General: Loosestrife Family (Lythraceae). Purple loosestrife is an erect perennial herb that grows up to 2.5 m tall, develops a strong taproot, and may have up to 50 stems arising from its base. Its 50 stems are four-angled and glabrous to pubescent. Its leaves are sessile, opposite or whorled, lanceolate (2-10 cm long and 5-15 mm wide), with rounded to cordate bases. Leaf margins are entire. Leaf surfaces are pubescent.

Each inflorescence is spike-like (1-4 dm long), and each plant may have numerous inflorescences. The calyx and corolla are fused to form a floral tube (also called a hypanthium) that is cylindrical (4-6 mm long), greenish, and 8-12 nerved. Typically the calyx lobes are narrow and thread-like, six in number, and less than half the length of the petals. The showy corolla (up to 2 cm across) is rose-purple and consists of five to seven petals. Twelve stamens are typical for each flower. Individual plants may have flowers of three different types classified according to stylar length as short, medium, and long. The short-styled type has long and medium length stamens, the medium type has long and short stamens, and the long-styled has medium to short stamens. The fruit is a capsule about 2 mm in diameter and 3-4 mm long with many small, ovoid dust-like seeds (< 1 mm long).

Mal et al., 1992, provide a detailed morphological description for L. salicaria. The authors also give details of the tristylous features of this species, as well as an account of its pollen structure and chromosome numbers. The plant’s habit, vegetative, and reproductive structures are illustrated with line drawings.

Other species of Lythrum that grow in the United States have 1-2 flowers in each leaf-like inflorescence bract and eight or fewer stamens compared to L. salicaria, which has more than two flowers per bract and typically twelve stamens per flower. Lythrum virgatum, another species introduced from Europe closely resembles L. salicaria, but differs in being glabrous (lacking plant hairs), and having narrow leaf bases. The latter two species interbreed freely producing fertile offspring, and some taxonomists (Rendall 1989) consider them to be a single species.

Distribution: Purple loosestrife is a hardy perennial herb with stunning spikes of purple flowers. A native of Eurasia, it was introduced to North America in the early 1800's where it first appeared in ballast heaps of eastern harbors (Stuckey 1980). Most likely seeds were transported as contaminants in the ballast or possibly attached to raw wool or sheep imported from Europe (Cole, 1926; Thompson et al., 1987).

The native range of L. salicaria is thought to extend from Great Britain to central Russia from near the 65th parallel to North Africa. It also occurs in Japan, Korea, and the northern Himalayan region. The species has been introduced to Australia, Tasmania, and New Zealand. Since its introduction to North America, this alien plant has spread rapidly into Canada, and throughout most of the United States where it has been reported from all states except Alaska, Florida, Louisiana, and South Carolina. Several factors have contributed to the spread of purple loosestrife such as its potential for rapid growth, its enormous reproductive capacity, lack of natural diseases or predators, its use as an ornamental, and for bee forage (Mal et al. 1992). For current U.S. distribution, please consult the Plant Profile page for this species on the PLANTS Web site.

The only other species that is similar to Purple Loosestrife is the native Lythrum alatum (Winged Loosestrife), which also occurs in wetlands. This latter species is a smaller and less aggressive plant with winged stems, while the stems of Purple Loosestrife are usually round (sometimes 4-angled). Their flowers are similar in appearance, although Winged Loosestrife has smaller flowers (½" across or less).

This introduced perennial plant is 2-5' tall, branching frequently below the inflorescence. The stems are variably hairy, becoming woody and glabrous below. The leaves are usually opposite, less often whorled in 3's; some of the upper leaves in the inflorescence may be alternate. These leaves are up to 4" long and ¾" across, becoming smaller as they ascend the stems. They are lanceolate, smooth along the margins, slightly hairy (especially the upper leaves), and clasp the stems. The upper stems terminate in long spikes of flowers about ½–2' long. Each flower is about ½–1" across, consisting of 6 purple petals, a green tubular calyx, 6 or more stamens, and a pistil with a stigma that is green and knobby. Each wrinkly petal has a dark purple line toward its base. The hairy calyx has 5 teeth at its apex and several veins along its length. Sometimes the flowers have fewer than 6 petals, and the relative length of their pistils and stamens is variable (in this regard, there are 3 different forms of flowers). The flowers are sessile against the flowering stalks, or they have very short pedicels. The blooming period occurs from mid-summer to early fall, and lasts about 2 months. Each flower is replaced by a small seed capsule that is surrounded by the tubular calyx. This capsule contains many tiny seeds that can float on water or be blown about by the wind. The root system is shallow and fibrous, frequently forming offsets by rhizomes. This plant often forms colonies, and can spread by its seeds, rhizomes, or segments of the roots and stems.

purple loosestrife, spiked lythrum, salicaire, bouquet violet

Lythrum salicaria var. tomentosum (Mill.) DC.:
Canada (North America)
United States (North America)

Lythrum salicaria L.:
Afghanistan (Asia)
Canada (North America)
India (Asia)
Japan (Asia)
Mongolia (Asia)
Peru (South America)
Russian Federation (Asia)
South Korea (Asia)
United States (North America)
China (Asia)

Canada

Origin: Exotic

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

United States

Origin: Exotic

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

Distribution: Europe, South-East and Central Asia, Siberia, North Africa, North America, Australia.

