The discovery of yellow starthistle on private land in Bingham County has alarmed state land managers and county weed superintendents in the region about its potential spread throughout eastern Idaho.

Yellow starthistle is identified as a noxious weed by the Idaho State Department of Agriculture. It is on the ISDA’s statewide containment list for terrestrial plants. The weed can be toxic to horses, causing ‘nervous chewing disease.’ An afflicted horse cannot chew or digest food, causing the horse to die from starvation. Horses with the affliction are often euthanized.

The weed is common in western Idaho, particularly in Idaho County. There are an estimated 86,222 acres inventoried for yellow star-thistle in Idaho County according to Connie Jensen-Blyth, the county’s weed control superintendent.

Jensen-Blyth said yellow starthistle has been a serious issue in Idaho County since the 1950s.

The USDA’s National Invasive Species Information Center states that the weed was first identified in eastern Idaho in 2011 on private grazing land east of Basalt.

Chad Taylor, senior lands resource specialist for grazing, agriculture and conservation for the Idaho Department of Lands, expressed concern about the weed’s potential impact should it spread from its current location on private land to the IDL’s public grazing lands.

“I think one of the bigger concerns for livestock, from my professional area, because what I do at the Department of Lands is manage a lot of lands for grazing, is that yellow starthistle when it establishes really well will destroy pastures,” Taylor said. “Essentially it will become a monoculture in a pasture or range land. Then you lose that forage that you need for grazing.”

He estimated that the current infestation in Bingham County was between 400 acres and 500 acres. It is native to Eurasia and was introduced to the U.S. in the 1800s through contaminated seed.

Taylor also serves as the chairman for the Upper Snake River Cooperative Weed Management Association. The Upper Snake River CWMA is composed of all of Bingham County, most of Bonneville County and all of Jefferson County south of State Highway 33. Weeds know no geographic boundaries and CWMAs are collaborative entities working together to manage invasive weeds.

Jeremey Varley, section manager for the ISDA’s noxious weed program, said that they allocated $15,000 this year to the Upper Snake River CWMA for application of an herbicide to try and control the spread of yellow starthistle this fall.

“It’s a fall germinator. It’ll put it’s seed down and then it will develop rosettes in the fall,” Taylor said describing the weed.

The weed is currently located in hilly terrain with limited accessibility requiring aerial application as well as ground spraying.

“We’re going to spray that and hopefully kill those rosettes. The chemical that we’re using Milestone, it persists in the soil long enough that it should have a pre-emergent effect on that seed. So, hopefully we don’t see the same amount of bolting on the plant next spring.”

Taylor said that the IDL’s largest continuous block of prime grazing areas — Bone, Brockman, Long Valley and Sawmill — are in close proximity to the infestation.

“We’re hoping to keep it contained to where it’s at and not spread over the mountain range,” Taylor said. “Once you get up over that mountain range you start getting into our better grazing land. From a public land perspective, it’s just a problem that we don’t want to have.”

On Oct. 20, Taylor and Mitch Whitmill, along with a handful of others, were driving ATVs through the infected grazing land applying herbicide to yellow starthistle stands. It was too windy that day and concerns about wind drift of the herbicide prevented the aerial application until later in the week.

Whitmill has been the weed control superintendent for Jefferson County since 2007.

Whitmill said he works collaboratively with IDL, the federal Bureau of Land Management, the federal Bureau of Reclamation, private landowners, other county land manager and a host of other agency leaders through the CWMA.

“That gives us the authority to work beyond our borders and our fence lines and that’s a concept that was put in place many years ago under the state department of agriculture, and it’s been a very effective program,” Whitmill said.

Whitmill said Idaho’s CWMA program has been a template modeled and used across the country by other states.

Whitmill said yellow starthistle is very aggressive, spreads rapidly and is easily moved by livestock.

Furthermore, it opens up the opportunity for other invasive plants such as cheat grass, medusa head and other types of annuals that we can weaken the natives stands of grasses thereby jeopardizing the carrying capacity of Idaho’s prime grazing lands for its cattle industry.

“Currently, it’s not anywhere else in our eastern Idaho region, so that’s what we’re trying to do is contain it in that area up there and gradually reduce the size of the infestation if possible,” Whitmill said of the CWMAs herbicide applications.

However it’s also going to take a buy-in from livestock producers to keep their equipment clean of yellow starthistle when moving cattle to different grazing lands, he said.

“We have livestock producers that are in that area that have land in other locations throughout our region here all up through the valley, and they move their livestock from that area up to different grazing areas from different times of the year,” Whitmill said, “and that’s going to be crucial that we work with them and make them understand that we got to be sure not to be moving this to other locations.”

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