Routt County Barry Castagnasso wants residents to be vigilant as they walk, hike the mountainsides or bike in the Yampa Valley. Castagnasso is the weed supervisor for Routt County and is concerned about the spread of noxious weeds. His goal is to help residents be able to identify the noxious weeds bullying their way into hayfields and natural areas, threatening livestock and game animals.
In Routt County, there are four knapweeds to be on the lookout for: diffused, spotted, Russian and meadow.
The Routt County Cooperative Extension Office has a free handy booklet, Troublesome Weeds of the Rocky Mountain West, available to help area residents identify noxious weeds and learn ways to manage their land.
Diffused knapweed is the most prevalent and thrives in semiarid soil along roadsides, in dry rangelands and around gravel pits. It develops a 1- to 2-foot stem that branches near the top and produces small white, sometimes purple flowers with bracts underneath ending in sharp, rigid spines. Flowering occurs from July to September. Its leaves are grayish green, divided and young plants have a rosette of leaves at the base of the plant.
Spotted knapweed is easily identified by its lavender to purple, thistle-like flower head with black-tipped bracts underneath. It grows 1 to 3 feet tall with branched shoots. The leaves are narrow and deeply indented or lobed and form a rosette around the stem. The weed's early spring growth competes with native grasses for soil moisture and nutrients. Spotted knapweed first appeared in Routt County last year along fiber optic trench lines.
Russian knapweed entered Routt County in a load of hay. The weed is reproduced not only by seed but also by its creeping roots. It is the only plant with black roots. It grows 1 to 3 feet tall and has lavender to white thistle-like flower heads with smooth, papery bracts underneath the flowers. Flowering from June to August, it grows in cultivated fields, along fence rows and roadside ditches. Russian knapweed is poisonous to horses.
The only locally known infestation of meadow knapweed is found at the lower end of Hot Springs Trail where it joins the Elk River at County Road 129. Meadow knapweed grows up to 3 feet tall with many branched shoots.
All knapweeds feel coarse along their stems. The flowers are large, with pink to purplish-red heads, and the bracts are deeply fringed, light to dark brown in color.
The best management plan for all knapweeds is to stress the weed with cultural, biological, mechanical or chemical controls and integrate two or more methods of control. Just mowing the weeds is not sufficient. Cultural control such as seeding with suitable perennial grasses is necessary to prevent reinvasion. For chemical controls, broad-leaf herbicides do not kill surrounding grasses, and 2, 4-D is the control for diffused knapweed and should be applied early in the spring to prevent it from going to seed. Otherwise, fall spraying for all knapweeds is best when they have turned brown, which is when the chemical treatment is easily transmitted to the roots. Escort and Curtail can be used for spotted or Russian knapweeds. As with all chemical controls, read the labels carefully and use as instructed. For information on chemical controls, call the extension office.
Ann Noye is a master gardener through the Colorado State University Cooperative Extension office in Routt County.