trying to manage. The discussion below will help you gather some of the most important information on the biology and habits of this plant, but other useful information can only be gathered on site and will be specific to your own problem situation.

Gather information that will help you and others identify the target weed. Include its common name, its scientific name, and if possible, a picture. Is the plant an annual or perennial? What is its growth form and habits? How tall does it grow? When does it flower and set seed? What do young plants look like? Is the weed easily confused with any other local plants? If so, find the distinguishing characteristics of the target weed.

The damage caused to native plant communities by noxious weeds is extensive. Not only do weeds directly compete with native species for space, light, moisture, and nutrients, but some invasive weeds also have the ability to physically alter the structure or the nutrient cycling of a system, disrupting natural ecosystem function to which native communities are adapted.

Spotted knapweed (Centaurea maculosa) uses water from different soil zones and during different seasons than do native plants. As a result, spotted knapweed invasion in eastern Oregon can convert pine communities to a desert-type community without trees. In these areas, a small difference in moisture can have a marked effect on forest succession (Isaacson 1996).

Wetland weeds such as purple loosestrife (Lythrum salicaria) and smooth cordgrass (Spartina alterniflora) grow in dense infestations that displace native plant communities. These invasive plants can choke waterways and alter the hydrology and function of infested areas. They also have a large impact on wildlife. Smooth cordgrass invades open mudflats and decreases foraging areas used by shorebirds. Dense infestations of purple loosestrife grow on the shores of lakes, streams, and ponds and can hinder wildlife access to water.

Invasive noxious weeds with the ability to fix their own nitrogen, such as the candleberry myrtle (Myrica faya) in Hawaii, can alter the nutrient cycling of a system.

Some weeds that invade and become established in agricultural lands decrease forage value. Cattle avoid many weed species because they are unpalatable due to their sharp spines or tough, fibrous leaves and stems. For example, yellow starthistle, Centaurea solstitialis, has sharp spines that deter animal grazing. Tansy ragwort, Senecio jacobaea, is toxic to cattle, deer, pigs, horses, and goats and if consumed in large amounts, can lead to death. In addition, dense infestations of noxious weeds such as knapweeds have decreased appraised land values in Oregon.

It is important to understand the damage caused by the target weed and whether it is threatening agricultural, natural, or cultural resources.

Research the geographical origin of the target weed. This information can often help in managing the weed. What is its general and local distribution? What specific sites are more vulnerable to infestation?

Life Cycle
Understanding the plant's life cycle and lifespan will help determine proper treatment methods. Perennial weeds store nutrients underground and can access these reserves to resprout repeatedly. How does the weed reproduce? If the weed spreads by seeds, note the flowering time since control measures will usually occur before the flowers produce seeds to prevent another seedcrop.

How many seeds are produced? What is the mechanism(s) of seed dispersal and how can it be reduced? How are seeds spread or transported? How long do seeds remain viable in the soil? When do seeds germinate?

Special Challenges to Management
Note any special plant characteristics that may cause difficulties in your management program so that you may plan accordingly.

For example, does the weed have seeds that remain viable in the soil for many years, or can one small fragment regenerate an entire plant? Is the target weed found in sensitive areas where treatment methods are limited? Is the weed resistant to certain control methods?

Site-Specific Questions
Some questions, such as those below, can only be answered on site.

Setting Management Objectives

When setting management objectives, the weed manager will need to balance the resources available with the requirements of the law. Answering the following questions will help you to clarify your objectives:

Levels of Control
Containment - keeping an established population of the weed in check so that the area infested by the weed does not increase. This strategy can be employed against newly-invading weeds or well-established species. It is especially useful when time and money are in short supply or when the infestation is very large.

Reduction - reducing the area covered by a weed, or reducing the dominance of that weed. 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) exemplifies a combination of 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.

Whatever strategy or strategies you choose, the next step is to set up a monitoring program.

Establishing a Monitoring Program

In IVM, monitoring is the repeated inspection of areas that may be subject to noxious weed problems. Written records will allow you to compare inspections over time to reveal how conditions are changing, especially whether noxious weed populations are increasing or decreasing.

Starting a Monitoring Program
Locate and record the undesirable vegetation 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 the Bibliography). Remote sensing has played an increasingly important role in identifying large-scale weed infestations.

Remote sensing provides information on the location, quantity and condition of land cover, which can be compared over time. The success of remote sensing as a monitoring tool largely depends on the instrument, the topography, size of infestation, timing, and the ability to distinguish target plants from the landscape. Proper timing is a critical factor in distinguishing the target weed from the surrounding vegetation. 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 (Lachowski 1998).

Prioritize the sites you will work on. Make a realistic assessment of your weed management resources, always keeping in mind that you must include 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 on incompletely controlling the weed at many sites. If the weed is very widespread, try to determine where it poses an economic, social, or environmental problem and concentrate on those areas.

