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Produced & Maintained by Idaho Mountain Express, Box 1013, Ketchum, ID 83340-1013 
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Copyright © 2002 Express Publishing Inc.
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For the week of November 20 - 26, 2002


County battles weeds of mass destruction

Invasion threatens wildlife habitat, rangeland

"Noxious weeds have become a threat to our way of life. If we donít get on top of it, it will destroy our whole ecosystem."

ó SARA MICHAEL, Blaine County commissioner

First of a three-part series

Express Staff Writer

A silent invasion, often taking the form of a lovely purple flower, is spreading terror into the hearts of Blaine Countyís native vegetation.

Known as noxious weeds, the foreign invaders have few natural controls and spread rapidly through pastures, forests and riparian areas. They annihilate food plants for wildlife and livestock, choke waterways and create spiky thickets impenetrable to hikers and anglers. Even after a stand of the invaders is wiped out, their seeds can lay dormant for 10 years before sprouting.

"Noxious weeds have become a threat to our way of life," said County Commissioner Sarah Michael. "If we donít get on top of it, it will destroy our whole ecosystem."

Blaine County Weed Superintendent John Cenarrusa conducts a field seminar on identification of noxious weeds that have invaded the Wood River Valley. Express photo by Willy Cook


Thirty-six species of plants have been designated "noxious" in Idaho. Once designated, the plants fall under a state law that requires landowners to eradicate them.

Native to Europe or the Middle East, the plants have been introduced to the United States at various times and in various places. Some have been brought in intentionally as flowering plants, others accidentally as seeds hidden in shipments of other products or stuck to the clothing of immigrants.

Noxious weeds dominate about 70 million acres of private, state and federal land throughout the West. The U.S. Bureau of Land Management believes the weeds are spreading on federal lands at the rate of about 2,300 acres per day.

"Far too many public land watersheds are rapidly undergoing what is perhaps the greatest permanent land degradation in their recorded history," stated two BLM scientists in a paper delivered to The Governorís Idaho Weed Summit in Boise in 1998.

The Idaho Department of Agriculture estimates that noxious weeds cause $300 million in damage to the stateís lands each year.

The most widespread noxious weed in Blaine County is spotted knapweed. The plant grows about 3 feet tall and has pinkish-purple, thistle-like flowers. It is common along roads.

Spotted knapweed, native to Europe, is thoroughly established in North America.


Spotted knapweed is thought to have entered the United States at the San Juan Islands in Washington in 1893, and spread east from there. The plant was first noticed in the Wood River Valley in the 1950s.

In its native Europe, spotted knapweed faces predators and other plant species with defenses against its spread, and so exists in only scattered patches. This is not the case here.

"It crowds out native plants and forms a monoculture," said Seth Phalen, rangeland management specialist with the Sawtooth National Recreation Area. "It really messes with the local ecology."

Phalen estimates that spotted knapweed covers 500 acres on the SNRA. About 200 acres of that is one infestation near the base of Durrance Mountain, north of Ketchum.

True, the plant adds a splash of color along roadsides in mid summer. But it destroys elk habitat, increases the rate of erosion and wipes out native wildflowers. Spotted knapweed out-competes native plants for soil nutrients and water, and secretes a toxic substance that kills surrounding plant species. Each plant produces about 25,000 seeds annually.

Joe Russell, fire use specialist with the BLMís Shoshone field office, said spotted knapweed is slowly but surely squeezing out elk populations in south-valley side canyons, an important winter range. He said the plant got a toehold along roads, and is spreading up the hillsides. The farther it gets from roads, the harder it is to eradicate.

"It has the potential to be a major problem," Russell said.

A weed called leafy spurge is a major invader in the south county. It aggressively colonizes riparian areas, and has become widespread along the Little Wood River and Silver Creek. It contains a milky substance that poisons livestock and wild animals, and can cause permanent blindness in humans if itís rubbed into oneís eyes. Protection is needed when handling it.

"Once it gets onto farmland, you can pretty much write off that ground for a couple of years," said Blaine County Weed Superintendent John Cenarrusa. "Youíve got to use such harsh herbicides that it kills the fertility of your soil."

The plantís ripe seed capsules rupture when touched, throwing seeds as far as 15 feet.

Other invasive species in the valley include:

∑  Yellow Starthistle, which is native to the Mediterranean and Asia. It is spreading in the area north of Hailey. It grows up to six feet tall and has yellow, dandelion-like flowers and sharp spines on its seed heads. Horses and cattle that graze on the plant can die a painful death from ingesting its spikes.

∑  Dyerís Woad, introduced to North America from Europe in the 17th century, and cultivated as a source of blue dye. It is spreading in the south end of Blaine County.

∑  Yellow toadflax, which has orange and yellow snapdragon-like flowers and was probably introduced from Europe as an ornamental. It has spread across about 600 acres in the Sawtooth Valley, especially near Busterback Ranch.

∑  Dalmation toadflax, native to the Mediterranean area, also has pretty yellow flowers. It dominates about 20 acres near Boulder Creek in the Boulder Mountains.

"We live in such a mobile societyóthere are always new invaders coming in," Cennarusa said.

A plant that may be poised to invade Blaine County from the south is purple loosestrife. It is a semi-aquatic plant with large purple flowers.

"It is a gorgeous weed," said Ron Thaemert, Blaine County extension agent for the University of Idaho Extension Service.

That beauty disguises an evil heartóthe plant sucks the oxygen out of the water in which it lives, killing the fish. Purple loosestrife grows in solid stands, crowding out food plants needed by ducks and geese, and reducing suitable nesting sites.

"I just hope we donít ever get that here," Thaemert said. "I cringe. In Silver Creek, it would just be devastating."

The spread of noxious weeds in Blaine County is accelerated by human activity. Grazing sheep, dogs and motor vehicles carry seeds. Seeds may be carried north by sanding trucks loading up near Shoshone. Spotted knapweed is one of the first plants to colonize areas disturbed by development, and it does well in areas recently burned.

The two BLM scientists at the 1998 Boise weed summit concluded their presentation by saying, "We have just begun to see the scope of the massive degradation that will occur in the futureóif we allow that to happen."

(Next week: Part 2ó"The Counterattack")



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