Top 10 Invasive Species in Idaho

Idaho, like many other places, is being invaded by a number of harmful exotic species. These trespassers walk, swim, fly or hitchhike to Idaho, settle in and quickly dominate their environment. Lacking natural predators, they spread rapidly and without obstruction, persistently altering the landscape. Fighting invasive species is a battle for everyone who cares about Idaho’s wildlife, forests, waters, and rangelands to win.

The Nature Conservancy works collaboratively with many partners, including landowners, to prevent, plan and treat the spread of invasive plants. We successfully used biocontrols in Hells Canyon, selected herbicide treatments in southern Idaho, and monitored conservation sites for early detection throughout Idaho. We hope you will join us in helping to combat the invaders.

First, you will need to be able to identify the culprits. Here is a list of the top ten:

#1 Yellow Starthistle

Yellow Starthistle is a major threat to wildlife and native plants in Hells Canyon. Its escalating presence decreases rangeland values, poisons horses and outcompetes native plants. 500,000 acres in Idaho are affected.

#2 Leafy Spurge

Leafy Spurge contains an irritant that causes blisters and blindness; as such it significantly reduces forage values for wildlife and livestock. It is found in nearly every county in Idaho. The seeds may remain viable in the soil for seven years, with roots that burrow down 26 feet making this plant highly competitive and difficult to control.

#3 Rush Skeletonweed

This unattractive plant displaces beneficial forage plants and cropland. It was first detected in Idaho on 5 acres in 1960, spreading to 4 million acres to date.

#4 Whitetop (hoary cress)

Whitetop crowds out native species and crops by getting a head start in spring. This perennial uses rhizomes to spread making mechanical control ineffective.

#5 Russian Knapweed

Various species of knapweeds are found throughout Idaho. These plants displace native plants, reduce forage value, and increase erosion. They suppress other plants by releasing a substance that inhibits their growth or germination.

#6 Dalmatian toadflax

Originally cultivated as an ornamental for use in fabric dye and medicinal purposes, this species can crowd out native species and be poisonous to livestock. Its flowers are similar to that of a snapdragon and can produce nearly 1/2 million seeds. Thousands of acres in the Northwest are infested. A weevil has been used as a biocontrol agent to combat the species.

#7 Large Thistles (Scotch Thistle pictured)

(Canada, Bull and Scotch) Though lovely to look at, thistles are one of Idaho’s most aggressive, widespread and damaging noxious weeds. Thistles crowd out native species; reduce crop and forage yields.

#8 Medusahead Rye and Cheatgrass (pictured)

Invasive grasses that have taken over 17.5 million acres in Idaho and Utah. The presence of these grasses has dramatically increased fire frequency and intensity on rangelands, and has degraded sagebrush & grassland habitats.

#9 Puncturevine

Commonly known as goatheads, these plants form dense mats up to 4 feet across with spiney seeds that are stout enough to puncture bicycle tires and injure pets. The seed coat is extremely durable and in the right conditions can last upwards of 20 years.

#10 Zebra and Quagga Mussels

Zebra and quagga mussels HAVE NOT been found in Idaho waters to date. Zebra and quagga mussels were introduced to North America’s Great Lakes in ballast water from Russia in the late 1980s. Both species of mussel can wreak havoc when introduced to a new environment by disrupting the natural food chain and crowding out native species. Idaho has been working hard to keep these damaging mollusks out of our waters.

What you can do:
— Learn to identify invasive plants and report them to land and wildlife managers.
— If you travel with pack animals, carry only certified weed-seed free forage.
— Thoroughly clean vehicles and livestock before entering backcountry or waters.
— Avoid traveling through weed-infested areas.
— Pull and pack out weeds in sealed containers.
— Avoid inadvertently planting invasive exotics in your garden.
— Get involved in local weed-control projects.

For more, visit the Idaho Weed Awareness Campaign.

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