noxious weed

Spotted knapweed adds a splash of purple color along roadsides in midsummer, but it destroys elk habitat, increases the rate of erosion and displaces native wildflowers.

    Local authorities fighting noxious weeds report that progress has been made over the past decade, but new infestations continue to pop up and new species of weeds continue to invade the Wood River Valley—from seeds carried in the wind, in the coats of animals and on vehicles.

    “It’s a mixed bag,” said Robert Garcia, range and weed program manager for the Sawtooth National Recreation Area, about the area’s weed-control efforts.

    Garcia said both of his most experienced weed-spraying employees say they’re using less spray each year.

    “That’s generally been the trend, but we still have these patches, so it’s a matter of staying on top of it,” he said.

    In 2002, when the Idaho Mountain Express published a three-part series on noxious weeds, there were 36 weeds on the state list; now there are 66. Blaine County Weed Superintendent John Cenarrusa said many of the new additions are aquatic plants that aren’t present in the county.

    “We’re probably no worse off than a lot of counties and probably in better shape than many,” he said.

    Cenarrusa said he’s seen progress in the fight against spotted knapweed, the most prolific noxious weed in the area.

    “I don’t think we’ve got as dense stands of knapweed,” he said. “People have really gotten with the program.”

    Cenarrusa said he noticed improvements on a “spray day” organized last year by the Blaine County Cooperative Weed Management Area north of Ketchum.

    “It wasn’t just solid purple the way it used to be,” he said. “You had to look around.”

    On the other hand, Garcia said, following a spray day on the north side of Greenhorn Gulch in 2015, weed managers decided they had done such a good job there that they wouldn’t have to respray the following year. They were wrong.

    “Then I went in this year and it just makes you want to cry,” he said.

    Besides spotted knapweed, other invasive weeds affecting Blaine County include:

l    Hoary alyssum, which has invaded higher elevations near Ketchum. “We’ve seen a real increase in this plant over the past two to three years,” Cenarrusa said. He said the plant crowds out other vegetation, creating monocultures that wildlife won’t eat.

l    Rush skeletonweed, which existed in only a few places in the early 2000s. “Now we’ve found it pretty much countywide,” Cenarrusa said. He said the weed’s seeds have blown in from the western part of the state, and the weed is hard to kill and it’s hard to predict where it will show up next. “Over the whole state, everybody’s pretty much losing ground on this one,” he said.

l    Dalmatian toadflax, which has been popping up on ridgetops even where there’s no grazing and no vehicle travel to spread seeds. “It’s just a really tough plant to control,” Cenarrusa said.

l    Yellow toadflax, which has a pretty, yellow flower resembling snapdragons. But it contains a poison that can harm livestock and it spreads through a horizontal underground stem that puts out lateral shoots and roots. “It’s actually a pretty attractive plant—until you know what it does,” Cenarrusa said. He said the plant’s seeds are spread by people picking it as a flower and then discarding it on their property when it dries.

    Idaho law requires landowners to control noxious weeds on their property. Cenarrusa said the Blaine County Noxious Weed Department sends out between 150 and 200 letters each year to landowners who have allowed invasive weeds to take over.

    “We send a nice letter first, and if that doesn’t work we’ll send an enforcement letter,” he said.

    He said the first letter usually brings about 85 percent compliance. But for some folks, even the enforcement letter doesn’t bring results, and each year the county has to send in a contractor to remove the weeds on 10 to 15 properties, at the landowner’s expense.

    Cenarrusa said the aftermath of the 2013 Beaver Creek Fire focused a lot of public attention on the impacts of invasive plants.

    In addition to using herbicides, weed managers have turned to biological controls, releasing insect species from the weeds’ native habitat in Europe or Asia.

    Ten years ago in the Lake Creek drainage, Garcia said, a species of stem-boring weevil was released on Dalmatian toadflax. Garcia said he was recently pleased by a comparison of before-and-after photos taken of the area.

    “Ten years ago, it was solid yellow,” he said. “The picture we took 10 years later was a green native-plant community.”

    But regarding biological-control efforts in general, it’s probably fair to say that weed fighters are still trying to get the bugs worked out.

    Garcia said that since 2006, a species of flower-eating weevil has been released in the area between the SNRA headquarters north of Ketchum and the Baker Creek drainage, about five miles to the north, and between state Highway 75 and the Big Wood River. He said the release was especially heavy in 2014.

    “We do have thousands and thousands of biological agents in that area, and I’m just hoping that one year we’ll see the tide change,” he said. “It does take years and years.”

    A herd of weed-eating goats has also played a role. In 2011, the Blaine County Recreation District began a three-year project using goats to reduce infestations of spotted knapweed and other weeds along the Wood River bike path. BCRD Executive Director Jim Keating said the goats put a good dent into the weed growth, but now the district has switched to other methods. He said the goats are usually considered a start to a program to get the weeds under control, eating their flowers and weakening them.

    “The native grasses then aren’t under full attack, so they can start to come back,” he said. “Then we’ve started to more surgically target with hand-picking and weed-whacking.”

    Cenarrusa said the county has obtained funds to fight weeds through the state’s Noxious Weed Cost Share Program, though the amount of those grants has been dwindling—from more than $40,000 a few years ago to about $15,000 this year.

    The county Noxious Weed Department provides property owners with free consultations on weed identification and potential treatments, and hosts a weed workshop every spring. Cenarrusa said workshop participation has risen from 20 to 30 people a few years ago to 70 this year.

    The Environmental Resource Center in Ketchum also has an extensive online “Weed and Pest Guide” for property owners and land managers.

    Garcia said the SNRA is seeking volunteer noxious weed locators, who will be trained in weed identification and GPS use. Volunteers will take a GPS camera with them when they go out hiking and collect data on weed infestation. Anyone interested can sign up on

    “It’s not a quick fix,” Cenarrusa acknowledged about the entire effort. “Just keep at it and keep fighting it. We’ve come a long way—there are areas that look a lot better. You can take a real problem and turn it into a small maintenance issue. It just takes perseverance.”

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