Yellow Starthistle infests hundreds of thousands of acres in the Northwest. From a distance, a quarter section of this weed in full bloom can appear very pretty. Nothing could be farther from the truth, however. A native of the Mediterranean region and member of the knapweed group, Yellow Starthistle is commonly classed as a winter annual.
It germinates with fall or spring moisture an is capable of germinating and producing seed during one growing season. This weed is easily recognized by its bright yellow flowers and long sharp spines below each flower.
In this recent photo (below), a thick "hedgerow" of Yellow Starthistle infests the railroad Right of Way along 6600 South in Uintah Township. A large commercial nursery in the background could suffer financial loss should the weed cross the fence line. The Uintah Town Counsel contracted with Weber County to apply herbicide along 6600 South and the railroad track in an effort to rid their city of Starthistle.
Yellow Starthistle is widespread in many areas of Idaho, Washington and Oregon. Here in Northern Utah, there are several relatively small problem areas. Development in the South Ogden area and the Weber County Fairgrounds has done much to minimize the weed populations there. A major Weber County Yellow Starthistle hotspot is still found at the US Army Reserve Unit property in Harrisville.
The mature plant is gray-green in color and grows to a height of one to three feet. Yellow Starthistle is an invasive competitor to desirable plants in ranges and pastures. It can crowd out grasses where soil moisture is limited or where forage has been weakened by grazing. Where this weed is well established, its sharp spines may exclude livestock from grazing any grasses growing beneath the Starthistle plants. Yellow Starthistle produces a toxin that causes death in horses through an illness called "Chewing Disease," which makes it impossible for the animal to swallow. The sharp spines may also damage the eyes of cattle or other livestock attempting to graze around the plants. Pictured at the top of this page is a mature Yellow Starthistle blossom. The insert is a typical fall rosette which will winter over and emerge the following spring (note - the foliage behind this flower is sage, not Starthistle leaves).
Effective control of Yellow Starthistle is best achieved by eradication of newly identified infestations and treatment of larger stands for containment of the weed. Combinations of cultural and chemical controls generally offer the best prospects for minimizing existing infestations. Changes in grazing management or other management practices should be examined for long-term control in larger areas of weed infestation. Increases in vigor and competition from desirable species can help reduce the growth and spread of Yellow Starthistle. Biological control is being tested for Yellow Starthistle.