Vegetation Management

Noxious weed calendar

The 2022 Weeds of Garfield County calendar is available. Produced by Garfield County Vegetation Management, the free calendar features stunning images of county landscapes, residents, wildlife, and livestock. Each month includes information about various noxious weeds and what is being done to prevent them from spreading.

The calendars are available at all county branch libraries; and the first floor reception office in the Garfield County Administration Building in Glenwood Springs and Rifle. You can also contact Garfield County Vegetation Management at 970-945-1377, ext. 4305 or 4315, or email Garfield County Vegetation Management and we’ll be happy to mail you a copy while supplies last.

Fall Weed Watch: Russian knapweed/Rhaponticum repens

Russian knapweed/Rhaponticum repens

Plant Characteristics
• Perennial forb growing 18-36″ tall
• Stems are erect, thin and stiff and covered with short gray hairs
• Plants reproduce primarily by deep, creeping adventitious roots but may also produce up to 1,200 seeds
• Roots have a distinctive black or dark brown color and scaly appearance
• Solitary, urn-shaped flowers typically pink to purple
• Can be distinguished from other knapweeds by the papery tips of its floral bracts

Management
Russian knapweed grows easily in many different areas, such as roadsides, riparian zones, pastures and croplands. The plants rapidly form dense colonies that outcompete desirable species or forage. Russian knapweed is allelopathic, meaning it can exude chemicals that inhibit growth of desirable plants. It is also poisonous to horses and can cause serious illness or death.

Russian knapweed shoots emerge early in spring to form rosettes and begin to bolt in late May to June. The plants flower from June through August and set seed in late summer to early fall. The rosette stage is the most effective time to control the plants with herbicide, so spraying should occur in early spring before the plants bolt or in fall after the first frost.

Prevention is the best method of knapweed control as the plants rapidly colonize bare or disturbed areas. Maintain healthy land with native, desirable species and continually monitor for knapweed presence. If found, treat immediately and plant competitive species in bare areas. Limit seed dispersal by avoiding driving through or bringing livestock into infested areas.

Mowing several times before the plants bolt may help limit nutrient reserves and stress the plants. A combination of mowing and herbicide application will further enhance control. There are also several biocontrol options available for Russian knapweed control, but this method is most effective when combined with other control options as part of an integrated weed management plan.

Annual follow-up treatments are essential and chemical recommendations will vary depending on the specific site and surrounding land use.

For more information or specific recommendations on Russian knapweed control, please contact Garfield County Vegetation Management:
Steve Anthony: 945-1377 x 4305 or email
Sarah LaRose: 945-1377 x 4315 or email