Noxious weeds taking toll on wildlife habitat in Idaho, across the West

Nationwide, noxious weeds run roughshod over 2,703 square miles of wildlife habitat every year.

Seventeen-million acres of federal land in the West are infested with noxious weeds, and the spread is growing at an annual rate of 8 percent to 12 percent.

“You can lose habitat to weeds as fast as you can to fire,” said Terry Thomas, regional habitat manager for the Idaho Department of Fish and Game’s Upper Snake Region. “At least with a fire, you often get some benefits. When you lose 1,000 acres to weeds there is no benefit. It’s just a pain.”

While exact numbers for the spread in Idaho aren’t available, experts say noxious weeds are one of the biggest contributors to the loss of wildlife habitat. According to the Idaho State Department of Agriculture, noxious weeds cost the state $300 million a year through eradication efforts and loss of resources.

Roger Batt, a spokesman for Idaho Weed Awareness, said 8 million acres of state land are infested with noxious weed. Across the West, Batt said noxious weeds would spread at a rate of 3,200 acres per day, if undeterred.

Noxious is a legal classification. According to the Department of Agriculture, there are 67 species of noxious weeds in Idaho. Under the designation, land owners are obligated to fight the spread of noxious weeds on their property.


Noxious weeds get mixed in with large shipments of imported seed and are nearly impossible to detect, Thomas said. Once here, they spread like wildfire because there are few, if any, predators to hold them in check.

“Most of the species that come over aren’t very palatable to our wildlife, so they take up space that native plants could take up and provide a benefit,” Thomas said. “(Noxious weeds) don’t provide a benefit, so they are essentially taking up habitat.”

For the most part, land management officials fight weeds with herbicides and biocontrol. Because of the negative effects of chemicals, biocontrol — or the introduction of predators — is a preferred method, but can be time-consuming.

“They bring insects from the (weeds’) native country, and it takes nearly 10 years of testing to make sure they won’t attack native species,” said Paul Faulkner, biologist for Idaho Fish and Game. “So that’s your Pandora’s box.”


Identifying the problem is one thing, but stopping the spread is nearly impossible. While efforts to better screen imported seed are in place, when dealing with a barge full of seed, finding the noxious weed seeds is something akin to searching for a needle in a haystack.

In addition, most people can’t identify noxious weeds. Nurseries sell them unknowingly, and many people have them in their yards.

Even if management officials were able to halt any new introduction of noxious weeds, the plants already in place can spread at an alarming rate. Faulkner said one of the newer problem weeds is rush skeletonweed.

“It has a tiny, tiny seed that can be dispersed by wind for miles,” Faulkner said. “It’s taken off and just spread.”


Batt sent out a news release Monday about an increase in the spread of poison hemlock. The weed has taken root in every county in Idaho.

“Poison hemlock is one of the most poisonous plants in the Western Hemisphere,” Batt said. “It’s extremely toxic. Large livestock animals have been known to eat it and die within hours.”

Humans occasionally eat it thinking it’s wild parsley or dill, Batt said, while livestock can ingest the plant when forage opportunities are low — or if it is mixed in with grasses.

In addition, Faulkner said humans often help spread weeds by taking trips into the backcountry on horses or ATVs.

“You can spread weeds for miles,” he said. “ATVs are especially notorious. They have so many little crevasses and skid plates. Everything collects on them. As you drive around, every bump you hit, you’re spreading seeds.”

Both Thomas and Faulkner said the problem is not going away, but with more help from the public, the effect of noxious weeds could be less catastrophic and expensive. That starts with becoming familiar with the plants that are noxious, and then making sure you aren’t helping to spread them.