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Matt Custer, Routt County's weed supervisor, has asked all residents of Routt County to be on the lookout for meadow knapweed and tamarisk. These invasive and noxious plants are top priority this year for detection and control.

Why is he concerned? Meadow knapweed (Centaurea pratensis Thuill) is an aggressive, non-native species that is invading pasture and meadows. It displaces grasses and other forage plants valuable to livestock and wildlife.

Tamarisk, also known as salt cedar, is destroying riparian areas and displacing native vegetation. As tamarisk steals our precious water, it deposits salt in the soil. If you have ever been canoeing or rafting on the Green River, you cannot help but notice its invasive habit.

For identification purposes, meadow knapweed grows 20 to 40 inches tall with many stiff, thin stems, covered with fine hair, branching halfway up the main stalk.

The 6-inch leaves at its base are narrow or lance-shaped with smaller leaves continuing to unfold up the stems ending at the deeply fringed bract under the single bloom.

Bracts are modified leaves that form a cup-like shape that support the flower head. The flower is usually rose to purple in color, but it also can be white. Meadow knapweed blooms from July to September, mainly in moist areas.

There are three other knapweed species -- spotted, Russian and diffuse knapweed -- that occur in Routt County and also require control. However, Routt County is the only county in Colorado where meadow knapweed is found. At this time, the infestation is along Routt County Road 129 near Mad Creek.

Tamarisk or salt cedar (Tamarix ramosissima Ledeb) is an evergreen shrub or small tree which grows 5 to 20 feet high. Its smooth, woody stems are reddish brown and crack and turn gray as the tree ages.

The leaves are small, often encrusted with salt secretions, giving the slender branches a wispy green appearance. Flowers are five-petalled with pink shading to white in color. The flowers appear in dense masses of 2-inch long spikes at the branch tips.

The distressing factor is that tamarisk has a long tap root which will intrude deep water tables and is capable of stealing up to 200 gallons of water daily displacing streams and ponds. This, in turn, may increase the frequency and intensity of fires. Its seeds are carried by wind and water and established easily in both alkaline and acidic, saturated soils.

Custer encourages us to be on the alert for meadow knapweed and tamarisk. Both are on the Routt County noxious weed list.

Control is required. If you find any infestations, please contact Custer at (970) 870-5246 as soon as possible. For photographs and descriptions, see the Routt County Web site, http://co.routt.co.us, and look under weed control.

Help is needed to control and eradicate the weeds on the wanted list.

Ann Noyes is a Master Gardener through the Colorado State University Cooperative Extension office in Routt County. Questions? Call 879-0825 or e-mail gardeners@co.routt.co.us.