USDA Forest Service

Blue Mountains National Resources Institute

Education Links
Information Providers
Managing Disturbance Regimes
Pacific Northwest Research Station
USFS Research & Development
Evaluate Our Service
Your comments and suggestions are very important to our service improvement.

Pacific Northwest Research Station
Blue Mountains National Resources Institute

Forestry and Range Sciences Laboratory
1401 Gekeler Lane
La Grande, OR 97850

United States Forest Service.

BMNRI Home > Publications > Weeds > Purple Loosestrife

Publications: Noxious Weeds

Explosion in Slow Motion: A talk by Jerry Asher about noxious weeds in the Blue Mountains

Click on a weed to learn about how to find it and kill it!

Common Crupina
Diffuse Knapweed
Russian Knapweed
Spotted Knapweed
Purple Loosestrife
Perennial Pepperweed
Tansy Ragwort
Medusahead Rye
Rush Skeletonweed
Yellow Starthistle
Canada Thistle
Musk Thistle
Scotch Thistle
Dalmatian Toadflax
Mediterranean Sage
St. Johnswort
Leafy Spurge
Dyers Woad

Wanted: DEAD!

Purple Loosestrife

Alias: Spiked willow-herb, long-purples, purple lythrum

  • Stems: Up to 6 feet tall, 4 sided and branched.
  • Leaves: Opposite, sessile, 1 to 4 inches long, whorled, lance-shaped, usually rough-hairy. In fall, they dry and turn bright orange.
  • Flowers: 1 inch across with six crumpled purple petals on crowded, interrupted, elongated, terminal spikes. Long flowering season between June and September.
  • Fruits: Two-celled, opening up to release seed.

Purple loosestrife is a perennial that is found in marshes, wet areas, stream courses, and ditch banks. It can spread by seed and by spreading densely matted, creeping, underground stems. It forms dense stands. It can produce 2.5 million seeds a year.


  • Mechanical: First-year plants are easy to pull. Remove all plant material after pulling. It can be difficult to pull established plants, owing to the extensive root mat. Plant will resprout unless entire root is removed. Mowing might be effective if cuttings dry rapidly. Cutting off budding stalks during the flowering season works.
  • Biological: Oregon Department of Agriculture has used a combination of four bioagents (two defoliators, a seed-boring weevil, and a root-boring weevil) to successfully control purple loosestrife on a site near Union, Oregon.
  • Chemical: Spot application of herbicides approved for use in aquatic areas is effective. Consult your local weed control office for more information.

Report all sightings to your local Weed Board

US Forest Service - Pacific Northwest Research Station, Blue Mountains National Resources Institute
Last Modified: Monday, 16 December 2013 at 14:18:43 CST

USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.