Scotch thistle (Onopordum acanthium L.) is a tap rooted biennial plant in the sunflower family that spreads through its copious seed production. It is a native of central Europe and Asia, arriving in this country around 1900. It has since spread through all of the western states and is found in scattered populations in Washington, the heaviest being in the southeastern counties of our state. Utah first found it in 1963. By 1981 it covered approximately 15,000 acres. By 1991 it had expanded to approximately 55,696 acres. Let’s stop the spread!!! Scotch thistle is an aggressive invader of pastures and meadows, but will grow on dry hillsides just as well. It can also be a problem weed in roadsides and crop situations. The size and hardiness makes this plant difficult to control by any means. Digging or pulling can be very effective with smaller populations if done when the plants are small. If cutting is used as a method of control the plants need to be checked and cut several times through the summer and well into the fall because they tend to regrow from the stalk. This thistle produces a huge amount of seeds- as many as 50,000 per plant!

In Stevens County, we know of only a few dozen sites where this noxious weed occurs. Many of the sites we know about are scattered over several acres because it can spread very fast when in a pasture situation where there is disturbed and open ground. We are concerned that there may be quite a bit more of the weed than we know about. Scotch thistle is sometimes mistaken for "just another thistle" and by the time it is realized just what it can do, the infestation will have quadrupled in size. The longevity of the seed life in the soil, up to 15 years, is one of the things that make eradication difficult. If we do indeed find that there are many more sites of Scotch thistle than we currently know about, our cost share program will likely alter significantly. In the mean time, we would like to keep this weed from spreading any farther and start the eradication process that begins with preventing seed production.

If you suspect you may have this weed or if you think you have seen it somewhere, please contact us! For 2011, we will continue with the cost share program we began in 2003 the key elements of which are as follows: