Gilpin County CSU Extension Agent, Jennifer Cook held a virtual Zoom meeting on identifying and treating noxious plants on Wednesday night August 23. She spent the hour identifying known noxious plants in the area and ways to treat them.

Cook started the webinar by giving a common description of what a noxious plant is and why they are detrimental to a local ecosystem. According to the Colorado Noxious Weed Act of 1990, a noxious weed is an alien plant or parts of an alien plant that have been designated by rule as being noxious or has been declared a noxious weed by a local advisory board, and meets one or more of the following criteria: Aggressively invades or is detrimental to economic crops or native plant communities, is poisonous to livestock, is a carrier of detrimental insects, diseases, or parasites, the direct or indirect effect of the presence of this plant is detrimental to the environmentally sound management of natural or agricultural ecosystems.

The Noxious Weed Act requires that public and private landowners manage noxious weeds on their property. A prioritized list has been established for noxious weeds that require eradication or containment. The Gilpin Community Development Department (gilpincounty.colorado.gov/departments-offices/community-development/303 582-5831) is responsible for enforcing noxious weed regulations and the department to register complaints.

In terms of seasons, Cook characterized plants as annual, bi-annual, or perennial. Annual plants complete their growing and flowering all in one season. A bi-annual plant grows in season one and flowers in season two. A perennial plant will survive multiple seasons and possibly flower in multiple seasons. Perennials can send out roots like an aspen so they can be pulled at one location and then show up some distance from the original.

Cook explained that the state noxious weed list is composed of three categories based on the threat that the plant poses to the ecosystem. The categories are List A (17), List B (32) and List C (16). Methods of treatment vary depending on which category a plant is listed.

Starting with List A plants, Cook showed photos of local noxious plants and explained why they are on a list and how to deal with them. List A plants are considered the most damaging and are designated for elimination/eradication on county, state, federal and private lands. Meadow knapweed and myrtle spurge are on this list.

List B plants identified by Cook are plants whose continued spread should be stopped. Local plants on this list include Canada thistle, scentless chamomile, leafy spurge, musk thistle, oxeye daisy, and yellow toadflax.

List C plants are nuisance plants that require specific containment programs. These include common mullein and cheat grass. Cook finished the webinar with a question and answer period.

Gilpin County CSU Extension has received 50 pamphlets called Noxious Weeds of Colorado which were prepared by the Colorado Weed Management Association. The pamphlets are free for as long as they last. The extension service also has a Herbicide Check Out Program for Gilpin County residents. For a deposit of $200 which is refundable, residents can check out sprayers for large patches of noxious weeds. The herbicide used in Gilpin County is considered safe for bees and other pollinators. Fall is a good time to treat noxious weeds before they go to seed. The general recommendation is to bag the plants that are pulled to contain the seeds.

After the webinar, Cook answered a question about the aspen blight marssonina which is the cause for leaves dropping off aspen during the summer. The blight is a type of fungus and while it doesn’t kill aspen, it can weaken them. Her recommendation is to rake up the leaves and bag them so the fungus can’t get into the soil when the leaf decomposes. If the fungus gets into the soil then it can get back into the trees. Cook also said that pulling noxious plants on public land is permissible, just know the difference and don’t pick the wildflowers.

Jennifer Cook can be reached at jennifer.cook@colostate.edu/303-582-9106 or 720-640-7330. The CSU Extension office is at 30 Norton Drive, Black Hawk, Colorado 80422.