Nobody likes weeds, especially when they can kill horses or other animals, destroy a land’s economic or recreational value or devastate the environment. I’m talking particularly about noxious weeds.
The term “noxious weed” is defined in Nevada state law as any species of plant which is or is likely to be detrimental or destructive and difficult to control or eradicate. Russian knapweed is noxious weed that can kill horses, outgrow native or beneficial vegetation, reduce property values and destroy valuable habitat.
Although Russian knapweed has pretty flowers, it can overrun a home landscape or pasture within a year if left unchecked. This problem plants emerge in early spring. They are gray-green in color with hairy surfaces and wavy edges. The stems elongate from May to June and then flower buds develop blooming from late June to October with pink to purple flowers about ¼-inch to ½-inch in diameter. When a mature plant is pulled out of the soil, the roots are black in color.
Russian knapweed can take several years to control because of its extensive root system. Keys to controlling Russian knapweed include stressing the plant to deplete the stored energy in the roots, preventing new seed production, controlling plant spread via root pieces or root bud growth, and establishing and maintaining competing vegetation. No single control method works.
Hand pulling, mowing and tilling may successfully control Russian knapweed if they are done frequently and consistently over several years. Herbicide application also requires vigilance and persistence. Ultimately, long-term success is dependent upon establishing competitive vegetation. The effectiveness of mowing, tilling, reseeding or planting new desirable plants increases after vegetative suppression of knapweed with herbicides.
Before spraying, remove last year’s dead foliage to allow chemicals to reach the underlying new growth of the weed. Bag the dead parts to eliminate any remaining seed and to avoid scattering seed to un-infested areas. When selecting an herbicide, make sure it will not prevent establishment of desirable vegetation. After spraying, do not remove sprayed plants until the plants wither and turn brown. This may take weeks to become evident. It is essential to reseed or transplant desirable plants into the area once the infestation has been reduced. It is then important to maintain seedling vigor with proper fertilization and irrigation.
By law, it is a property owner’s responsibility “to cut, destroy or eradicate all weeds declared noxious ... before such weeds propagate and spread ...” (Nevada Revised Statute 555.150).
For more information on managing Russian knapweed, see http://www.unce.unr.edu/publications/files/ho/2005/fs0551.pdf.
JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension and may be reached at firstname.lastname@example.org or 887-2252.