BY ANDREA WALTON
Canada thistle (Cirsium arvense) is a perennial weed that can grow from 1 to 4 feet tall and came to us from Eurasia, probably from a crop seed prior to 1800. This is the most widely spread weed we have in Idaho. This thistle usually has a pink flower, but has also been seen with a white flower. In the spring, the rosettes are normally small and hairless and are not normally found alone, as many of the plants are connected by the roots. Although this plant, and other thistles, are completely edible by livestock and humans, both usually stay away from them due to the spines that grow along the leaf margins.
It has been seen in our lowest agricultural fields as well as in meadows at our highest elevations; thus, it has become one of our most damaging weeds. Once the seeds mature, they develop a plume (like dandelions) that allow the seed to be blown for miles by the wind. But, interestingly enough, I would challenge anyone to see if any of the seeds actually grow into a plant. Instead, the plant has a vast horizontal root system (rhizomes) that allows the plant to ‘creep’ into adjacent properties and even through asphalt.
Warnings about noxious weeds may seem trivial until you look at their damages based on numbers: $300 million annually in losses to our economy; $20 million to fight noxious weeds on the ground; and more than 8 million acres of land and water infested by noxious weeds. (Resource: www.idahoweedawareness.org).
Noxious weeds are a serious matter and you can help us fight them. The Blaine County Noxious Weed Department, along with the Blaine County CWMA [Cooperative Weed Management Area], would like to assist you in identifying the 67 noxious weeds in the state of Idaho.
The Blaine County Noxious Weed Department is a great resource for property owners (remember, property owners are obligated by law to control all noxious weeds on their property) and can assist with weed identification, management plans, tools, and general information. For more information, call (208) 788-5543 or visit www.blainecounty.org.
Andrea Walton is an administrative specialist with Blaine County.