PNW0380 Purple Loosestrife (Lythrum salicaria L.)

Purple loosestrife (Lythrum the Cascades, in Idaho, Oregon, bloom (late June to early Sep- salicaria L.), sometimes known and Washington, it is less tember in most areas). At this as purple lythrum, is an emer- prevalent west of the Cascade time, people can recognize the gent aquatic plant of Eurasian Range. characteristic purple-magenta origin. An erect, herbaceous floral mass easily at 100 yards. perennial, it became estab- It may be confused with fire- lished in the estuaries of north- IDENTIFICATION weed (Epilobium angustifolium), eastern North America by the blue vervain (Verbena hastata), early 1800s. It has since spread The name loosestrife has been and spirea (Spiraea douglasii). across mid-latitude North associated with several mem- Upon closer examination, American wetlands. Several bers of the loosestrife family subtle differences in color and modes of colonization or (Lythraceae), also with the floral structure among these escape are probable, including genus Lysimachia in the prim- plants make positive field ships’ ballast, livestock bed- rose family (Primulaceae). identification easy. Differences ding and forage, wool, and Although L. salicaria has more in site preference also help to purposeful import as seeds than 10 common names in separate purple loosestrife or rootstocks for gardens and America and Great Britain, from superficially similar spe- herb beds. Purple loosestrife the most established name is cies. Usually loosestrife grows was first found in 1929 in the purple loosestrife. Purple loose- on moist or saturated soils. Puget Sound area of Washing- strife is identified most easily Also, it is the only purple- ton. Now widespread east of during its long season of magenta flowered plant to

Purple loosestrife infesting a wetland. Purple loosestrife flower.

A Pacific Northwest Extension Publication Washington State University ¥ University of Idaho ¥ Oregon State University develop massive monospecific characteristic of the older blocks of showy floral displays clumps. Although lateral root over large wetland tracts. In crown growth offers new sites early autumn, a distinctive of origin for peripheral stems, but temporary color change purple loosestrife does not usually occurs after the grow- spread far by its roots. The ing season when leaves dry roots are not the creeping and turn bright red. The red type found in Canada thistle color may persist for 10 days. or field bindweed. Dead stalks remain standing through winter and have a characteristic brown tone that, BIOLOGY in combination with spire- shaped capsule clusters, Purple loosestrife is a prolific readily identifies the species. seed producer and spreads primarily by floating seeds. Usually purple loosestrife The type of watershed strongly leaves grow opposite each influences the rate and ease other on the four-sided (some- of expansion of a local infesta- times six-sided) stem. Leaves tion. Slow-moving streams Purple loosestrife growing are linear with smooth edges with broad alluvial deposits in a typical habitat. and do not have a petiole or offer many sites for wetland leaf stem. The leaves are more plants to colonize. These areas or less covered with fine hairs.

The purple-magenta colored, Usually loosestrife grows five- to six-petalled flowers on moist or saturated soils. grow on long spikes. Seeds Also, it is the only purple- develop in capsules that dehisce magenta flowered plant when mature, releasing the seed. Purple loosestrife seed to develop massive mono- production depends on plant specific blocks of showy age, size, and vigor. A 4- to floral displays over large 5-year-old plant with 30 stems wetland tracts. reportedly can contain about 1,000 capsules per stem and 90 seeds per capsule, producing are highly susceptible to purple an estimated 2,700,000 seeds. loosestrife infestation and Each seed is about the size of spread. Streams and wetlands a grain of sand. having shade-covered banks are less susceptible to invasion. A mature, well established Spread into other areas may purple loosestrife plant often have occurred from seed trans- grows up to 10 feet tall and ported by highway and recre- 5 feet wide. Thirty to 50 herba- ational vehicles, birds and Purple loosestrife flowers ceous stems arise from a com- other animals, including people. and opposite leaves on the mon rootstock to make the Seed maintains viability of more flowering spike. graceful, wide-topped crown than 80% for at least 3 years. Flower spikes of purple loosestrife. Purple loosestrife plants.

