: Acosta diffusa
: Tumble knapweed, white-flowered knapweed
: Introduced in the early 1900s as a contaminant of alfalfa seed.
: Short lived perennial, annual or monocarpic perennial with a long fibrous taproot.
: Finely divided and alternate. May have a gray appearance due to tiny fine hairs.
: Single, upright stem with many branches, growing up to 40 inches tall. Stems break at ground level, resulting in increased seed dispersal.
: Usually white in color, sometimes pinkish to purple and form at the tip of branches. Bracts contain multiple lateral spines and one prominent terminal spine.
Fruit and seeds
: Seed heads are urn-shaped, with many seeds compact in the flower head. Nodding flower head gives the plant its mobility, turning into "tumbleweed" when flowering stalks break off facilitating seed transport over long distances. Plants can produce over a thousand seeds per plant. Seeds to not have pappus, the parachute-like structure that aids in dispersal.
: Native to Eurasia. Found in open grasslands, prairies, open forests, orchards, and disturbed areas such as ditches, cultivated fields and field edges. Also commonly found near water sources.
: By seed.
: Other species of knapweed (Centaurea
Monitoring and rapid response
: For smaller infestations, hand pulling can be effective, removing as much of the tap root as possible. Mowing during flower stage is effective in preventing seed production. Tilling at a depth of 7 inches followed by dense reseeding of native species can help prevent reinvasion. Prescribed fire alone is not effective. Herbicide treatments most effective when combined with other control techniques.
: The information provided in this factsheet was gathered from the Wisconsin Department of Natural Resources and the IVM Technical Bulletin on Spotted, Diffuse & Russian knapweed.
Individual species images that appear with a number in a black box are courtesy of the Bugwood.org network (http://www.invasive.org).Individual photo author credits may not be included due to the small display size of the images and subsequent difficulty of reading the provided text. All other images appear courtesy of Google (http://images.google.com).