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Don’t Wish Upon This Star

‘Yellow Starthistle’

BY The Blaine Bug Crew

As you are walking, enjoying the peaceful amenities of Mother Nature, you pause to admire a cheerful yellow bloom. You take a step closer, then a feeling of horror comes over you, realizing this plant is not as benign as it once seemed to be. Wicked spines, longer than your thumbnail, are stretching outward to impale you. You gasp, and start to tumble back, but it’s too late. You’ve been pricked by this femme fatale of the plant world.

The yellow starthistle has not yet dug its spiny bracts into southern Idaho, and we want help to keep it that way. To keep southern Idaho free from the yellow starthistle’s treacherous embrace, here is a description of the plant to help you identify it.

Yellow starthistle is an herbaceous annual. Large specimens are capable of producing 100,000 seeds, which will remain viable for a decade. Flowers bloom July through October, and seeds disperse by late August.

The starthistle deploys two kinds of seeds: plumed seeds are a mottled tan and brown and grow in the center of the flower head; non-plumed seeds are black in color and occur around the periphery of the flower head. Stems grow between 60-120 cm tall. Basal leaves are lobed while upper leaves are linear and attach to the stem with wings.  Yellow starthistle is found in disturbed areas, like hayfields, orchards, and abandoned places.

Six insects and one rust have been released as biological control agents for this plant in the Western U.S. that have had varying levels of impacts, the most successful agent being Ceratopion Bascicorne, a root-crown weevil. These agents cannot exterminate starthistle on their own. To successfully eradicate this noxious weed, we need your help. If you identify this plant, please notify Bronwyn Nickel at the Blaine County Weed Department at (208) 788-5543.

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