Russian knapweed is toxic to horses. The key to Russian knapweed control is to stress the weed and cause it to expend nutrient stores in its root system. Lower leaves are 2 to 4 inches long and deeply lobed. Upper leaves are smaller, generally with smooth margins, but can be slightly lobed. Shoots and leaves are covered with dense gray hairs.
Flowers can be pink, lavender or white.
Russian knapweed has vertical and horizontal roots that have a brown to black, scaly appearance, especially apparent near the crown. A 1998 survey showed Colorado with more than 152,000 acres infested with Russian knapweed. Russian knapweed is toxic to horses. It produces seeds sparingly, approximately 50 to 500 per shoot. Seeds are viable for two to three years in soil.