About Weeds and Invasive Species

The term "weed" means different things to different people.  In the broadest sense, it is any plant growing where it is not wanted. Weeds can be native or non-native, invasive or non invasive, and noxious or not noxious. Legally, a noxious weed is any plant designated by a Federal, State or county government as injurious to public health, agriculture, recreation, wildlife or property. (Sheley, Petroff, and Borman,1999) A noxious weed is also commonly defined as a plant that grows out of place and is "competitive, persistent, and pernicious." (James, et al, 1991).

Frequently Asked Questions

Are invasive plants the same as noxious weeds?

Not necessarily, although many noxious weeds are invasive. Invasive plants include not only noxious weeds, but also other plants that are not native to this country or to the area where they are growing. The BLM considers plants invasive if they have been introduced into an environment where they did not evolve. As a result, they usually have no natural enemies to limit their reproduction and spread (Westbrooks, 1998).  Some invasive plants can produce significant changes to vegetation, composition, structure, or ecosystem function. (Cronk and Fuller, 1995).

How are noxious weeds different from regular weeds?

For the most part, no. These plants have existed for centuries in their host country, but their populations have been kept to manageable levels naturally by other plant competition, insects, pathogens and a host of other predators. When plant populations in these countries of origin increase, insects and other predators increase accordingly to help keep them in check.

How did these weeds get here and where did they come from?

Most of these weeds came from Eurasia and were transported to the United States both accidentally and intentionally. Accidental transport occurred in the ballast of ships, in the fleece and hair of livestock, in clothing, and as contaminants in seed lots. Other weeds came in as medicine, dyes, and ornamental plants.

How are these weeds spread?

Weeds are spread in any number of different ways: by human activity, birds, animals, wind, water, vehicles, and seed and plant parts, to name just a few. 

If a plant is noxious or invasive, does that mean I can remove or replace it?

You can remove any weed if it does not meet your landscape or land management objectives. The local land management plan, Environmental Protection Agency or State regulations will determine the appropriate tools and methods for removal.

What are the health hazards of some of these weeds?

Health hazards to the public include the following examples:

• Leafy spurge can cause blindness and skin irritation or blisters.
• Poison hemlock is extremely poisonous if eaten and may cause death in a short period of time
• Water hemlock, especially the root, is extremely poisonous if eaten, causing death in a short period of time
• Jimsonweed and black henbane have hallucinogenic properties and can cause death.
• Many weeds cause allergic reactions in susceptible humans

In addition, weeds can present other public health hazards. For example, dense weed growth along public rights-of-way can obstruct vision leading to vehicle collisions.

How can I manage noxious or invasive weeds?

There are several opportunities and strategies that are effective in the control and management of noxious or invasive weeds, including:

• Education and Awareness - making others aware of the problem and how they can help will greatly increase your chance for success;
• Prevention and Detection - by taking certain precautions we can prevent weeds from encroaching and occupying lands that are currently weed-free;
• Inventory - before you treat weeds, you must know where they are and the extent of the infestation;
• Planning - knowing whom to work with, how to treat the area, and how to manage the land after it is treated is vital to the success of your project;
• Treatment - knowing which tools to use for each weed in a specific situation is imperative to the success of your project;
• Coordination - two or more landowners or land managers working together may help reduce costs and achieve a higher degree of success; and
• Monitoring, Research, and Evaluation - keeping track of what works and what doesn’t will prevent you from repeating mistakes in the future and may help others in their efforts.

Once I know where these weeds are, how can I treat them?

There are four treatment methods that can be used to control, and in some cases, eradicate weeds.

1. Physical (hand-pulling, cutting, mowing, digging, disking, plowing, burning, etc)
2. Biological (use of insects, domestic animals, pathogens, etc)
3. Chemical (use of herbicides)
4. Cultural (development of weed prevention programs, weed free forage, weed free gravel, vehicle washing, etc).

