Frequently Asked Questions

1.   What is a noxious weed?

3.   What are some of the challenges to managing Idaho’s noxious weeds?

4.   Whom should I contact if I see a noxious weed or unknown weed on my property?

5.  Where can I get a copy of the Idaho's Noxious Weeds booklet?

6.   What is a Cooperative Weed Management Area?

7.   What is the difference between a pesticide and a herbicide?

8.   What is biological control?

9.   How can I get involved in noxious weed control?

10.   Reducing the spread of noxious weeds.

11.   Collecting plants for identification and verification.

12. How to press a plant.

1.  What is a noxious weed?

A weed is designated noxious when it is considered by a governmental agency to be injurious to public health, agriculture, recreation, wildlife, or property. In Idaho, noxious weed regulations are covered by Title 22, Chapter 24, Idaho Code, Noxious Weeds Law. Some general characteristics of noxious weeds are their ability to spread rapidly, reproduce in high numbers, and crowd out native plants. Noxious weeds also tend to be very difficult to control.

Noxious weeds can be annuals (completing their life cycle in one growing season) or perennials (having a life cycle spanning more than one growing season). Most noxious weeds were originally from other countries. Many arrived in shipments of desirable seeds, in the ballast of sailing ships, or were introduced intentionally as garden plants. Noxious weeds thrive in disturbed areas like roadsides, building sites, maintenance areas, irrigation ditches, dirt parking areas, trails, and campgrounds. Once noxious weeds gain a foothold, they can increase water and wind erosion, alter nutrient cycling, destroy wildlife habitat, reduce the usefulness of recreation areas, and decrease agricultural productivity.

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2.  Why should I care about noxious weeds?

Noxious weeds can have a direct impact on land value. Lands infested with noxious weeds often have restricted uses. For example, pasture infested with yellow starthistle cannot be used for horses. If you own land infested by noxious weeds, you are responsible for controlling the weeds on your property. The larger the infestation, the higher the cost to you for yearly treatments, and the longer it will take to eradicate the infestation. Also, the estimated annual loss of productivity caused by noxious weeds in 64 crops grown in the U.S. is $7.4 billion. This loss in productivity affects the cost of food you purchase in the grocery store. Noxious weeds are estimated to have a direct cost to all Idaho lands of $300 million annually. This cost is often passed on to you, the taxpayer. Noxious weeds are also responsible for depredating Idaho’s wild lands. Lands infested with noxious weeds have higher erosion potentials, lower habitat values for native animal species, crowd out native plant species, and impact recreational opportunities by infesting campsites.

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3.  What are some of the challenges to managing Idaho’s noxious weeds?

There are many challenges to managing noxious weeds. Noxious weeds are by definition difficult to control. They are often resistant to mechanical and cultural practices and existing herbicides. There are several other barriers to effective weed control. There is often a lack of public awareness of the extent and seriousness of the weed problem, which leads to limited public and legislative support and involvement in combating weeds. This limited support leads to a lack of effective partnerships for pooling resources and insufficient human and fiscal resources. With insufficient resources, weed control efforts are often spotty and lack planning and monitoring for effectiveness.

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4.  Whom should I contact if I see a noxious weed or unknown weed on my property?

Contact your county weed superintendent.  A list can be found at County Weed Control Superintendents.

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5.  Where can I get a copy of the Idaho's Noxious Weeds booklet?

Tfhe Idaho Weed Awareness Campaign will provide a copy free of charge. You may order online or by contacting Roger Batt, coordinator at (208) 888-0988. Quantities may also be purchased from the University of Idaho Extension Office.

6.  What is a Cooperative Weed Management Area?

A Cooperative Weed Management Area (CWMA) is a distinguishable hydrologic, vegetative, or geographic zone based upon geography, weed infestations, climatic or human-use patterns. A CWMA may be composed of a portion of a county, a county, portions of several counties, or portions of more than one state pusuant to Title 22, Chapter 24, Idaho Code, Noxious Weeds Law. CWMAs are formed when the landowners of a given area come together and agree to work cooperatively to control weeds. For a CWMA to be recognized by the Idaho State Department of Agriculture, an Annual Operating Plan (AOP) and Integrated Weed Management Plan (IWMP) must be developed and submitted.

7.  What is the difference between a pesticide and an herbicide?

"Pesticide" means, but is not limited to, any substance or mixture of substances intended to prevent, destroy, repel, or mitigate any insect, rodent, nematode, snail, slug, fungus, weed, and any other form of plant or animal life or virus, except virus or fungus on or in living man or other animal, which is normally considered to be a pest or which the director may declare to be a pest, and any substance or mixture of substances intended to be used as a plant regulator, defoliant or desiccant, and any spray adjuvant pursuant to Title 22, Chapter 24, Idaho Code, Noxious Weeds Law.  An herbicide is a substance used to destroy plants, especially weeds.

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8.  What is biological control?

Biological control is the deliberate introduction or manipulation of a weed’s natural enemies with the goal of suppressing a weed’s population. A biological control agent can be an insect, a fungus, a nematode, or any other organism that retards the weed’s growth and/or reproduction. Most biological control agents are imported from the weed’s country of origin. Biological control agents never completely eradicate a weed from an area but can keep a weed population below economic impact levels. Additional information may be found at Idaho's BLM/ISDA Biological Control Program.

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9.  How can I get involved in noxious weed control?