Purple Loosestrife occurs occasionally in NE Illinois and scattered counties elsewhere (see Distribution Map). It was introduced into the United States from Europe as a horticultural plant because of the showy flowers. Habitats include fens, marshes, borders of ponds and rivers, and ditches. This is species is still grown in flower gardens, using hybrids that are supposedly sterile. However, research has revealed that many of these hybrids can form viable seeds when wild forms of Purple Loosestrife are present in a given locality as a result of cross-pollination between these two groups of plants. Purple Loosestrife often escapes from cultivation and invades wetlands, sometimes forming dense stands that exclude other plants. This plant has become a major problem in Wisconsin and some of the northeastern states.

Great variability, especially in degree of indumentum and leaf shape, has led to recognition of many microspecies and infraspecific taxa that are not satisfactorily separated when the species is investigated over its geographic range. Apparent hybridization between Lythrum salicaria and L. virgatum and among the many races of L. salicaria in E Europe and Asia have further confused the taxonomy. Lythrum salicaria is recognized here as a single species with localized variants. Formal names are not recognized for variants within the species until a biosystematic study of the species complex can be made.

Perennial herbs or subshrubs, 0.3-1.5 m tall, scabrous or sparsely to densely gray pubescent [or tomentose], sometimes somewhat glabrescent. Stem erect, 4-angled. Leaves opposite or 3-whorled, sometimes alternate toward stem apex, ovate-lanceolate to broadly lanceolate, 2.5-10 × 0.5-1.5 cm, base rounded, truncate, or semiclasping, apex acute to subobtuse. Inflorescences terminal, spicate, 15-35 cm; bracts broadly lanceolate or deltoid-ovate. Flowers in 1- to multi-flowered whorled axillary cymes, shortly pedicellate. Floral tube 5-8 × 1.5-2 mm, 12-ribbed; sepals deltate, 0.5-1 mm; epicalyx segments erect, linear, 1.5-2 mm, much longer than sepals. Petals reddish purple to rose-purple, lanceolate-oblanceolate, 7-10 × 1.5-3 mm. Fl. Jul-Sep, fr. Oct. 2n = 30, 50, 58, 60.

Perennial, 40-70 cm tall. Leaves ovate-lanceolate, elliptic or lanceolate, acute to acuminate, base cordate-amplexicaul, 6-60 mm long, 2.5-15 mm broad. Spikes 9-45 cm long. Pedicels 1-2 mm. Hypanthium 12-ribbed. Epicalyx longer than or equalling the calyx. Petals 5.5-8.5 mm long, 2-3 mm broad, obovate-spathulate or obovate-oblanceolate. Ovary subsessile, 2-5 mm long, 0.75-1.5 mm broad. Capsule 4 mm long, 1.5 mm broad, narrowed. Seeds obovate, tip ±membranous.

Common in rice fields and wet places, 600-1500 m.

Lythrum anceps (Koehne) Makino; L. argyi H. Léveillé; L. intermedium Ledebour ex Colla; L. salicaria var. anceps Koehne; L. salicaria var. glabrum Ledebour; L. salicaria var. intermedium (Ledebour ex Colla) Koehne; L. salicaria var. mairei H. Léveillé.

At a distance, L. salicaria may be confused with Epilobium angustifolium, Verbena hastata, Teucrium canadense, or Liatris spp. Upon closer examination however, purple loosestrife is easily distinguished from these other magenta-flowered plants.

Comments: L. salicaria is native to Eurasia and was first reported from the northeastern coast of North America in 1814, (Stuckey 1980). Although purple loosestrife occurs in nearly all sections of the United States, the heaviest concentrations are in the glaciated wetlands of the northeast. Occurrences west of the Mississippi River appear to be scattered (Stuckey 1980), with the species establishing in reclamation projects in the west (Thompson and Jackson 1982).

Purple loosestrife is found in wetlands such as cattail marshes, sedge meadows, and open bogs. L. salicaria also occurs along stream and river banks and lake shores. In addition, the plant is found in ditches and other disturbed wet soil areas.

L. salicaria grows best in high organic soils, but tolerates a wide range of soils including clay, sand, muck, and silt (Thompson and Jackson 1982). Generally, the plant is found in full sun, but it can survive in 50% shade (Thompson and Jackson 1982). Typical associates include Typha latifolia, T. glauca, Phragmites australis, Spartina sp., Scirpus spp., and Carex spp. (Thompson and Jackson 1982).

Damp grasslands, banks. Almost throughout China [widespread in northern latitudes worldwide, Afghanistan, India, Japan, Korea, Mongolia, E Russia; N Africa, Europe, North America].

Purple Loosestrife occurs occasionally in NE Illinois and scattered counties elsewhere (see Distribution Map). It was introduced into the United States from Europe as a horticultural plant because of the showy flowers. Habitats include fens, marshes, borders of ponds and rivers, and ditches. This is species is still grown in flower gardens, using hybrids that are supposedly sterile. However, research has revealed that many of these hybrids can form viable seeds when wild forms of Purple Loosestrife are present in a given locality as a result of cross-pollination between these two groups of plants. Purple Loosestrife often escapes from cultivation and invades wetlands, sometimes forming dense stands that exclude other plants. This plant has become a major problem in Wisconsin and some of the northeastern states.

