This week we are going to talk about yellow starthistle (Centaurea solstitialis). Yellow starthistle has spines all around the bracts just underneath the flowers. If cattle or horses try to graze on this plant, they can get spines stuck in their mouths. It is also poisonous to horses, causing a nervous disorder called “chewing disease” (nigropallidal encephalomalacia), which is fatal once symptoms develop. Horses are the only animal known to be affected in this manner and should not be allowed to graze on yellow starthistle.

Yellow starthistle can be spread by hay trucks, as it can be a contaminant in hay. Yellow starthistle can be a big problem in pastures, grazing land, as well as crop fields. Although this plant is only an annual and can only reproduce by seed, it can quickly take over an area if not controlled right away.

Like many of the noxious weeds on our county noxious weed list, yellow starthistle has the capability of producing monotypic stands. It forms dense infestations and rapidly depletes soil moisture, thus preventing the establishment of other species. Disturbances created by cultivation, poorly timed mowing, road building and maintenance or overgrazing favor this rapid colonizer.

So how do we control this nasty plant? Control of yellow starthistle cannot be accomplished with a single treatment or in a single year. Effective management requires control of the current population and suppression of seed production, combined with establishment of competitive, desirable vegetation. Both post-emergent and pre-emergent herbicides are available to control yellow starthistle along roadsides, rights-of-way, and non-crop areas. Most herbicides registered for use in rangeland and pastures are only active post-emergence. Clopyralid, however, has both pre-emergence and post-emergence activity on yellow starthistle. Generally, mowing and burning are not recommended as the first means of control. This is because yellow starthistle has such a long root system that it can regrow, and those methods only control the above ground portion of the plant.

Though herbicides can be an effective approach to controlling yellow starthistle, there are also positive results being reported with use of bioncontrol agents. Another interesting control method is done by bringing in goats to graze on yellow starthistle. Apparently, goats will eat the plants even in the spiny stage. The old saying that goats will eat anything seems to apply here.

If you have any questions about identifying or controlling this noxious weed, please contact the Noxious Weed Control Board of Grant County at (509) 754-2011, Ext. 4710. We will be happy to help. Also, if you think you have found an infested area, let us know and we will come check the site to verify. Visit our website at www.grantcountyweedboard.org.