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Invasive Weeds

Invasive weeds are not just non-native or undesirable weeds. They take over at the expense of the existing environment, reducing forage for livestock and wildlife.

Valley County residents must monitor and maintain their properties against invasive weeds.

Top Invasive Weeds in Valley County

Also known as Wolf’s Milk for the white sap in leaves and stem, leafy spurge is unpalatable to most livestock and wildlife. It takes over entire pastures and areas. The latex sap (wolf’s milk) can permanently blind people who get it in their eyes.

Rush skeleton weed hitched a ride from Ada County. It is now well established in Valley County and crowds out native plants. Note the dandelion-like rosettes that form in the fall and die as the plant ages.

Spotted knapweed destroys feeding grounds for wildlife and cattle. It has reduced elk habitat in backcountry areas.

It also promotes a fungus that poisons the soil for native grasses and other helpful plants. This creates a monoculture of knapweed and can blanket entire areas, eliminating healthy feeding grounds. It has spread across undeveloped parcels of land and continues to rapidly spread to other areas.

Transferred by boats, trailers and bilge-water, milfoil creates dense mats that clog our lakes and rivers. The weed changes the acidity of the water and reduces the amount of oxygen, killing fish and other life. It also creates a breeding ground for mosquitoes.

Canada thistle is one of Idaho’s most widespread and damaging noxious weeds. It can grow up to 5 feet tall and spreads by both seeds and a horizontal creeping root-system from which new plants sprout.

Once established, Oxeye Daisy (pdf) competes against grasses and reduces forage production for cattle. It also exposes soil in the fall, making the infested area vulnerable to erosion and other aggressive weeds.

Oxeye Daisy looks similar to the (mostly innocent) Shasta Daisy and may alter the taste of milk from dairy cows that have consumed it.

Both Dalmatian and Yellow Toadflax are invasive weeds in our pastures. Yellow Toadflax contains a poisonous glucoside that may be harmful to livestock.

Houndstongue (pdf) is toxic to livestock and the seeds disperse easily with their hooked barbs. When not in bloom, it is sometimes confused with the native arrowleaf balsamroot.

Orange hawkweed can be found in moist grasslands, forest meadows, abandoned fields, clear cuts, roadsides, established lawns and gardens. Once introduced it can quickly form dense patches and take over forage for cattle and wildlife.

New plants can arise from buds on the rhizomes and can develop several creeping stems (like strawberries).

Know the Land, Save the Land

Learn, wear, share

Learn about invasive weeds from apparel designed by UI students in cooperation with UI Extension, Valley County.

Order online

Questions about weeds?

Contact Valley County Noxious Weed Control. It has resources ranging from help with identification and control methods to loaner spray equipment and cost-share programs.

Weeds to identify?

More Help

University of Idaho Extension

Physical Address:
Mill Street Building
501 Kelly's Parkway
Cascade, ID 83611

Mailing Address:
PO Box 510
Cascade, ID 83611

Phone: 208-382-7190

Email: valley@uidaho.edu

Web: uidaho.edu/valley

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UI Extension, Valley County