Foodplant / open feeder
imago of Altica lythri grazes on leaf of Lythrum salicaria

Foodplant / open feeder
imago of Altica palustris grazes on leaf of Lythrum salicaria

Foodplant / open feeder
larva of Ametastegia equiseti grazes on leaf of Lythrum salicaria
Other: major host/prey

Foodplant / open feeder
imago of Aphthona lutescens grazes on leaf of Lythrum salicaria
Other: sole host/prey

In Great Britain and/or Ireland:
Foodplant / saprobe
effuse colony of Coremiella dematiaceous anamorph of Coremiella cubispora is saprobic on dead stem of Lythrum salicaria
Remarks: season: 7-10
Other: major host/prey

Foodplant / parasite
Erysiphe lythri parasitises Lythrum salicaria

Foodplant / open feeder
imago of Galerucella calmariensis grazes on leaf of Lythrum salicaria

Foodplant / open feeder
imago of Galerucella pusilla grazes on leaf of Lythrum salicaria

Foodplant / internal feeder
larva of Hylobius transversovittatus feeds within rootstock (woody) of Lythrum salicaria
Other: sole host/prey

Foodplant / saprobe
apothecium of Lachnum salicariae is saprobic on dead stem (base) of Lythrum salicaria

Foodplant / open feeder
imago of Lythraria salicariae grazes on leaf of Lythrum salicaria

Foodplant / internal feeder
larva of Nanophyes marmoratus feeds within ovules of Lythrum salicaria
Other: sole host/prey

Foodplant / feeds on
larva of Phytobius comari feeds on Lythrum salicaria

Foodplant / open feeder
imago of Psylliodes picina grazes on leaf of Lythrum salicaria

Foodplant / spot causer
epiphyllous, punctiform pycnidium of Septoria coelomycetous anamorph of Septoria brissaceana causes spots on live leaf of Lythrum salicaria
Remarks: season: 7-9

Foodplant / saprobe
fruitbody of Sistotrema octosporum is saprobic on dead, decayed stem of Lythrum salicaria
Other: minor host/prey

Foodplant / parasite
hypophyllous colony of Stenella dematiaceous anamorph of Stenella lythri parasitises dying leaf of Lythrum salicaria

The flowers attract long-tongued bees and butterflies, including Bombus spp. (Bumblebees) and the butterfly Pieris rapae (Cabbage White). The seeds are too small to be of any interest to birds, and it is unclear to what extent mammalian herbivores feed on the foliage. There have been attempts recently to release leaf beetles from Europe as a biocontrol measure. This species probably provides cover to some wetland species of birds because of its tall dense vegetation.

Purple loosestrife begins to bloom in July and continues until September or October. The flowers are pollinated by several different types of bees from the Megachilinae, Apinae, Xylopinae, and Bombinae; and by several butterflies: Pieris rapae, Colias philodice, and Cercyonis pegala (Balogh 1985). Seed production is prolific. There is an average of 120 seeds per capsule and up to 900 capsules per plant (Rawinski 1982). The lowest capsules on the stem are dehiscing while the upper stem capsules are still green.

The seeds are small, weighing 0.06 mg each (Shamsi and Whitehead 1974). Dispersal is mainly by wind, but seeds can also be transported on the feet of waterfowl or other wetland animals. Red-winged blackbirds have been observed eating the seeds (Rawinski 1982). Humans carry seeds inadvertently on clothing and shoes and in some instances, bee-keepers have purposely sown seeds in headwaters and wetlands to provide a steady source of nectar for their bees. The seeds and cotyledon stage seedlings are buoyant and can be dispersed by water currents (Balogh 1985). The seed bank potential for L. salicaria is enhanced by the high viability of the seeds. Viability decreased from 99% to 80% after two years of storage in a natural body of water (Rawinski 1982).

Seeds of L. salicaria can germinate in acidic or alkaline soils; in soils that are nutrient rich or nutrient poor. Light requirements for germination are minimal (Shamsi and Whitehead 1974). Temperature at the soil surface is a critical factor for germination. Seeds will germinate at temperatures ranging from 15 to 20 degrees C (Balogh 1985). Seeds germinate in high densities--about 10,000 to 20,000/sq. meter (Rawinski 1982). The interval between germination and flowering is eight to ten weeks (Rawinski 1982).

Seedlings that germinate in the spring grow rapidly and will produce a floral shoot up to 30 cm in length the first year. Summer-germinated seedlings develop only five or six pairs of leaves before the end of the growing season (Shamsi and Whitehead 1974). Spring-germinated seedlings have a higher survival rate than summer-germinated seedlings. Open grown shoots have a greater reproductive output than shoots growing in dense stands (Rawinski 1982). Once established, seedlings can survive shallow flooding of up to 30-45 cm in depth (Thompson and Stuckey 1980.).

The taproot is strongly developed in the seedling stage and persists throughout the life of the plant (Shamsi and Whitehead 1974). In mature plants, the taproot and major root branches become thick and woody (Rawinski 1982). The semi-woody aerial shoots die in the fall but persist for one to two years making stands of L. salicaria very dense. New shoots arise the following spring from buds at the top of the rootstocks (Rawinski 1982).

The rootstock is the main organ of perennation and vegetative spread is therefore limited (Shamsi and Whitehead 1974). L. salicaria can spread vegetatively by resprouting from cut stems and regenerating from pieces of root stock (Rawinski 1982).

Infestations of purple loosestrife appear to follow a pattern of establishment, maintenance at low numbers, and then dramatic population increases when conditions are optimal. L. salicaria flourishes in wetland habitats that have been disturbed or degraded from draining, natural drawdown in dry years, bulldozing, siltation, shore manipulation, cattle trampling, or dredging. Mudflats exposed following drawdowns will be quickly colonized if a loosestrife seed source is present. Seeds are usually present in such large numbers and germinate in such high densities that growth of native seedlings is suppressed (Rawinski 1982). Loosestrife crowds or shades out native species and eventually becomes a virtually monospecific stand.

