An herbaceous, multi-stemmed, wetland perennial to 2-3 m tall, becoming somewhat woody at the base. Has opposite leaves with smooth margins, and a terminal spike of showy, pinkish-purple flowers.
Purple loosestrife changed soil organic matter, nitrogen cycling, and water chemistry in New York wetlands, resulting in higher levels of available nitrogen.3 It had double the transpiration rate of cattail (high transpiration can have a positive, cooling effect on the surroundings as well as a potential negative effect of wetland drying), and outcompeted cattail in high-nutrient conditions.3 Purple loosestrife may have negative effects on detrital food chains, and suppress the growth of aquatic plants that are important food sources.2 It can reduce or eliminate open water and open mudflat areas, important for foraging waterfowl.2 Purple loosestrife tannins added to water decrease survival of American toad tadpoles.1 Purple loosestrife may decrease habitat quality for muskrat, because muskrats prefer to eat cattail and thereby give loosestrife a competitive advantage.2 Purple loosestrife-dominated habitats may support higher densities but lower diversities of birds than other wetland vegetation types.4
Although purple loosestrife is purported to decrease native plant diversity, evidence is lacking. In Ontario wetlands, nonnative and native species richness were positively correlated, nonnatives were not more likely to be dominant, and purple loosestrife did not reduce plant diversity.5 A study of Hudson River tidal wetlands found modest effects of loosestrife on native plant abundance, but none on species composition or richness.6 In the Pacific Northwest, however, purple loosestrife cover was negatively correlated with species richness,7 although it was not a stronger competitor than native tidal marsh plant species.8 Loosestrife is very efficient at pollution removal and wastewater treatment.9 Many birds nest in purple loosestrife stands, including goldfinch,10 pied-billed grebe, and red-winged blackbird.4 Swamp sparrow preferred wetland areas with loosestrife for nesting,4 but marsh wren and common grackle avoided nesting in loosestrife stands11 (although marsh wren in Tivoli North Bay, which nested only in cattail in the 1970s, has gradually begun to nest in loosestrife). Loosestrife stands are also used for roosting, and there are some reports of birds eating its seeds (or arthropods on seedheads). Tender, new growth is a preferred forage for livestock and deer, and grazing can limit purple loosestrife. Native saturniid moths, including polyphemus (Antheraea polyphemus), cecropia (Hyalophora cecropia), io (Automeris io), and buck moths (Hemileuca sp.) occasionally to frequently feed on loosestrife, although the buck moths suffer from increased parasitism compared those feeding on native hosts.12,13 Short-statured purple loosestrife in rich fens seems to permit the coexistence of fen plants, and can be used by bog turtle, but dense, tall loosestrife is very poor bog turtle habitat. The woody root crowns (“hummocks”) of vigorous clumps are good substrates for many mosses and liverworts. The flowers are often intensively visited by diverse butterflies, moths, bees, and flies.
This page focuses on biological and manual best management practices only. Please contact firstname.lastname@example.org with specific questions on chemical control options.
Four biocontrol agents have been approved for purple loosestrife: two leaf-feeding beetles (Galerucella calmariensis, G. pusilla) and two weevils, a flower bud-feeder (Nanophys marmoratus) and a root-feeder (Hylobius transversovittatus). Effects of the different beetles on purple loosestrife are variable, but all of them (often in combination) are capable of significantly decreasing plant height, cover, and/or seed production under at least some circumstances. The Galerucella (leaf-feeding) beetles are the most studied. Sometimes their release has little effect, but sometimes there is a reduction in seed production (after 1-2 years) or plant height, cover, and biomass (after 4-10 years).14,15,16 Interestingly, Galerucella beetles have been most successful in controlling purple loosestrife in wetlands with low nutrient availability (measured as total soil nitrogen).16 All the biocontrol beetles have been released and have established populations in New York. Even though they have spread naturally and are widely distributed, release sites have higher herbivory levels, so it may be worthwhile to release more even when they are present. The Galerucella beetles are licensed in New York, but may require permits to transport across county or state lines (contact NYS DEC). They can be collected from existing populations in the field (by you or a cooperator), reared on plants in pots, or bought from a supplier (generally the most expensive option).17 See  for detailed methods on collecting and rearing.
Manual or Mechanical Control
- Plant native woody species to eventually shade out areas of purple loosestrife.
- Where possible, minimize water fluctuations that lead to areas of exposed, wet soils.
- For small or sparse patches, hand-pull or dig with weed wrench when ground is wet. (Use a small piece of wood for leverage with the weed wrench in mucky conditions.) All plant parts can re-root and re-sprout, so bag and dispose of all material. Soil disturbance will promote loosestrife germination and resprouting, so hand-pulling must be repeated until seed bank and viable root fragments are depleted (2-3 years).
- Seeds (including those from previous years) are easily spread, so clean boots, clothing, and equipment of seeds, dirt, and mud before leaving the site.