Schedule monitoring efforts to coincide with critical life stages of the weed or its biological controls. If possible, plan monitoring sessions alongside other scheduled activities in the area to save time and labor. After treatment activities and at the end of the season, schedule monitoring sessions to help you evaluate your program.

Focusing Monitoring Efforts
It is not practical to monitor every area that may have a weed infestation. Monitoring activities must be focused on sites where problems are most likely to occur. Encourage public sightings of new weed infestations through an education or incentive program (see Educating Vegetation Management Personnel and the Public).

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, 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.

Setting Treatment Action Levels

Sufficient resources to follow the letter of the law are seldom available. Weed management is a process that continues over many years, and weed managers are continually prioritizing treatment areas and balancing the priorities with their resources. This process is called "setting treatment action levels." When the weed population reaches a level you can no longer tolerate, you take action to treat it. In some cases this level may be just a few weeds, and in other cases the number of weeds you can tolerate may be much greater.

Two situations that increase the priority of a site are 1.) the discovery of a small "outlier" population, a recent invasion from another area that must be taken care of soon in order to prevent a bigger problem later, or 2.) the discovery that the weed population has become a threat to agriculture, native plants, food sources for wildlife, highway safety, water resources, etc. Inevitably there are areas that are lower in priority and will be tolerated for the short-term. Complete eradication may not be practical unless the patches are very small. Moreover, to maintain populations of natural enemies, some individual plants must be permitted to persist.

Setting Treatment Thresholds

Setting treatment thresholds includes prioritizing and balancing treatments with resources. Weeds will be 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 number of weeds you can tolerate 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 weed population changing? Is it in an area where soils are frequently disturbed? Does it threaten agriculture, 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 modern herbicides, prevention as a weed management technique has been neglected; however, it is a practical, cost-effective, and extremely important part of noxious weed control. The following is a list of things you can do to prevent noxious weed establishment in general:

Most weeds are opportunistic and become established following a disturbance or opening in the canopy. Thus, it is very important to cover the soil with dense, vigorous vegetation to prevent the establishment of noxious weeds. Since weed treatments often disturb the soil, open the canopy,or leave bare soil, revegetation after treatments is crucial in suppressing weed seedlings and preventing weed infestations from re-occurring. In some situations you may be able to encourage desirable vegetation that is already in place, but because of the aggressive nature of most noxious weeds, it is more likely that you will need to thickly sow seeds of desirable, competitive plants.

Applying Management Methods

Although there is disagreement on the specifics of how weeds can best be managed, authorities agree that integrating a number of tactics into a management program will be far more effective than using a single tactic alone. No individual method will control noxious weeds in a single treatment; diligence and persistence will be required over a number of years to subdue a weed. The success of different treatment methods depends on the type of weed you are trying to control. It is important to think of these treatment methods as they relate to specific weed characteristics. The descriptions of the tactics below will help you to design an integrated program that will suit the circumstances of your particular situation. As with all methods, include follow-up monitoring, treatments, and revegetation to prevent new infestations and the resurgence of the target weed.

Biological Controls
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 cause damage. Once established, biological controls provide an inexpensive, long-term, and non-toxic means to control weed populations.

It is important to match the insect or pathogen to the weed management site. Biocontrol agents are living organisms that have specific requirements for growing and thriving. Understanding the life cycle, habitat requirements, and mode of attack will help you find a hospitable release site and allow you to integrate the biocontrols into your other control efforts. When you release biocontrols, continue using other control methods, but avoid using them in the areas where you have released the natural enemies.

Information on biocontrols for various weeds can be found in Biological Control of Weeds in the West (see Bibliography) or you can contact commercial weed biocontrol insectaries (see Insectaries).

Grazing is a biological alternative to mowing. Continual grazing of the tops of young plants can retard plant development and seed formation and can gradually deplete root reserves. Since animals might prefer to eat nearby grasses in lieu of the target weed, enclose them in a fenced-off, weedy area.

Goats and sheep are economical and they do not pose the environmental dangers of applying chemicals. In addition to their value for weed control, sheep can be used for income from the sale of their wool. If confined, Angora and Spanish goats will trample or browse virtually any vegetation within a fenced area. Desirable trees or shrubs can be protected with light-weight flexible fencing reinforced with electrified wire (Olkowski and Olkowski 1992; Daar 1983).

Sedivec (1995) defines four classes of grazing management plans that can be used for weeds in general:

Physical Controls

Manual Removal
Pulling weeds by hand is practical and efficient on small, isolated patches of weeds. Hand pulling is most effective on annuals and biennials that do not resprout from root fragments. Since perennial weeds can resprout from extensive root systems, hand pulling is not practical.

