Yellow starthistle rosette
The Extension offices recently received a revised MontGuide about the invasive weed, yellow starthistle. While it has not taken hold in our area and we can still focus on eradication of the weed as it does pop up sporadically, I felt it was important that everyone knew a bit about it so that it is recognizable for each of us.In eastern Washington, where I grew up, yellow starthistle was a part of life as it blanketed the hills of our out-ground. It is an erect, branching plant that can grow from one to five feet tall. As the name implies, its flowers are yellow. When in bud, and during or after flowering, this plant is easy to recognize due to the long, sharp spines on the flower bracts. These spines can be from ¾ to 1 inch long. These spines make contact with the plant a sensitive issue and one that I personally try to avoid.
Not only is yellow starthistle a pain to deal with, but it is also a prolific seed producer, with one plant potentially producing more than 150,000 seeds under ideal conditions. There are two types of seed, plumed and plumeless. By producing two different seed types that differ in how they disperse and when they disperse, or their ideal conditions for germination, the plants may increase their chances for new populations to establish. Plumed seeds may not carry extremely far but long distance dispersion can be aided through human activities as seed heads are caught in vehicles, or carried in contaminated seed or soil. Birds can also play a role in long distance dispersion as some birds such as pheasants, quail and finches feed heavily on the plant.
Yellow starthistle grows in many different locations but is most common in sunny, disturbed areas. As it reduces wildlife habitat, land values, forage yield, rangelands and recreational areas, there needs to be methods to control its spread. For us, a great option right now is prevention and eradication. If isolated plants are found, hand pulling and herbicides are recommended. There are other methods that can have differing degrees of success depending on circumstances, such as biological control agents and mechanical means of mowing and tilling. Chemicals available for yellow starthistle control include the active ingredients clopyralid, aminopyralid, and picloram. You might recognize them by their common names of Curtail, Milestone or Tordon, to name a few. Whatever chemical is used, please be sure to read over and follow the pesticide label.
If you have further questions about yellow starthistle, or would like a copy of the MontGuide, I would encourage you to visit with your local county Extension office.