Judge habitat vulnerability to if you do not remove the entire range of purple loosestrife in invasion by purple loosestrife root. Plants less than 1 year old Eurasia. The insects introduced by existing plant associates. are easier to control by pulling. into the Pacific Northwest Presence of cattails, reed can- include a root mining weevil arygrass, sedges, or rushes in If you mow plants, cut stem (Hylobius transversovittatus), marshy areas or along riparian pieces can send out roots and two bud and leaf feeding wetlands identify an invasion establish new plants. Frequent beetles (Galerucella calmariensis prone habitat. Impacts on native mowing may be effective if the and G. pusilla), and a flower vegetation have been disas- cut stems dry rapidly. Purple bud weevil (Nanophyes mar- trous; purple loosestrife is a loosestrife is not a threat to moratus). vigorous competitor and can most cultivated crops. Large crowd out native vegetation, perennial rootstocks lie mostly • Root weevil adults feed completely dominating a site. within 12 inches of the soil on newly formed purple Although it can invade some- surface and are susceptible to loosestrife foliage. These what undisturbed habitats, any form of crop culture that weevils deposit their eggs the spread and dominance of includes annual tillage. How- in the soil or in the lower this weed accelerates greatly ever, cranberry beds, wild rice stem. Root weevil larvae in disturbed habitats. Impacts beds, and riparian meadows in penetrate and feed within on wildlife have not been well the Pacific Northwest may be the root, where they deplete studied; however, purple loos- highly susceptible to invasion. important sugar reserves estrife appears to reduce water- and diminish plant survival. fowl and aquatic fur bearer Biological control of purple activity severely. loosestrife appears to be a • Leaf feeding beetles affect sound management option. purple loosestrife in two No native herbivores or patho- ways. Adults consume CONTROL gens are known to suppress newly formed buds and infestations in North America. leaves, while larvae feed The shallow woody root system Research conducted during on buds, leaves, and stems. forms a dense mat, making it the last decade has focused on Severely infested stands difficult to pull established importing and releasing host- appear as though treated plants. The plant will resprout specific insects from the native by a foliar desiccant. • Flower bud weevil adults ing beetles have been the most advantage over more palatable initially feed on develop- effective thus far in the Pacific species. ing leaves near shoot tips Northwest. Plant biomass and later on closed flower and stand density have been For chemical control, refer buds. Flower bud larvae reduced by more than 90% at to the Pacific Northwest Weed develop within closed some infestations. The biocon- Management Handbook, an flower buds and consume trol agents are being widely annually revised extension the developing petals, sta- redistributed throughout the publication available from mens, and ovaries, thereby Pacific Northwest. the extension offices of inhibiting seed production. Oregon State University, Livestock graze early foliage Washington State University, Of these biological control but utilize the mature plant and the University of Idaho. organisms, the two leaf feed- less, giving plants a growth

By Robert Parker, Ph.D., Washington State University Extension weed scientist, and Larry C. Burrill, M.S., retired Oregon State University Extension weed scientist. Photos by Robert Parker and Dean G. Swan.

Use pesticides with care. Apply them only to plants, animals, or sites listed on the label. When mixing and applying pesti- cides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.

Pacific Northwest extension publications are produced cooperatively by the three Pacific Northwest land-grant universities: Washington State University, Oregon State University, and the University of Idaho. Similar crops, climate, and topography create a natural geographic unit that crosses state lines. Since 1949, the PNW program has published more than 550 titles, preventing duplication of effort, broadening the availability of faculty specialists, and substantially reducing costs for the participating states.

Issued by Washington State University Extension, Oregon State University Extension Service, University of Idaho Cooperative Extension System, and the U. S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Extension programs and policies comply with federal and state laws and regulations on nondiscrimination regarding race, sex, religion, age, color, creed, national or ethnic origin; physical, mental, or sensory disability; marital status, sexual orientation, and status as a Vietnam-era or disabled veteran. Evidence of noncompliance may be reported through your local Extensive office. Trade names have been used to simplify information; no endorsement is intended. Revised February 2002, reprinted April 2005. $1.00 PNW0380