Tyrol knapweed
(Centaurea nigrescens)
Perennial knapweed with lavender flowers and fringed long and slender bracts with dark brown tips.
Other names for this plant include:
- Common names: Vochin knapweed, alpine knapweed, Wocheiner knapweed, and short-fringed knapweed
- Scientific names: Centaures vochinensis, C. dubia
Classification in Wisconsin: Restricted
- Ecological Threat
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- Invades open grasslands, prairies, 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 facilitate seed dispersal across long distances.
- Plants produce hundreds of seeds per plant.
- It increases soil erosion and consumes soil nutrients.
- Identification
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Leaves & stems: A single upright stem branch near the top. Basal leaves are oblanceolate to elliptic. Upper leaves are lanceolate and progressively decrease in size up the stem. Leaves are hairless or lightly hairy on the undersides, deeply lobed to irregularly cut. The terminal lobe is much larger than the others.
Flowers: Flowers are lavender to purple and occur singularly at the ends of branches. Bract (long fringes beneath the flowerhead) tips are dark brown in color and long and slender. Bract tips have a somewhat triangular boundary.
Fruits & seeds: Seeds are tan in color with fine hairs. Plants produce on average a few thousand seeds per plant.
Roots: Plants have taproots.
Similar species: Tyrol knapweed closely resembles other knapweeds, most of which are invasive in Wisconsin.
- Control
- Mechanical:
- Handpull the plants, being sure to remove the entire taproot.
- Mow or cut plants before flowering to prevent seed set. Note this will not immediately kill the plants; continual cutting is needed to exhaust root reserves.
- Monitor for regrowth.
- Herbicide treatments are most effective when combined with other control techniques and followed by re-seeding. The timing of herbicide treatments is essential to effectiveness.
- A three percent 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.
- Gall flies (Urophora affinis and Urophora quadrifasciata) feed on the developing seed heads.
- Resources
- Sources for content:
- Alberta Agriculture and Rural Development
- Washington State Noxious Weed Control Board
- USDA Forest Service