L. salicaria is an extremely successful invader of wetlands that have been subjected to some type of disturbance: drawdown, siltation, drainage, ditching. Expansion in a wetland can be extensive and sudden due to the abundance of seeds produced and the rapid growth of seedlings. High seed viability and prolific seed production can build up a seed bank of massive proportions.

Purple loosestrife seed germinates in such high densities that it outcompetes native seedlings. The buildup of debris around the roots enable loosestrife to invade deeper water and to form dense stands that shade out other emergents and push out floating vegetation by closing open water spaces.

Fl. Per.: July-Sept.

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 1
Species: 7
Species With Barcodes: 1

Canada

Rounded National Status Rank: NNA - Not Applicable

United States

Rounded National Status Rank: NNA - Not Applicable

Rounded Global Status Rank: G5 - Secure

Please consult the PLANTS Web site and your State Department of Natural Resources for this plant’s current status, such as, state noxious status, and wetland indicator values.

Management Requirements: Once purple loosestrife becomes established in a wetland it displaces endemic vegetation through rapid growth and heavy seed production (Rawinski 1982). L. salicaria has a detrimental impact on native wetland vegetation and associated wildlife. Important wildlife food plants such as cattails and pondweed are displaced or shaded out as L. salicaria expands across a wetland. If purple loosestrife is left unchecked, the wetland eventually becomes a monoculture of loosestrife (Rawinski 1982). The invasion of L. salicaria leads to a loss of plant diversity, which also leads to a loss of wildlife diversity.

Management objectives may include eradicating populations, containing populations or preventing establishment. Monitoring should be used to track the accomplishment of these objectives.

The best time to search for purple loosestrife is in July and August when the plants are blooming. The bright magenta flowers are easy to spot at a great distance. Aerial surveys can be used to note the yearly position of large populations. An advancing or receding boundary would be identifiable from air photos. Ground surveys are more feasible for tracking small populations and finding newly established populations. Look for seedlings in June.

The following individuals are involved in public awareness campaigns or wetland surveys:

John Schwegman, Director, Botany Program, Illinois Dept. Conservation, Springfield, Illinois 62706.

Rich Henderson, Consultant, Natural Areas Management, 2845 Timberlane Verona, Wisconsin 53593.

Noel Cutright, Purple Loosestrife Task Force, 3352 Knollwood Rd., West Bend, Wisconsin 53095.

Purple loosestrife Survey-Nevin, Wisconsin Dept. Natural Resources, P.O. Box 7921, Madison, Wisconsin 53791.

Jay Rendall, Coordinator, Purple Loosestrife Program, Minnesota Dept. Natural Resources, Box 25, 500 Lafayette Rd., St. Paul, MN 55155.

Several control methods have been attempted with varying degrees of success. Natural area managers must determine their objectives first. Is it more feasible to contain or control populations of purple loosestrife? Large populations extending over three acres or more will be difficult if not impossible to completely eradicate using presently known methods. These large populations should be contained at their present position. Preventing the expansion can be accomplished through hand-pulling new plants along the periphery or spraying herbicide on plants extending beyond the main body of the population. Smaller populations can be controlled through eradication. Populations up to three acres can be cleared with herbicides or hand-pulled, depending upon the size of the work crew and time available.

CHEMICAL: The herbicide glyphosate is most commonly used to control L. salicaria. Glyphosate is available under the trade names RoundupTM and RodeoTM, manufactured by Monsanto. Roundup cannot be used over water. Another formulation of glyphosate known as Rodeo contains a non-ionic surfactant and has been approved for use over water. Ortho X-77 is the non-ionic surfactant recommended for use with Rodeo, but several other non-ionic surfactants were cleared for use with Rodeo in 1985 (Balogh 1985).

The major disadvantage in using Rodeo is that glyphosate is a non-specific systemic. Broadcast spraying of non-selective herbicides kills all of the vegetation and may result in an increase in loosestrife density because of seed germination following the removal of competing perennial vegetation (Minnesota DNR 1987). Spot application of Rodeo directly onto L. salicaria would ensure that no large holes would appear in the marsh vegetation and that competition would be unaffected. The safest method of applying glyphosate herbicide is to cut off all stems at about 6 inches and then paint or drip onto the cut surface a 20-30% solution (Henderson 1987).

Spraying should be done after the period of peak bloom, usually late August (Balogh 1985, Rawinski 1982). One to two percent solutions of Rodeo have been recommended as sufficient to kill L. salicaria (Henderson 1987, Minnesota DNR 1987, Balogh 1985, Thrune pers. comm.). Work done by Jim Reinartz at the U.W.-Milwaukee Field Station indicates it is best to spray no more than 25-50% of a plant's foliage (Henderson 1987). This will help protect against overspraying which might damage adjacent vegetation.

It is critical that any control effort be followed up the same growing season and for several years afterwards since some plants will be missed, new seedlings may sprout from the extensive seed bank, and a few plants will survive the low-dosage treatment (Henderson 1987, Minnesota DNR 1987). Higher dosage and careless application, however, inevitably kills more surrounding vegetation and leads to establishment of loosestrife seedlings (Minnesota DNR 1987).

For larger infestations where spot application of glyphosate is not practical, broadleaf herbicides can be used. They have the advantage of not harming monocot species, which are the dominants in most wetland types. Broadleaf herbicides (2,4-D based) can be effective on loosestrife if applied in late May or early June (Henderson 1987). The disadvantage of treating early in the season is that purple loosestrife plants are easily overlooked when not in flower. A combination of 2,4-D and dicamba has been used on a limited basis in western irrigation ditches (Jackson pers. comm.). The EPA has approved a 1:1 tank mix of these two products. Once L. salicaria has reached 10-15% of its mature growth, it can be sprayed with good results. To ensure complete coverage and compensate for spotty application, repeat the treatment once during the growing season (Jackson pers. comm.).

