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Pest SolutionsPESTS + WEEDSUSING PESTICIDES OR HERBICIDES?
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Purple loosestrife
Lythrum salicaria
Updated Mar 29, 2024
Make a Positive Identification
- Purple loosestrife grows in wet areas. It has showy pink to purple flowers.
- It is a perennial plant that lives more than two years. It dies back in the winter. Stems sprout in spring and can grow up to 10 feet tall.
- Purple loosestrife spreads by seed. Each plant produces many thousands of seeds. Seeds are carried by the water, wind, and animals to new areas. It can quickly dominate wet areas. It reduces habitat quality and clogs waterways.
Species: Purple loosestrife
"Purple Loosestrife Lythrum salicaria" by gailhampshire is licensed under CC BY 2.0
Purple loosestrife has square sided woody stems. It grows up to 10 feet tall. Mature plants may have many dozens of stems. The stems grow from a robust taproot.
Showy, abundant pink to purple flowers grow in spikes throughout summer.
Species: Purple loosestrife
"Lythrum salicaria - stem, leaves" by The NYSIPM Image Gallery is licensed under CC BY 2.0
Mature leaves are lance-shaped and rounded or heart-shaped at the base. Leaves are whorled and arranged opposite each other along the stem.
Species: Purple loosestrife
Gary L. Piper, Washington State University, Bugwood.org
Plants produce ¼ inch long fruits with many small, flat seeds. Each plant makes many thousands of seeds. They are dispersed in water and wind or on animals and people.
Species:
"Purple loosestrife infestation" by Oregon Department of Agriculture is licensed under CC BY-NC-ND 2.0
Purple loosestrife spreads quickly by seed. It transforms wet areas and reduces habitat value for wildlife. It has a harmful effect on recreational areas and can clog waterways and irrigation systems.
LOOK-ALIKE: DOUGLAS SPIREA and FIREWEED
Species: Douglas' Spirea
"J20170608-0025—Spiraea douglasii—RPBG—DxO" by John Rusk is licensed under CC BY 2.0
Douglas' spirea (Spiraea douglasii) is a native woody shrub. It often grows to 6 ft tall and occurs in wet areas. Its showy pink flowers form in spikes at the end of branches throughout summer. The leaves alternate along the stem. In comparison, purple loosestrife has an opposite and whorled leaf arrangement.
Helpful
Douglas' spirea is a native woody shrub. Tolerate it if possible.
Species: Fireweed
Dave Powell, USDA Forest Service (retired), Bugwood.org
Native fireweed (Chamerion angustifolium) has spires of pink flowers like purple loosestrife. The leaves alternate along the stem. In comparison, purple loosestrife has an opposite and whorled leaf arrangement. Purple Loosestrife stems are square, while those of fireweed are round.
Purple loosestrife Benefits
- Purple loosestrife flowers attract pollinators
Purple loosestrife Risks
- Purple loosestrife spreads quickly. It is difficult to control.
- It displaces desirable vegetation. It degrades wildlife habitat and reduces recreational opportunities.
- Purple loosestrife will dominate an area if not controlled.
Risk Card
Does it cause harm?
Adults & Children
Low
Abundant plant stems limit access to areas
Property
High
Dominates an area when left unmanaged
Pets
None
Annoyance
High
Difficult to control
Environment
High
Rapidly spreading to new areas
Action Highly Recommended
Take action to report and control this invasive weed
NEED HELP?
Consider a licensed pest control company. Learn How to Hire a Pest Control Company.
Your local Extension Specialist in Oregon and other states can suggest other methods.
Content provided by Weston Miller, Jessica Green and J. Jeremiah Mann. Pesticide safety information edited by Kaci Buhl.
Peer reviewed by OSU Department of Horticulture.
Purple Loosestrife
Washington Noxious Weeds Control Board
Purple Loosestrife Identification and Control
King County, Washington
Purple Loosestrife (PDF)
Weed Control in Natural Areas in the Western United States
"B" Rated Weeds - Purple Loosestrife
Oregon Department of Agriculture Noxious Weed Control Program