Deb Babcock: Controlling invasive weeds
May 20, 2013
Often, we gardeners call a weed anything that we don't like in a location we planned for something else. It often is just a benign plant whose seeds were scattered to other parts of the garden via wind, birds or chipmunks.
Invasive weeds are another problem, altogether. They are not benign and actually are harmful to our environment and our animals.
Meadow knapweed (Centaurea pratensis Thuill.), for example, is an aggressive, non-native species that is invading pasture land and meadows in Routt County. Its seeds are carried to our properties via streams and rivers, in hayseed and on equipment that has been used in infected areas.
Besides being somewhat unattractive and painful to rub against when hiking because of its sharp barbs, this invasive weed displaces good native grasses and other forage plants valuable to our livestock and wildlife. And this is somewhat ironic because this plant was introduced into the environment as a forage plant for animals, but then was found to be highly unpalatable for livestock with little nutritional value.
You can identify meadow knapweed by looking for a plant that grows about 3 1/2 feet tall with many stiff, thin stems, covered with stiff fine hair, branching halfway up the main stalk. The 6 inch leaves at its base are narrow or lance shape 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 itself is usually rose to purple in color. Meadow knapweed blooms from July to September in our part of the state.
This noxious weed is usually found along streams — a particularly bad infestation can be found in the Mad Creek area — but you'll also find it along roadsides and open forest areas.
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If you spot an infestation on your own property, the best way to deal with it is to dig it up if it is a small infestation. Be sure to get the entire root system or it will regenerate.
Avoid overgrazing your pastures, and keep them healthy with adequate fertilizer and water. Reseed bare spots. Weeds have a hard time competing in healthy pastures.
Certain herbicides have proven effective: Milestone should be applied either in spring during bolting or during the fall. Tordon can be applied either in spring during bolting to bud growth or during the fall. (The Master Gardener program does not endorse any products, but simply provides these brands names for informational purposes. Always read and follow label directions.)
Simply mowing down this weed is not an effective control since it will regenerate in a short time producing flowers and seeds on a shorter plant.
The Routt County Weed Program has been working rigorously to eradicate this noxious weed in Routt County since 1983. Greg Brown, supervisor of the Routt County Weed program, states, "the initial infestation has been reduced from 30 acres in 1983 to 67 plants in 2012. It is a List A noxious weed in Colorado and must by law be eradicated wherever it is found." Greg and others working on our noxious weed program believe the infestation is still confined to the Mad Creek-Hot Springs Creek area and has been targeting control efforts there. If you think you have spotted this weed elsewhere in the county, call Greg at 970-870-5246 for an inspection and identification of the suspect weeds.
Deb Babcock is a volunteer Master Gardener through the CSU Extension Routt County. Call 879-0825 or email firstname.lastname@example.org with questions.