PULLING: Hand-removal is recommended for small populations and isolated stems. Ideally, the plants should be pulled out before they have set seed. The entire rootstock must be pulled out since regeneration from root fragments is possible. Be sure to minimize disturbances to the soil and native vegetative cover. Remove uprooted plants and broken stems from the area since the broken stems can resprout (Rawinski 1982).

REPLACEMENT: Replacement control has been attempted in several wildlife refuges (Balogh 1985, Rawinski 1982). Rawinski (1982) sowed Japanese millet (Echinochloa frumentacea) with L. salicaria and found that the millet seedlings outcompeted the loosestrife seedlings. The millet must be planted immediately after marsh drawdown has occurred. Balogh (1985) found that Japanese millet does not regenerate well and would have to be replanted every year. Balogh (1985) attempted a replacement treatment using native seed. Polygonum lapathifolium was seeded with purple loosestrife and the Polygonum outcompeted the loosestrife. However, the following spring L. salicaria would start growing first due to its overwintering rootstock. Replacement methods would have a very limited application within a natural area, but they may be useful to control or contain loosestrife populations on buffer property.

BIOLOGICAL: Several characteristics of L. salicaria make it an ideal candidate for biological control (USFWS 1987). Batra (et al. 1986) recommends detailed ecological and host-specificity studies for six European species: a cecidomyiid fly whose galling can reduce purple loosestrife foliage by 75% and seed production by 80%; a stem and root boring weevil; two chrysomelids that can cause nearly 50% defoliation; and two weevils that mine ovaries and seeds. The results of Batra et al. (1986) indicated that the chances of successful biological control of L. salicaria in North America are excellent.

The following individuals are familiar with L. salicaria and can suggest control strategies:

Dottie Thompson, Horicon National Wildlife Refuge, Rt. 2, Mayville, Wisconsin 53050. (414) 387-2658.

Rich Henderson, Consultant, Natural Area Management, 2845 Timberlane, Verona, Wisconsin 53593. (608) 845-7065.

John Schwegman, Director, Botany Program, Illinois Dept. Conservation, Springfield, Illinois 62706.

Tom Jackson, Leader, Field Research Station, U.S. Fish and Wildlife Service, P.O. Box 25007, Denver, Colorado 80225.

Jay Rendall, Coordinator, Purple Loosestrife Program, MN Dept of Natural Resources, Box 25, 500 Lafayette Rd, St. Paul, MN 55155.

Management Research Programs: A research project in Wisconsin includes investigations on different methods of control and different herbicide treatments. The ecology of L. salicaria including seed bank buildup is also under investigation. Contact: Rich Henderson, Consultant-Natural Area Management. 2845 Timberlane, Verona, Wisconsin 53593.

Hand cutting purple loosestrife and fertilizing cattails under varying degrees of wetness is being studied at Indiana Dunes National Lakeshore. Contact: Ron Heibert, Chief, Division of Science, 1100 N. Mineral Springs Rd., Porter, Indiana 46304.

Research on the effectiveness of various chemical controls will be conducted in Illinois, pending funding. Contact: John Schwegman, Director, Botany Program, Illinois Dept. Conservation, Springfield, Illinois 62706.

A research project funded by the Metropolitan Council (MN) is being conducted by Hennepin County Park Reserve. Chemical control techniques are to be evaluated for 2 years in control plots. Contact: Tom Hollenhorst, Hennepin County Park Reserve, 3800 Co. Rd. 24, Maple Plain, MN 55359.

The Minnesota Legislative Commission on Minnesota Resources (LMCR) has funded a comprehensive control program over a two year period. The program will inventory purple loosestrife in Minnesota, keep abreast of current contol methods and research, implement a prioritized control program, monitor environmental impact and effectiveness of control, promote public awareness campaigns, and coordinate agencies control efforts within the state. Contact: Jay Rendall, Coordinator, Purple Loosestrife Program, MN Dept of Natural Resources, Box 25, 500 Lafayette Rd, St. Paul, MN 55155.

Management Research Needs:

Biological control methods should be a priority for research. Repeated chemical treatments are costly and the long-term effects on natural systems are not fully understood. Preliminary investigations in Europe have revealed several host-specific insects that keep L. salicaria in check. Further research is warranted. Research is needed to assess the potential productivity of the seed bank. How extensive is the seed bank in a wetland in comparison to the size of the above-ground population? What is the rate of seed buildup? Can the age of a seed bank be determined? What is the viability of purple loosestrife seed? More research is needed on herbicide treatments that will give the most selective application with the least impact to the surrounding competitive vegetation, i.e. wick applications, etc. Available information suggests that research on mechanical treatments will not yield helpful results.

Please contact your local agricultural extension specialist or county weed specialist to learn what works best in your area and how to use it safely. Always read label and safety instructions for each control method. Trade names and control measures appear in this document only to provide specific information. USDA, NRCS does not guarantee or warranty the products and control methods named, and other products may be equally effective.

An important consideration in controlling purple loosestrife is its prolific seed production, the ease with which seeds are dispersed, and their ability to remain viable for several years. Also, this plant can spread vegetatively by resprouting from stem and rootstock cuttings. Other considerations in selecting control methods are their detrimental effects on native species and the possibility for reinvasion by purple loosestrife or other exotic species. In addition, native plants of similar appearance should not be subjected to control. Purple loosestrife may superficially resemble plants of the mint family or species of the genera Epilobium and Liatris. Proper identification is an important consideration in controlling exotic loosestrife.

