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Centaurea maculosa syn. C. biebersteinii Description: Spotted knapweed is an invasive weed that readily colonizes disturbed areas. Leaves and stems are pale grayish green and covered in short white hairs. Lower leaves form a basal rosette. Stems are wiry, erect with many branches and a solitary flower at each branch tip. The flowers are pink, 3/4 to 1 inch across, with small black-tipped bracts just below. Spotted knapweed quickly invades native plant communities and can easily sustain its population once established through a very large seed production. A single spotted knapweed plant can produce 600-1000 seeds in a single flowering season. Wildlife and domestic grazers do not favor spotted knapweed because of irritating chemicals. Seed head flies, moths and weevils, and root boring moths and weevils, have been released as biological controls for spotted knapweed in many areas but only one moth has shown to cause reductions in knapweed biomass. Large enough populations of seed head insects cannot become established to reduce stand densities, mainly because seeds can remain viable in the soil for 5 or more years. Chemical application can be successful but requires multiple applications because of seed longevity.    black tipped bracts, stand and flower heads images 1 & 2 by Norman E Rees, USDA ARS; 3 by Jim Story, Montana State University - forestryimages.org Quick Guide (single page info sheet in pdf format) Selected Publications: Davis, E.S., P.K. Fay, T.K. Chicoine and C.A. Lacey. 1993. Persistence of spotted knapweed (Centaurea maculosa) seed in soil. Weed Science 41:57-61. Kedzie-Webb, S.A., R.L. Sheley, J.J. Borkowski and J.S. Jacobs. 2001. Relationships between Centaurea maculosa and indigenous plant assemblages. Western North American Naturalist 61:43-49. Lacey, J.R., C.B. Marlow and J.R. Lane. 1989. Influence of spotted knapweed (Centaurea maculosa) on surface runoff and sediment yield. Weed Technology 3:627-631. Sheley, R.L., J.S. Jacobs and M.F. Carpinelli. 1998. Distribution, biology, and management of diffuse knapweed (Centaurea diffusa) and spotted knapweed (Centaurea maculosa). Weed Technology 12:353-362. Links: |
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