Diffuse Knapweed

Centaurea diffusa

Family: Asteraceae

Description and Life Cycle

A biennial to short-lived perennial, spreading primarily by seed dispersed with the movement of plant material. Stems are 60-90 cm in height with many branches. Leaves are 5-20 cm long, hairy, and highly divided. Leaves alternate from the stem, with basal leaves forming a rosette. Flower heads are numerous, urn shaped, and covered with small, narrow bracts ending in sharp, rigid spines. Flowers are white or occasionally pink or purple. Seeds are black to dark brown, 3mm long, and lack a developed fringe of hairs. Diffuse knapweed contains volatile oils with a distinctive smell and extremely bitter taste.

Biological Control Agents

• Agapeta zoegana – Moth
• Chaetorellia acrolophi - Fly
• Cyphocleonus achates – Beetle (weevil)
• Larinus minutus - Beetle (weevil)
  
• Larinus obtusus - Beetle (weevil)
  
• Pelochrista medullana - Moth
  
• Pterolonche inspersa - Moth
  
• Puccinia jaceae - Stem and leaf rust
• Sclerotinia sclerotiorum - Fungus (pathogen)
• Sphenoptera jugoslavica - Beetle
• Subanguina picridis – Nematode (gall forming)
• Urophora affinis - Fly
• Urophora quadrifasciata - Fly

References

Cranston, R., D. Ralph and B. Wikeem. 2005. Field guide to noxious and other selected weeds of British Columbia. Gov. of BC. 94 p.

Powell, G. W., A. Sturko, B. Wikeem and P. Harris. 1994.  Field guide to the biological control of weeds in British Columbia.  B.C. Min. For. Res. Prog.