Idaho Weed Awareness Campaign
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Purple and Iberian Starthistle

Be sure to visit the Purple Starthistle interactive panorama with video clips
in the Virtual Field Guide - Interactive Map of Idaho section.

The Strategy - Purple and Iberian Starthistle (Centaurea calcitrapa and C. iberica) are so similar that its worth a single discussion. Mature seed heads are needed to distinguish between the two species. These were most recently found near the Nevada border in Twin Falls County. These often annual plants but generally biannual plants invade pastures, rangelands, agriculture, and most other sites. This asteracea family plant is covered with fine hairs and the leaves are divided into narrow segments with the leaf tip being narrow and undivided. Leaves have a distinct light colored mid-rib. The bracts have long, sharp, stiff spines about an inch long. This starthistle spine starts out flat at the base, Yellow starthistle is needle-like from origin. It grows to a height of 4-6 feet, has a purple to red flower color, of which produces a small seed with a plume to allow it to disperse through the wind.

The Attack - This is one of the most aggressive invaders to be introduced. Once established it discourages grazing, thus other species are over-grazed which gives an advantage to more invasion of the weed. Although forageable in the early spring, it has an extremely bitter taste. Spines are so stiff that livestock and wildlife will not travel through the areas, not to mention the inability of recreationist to utilize the site.

The Defense - Once detected mechanical control can be used. No insects are available to control it. Greatest recommendation is to remove the plant, if feasible, then return to the site in the fall and apply either Milestone®, Opensight® (formerly known as Chaparral®) and Tordon® 22k. Thus, when it starts growing in the spring the herbicides residual will prohibit it from growing. Definitely notify your county weed superintendent if you suspect this plant and get an early jump on controlling it.

DOW LogoDow recommends their herbicides such as Milestone®, Opensight® (formerly known as Chaparral®) and Tordon® 22k.

Link to Milestone label. Link to Opensight label. Link to Tordon® label.

PLEASE NOTE -The proper use and application of herbicides can be an effective way to control and eradicate noxious and invasive plants. Before using herbicides, always carefully follow the label and safety instructions on the label. While we recommend the use of herbicides as one of the effective tools for integrated pest management, the Idaho Weed Awareness Campaign assumes no liability for herbicide applications.

For more information, click on the link below to download the Idaho's Noxious Weeds Control Guidelines publication produced by the University of Idaho Extension.

U of I Idaho's Noxious Weeds Control Guidelines (183 KB PDF download)

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