Often, you may obtain best results by using several of these control methods together. For example, burn and reseed in the first year, spot treat remaining plants with herbicides in the second year, change to fall grazing and restrict vehicle use in the area. You may obtain advice on control methods, as well as specific, local concerns from local land managers, extension specialists, and weed control specialists. After performing weed control, you may find it necessary to perform site restoration.

Where can I get insects for noxious or invasive weeds?

There are several companies that specialize in biological control agents. You can find their addresses and phone numbers via the Internet. Local land managers and weed specialists may also know where to get insects that are established locally.

If I have a small patch of a noxious or invasive weeds on my property, what is the best way to control it?

There is no one particular control method that will work on all weeds. Therefore, it is important to speak with your local weed control specialist or county agent to find out what approach is best to deal with your specific weed problem. Several states have published weed control handbooks that are excellent sources of information.

Does the BLM use herbicides to eradicate weeds?

Yes. Currently all Western BLM land managers (except Oregon) are managing weeds under the guidelines of the Final Environmental Impact Statement for Vegetation Management on BLM Lands in Thirteen Western States (1991). Oregon is managing weeds under the guidelines of the Final Northwest Area Noxious Weed Control Program EIS (1985) and the Finale Supplemental EIS for Noxious Weeds (1987). These documents provide for integrated pest management, which includes the use of herbicides, on lands managed by the BLM.

What should I do if I find a noxious or invasive weed?

Always make sure you record and mark the location, species (if known) and the approximate size of the population. You should then give this information to the nearest land management agency or extension service.

If you are sure of the identity of a noxious or invasive weed and know whether it is an annual or biennial, you may decide to pull a small patch. Remove the mature plants (below the root crown) then bag and remove it for proper disposal, which will destroy any viable weed seeds. You may remove immature plants without buds or flowers in the same manner, but leave them out to dry on site. Generally, perennial weeds do not respond well to this treatment, but removal of top growth may stop seed dispersal for that season or until full treatment. Even if you pull the entire weed population, always record site information and provide it to the responsible land management agency.

If you are unsure of what the plant is and decide to take a sample in for identification, take care in the collection process. Some plants are poisonous. If you are unsure of the identity, you should assume that it is. Wear gloves and don't let the plant touch bare skin or to get near the eyes. To aid in identification, collect the entire plant, including the root and flowers or buds. Place the plant in a plastic bag, and keep in a cool, dark place while transporting to be identified. You should keep your hands away from your eyes and mouth until they can be washed thoroughly with soap and water. You should also wash any tools used for collection.

Where can I get more information on weeds, specifically which species are considered noxious weeds for each state?

The Invaders Data Base http://invader.dbs.umt.edu developed by Peter Rice, University of Montana, Division of Biological Sciences, is a distribution database for exotic plant species and weed natives in all Northwestern states. It provides a list of all known noxious weeds in the northwest states and links to web sites that list noxious weeds for all other States and Canada. Also, each State department of Agriculture maintains a list of noxious weeds. In many cases, this information is available through the agricultural extension service.

Where have there been success in noxious or invasive weed control?

There are a number of success stories. Read about them on the BLM Blog using "Weeds and Invasives" for a Topic.

What chemicals may be used on noxious weeds?

Consult with your local BLM office for information on approved chemicals and application methods for use on BLM lands. In addition, your local weed specialist or extension office are excellent sources of herbicide information.

What non-chemical treatments work well on noxious weeds?

You may contact the weed or agriculture extension specialist in your area for information on integrated weed management treatments.

Is eradication possible for all species?

Weeds have overrun so much land that it is physically and financially impossible to eradicate them all. With adequate funding, however, control is possible.

What biological control agents are approved for use in the US?

The Western Society for Weed Science has published an excellent book, "Biological Control of Weeds in the West," which provides information on approved biological control agents, target species, availability, etc. You may also obtain additional information from State Departments of Agriculture.