- For medium- to high-density patches of at least ½ acre, release biocontrol agents (Galerucella beetles). To increase chances of success with this method, consider having soil samples analyzed for total nitrogen, and prioritize beetle release for sites with soil N < 0.33%.16
- Cutting stems during flowering prevents seed production and depletes the seed bank, and may be helpful when combined with other control measures. Mowing can result in spread via stem fragments, but regular mowing can also stunt or kill loosestrife and can be a good way to contain a stand if the soil is not too soft, such as around the edge of a pond.
- Intensive rotational grazing (a specific type of grazing) with sheep has greatly reduced loosestrife cover and increased plant diversity in wet meadows.18 Light cattle grazing is effective at inhibiting loosestrife but might not eradicate it.
- Monitor to prevent establishment of other nonnative wetland plants such as reed canarygrass (Phalaris arundinacea) or common reed (Phragmites australis).17
- Eradicate small/light infestations early.
- For large/dense patches, reduce height, density, and seed production.
- If purple loosestrife exists as a stable (not increasing) part of a diverse wetland flora, it may not need management.
- If it occurs in a rich fen, calcareous wet meadow, acidic bog, kettle shrub pool, or other rare wetland or wetland that may support rare species, consult with the NYS DEC or appropriate conservation organizations about management.
- Lavoie, C. 2010. Should we care about purple loosestrife? The history of an invasive plant in North America. Biological Invasions 12:1967-1999.
- Munger, G.T. 2002. Lythrum salicaria. In: Fire Effects Information System. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. http://www.fs.fed.us/database/feis/plants/forb/lytsal/all.html [Accessed 16 August, 2016].
- Fickbohm, S.S., and W.-X. Zhu. 2006. Exotic purple loosestrife invasion of native cattail freshwater wetlands: Effects on organic matter distribution and soil nitrogen cycling. Applied Soil Ecology 32:123-131.
- Whitt, M.B., H.H. Prince, and R.R. Cox, Jr. 1999. Avian use of purple loosestrife dominated habitat relative to other vegetation types in a Lake Huron wetland complex. Wilson Bulletin 111:105-114.
- Houlahan, J.E., and C.S. Findlay. 2004. Effect of invasive plant species on temperate wetland plant diversity. Conservation Biology 18:1132-1138.
- McGlynn, C.A. 2009. Native and invasive plant interactions in wetlands and the minimal role of invasiveness. Biological Invasions 11:1929-1939.
- Schooler, S.S., P.B. McEvoy, and E.M. Coombs. 2006. Negative per capita effects of purple loosestrife and reed canary grass on plant diversity of wetland communities. Diversity and Distributions 12:351-363.
- Denoth, M., and J.H. Myers. 2007. Competition between Lythrum salicaria and a rare species: Combining evidence from experiments and long-term monitoring. Plant Ecology 191:153-161.
- Camacho, J.V., A.D.L. Martinez, R.G. Gomez, and J.M. Sanz. 2007. A comparative study of five horizontal subsurface flow constructed wetlands using different plant species for domestic wastewater treatment. Environmental Technology 28:1333-1343.
- Kiviat, E. 1996. American goldfinch nests in purple loosestrife. Wilson Bulletin 108:182-186.
- Maddox, J.D., and R.N. Wiedenmann. 2005. Nesting of birds in wetland containing purple loosestrife (Lythrum salicaria) and cattail (Typha spp.). Natural Areas Journal 25:369-373.
- Barbour, J.G., and E. Kiviat. 1997. Introduced purple loosestrife as host of native Saturniidae (Lepidoptera). Great Lakes Entomologist 30:115-122.
- Gratton, C. 2006. Interactions between a native silkmoth Hemileuca sp. and an invasive wetland plant, Lythrum salicaria. Annals of the Entomological Society of America 99:1182-1190.
- Grevstad, F.S. 2006. Ten-year impacts of the biological control agents Galerucella pusilla and G. calmariensis (Coleoptera: Chrysomeliae) on purple loosestrife (Lythrum salicaria) in central New York State. Biological Control 39:1-8.
- Albright, M.F., W.N. Harman, S.S. Fickbohm, H. Meehan, S. Groff, and T. Austin. 2004. Recovery of native flora and behavioral responses by Galerucella spp. following biocontrol of purple loosestrife. American Midland Naturalist 152:248-254.
- Hovick, S.M., and W.P. Carson. 2015. Tailoring biocontrol to maximize top-down effects: On the importance of underlying site fertility. Ecological Applications 25:125-139.
- Wilson, L.M., M. Schwarzlaender, B. Blossey, and C.B. Randall. 2004. Biology and Biological Control of Purple Loosestrife. Forest Health Technology Enterprise Team, USDA Forest Service, FHTET-2004-12. 83 p. http://www.fs.fed.us/foresthealth/technology/pdfs/Loosestrife.pdf [Accessed 1 December, 2016].
- Kleppel, G.S., and E. LaBarge. 2011. Using sheep to control purple loosestrife (Lythrum salicaria). Invasive Plant Science and Management 4:50-57.