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Brown knapweed

Brown knapweed
(Centaurea jacea)

Perennial knapweed with upright stems, that branch near the top. Flowers are lavender colored with fringed bracts that have brown tips.



Overview

Regulated areas of brown knapweed
This species is listed as Restricted (Orange counties)

Other names for this plant include:

  • Common names: Brownray Knapweed

Ecological threat:

  • Invades open grasslands, prairies, open forests, orchards, cultivated fields, field edges, and travel corridors.
  • Aggressively outcompetes desired vegetation, reducing overall biodiversity and forage quality.
  • Plants are easily spread by human activity via seed and the plants characteristics faciliates increased seed dispersal across long distances.
  • Plants produce up to 800 seeds per plant. Upon maturation, seeds eject and can be dispersed as far as 20 feet from parent plant.
  • Increase soil erosion and consume soil nutrients.

Classification in Wisconsin: Restricted

Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for brown knapweed was based upon this literature review developed by the department.

Identification

Leaves & stems: A single upright stem branches near the top. Leaves are lanceolate and undivided. Leaf size progressively decreases from bottom to top. Stems are ridged sometimes with purple-colored striations.

Flowers: Flowers are rose to lavender to purple in color. Bracts (long fringes beneath the flowerhead) tips are brown in color and wider than at the base. They have papery thin margins with a dark brown center.

Fruits & seeds: Seeds are tan in color with fine hairs. There is no pappus. Plants produce on average a few thousand seeds per plant.

Roots: Plants have woody taproots and a woody root crown.

Similar species: Brown knapweed closely resembles other knapweeds, the majority of which are also invasive in Wisconsin.

Distribution

Centaurea_jacea
Counties in WI where brown knapweed has been reported (as of April 2013). Both vouchered and unvouchered reports included.

Do you have brown knapweed in your county but it isn't shaded on the map? Send us a report.

Control

Mechanical:

  • Handpull the plants, being sure to remove the entire tap root.
  • Mow or cut plants before flowering to prevent seed-set. Note this will not kill the plants.

Chemical:

  • Herbicide treatments are most effective when combined with other control techniques and followed by re-seeding. Timing of herbicide treatments is essential to the effectiveness.
  • A three percent solution of triclopyr herbicide mixed with water can be applied to the leaves in early spring or fall.
  • Glyphosate, picloram, 2, 4-D, and clopyralid have all been used on other knapweeds

Biocontrol:

  • Gall flies (Urophora affinis and Urophora quadrifasciata) are used to feed on the developing seed heads.

Photos

View brown knapweed pictures in our photo gallery!

Resources

Sources for content:

  • Washington State Noxious Weed Control Board
  • USDA Forest Service

Links for More Information:

Last revised: Friday May 31 2019