Spotted knapweed is a short-lived perennial or biennial plant that can grow up to four feet tall. This plant has a strong taproot as well as lateral roots. Rosettes of this plant are grayish-green in color with leave that up to six inches in length. Each rosette may produce many stems. This plant will adapt if it is mowed and will grow shorter and shorter to bloom in very low heights which can vary from two inches to four feet. The stems and leaves are a blue-green color but short with thin hairs on the leaves that can give a silver-gray cast. One flower that is pink to pinkish-purple flower grows on each stem and the flowers are surrounded by oval bracts with black tips, giving the plant the name of Spotted knapweed. One plant can produce up to 300 flower heads and produce up to 140,000 seeds. This plant blooms from June to September. Many mistake Spotted knapweed as Canada thistle. Reproduction is primarily by seeds.
KEY FEATURES OF SPOTTED KNAPWEED:
Pink to purple bachelor-button looking flowers, bracts with black tips directly under the flower head and deeply lobed lower leaves are fine with cob-web type hairs.
Spotted knapweed is highly adaptable plant and can be found in various elevations in moist or dry conditions, is shade tolerant but is commonly found in sunny area and prefers well drained or gravel/sandy soils. This is the number one weed for Montana that has over 1 million acres of Spotted knapweed.
There are herbicides and other control methods that commonly control spotted knapweed. For more information on these herbicides and other control methods contact the CCWP office.
Spotted knapweed produces its own natural herbicide called “catechin” that eradicates other plants around it.