Light blue markings on this map indicate the presence of Canada thistle. Courtesy graphic

On Feb. 14, Carbondale Trustees unanimously approved limited use of herbicides at the Carbondale Nature Park — a popular place for off-leash dog walking — in the early spring and late fall for two or three consecutive years. As its name implies, the 33-acre Nature Park is also home to many wild species, including 134 bird species counted by the Roaring Fork Audubon Society and the native western painted turtle, Colorado’s state reptile.

Application will be targeted and the sprayed areas will be fenced for about two weeks while the chemicals dissipate. Also approved for herbicide use were North Face Bike Park and the roundabout and bulb-out gardens on Highway 133.

It’s not a proposal that the Town came to lightly. “We didn’t necessarily want to do this,” said Parks and Rec Director Eric Brendlinger, whose employees are receiving training for the spot treatment. Carbondale’s Integrated Weed Management plan, developed over several years and adopted in 2019, places the use of chemicals at the bottom of its list of strategies for eradicating plants labeled “noxious” by the state.

The Noxious Weed Act (C.R.S. 35-5.5), signed into law in 1990 and amended in 1996, declares that “noxious weeds pose a threat to the natural resources of Colorado,” and requires municipalities adopt a Noxious Weed Management Plan for all lands within their jurisdiction.

Carbondale’s plan requires the use of chemicals remain a last resort and receive approval from the Environmental Board and Trustees. This is the first time since the plan’s adoption that such a request was made, said Brendlinger.

The impetus is Canada thistle, Cirsium arvense, a persistent perennial that Brendlinger was told could take over the park. Over the course of several years, the Town has attempted controlled burns when possible, manual pulling of the thistle, applying a rust fungus supplied by the Palisade Insectary (which was effective but is no longer available) and natural methods developed by a consultant (which proved minimally successful). Goats were considered too indiscriminate of eaters, cost prohibitive and a poor mix with the loose dogs at the Nature Park.

Garfield County Vegetation Manager Steve Anthony has worked with the county’s program since 1999. He said that a patch of Canada thistle can double in five years and could get out of control if left unmanaged. Canada thistle has a tenacious, rhizomatic root system, which tends to spread when the plant is disturbed. ( The thistle also grows a head of tiny flowers which become seeds with fluffy wings.

Brendlinger assured The Sun that soil testing will be conducted before and after applying herbicides, which could begin as soon as April and would require 48-hour notice. Key to this strategy, as prescribed by Anthony, is to introduce native grasses to outcompete the thistle after it is knocked back with Opensight in the spring and Milestone in the fall. Both contain Aminopyralid, a chemical known to spread through the manure of foraging animals and persist in soils with a half-life ranging from 32 to 533 days.

According to Katrina Blair, author of “The Wild Wisdom of Weeds” and founder of Bee Happy Lands in Durango, the qualities that make Canada thistle so challenging to eradicate are beneficial to both the soil and humans. Thistle is an ecological succession plant, she explained, adapted to disturbed soil conditions. Thistle remediates the earth, aerating and shading compacted soil, providing nectar to pollinators and keeping away animals with its prickly leaves.

Blair intentionally allows patches to grow for harvest at her Turtle Lake Refuge. She will juice the alkaline stems and leaves, make milk from the seeds and chai tea from its mineral-rich roots, claiming benefits for the liver and kidney.

“The very problem is that we look at them [noxious weeds] as a problem,” she said. “As human beings, what if we interacted with our environment differently? What if we didn’t have to control it but actually saw it as an ally, a life force and a teacher?”

Asked what she would do for the thistle in Carbondale’s Nature Park, Blair said the flower heads could be manually removed before going to seed, which would tax the roots and diminish the plant’s energy underground. Compost, mulch, amendments and seeds should then be applied to nourish the earth, “adding fertility and stability to the land.” She warned that disturbing the soil by spraying “is just going backwards, even if it feels like a quick fix.”

“With an integrated weed management plan that works, you’re being a good neighbor,” said Brendlinger, acknowledging the pastures that neighbor this park. “You don’t want to be a bad neighbor and not control your noxious weeds.” He admitted pessimistically, “They’re really good at what they do.”