A biennial or short-lived perennial beginning as a rosette. One to three feet tall with a tough tap root. Usually two or three stems will rise from the rosette with multiple branches above. Will produce an urn shaped seed head at branch tips with pink to purple flowers. Seed heads appear spotted as the bract tips turn dark brown or black at maturity. Usually much taller than other knapweeds present in the area and will have a more open structure. Leaves and branches have a blue green or muted green color, particularly later in the season.
Spotted knapweed can be controlled with common herbicides; 2-4,D, Glyphosate, Dicamba among others. Fall applied Clopyralid (Transline, Redeem, Curtail) also works very well while preserving perennial grasses. Aminopyralid (Milestone) has also been uses to effectively control spotted knapweed. Spreading only from seed, any mechanical control should be initiated before flowering. If plants are removed below the growing point; at least one inch below soil surface they will not usually re-sprout. Biological control insects have worked well in areas that have large populations.
Modified from Selected Noxious Weeds of Eastern Oregon, Gary Page, Malheur County Weed Inspector.
For more information on noxious weeds and how to properly control them, contact your local CWMA or County Weed Department.
Most likely arrived in North America with alfalfa seed from Eurasia. It is particularly abundant in southern France and Spain. It can be found scattered throughout the Near East as far as the Caucus region. Has been in Oregon since the 1930s and in Malheur County since the 1970s in limited amounts.
Often called a pioneer specie, it prefers sites with some kind of soil disturbance to get established. Found in permanent and ephemeral stream beds, gravel piles, roadsides campgrounds and similar environs.
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