This Oriental poppy in the Palouse
prairie remnant is a weed
because it is out of place
and a prolific re-seeder.
The seed was probably
brought in by a bird or a hiker.
It may not be a weed in
a different landscape

Simply put, a weed is any plant that is out of place. A native plant may be considered a weed in a pasture because it is poisonous to livestock. Often it is of vigorous growth and tends to overgrow or displace more desirable plants.

In order to define the nature of undesirable plants in our prairie remnant , we focus on invasiveness and whether they are native to the area. For our purposes, weeds are invasive “exotics or non-natives” when they threaten to displace the native plants or other favorable plants. Invasive plants like to move and spread; they are opportunistic.

Noxious weeds are invasive weeds that a state or federal agency deems harmful to our public health, agriculture, recreation, wildlife, or property. 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. 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. One Inland Northwest weed specialist says “Once a weed is on the noxious weed list it too late to eradicate it”. All you can do is prevent its introduction to new areas.

Meg Booth clipping Yellow Starthistle
in neighbor’s prairie remnant

Noxious weed eradication is the focus of much labor and study. Yellow starthistle (Centaurea solstitialis), Spotted knapweed (Centaurea maculosa), and Leafy spurge (Euphorbia esula) are just a few noxious weeds in our area.

Listed noxious weeds are unlawful to import, transport, propagate or sell. Land owners are responsible for the control of listed noxious weed species. Idaho has 57 listed noxious weeds out of hundreds of invasive weeds in the state.

Noxious weed list for the Inland Northwest:





Multiflora rose and Teasel are
rapidly replacing favorable grasses

How did weeds get here?
Most of our problematic weeds were brought here from other parts of the world or North America for their medicinal, ornamental, forage, or edible qualities. For example the Russian olive was brought here in the 1800’s to be used as a windbreak. Now, Russian olive is a problem as it chokes out the native vegetation. Canary Reed grass, a native of California, was purposely planted on Inland northwest stream banks for erosion control. Many streams are now clogged with this grass. The Multiflora rose (Rosa Multiflora), a native of Japan, was cultivated as an ornamental, for erosion control, and as a living fence in the 1860s. It is invading our pastures and natural lands by displacing most vegetation. Common Teasel came over from Europe in contaminated seed in the 1700s. Other weeds came over accidentally by hitching a ride on the ballasts of ships or in nursery plant pots. Regardless of how they arrived, many exotics have been able to spread and thrive.


Prevention is the first line of defense to keep invasive weeds from occurring on our lands. Plant high quality, weed-free grass and wildflower seed in recently disturbed areas. Your first choice should be to purchase state “certified” seed so you know that it is free of noxious weeds. Also, when leaving an area that has noxious or invasive weeds, brush of your boots and pants so the weed seed stays there and is not moved to a new area. Do the same with ATVs, cars, dogs and horses.

Early detection and rapid response
Noxious weeds are difficult to control once they have a strong foothold. Early detection and rapid response are very important components of the “war on weeds”. It is essential to pay close attention and to have unknown plants identified quickly. Once a plant is identified as invasive, noxious, or undesirable, respond fast and prevent the weed from going to seed. “One year’s weed leads to seven years of seeds”. Weed seeds may remain viable for those 7 (or more) years.

Early detection and rapid response patrol. Guy, Earl, Carl and Abbie
are scouting for noxious and invasive weeds

Weed experts in local extension offices should be able to help with identification of unknown plants. Plants have different strategies for growth and this affects the method of control that will be most effective for that particular plant. For instance an annual grass will need different methods of control than a rhizomatous perennial forb (Canada thistle). Extension agents and local weed experts should be able to help determine the best method for each individual situation. Most weeds require several methods of control for several years depending on the extent of the infestation. For example, a combination of chemical (spraying) and mechanical (mowing) methods might work best in a large field while mechanical (hand-pulling) may be all that is necessary in a small home landscape.

Wildflower Mixes and Wild bird food: A potential source of weeds

Bachelor button moving into a prairie ecosystem.

One way to prevent the spread of invasive weeds is to pay attention to the seeds in many “wildflower” and bird feed mixes. In 2006, Idaho State Seed Lab found noxious weed seeds in bird feed from 24 manufacturers.

Many of wildflower mixes contain weeds like Bachelor button (Centaurea cyanus), a native to Europe but invasive on the Palouse prairie. In fact, a study done by the University of Washington found that all 19 wildflower seed packets selected for the study contained anywhere from 3 to 13 invasive species. Plants like Bachelor button are often included because of their ability to quickly germinate and produce flowers. However, when released in the wild, in fields and in pastures, this plant displaces favorable grasses, crops and native wildflowers. Bachelor button is listed as a noxious weed in Oregon and is considered invasive in the lower 48 states, Hawaii, and Canada.

Beware when purchasing commercial “Wildflower” mixes and be sure to receive full disclosure on the contents of the mixes. Purchasing wildflower seed from local sources may help prevent this problem. Make sure your bird feed is listed as “Weed-free”. Try to purchase seed for fields or landscape that are certified with the state seed certification agency to assure that the seed comes without weeds and that the genetic identity and purity is preserved.

Thorn Creek Native Seed Farm Standard: Our seed is certified, and our seed-increase plot and fields get inspected annually, through the Idaho Crop Improvement Association.

Weed- any plant that is out of place

Invasive weed- threatens to displace the native plants or favorable plants

Native plant- present in the local region prior to European American arrival

Noxious weed – Defined and designated by state law:
“Any plant having potential to cause injury to public health, crops, livestock, land, or other property and which is designated noxious by the director of the state Department of Agriculture.”

“One year’s weed leads to seven years of seeds”

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1461 Thorn Creek Road, Genesee, Idaho 83832