Pull plants when soils are moist and before seeds are produced to prevent additional spread of the weed. Try to remove the entire root system since many weeds can resprout from remaining root fragments. The success of hand pulling often depends on the thoroughness of the worker. Try to keep soil disturbance to a minimum so that other weeds are not invited onto your site.

Mechanical Removal
Mechanical removal employs tools to combat weed infestations. Weeding tools such as weed knives, weed poppers, briar hooks, pulaskis, and mattocks have hooks and prongs to help dig out the plant. The Weed Wrench is a hand-operated tool that was specifically designed to pull shrubs. The tool acts like a lever to pull the entire plant out, including roots, so that resprouting does not occur. Moist soils facilitate pulling. In very moist soils, place a board underneath the corner of the lever arm to prevent the Weed Wrench from sinking into the soil. These hand-carried tools are used for small infestations or plants that are scattered within desirable vegetation.

Controlled Burns
Controlled burns often stimulate natural vegetation in areas adapted to fire. In other areas, fires can cause disturbance and create establishment sites for new weed infestations. The fire intensity, continuity, and duration are factors to consider in the success of a treatment. Revegetation after a fire is important in reducing bare ground and preventing the establishment of other weeds.

Flaming involves hand-held or tractor-mounted torches that heat plant cells and cause them to burst. Treated plants wilt and eventually die. Hand-held flamers are useful in spot treatments near drainage canals, roadsides, or for isolated patches of weeds.

Covering plants deprives them of the sunlight needed for growth and hastens plant decomposition by contact with soil microbes. Materials used to cover plants should block all light. Common materials include thick black plastic, black geotextile fabric, and mulches. Black plastic can be found in many hardware stores and black geotextile mats are often used under highways, as landfill lining, and in landscaping projects.

Before covering, cut, burn, or mow the weed close to the ground to reduce biomass and to put stress on the plants. Treatment sites require regular monitoring to detect and repair torn fabric.

Although covering can be very useful, it has several drawbacks. Unless the material is biodegradable, the cover must be removed after the treatment. In addition, the amount of time needed to kill weeds varies and will need to be experimentally determined.

Cultural Controls
Cultural controls include land management and farming practices that inhibit weed growth and prevent conditions that lead to weed establishment. For instance, planting and maintenance activities can be modified to reduce weed infestations. Attention to suitable seedbed preparation and proper fertilization can help prevent colonization by weeds. Planting in narrow rows reduces bare ground and increases the shaded area between rows, further decreasing potential weed habitat.

Chemical Controls
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 it in a judicious manner.

Use Herbicides Properly
Use herbicides in accordance with their EPA-approved label directions. Protective gear should always be worn when applying herbicides, and applicators should be certified to apply pesticides. Maintain labels and Material Safety Data Sheets (MSDS) of the pesticide products on file. Check the label to make sure that the product you choose is registered for the site you are treating. Consult the Cooperative Extension Service, State Agricultural Experiment Stations, or County Agriculture Commissioner for specific herbicide recommendations and information on their use in particular localities.

Herbicide Information Resources
Information on herbicides can be found in the Herbicide Handbook, Federally Registered Pesticides, Farm Chemicals Handbook, Montana-Utah-Wyoming Weed Management Handbook, The Pacific Northwest Weed Control Handbook, and The Pesticide Manual (see Pesticide Information Resources). These publications list specific information on the chemical and physical properties of active ingredients as well as recommendations and precautions for use.

Criteria for Selecting an Herbicide
When choosing an herbicide, it is essential to avoid or minimize negative impacts on non-target organisms, including the capability of the soil to support desirable vegetation. Remember, the site (croplands, rangelands, rights-of-way, etc.) you plan to treat must be listed on the label. The following questions are useful when making a site-specific decision about which herbicide to use.

Is the herbicide:

  • effective against the target species?
  • least-toxic to humans and other non-target organisms such as desirable vegetation, animals, and beneficial insects?
  • one that requires a surfactant? If so, is the surfactant safe to use in areas with sensitive organisms such as salamanders and other amphibians?
  •  least-likely to leach into ground or surface water?
  • compatible with vegetation and revegetation programs?
  • compatible with other management methods?
  •  low in volatility so drift is minimized?
  • quickly degraded in the soil?
  • cost effective?
  • Proper Timing
    The best time to apply herbicides is when the weed is most susceptible, and preferrably before seeds are produced. Proper timing will depend on the herbicide, ceratin weed characteristics, and other physical factors such as soil moisture and site characteristics. Knowledge of the herbicide’s mode of action and how it affects the target weed is valuable information. For example, many herbicides interrupt a stage in photosynthesis and are best applied when the weed is actively growing; while other herbicides kill upon contact and the growth stage of the weed is not as important.