In natural areas, it may be more feasible to contain populations of purple loosestrife than control them. Large populations extending over one hectare or more will be difficult to eradicate. Containing them may be more feasible. Removing plants or applying herbicides to ones extending beyond the main population can accomplish this. If loosestrife cannot be eradicated, efforts should then concentrate on keeping it from invading the highest quality areas (Butterfield et al., 1996.

Manual, Mechanical, and Replacement: Mowing, burning, and flooding are largely ineffective. Cutting followed by flooding so that cut plant stalks are completely immersed has shown some success. However, flooding may encourage the spread of purple loosestrife seed present in the soil and may result in the regeneration of new plants from stem fragments. Mature plants can withstand short-term immersion. Burning is largely ineffective and it may also stress native plants and subsequently enhance loosestrifes’ competitive advantage (Butterfield et al., 1996).

Hand removal is effective for small populations and isolated plants. Younger plants (one to two years old) can be pulled by hand. Plants should be removed, prior to seed set, with minimal disturbance to the soil. Removal after seed-set will scatter the seeds. The entire rootstock must be pulled out because of the potential for regeneration from root fragments. A hand cultivator or similar implement will be helpful for older plants, especially those in deep organic soils. Uprooted plants and broken stems need to be removed from the site since such fragments can re-sprout. Bagging plants for removal will prevent their spread along the exit route. Follow-up treatments are recommended for three years after plants are removed. Clothing and equipment used during plant removal should be cleaned to remove contaminating seeds.

Replacement control has been attempted in several wildlife refuges. Research has shown that Japanese millet (Echinochloa frumentacea Link) seedlings outcompete purple loosestrife seedlings. The millet must be planted immediately after marsh drawdown and replanted each year because it does not regenerate well. Replacement seeding trials using native pale smartweed (Polygonum lapathifolium L.) showed that it also out-competed purple loosestrife. Replacement methods have obvious limited application in natural areas, but they may provide control of loosestrife populations on bordering property (Butterfield et al. 1996).

Herbicide Control: Various chemical treatments have been used on purple loosestrife with varying success. Many herbicides are not specific to purple loosestrife and may not be specifically licensed for such use. Label directions for application and use according to local, state, and federal regulations must always be observed.

In areas with populations exceeding 100 plants (up to 1.6 ha in size) where hand-pulling is not feasible, application of a glyphosate herbicide to individual purple loosestrife plants provides effective control Glyphosate is available under the trade names Roundup® and Rodeo®. Rodeo is registered for use over open water and is the most commonly used herbicide to control purple loosestrife. Glyphosate is nonselective and can kill desirable plants associated with loosestrife if applied carelessly. Application to the tops of plants alone can be effective and limits exposure of non-target species (Butterfield et al. 1996).

Herbicide treatment should be conducted as early as possible during the manufacturer's recommended time of application in order to kill the plants and prevent seed production. Application is most effective when plants have just begun flowering. Timing is important because seed set can occur if plants are in mid- to late flower. Where possible, the flower heads should be cut, bagged, and removed from the site prior to application to prevent seed set. Rodeo applied as a 1.5% solution (2 oz. Rodeo/gallon clean water) with the addition of a wetting agent, as specified on the label has been shown to provide control. Another option, which may be more effective, is to apply glyphosate twice during the growing season. The plants should be sprayed as described above when flowering has just started and a second time two to three weeks later (Butterfield et al. 1996).

Application of ghyphosate from a vehicle-mounted sprayer is generally necessary in areas with extensive stands of purple loosestrife. The most effective control can be achieved by beginning treatment at the periphery of large patches and working toward the center in successive years. This technique allows native vegetation to re-invade the treated area as the loosestrife in eliminated (Butterfield et al. 1996).

A combination of 2,4-D and Banvel® (dicamba) has been used on a limited basis. This formulation is broadleaf specific and apparently would not hurt the dominants if sprayed in a cattail marsh or communities dominated by rushes, sedges, and grasses. Spraying produces good control once loosestrife has reached 10-15% of its mature growth. Treatment is more effective if repeated once during the growing season (Butterfield et al. 1996).

Biological Control: Several biological control agents have the potential to aid in the control of purple loosestrife. Of 120 species of phytophagous insects associated with purple loosestrife in its natural range in Europe, 14 species were considered host-specific to the target plant. From this group, six species have been selected as the most promising for biological control. These species were a root-mining weevil, Hylobius transversovittatus Goeze, which attacks the main storage tissue of purple loosestrife; two leaf-eating beetles, Galerucella calmariensis L., and G. pusilla Duftschmid, which are capable of completely defoliating the plant; two flower-feeding beetles, Nanophyes marmoratus Goeze and N. brevis Boheman, which severely reduce seed production; and a gall midge, Bayeriola salicariae Kieffer, which similarly reduces seed production by attacking the flower buds. Five of the six species are found throughout its range in Europe and the sixth, N. brevis, is restricted to southern Europe (Malecki et al. 1993; Weedin et al. 1996).

The most promising insects appear to be the root-mining weevil, H. transversovittatus, and the two leaf-eating beetles, G. calmariensis and G. pusilla, because of their broad geographic ranges and the amount of damage done to the host plant. In June of 1992, all three species were approved by USDA, APHIS for introduction into the United States. The insects were released in New York, Pennsylvania, Maryland, Virginia, Minnesota, Oregon, and Washington. Releases were also approved in Canada (Malecki et al. 1993).

