Get Wild: Invasive musk thistle will take a lot of work to get out of our wild places

John Taylor
Get Wild
Musk thistle is an invasive weed that is prolific in Summit County.
John Taylor/Get Wild

As the days shorten and the fall colors begin to show, we think back on our experiences of taking on the noxious and invasive species in Summit County and how we might make our endeavors, or lack theof, more productive going forward.

 Let’s take a good look at the musk thistle, Carduus nutans, that appears to love Summit County as much as we do. Musk thistle is a biennial, meaning it lives two years. The first-year plant arrives as a seed about the size of a grain of pepper. It arrives at its new surroundings by wind by way of a pappus, much like a dandelion spreading its seeds. It can float with the wind a long distance from the parent plant finding new lands to take over and spread.

Once it has arrived, a mature musk thistle may grow and produce many branches. From each, a number of single barbless stalks develops one seed head at the end of each. How many seeds do you think a healthy musk might produce and spread? Would you believe 120,000 according to the Colorado Weed Management Association? But that is not all, these seeds can lay around for up to 10 years until conditions are right. Every single seed is ready to start germinating as soon as they find their optimal surroundings. A little rain here and there, slipping into some disturbed soil and away we go, new thistle rosettes grow all summer long and early into fall.

Musk thistle seeds can lay dormant for several years waiting for good conditions. After that, they can quickly germinate into immature plants, called rosettes, pictured here.
John Taylor/Get Wild

How else does a noxious musk thistle spread? We see plenty of soon-to-be-developed properties that have noxious weeds. Construction and movement of contaminated soils to other locations, as well as dirty equipment coming onto clean property spread the problem. Shouldn’t these ventures be weed-free beforehand? Seeds also spread by foot traffic and on animals.

Considering the 10 years of accumulating seed bank and the number of bolting second-year thistles in Summit County, the infestation is out of control. Knowing that not all seeds germinate as rosettes at the same time, applying only one spray application a year only exasperates the situation. It is not uncommon to find a huge 24-inch rosette next to a late 1-inch tall plant later on in the season.

Why the concern? Musk thistle, as it spreads, covers and eliminates native vegetation in the soil beneath the plant.

A single musk thistle can produce 120,000 seeds, according to the Colorado Weed Management Association.
John Taylor/Get Wild

“One and done” for the year will not bring success. It make look visually good for a while to not see the thistle heads but there are more to come! Whether it is the U.S. Forest Service or county weed departments that provides a once-a-year treatment, it may help, but won’t solve the need to reduce the seed count and bring the infestation under control. The government organizations are not staffed to spend countless hours on foot, attempting to both eliminate the mature “bolted” senior citizens, and come back a number of times later to treat new rosettes.

It is time, come 2023, that we provide the needed ongoing volunteer support to rid our lands both public and private of these unwanted invasive weeds. There are plenty of opportunities for service organizations, homeowner associations, hiking and biking clubs as well as groups like Friends of the Fillon Ranger District, the Eagle Summit Wilderness Alliance, and the Blue River Watershed Group who are involved today to step up to the challenge to make a difference.

John Taylor

John Taylor was recognized by the Summit Foundation John Taylor in 2009 for its Outstanding Citizen award in recognition of his volunteer work with the American Red Cross, Wildfire Mitigation and Emergency Planning, Friends of the Eagles Nest Wilderness noxious weed program, State Weed Advisory Board, wilderness protection and Summit Senior Center. He’s a past chair of the Colorado Department of Agriculture Noxious Weed Board and past licensed Department of Agriculture Pesticide Applicator Program member.

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