Weed managers seek to stop spread of yellow starthistle

By Bill Schaefer

For Idaho Farm Bureau Federation

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 to spread throughout eastern Idaho.

Yellow starthistle is identified as a noxious weed by the Idaho State Department of Agriculture and it is on the ISDA’s statewide containment list for terrestrial plants.

Besides having the potential to severely harm grazing land, the weed can be toxic to horses, causing ‘nervous chewing disease,’ in which 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 of it in Idaho County, according to Connie Jensen-Blyth, the county’s weed control superintendent.

Jensen-Blyth said that 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 … is that yellow starthistle when it establishes really well will destroy pastures,” he 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 the current infestation in Bingham County was between 400-500 acres.

Taylor also serves as 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, and the weed management associations are working together to manage invasive weeds.

Jeremey Varley, section manager for the ISDA’s noxious weed program, said the department 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 its seed down and then it will develop roseates 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 roeseates,” he said. “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 (let it) 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.”

Jefferson County weed control superintendent Mitch Whitmill said that yellow starthistle is very aggressive, spreads rapidly and is easily moved by livestock.

He said the invasive weed opens up the opportunity for other invasive plants such as cheatgrass, medusa head and other types of annuals that can weaken the native stands of grasses, thereby jeopardizing the carrying capacity of Idaho’s prime grazing lands for the cattle industry.

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

However, he added, 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.

“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 (it’s) going to be crucial that we work with them and make them understand that we have got to be sure we are not moving this to other locations.”