The two Galerucella species successfully over-wintered and began oviposition at all release sites. The other species, H. transversovittatus, was proving more difficult to establish, because of its long life cycle and low fecundity. The investigators predict that all three species will become established throughout the North American range of purple loosestrife. Furthermore, H. transversovittatus is expected to have the greatest negative impact to L. salicaria. However, a combination of various phytophagous insects will provide greater control than any one species. Control of purple loosestrife will be achieved more rapidly in mixed plant communities where competition for space and nutrients is greater. A reduction in the abundance of purple loosestrife to approximately 10% of its current level over about 90% of its range is expected (Malecki et al. 1993).

In order to evaluate the potential of fungus pathogens to control purple loosestrife, a survey was conducted on fungi associated with that plant. During the three year study, 5265 fungal isolates were obtained. Thirty-one taxa were found that had not previously been reported from purple loosestrife. Tests for the pathogenicity to purple loosestrife are being tested (Nyvall 1995).

Noxious and highly invasive.

Ethnobotanic: Immigrants might have deliberately introduced L. salicaria for its value as a medicinal herb in treating diarrhea, dysentery, bleeding wounds, ulcers, and sores, for ornamental purposes, or as a source of nectar and pollen for beekeepers (Hayes 1979; Jones 1976; Malecki et al. 1993; Stuckey 1980). In states where it is permitted, purple loosestrife continues to be promoted by horticulturists for its beauty as a landscape plant and for bee-forage. Purple loosestrife has been of interest to beekeepers because of its nectar and pollen production. However, honey produced from it is apparently of marginal quality (Feller-Demalsy & Parent 1989).

Horticultural: Horticultural cultivars of purple loosestrife (Lythrum spp.) were developed in the mid-1900s for use as ornamentals. Initially, these were thought to be sterile, and therefore safe for horticultural use. Recently, under greenhouse conditions, experimental crosses between several cultivars and wild purple loosestrife and the native L. alatum produced hybrids that were highly fertile (Ottenbreit 1991; Ottenbreit & Staniforth 1994). Comparable, subsequent experiments performed under field conditions produced similar results, suggesting that cultivars of purple loosestrife can contribute viable seeds and pollen that can contribute to the spread of purple loosestrife (Lindgren & Clay 1993). Ottenbreit & Staniforth (1994) indicate that such results suggest the need to prohibit cultivars of this species.

Noxiousness: Purple loosestrife grows most abundantly in parts of Canada, the northeastern United States, the Midwest, and in scattered locations in the West. Although this species tolerates a wide variety of soil conditions, its typical habitat includes cattail marshes, sedge meadows, and bogs. It also occurs along ditch, stream, and riverbanks, lake shores, and other wet areas. In such habitats, purple loosestrife forms dense, monospecific stands that can grow to thousands of acres in size, displacing native, sometimes rare, plant species and eliminating open water habitat. The loss of native species and habitat diversity is a significant threat to wildlife, including birds, amphibians, and butterflies, that depend on wetlands for food and shelter. Purple loosestrife monocultures also cause agricultural loss of wetland pastures and hay meadows by replacing more palatable native grasses and sedges (Mal et al. 1992; Thompson et al. 1987).

Having a noxious weed designation in some states prohibit its importation and distribution, but it is readily available commercially in many parts of the country. Lythrum salicaria has been labeled the “purple plague." because of its epidemic devastation to natural communities. The species is included on the Nature Conservancy’s list of “America’s Least Wanted -The Dirty Dozen” (Flack & Furlow 1996).

Impact/Vectors: Naturalized purple loosestrife was relatively obscure from the time of its introduction into North America in the early 1800s (Pursh 1814) until 1930, when a significant increase in populations invading wetlands and pastures was documented (Strefeler et al. 1996b). Reasons for the apparent sudden colonization and spread of this species include the disturbance of natural systems by human activities including agricultural settlement, construction of transport routes such as canals, highways, and perhaps, nutrient increases to inland waters (Mal et al. 1992; Malecki et al. 1993). Absence of natural enemies and ornamental use are other possible causes for purple loosestrife’s rapid expansion in North America (Thompson et al, 1987). Recently created irrigation systems in many western states have supported further establishment and spread of L. salicaria (Malecki et al. 1993).

The acquisition of adaptive characteristics from native species of Lythrum may have enhanced purple loosestrife’s invasive success. It will hybridize with Lythrum alatum, a widespread, native North American species, in natural settings. Under certain circumstances fertile hybrids are produced that can cross with weedy purple loosestrife. Such interspecific hybrids could serve as a “hybrid bridge” for the transfer of adaptive traits from native L. alatum into weedy populations of purple loosestrife (Anderson & Ascher 1993; Strefeler et al. 1996b).

North American naturalized populations of purple loosestrife often form monospecific stands, whereas, in its native Eurasian habitat the species comprises 1-4% of the vegetative cover (Batra et al. 1986; Strefeler et al. 1996b). Purple loosestrife causes annual wetland losses of about 190,000 hectares in the United States (Thompson et al. 1987; Mal et al. 1997). The species is most abundant in the Midwest and Northeast where it infests about 8,100 hectares in Minnesota, 12,000 ha in Wisconsin, over 12,000 ha in Ohio, and a larger area in New York State. Recent distributional surveys document the occurrence of monocultures in every county in Connecticut, where it has been found in 163 wetland locations (Ellis and Weaver 1996; Ellis 1996). At the Effigy Mounds National Monument (EFMO), combined populations of purple loosestrife cover an area of 5 to 10 hectares growing in regularly disturbed sites. This species has a major visual impact on the vegetation of EFMO, and it has the potential to invade and replace native communities endangering the areas' primary resources. (Butterfield et al. 1996). In response to the alarming spread of this exotic species, at least 13 states (e.g., Minnesota, Illinois, Indiana, Ohio, Washington, and Wisconsin) have passed legislation restricting or prohibiting its importation and distribution (Malecki et al. 1993; Strefeler et al. 1996b).