  • Become informed. Know which plants look like noxious weeds and note any growing on your property.
  • Take steps to eliminate noxious weeds on your property. Idaho law requires landowners to control noxious weeds on their property - Title 22, Chapter 24, Idaho Code, Noxious Weeds Law. Don’t ignore noxious weeds growing around outbuildings. Dig the weeds out or arrange to have the appropriate herbicide applied.
  • Talk to your neighbors. Noxious weeds do not respect property boundaries. That weed just on the other side of the fence will soon be on your side.
  • Wash all vehicles thoroughly. Noxious weed seeds could be hiding in tire treads, in the coils of a winch, behind the license plate, or in any cracks and crevices on the underside of your vehicle. These seeds could travel hundreds of miles before being dislodged.
  • Check your irrigation systems. Noxious weeds like Purple Loosestrife, Hoary Cress, and Leafy Spurge thrive on the banks of irrigation ditches. These plants will spread through the irrigation system to other areas.
  • Livestock and other animals can spread weed seed. Livestock can transport weed seed in their fur, in dried mud on their feet, and in their digestive tracts. Weed seed can be in contaminated hay and therefore move throughout the pasture with the livestock. Also, moving livestock from a weed infested area to an uninfested area without a quarantine can transport weed seed.
  • Don’t pick the wildflowers. The wildflowers may be noxious weeds.
  • Join a Cooperative Weed Management Area. Cooperative Weed Management Areas are formed when a group of landowners come together and agree to control noxious weeds in a particular geographic area. For more information on Cooperative Weed Management Areas, please click here.

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10.  Reducing the spread of noxious weeds

Here are a few guidelines to help lessen the spread of noxious weeds in Idaho:

  • Avoid driving in noxious weed-infested areas. Seeds can become stuck in tire treads or mud on the vehicle and be carried to unaffected areas.
  • Don't transport flowering plants that you cannot identify.
  • If you find a small number of isolated noxious weeds that have no flowers or seeds, pull the weeds and leave them where you found them to dry out, or place them in a plastic bag and dispose of the bag when you reach an appropriate trash receptacle.
  • If you find noxious weeds and they have flowers or seeds, pull them and place them in a plastic bag or container to avoid spreading seeds, and either burn them or dispose of them in a sanitary landfill.
  • Report newly found noxious weeds to the county weed superintendent or county extension office.

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11.  Collecting plants for identification and verification

If you are not certain if a plant is a weed or would like to verify that a plant is on the noxious weed list, please do the following:

  • Select a plant typical of the population or collect several specimens showing the range of variation.
  • Select a plant in flower or in fruit if possible. The flower and fruit of the plant is often required to identify a plant species.
  • Collect all the plant when possible, including roots, leaves, flowers, and/or fruits. If it is a large plant, bend or fold it.
  • If it is a tree or shrub, collect branches with adequate leaves, as well as the flower and/or fruit and the root.
  • Press the plant. (How to press a plant.)

On the edge of the newspaper where the plant is pressed, please note:

  • Your name.
  • The date you collected the plant.
  • The location you found the plant. The more specific, the better, but at minimum the nearest town, the county, and state you collected the plant from.
  • The habitat or local conditions under which the plant grows.

It would also be to your advantage to keep a notebook with the above information. Once you have the information, hand deliver to:

Your county extension agent.

OR: You may mail the weed and information to:

Idaho State Department of Agriculture
Attention: Noxious Weeds
P.O. Box 790
2270 Old Penitentiary Road
Boise, Idaho 83701

University of Idaho Erickson Weed Diagnostic Laboratory
Department of Plant, Soils, and Entomological Sciences
College of Agriculture
University of Idaho
Moscow, Idaho 83844

When sending your plant and note, please place in a reinforced package and do not bend after pressing. Remember, the pressed plant is very fragile.

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12.  How to press a plant

Pressing plants is an inexpensive and effective method for preserving plants for later identification. The primary instrument used to press plants is a plant press. A plant press is traditionally constructed of two metal or wood grid frames approximately 12 X 18 inches. Inside each of the frames is a series of corrugated cardboard ventilators and paper blotters. The cardboard is approximately 1/8 inch thick. Paper blotters can be purchased from botanical supply houses, or folded newspaper can be used. The cardboard ventilators allow for airflow through the press, and the blotters hasten drying by removing moisture from the plant. The press is closed and pressurized by two belts around the outside. If you do not have a plant press, a good, heavy hardcover book will often suffice.

Place the plant in a half sheet of black ink newspaper. Do not use colored newsprint or it will color the specimen. Write your name, the date, and the location where the plant was found on the edge of the newspaper. (Please do not write on the print. It will be hard to read your notations.) Arrange the plant on a quarter sheet of newspaper so that the flowers are open, and the fruits and leaves are well displayed. All parts of the plant should be on the quarter sheet. Fold the other portion of the newspaper on top of your plant. Place the newspaper with the plant between two blotter sheets. Place the blotters with the plant between two cardboard ventilators. Finally, place the plant with the blotters and the ventilators between the frames and strap the press together. You can put several plant specimens into your press at one time. The press should be organized by ventilator – blotter – plant – blotter – ventilator- blotter – plant – blotter- ventilator – etc. Place your press in a warm, dry area with good airflow. The back window of your car often works. You may need to replace the blotters occasionally to facilitate drying.

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Be careful handling the plants when they are pressed. They are very fragile.


  • How to Identify Plants, H.D. Harrington and L.W. Durrell, Swallow Press. (1957).
  • Contemporary Plant Systematics, D.W. Woodland, Prentice-Hall, Inc. (1991).