Loosestrife, Purple

Fact SheetLythrum salicaria

Images of this species:

Common look-alikes:



Lythrum salicaria is a tall, multistemmed (30-50 per plant), perennial forb that can grow up to 5 feet in height.


The opposite or whorled leaves are dark-green, lance-shaped, sessile, 1.5-4 inches long and round or heart-shaped at the base.


Flowering occurs in July to October, when pink to purplish flowers develop in 4-16 inch long spikes at the tops of the stems. Flowers have 5-7 petals and twice as many stamens as petals.


Fruits are capsules that are enclosed in the hairy sepals and contain several reddish brown seeds.



Purple loosestrife is native to Europe and Asia. It was first introduced into North America in the early 1800s for ornamental and medicinal purposes.


Purple loosestrife grows in a variety of wet habitats, including wet meadows, marshes, river banks, and the edges of ponds and reservoirs. It tolerates a wide variety of moisture, nutrient, and pH conditions.


Purple loosestrife can quickly form dense stands that completely dominate the area excluding native vegetation. This plant can spread very rapidly due to its prolific seed production; each plant can produce up to 2.5 million seeds per year. It can also hybridize with native loosestrife species, potentially depleting the native species gene pool.

Loosestrife invades both natural and disturbed wetlands and alters their ecological structure and function.

Life Cycle 

This aggressive plant spreads both vegetatively and by abundant seed dispersal.

With an extended flowering season, and an unusually high number of flowering stems, each purple loosestrife plant is capable of producing two to three million seeds per year. Research has shown that cultivars, advertised as sterile, are capable of producing viable seed. This plant can also reproduce vegetatively by underground stems at a rate of one foot per year.

Management Options

This species is Quarantined: Class B Noxious Weed  

Treatment Concerns: 

  • A single purple loosestrife plant can produce over a million seeds, and those seeds have high germination rates and can remain viable in the seedbank for years. This impacts the overall effectiveness of any treatment.  
  • Because of the high risk of spread by seeds, treatments are most effective before the plants go to seed.  
  • This species is so widespread, and most populations are large or dense, making eradication unlikely. Preventing spread, containing existing infestations, and removing plants from new sites are the best strategies.  

General Guidance  

Summary of Mechanical Treatment Options
  • Mechanical treatment can sometimes cause greater disturbance than if the site was left alone or if another treatment option was utilized. 
  • If pulling or digging, remember that soil disturbance can encourage growth from seed bank.

text in a table describing mechanical treatments for Purple Loosestrife

Summary of Chemical Treatment Options
  • There are a limited number of pesticides found to effectively treat purple loosestrife. This is compounded by the fact that the location of most infestations necessitates an aquatic formulation. And the effective aquatic formulations for purple loosestrife are often chemicals that are non-specific, killing all vegetation that is treated. Broadcast applications, like foliar, of these aquatic formulations are more likely to result in non-target impacts.  
  • Be careful not to damage or kill nearby native plants when conducting management work.
  • Always read and follow pesticide label directions. Application of pesticides may require a certification from the Agency of Agriculture, Food and Markets. The Agency website provides information on what applicator certification is needed.
  • If a treatment for a specific species isn’t listed on a given product, don’t use it. 
  • Product labels may require you to check Endangered Species Protection Bulletins. Learn more about protection bulletins here.  
  • Understand the risk of, and how to avoid, drift.  
  • The timing of some chemical treatments may overlap with when certain plants are flowering, and, in order to protect pollinators, herbicides should not be applied when plants are flowering. To mitigate the risk, consider utilizing an integrated pest management plan, such as cutting the plants to set back flowering time, and then applying pesticides in the lowest effective volume. 
  • Chemical treatments pose a risk to plants, animals, and humans, but can be used in ways that greatly reduce this risk, and provide a solution to otherwise hopeless scenarios. 
  • For questions regarding the appropriate chemical to use for a particular situation, or general information on pesticide safety, ingredients, and more, contact the Vermont Agency of Agriculture, Food & Markets’ Pesticide Program.  
  • For questions about certification and continuing education credit opportunities, contact the Vermont Agency of Agriculture, Food & Markets’ Pesticide Program.  
  • For questions about additional training opportunities, contact the UVM Extension Pesticide Safety Education Program.  
  • Special permits are required to apply herbicides in a wetland. Contact Vermont Department of Environmental Conservation’s Wetlands Section for more information.  
  • Herbicides cannot be applied within 200 feet of a Public Water Source Protection Area unless the Water Supply Division is notified. Call 1-800-823-6500 for more information. Similar requirements may be in place for proximity to private water sources.  
  • Forests that are certified organic or adjacent to organically certified agricultural lands may carry restrictions regarding chemical application. Check with the Northeast Organic Farming Agency of Vermont for more information.  
  • The National Pesticide Information Center provides objective, science-based information about pesticides. Check out their website for more information or call 1-800-858-7378. 

text in a table describing chemical treatments for Purple Loosestrife


Although they will not eradicate purple loosestrife, biocontrol agents can reduce the severity of impacts from an infestation.

  • Insects: There are four species of beetles from Europe, which are fairly host-specific on purple loosestrife, that are currently available for control efforts, though availability varies; insects can be collected from known wild populations, or potentially from a supplier, though this may be regulated.  
  • Livestock: Intensive, rotational grazing by large herbivores (sheep, etc.) can potentially reduce flowering but this is not well studied, nor is it ideal for all areas and habitats. Grazing can help reduce cover, thus helping other desirable vegetation thrive. Appropriate precautions should be taken if utilizing this method and may require special permissions if occurring in or near a wetland.



photo credit

Purple loosestrife1, 5535247, Richard Gardner, UMES, Bugwood.org

Purple loosestrife2, 5479559, Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Flower, 5530447, Becca MacDonald, Sault College, Bugwood.org

Fruit, 5479532, Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Infestation, 5488974, Eric Coombs, Oregon Department of Agriculture, Bugwood.org

Narrow-leaved fireweed, 5356530, Terry L Spivey, Terry Spivey Photography, Bugwood.org

information credit

Adirondak Park Invasive Plant Program

Center for Invasive Species and Ecosystem Health

Go Botony 

Pennsylvania Department of Conservation and Natural Resources

Ontario Invasive Plant Council Best Management Practices for Purple Loosestrife 

PennState Extension Resource on Purple Loosestrife 

Invasive Species Council of Metro Vancouver Factsheet on Purple Loosestrife 

US Forest Service Fire Effects Information System Report on Purple Loosestrife