    Most summer or winter annuals, biennials, or newly-germinated perennial weeds can be successfully treated in the seedling or rosette stage prior to bolting. The rosette stage is often preferred because it is easier to distinguish weeds from desirable plants when they are rosettes rather than seedlings. Also, the rosette stage may last for several months, thus providing a wider treatment period.

    Established perennial plants, particularly woody species, are more difficult to control with herbicides, and timing according to the stage of growth is critical. In general, the best time to apply translocating herbicides to an established perennial plant is toward the end of the growing season. At this time, food reserves in the roots have been used up, thus reducing the plant’s ability to resprout. It is also the time when the plant shuttles nutrients from photosynthesis down to roots and stems for winter. Woody species treated at other growth stages when nutrient reserves are high, can often recover and resprout.

    Application Methods
    In IVM programs, spot-treatment rather than broadcast application over wide areas is the preferred herbicide application method. Spot-treatment consists of various techniques for applying herbicides to target weeds without impacting desirable vegetation or other non-target organisms. Spot-treatment can reduce herbicide use, lower costs, lower risks to non-target organisms including humans, and reduce drift. Broadcast herbicide applications are recommended only when necessary (e.g., where weed infestations are very dense and extensive, or when plant fuel must be dry prior to controlled burns). In a weed containment program, herbicides can be useful as a "border" spray to prevent infestations from moving into non-infested areas.

    Educate Vegetation Management Personnel
    and the Public

    Evaluate the Vegetation Management Program


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    Dewey, S.A. and J.M. Torell. 1991 What is a noxious weed? In: James et al., Noxious Range Weeds. Westview Press, Boulder, CO.

    Doll, J.D. 1988. Controlling Weeds in Sustainable Agriculture. University of Wisconsin-Cooperative Extension Publication. pp. 1-13.

    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 Univ., Bozeman, MT. 245 pp.

    Fuller, TC., and GD. Barbe. 1985. The Bradley method of eliminating exotic plants from natural reserves. Fremontia 13(2):24-25.

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    Jacobs, J.S., R.L. Sheley, and B.D. Maxwell. 1997. Yellow starthistle population dynamics model. Colorado Weed Management Association 1997 Annual Conference Proceedings. Granby, CO.

    Lachowski, H. 1998. What is the role of remote sensing in locating noxious weed infestations? Abstract from Science in Wildland Weed Management Symposium. Denver, CO.

    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).

    Olkowski H. and B Olkowski. 1992. Using animals for weed management. Common Sense Pest Control 8(2): 5-13.

    Pearson, W. 1998. Pers. Comm. County Weed Extension Agent. Stillwater County, Columbus, MO.

    Randall, J.M. and J. Marinelli eds. 1996. Invasive Plants: Weeds of the Global Garden. Brooklyn Bot. Garden , Inc. Brooklyn, NY. 108pp.

    Rees, N.E., et al., eds. 1996. Biological Control of Weeds in the West. Western Society of Weed Science, USDA/ARS, Montana Dept. Agric., Montana State University, Bozeman, MT.

    Sedivec, K., T. Hanson, and C. Heiser. 1995. Controlling leafy spurge using goats and sheep. North Dakota State Univ. Ext. Circ. R-1093.

    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.

    Further Information

    Credits and Citations from original printed version of this document:

    Project Director:  Sheila Daar
    Project Manager:  Tanya Drlik
    Contibutors:  Isa Woo, Tanya Drlik, Laurie Swiadon, Sheila Daar, Shawn King
    Acknowledgements:  Steve Abbors, David Amme, Dave Boyd, Eric Coombs, John Farmer, Dennis Isaacson, Richard Kincaid, Rod Lym, Hugh McEachen, Barbara Mullen, Mike Pitcairn, Ray Read, Norman Rees, Roy Renkin, Roger Sheley, Debra Smith, Tom Whitson, and one anonymous reviewer.

    This is one of a series of vegetation management bulletins available from the Bio-Integral Resource Center, PO Box 7414, Berkely, CA. 510-524-2567 (ph); 510-524-1758 (fax); (email).  Others in the series are broom, Canada thistle, gorse, knapweeds, leafy spurge, purple loosestrife, purple starthistle, smooth cordgrass, tansy ragwort, and yellow starthistle.

    This project was supported by a grant from the U.S. Environmental Protection Agency, and the members of the non-profit Bio-Integral Resource Center.

    Document Citation
    Drlik, T., I. Woo, and S. Swiadon, Editors. 1998. Integrated vegetation management guide. Bio-Integral Resource Center, Berkeley, CA. 16pp.

    Internet Publisher: IPM Access, an online service for integrated pest management information from the IPM Practitioners Association.  These bulletins have been published on the Internet at IPM ACCESS through a separate EPA grant as a result of the EPA's interest in this type of information being made freely available to a wider audience.  The text is identical to the originally published documents.

    Last modified:  September 27, 2000

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