Numerous studies demonstrate the aggressive and competitive nature of purple loosestrife. Fernald (1940) reported a loss of native plant diversity in the St. Lawrence River floodplain following the invasion of purple loosestrife and another exotic, Butomus umbellatus L. Gaudet and Keddy (1988) report declining growth for 44 native wetland species after the establishment of Lythrum. Among the species tested, Keddy (1990) found that purple loosestrife was the most competitive. His hierarchical rank, arranged from most to least competitive, illustrates the dominance of this invasive weed over many common natives: Lythrum>Cyperus>Juncus> Eleocharis> Mimulus>Verbena. In the Hamilton Marshes adjacent to the Delaware River, annual above-ground production of L. salicaria far exceeded all other plant species’ production combined.

Purple loosestrife provides little food, poor cover, and few nesting materials for wildlife (Mann 1991). Waterfowl nesting becomes more difficult as clumps of L. salicaria restrict access to open water and offer concealing passageways for predators such as foxes and raccoons (Mal et al. 1992). Non-game species, including black terns and marsh wrens, also lose nesting sites when purple loosestrife infests their normal habitats. Balogh and Bookhout (1989a) report that dense stands of purple loosestrife provide poor waterfowl and muskrat habitat. Red-wing blackbirds appear to be the only species to cope with changes in wetlands caused by purple loosestrife (Balogh and Bookhout 1989a). In many areas where L. salicaria populations have increased, wildlife species have declined. While some studies may fail to demonstrate cause and affect relationship, they firmly establish circumstantial evidence implicating that Lythrum’s invasion is responsible for major changes in wetland communities (Mal et al. 1992).

Purple loosestrife prefers moist, highly organic soils but can tolerate a wide range of conditions. It grows on calcareous to acidic soils, can withstand shallow flooding, and tolerates up to 50% shade. Purple loosestrife has low nutrient requirements and can withstand nutrient poor sites. Under experimental, nutrient-deficient conditions, the root/shoot ratio increased and provided purple loosestrife with a competitive advantage over the native species Epilobium hirsutum. Survival and growth of L. salicaria was greatly improved by fertilizer treatment and greater spacing between plants. Such results suggest that excessive use of fertilizers and the release of phosphates, nitrates, and ammonia into the environment has enhanced the success of Lythrum (Mal et al., 1992; Shamsi and Whitehead, 1977a and b).

Purple loosestrife flowers from July until September or October. Flowering occurs 8-10 weeks after initial spring growth. The lowermost flowers of the inflorescence open first and flowering progresses upward. The capsules mature in the same sequence and the lowermost will ripen and disperse its seeds while flowering is still occurring further up the inflorescence (Butterfield et al. 1996). Thompson et al. (1987) estimated that on average, a mature plant produces about 2,700,000 seeds annually. Purple loosestrife seeds are mostly dispersed by water, but wind and mud adhering to wildlife, livestock, vehicle tires, boats, and people serve also as agent. Seeds are relatively long-lived, retaining 80% viability after 2-3 years of submergence (Malecki 1990). Welling & Becker (1990) investigated seed bank dynamics in three wetland sites in Minnesota and noted a mean density of 410,000 seeds per square meter in the top 5 cm of soil, which was more than all other species combined.

Spring-germinated seedlings have a higher survival rate than summer-germinated seedlings. Seedlings that germinate in the spring will flower the first year, whereas, summer-germinated seedlings develop only five or six pairs of leaves before the end of the growing season. Since its seeds are small, weighing about 0.06 mg each and carry little food reserves, germination must occur under conditions where photosynthesis can occur immediately. A strong taproot develops quickly in seedlings and persists throughout the life of the plant. The aerial shoots die in the fall and new shoots arise the following spring from buds on the rootstocks. Shoots destroyed by fire, herbicides, or mechanical removal can also regenerate from the rootstock. As plants mature, they produce more and more aerial shoots forming very dense clumps of growth. Purple loosestrife can spread vegetatively by resprouting from stem cuttings and from regeneration of pieces of root stock (Mal et al. 1992). Rhizomatous growth is insignificant in purple loosestrife (Shamsi & Whitehead 1974a; Thompson et al. 1987).

The preference is full or partial sun, wet to moist conditions, and a mucky soil containing organic matter. Ordinary garden soil containing loam is satisfactory as long as there is adequate moisture. This plant can spread aggressively in some situations and can be difficult to destroy.

Stewardship Overview: Monitor natural areas for the presence of L. salicaria. Maintain preserves so that purple loosestrife cannot invade and flourish. For small infestations, eradication is possible with spot applications of glyphosate herbicides. Monitor the containment and control procedures.

Current methods for eradicating large, dense populations of loosestrife are not totally effective. Mechanical contol methods are ineffective, and the herbicide most effective is non-selective. Realistically, the long-term control of large populations may require biological controls and/or better herbicides, but their development is at least several years away. Therefore, containment and minimizing seed production are the present contol objectives for large dense populations. (MN DNR 1987)