Purple loosestrife [Lythrum salicaria L.][LYTSA][CalEPPC: Red Alert][CDFA list: B] Photographs Map of Distribution Biocontrol

Hyssop loosestrife [Lythrum hyssopifolium L.][LYTHY] Photographs

• purple loosestrife: purple lythrum, bouquet-violet, Lythrum salicaria vars. gracilior Turcz., tomentosum (P. Mill) DC., vulgare DC.
• hyssop loosestrife: grass poly, hyssop lythrum, Lythrum adsurgens Greene. The original spelling Lythrum hyssopifolia L. is sometimes used.

GENERAL DESCRIPTION:

• purple loosestrife: Erect perennial with showy pinkish-purple flower spikes, to 2(3) m tall. A mature plant can develop into a large clump up to 1.5 m in diameter. Above ground foliage usually dies during the cool season, and new shoots sprout from a broad woody crown in spring. Originally cultivated as an ornamental and medicinal herb, purple loosestrife has escaped cultivation and become a noxious weed of wetlands in many regions throughout temperate North America. Plants often form dense colonies that displace native vegetation and wildlife. In the Northeastern U.S., monotypic stands have perpetuated themselves for at least 20 years. Introduced from Eurasia. The black-margined and golden loosestrife beetles (Galerucella calmariensis, Galerucella pusilla), loosestrife root weevil (Hylobius transversovittatus), and loosestrife seed weevil (Nanophyes marmoratus) were released in certain states between 1992-94 as biocontrol agents. They are established in some areas, but do not exist in California at publication time.
• hyssop loosestrife: Prostrate to erect summer annual or biennial with small pale pink to lavender flowers, to 0.6 m tall. Hyssop loosestrife is a common weed of seasonal wetlands and agronomic crops, especially rice fields. Introduced from Europe.

SEEDLINGS:

• purple loosestrife: Cotyledons ovate, 3-5 mm long, tips rounded, bases wedge-shaped, glabrous, on petioles 1-2 mm long. Stalk below cotyledons (hypocotyl) often purplish-dotted. First and subsequent few leaves opposite, 5-8 mm long, resemble cotyledons.
• hyssop loosestrife: Cotyledons ovate, +/- fleshy, tips rounded, bases tapered, +/- sessile. First and subsequent few leaves resemble cotyledons.

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MATURE PLANT: Stems simple or branched, sometimes +/- square or 5-angled. Leaves sessile, margins smooth. Stipules lacking.

• purple loosestrife: Stems typically covered with short hairs. Leaves lanceolate, 5-14 cm long, base slightly lobed (cordate), covered with short hairs or glabrous, mostly opposite or whorled. Upper leaves sometimes alternate.
• hyssop loosestrife: Foliage pale green, glabrous. Leaves linear to oblong, 5-30 mm long, +/- rounded at the tip, typically ascending toward stem tip. Lower leaves opposite. Upper leaves usually alternate.

ROOTS and UNDERGROUND STRUCTURES:

• purple loosestrife: Taprooted and/or with locally spreading roots. Spreading roots typically form an expanded crown to ~ 0.5 m in diameter. New shoots grow from the expanded crown in spring. Roots can associate with mycorrhizae.
• hyssop loosestrife: Taproot to ~ 10 cm long, with fine lateral roots to ~ 5 cm long. Lower stems sometimes develop adventitious roots.

FLOWERS: Calyx tube (hypanthium) cylindrical, 4-6 mm long, longitudinally 8-12-ribbed, with 4-6 triangular sepal lobes 0.5-1 mm long at the top and longer appendages in between. Petals 4-6(7). Ovary superior but appears inferior, surrounded by and not fused to calyx tube. Insect-pollinated.

• purple loosestrife: June-September. Spikes showy, terminal, +/- dense, with 1-2 flowers per bract (reduced leaf) axil. Bracts ovate, slightly pinched-in at tip (acuminate). Petals bright pinkish-purple, 8-14 mm long, with +/- ruffled margins. Calyx tube appendages linear, 2-3 mm long. Stamens +/- 12. Flower types consist of 3 combinations of style and stamen length (heterostyly). Primarily out-crossing.
• hyssop loosestrife: April-October. Flowers solitary in axils. Petals pale pink to lavender, 2-5 mm long. Calyx tube appendages awl-shaped, ~ 1 mm long. Stamens 4-6. Self-compatible and out-crossing.

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FRUITS and SEEDS: Capsules oblong-ovoid, surrounded by persistent calyx tube, open into halves at tip. Seeds numerous, flattened, sometimes 3-angled in cross-section, often concave on 1 side, 0.5-1 mm long.

• purple loosestrife: Capsules ~ 3-4 mm long. Seeds +/- narrowly ovoid to triangular, reddish-brown.
• hyssop loosestrife: Capsules ~ 4-6 mm long. Seeds +/- ovoid, shiny brown to straw-colored, striated.

POSTSENESCENCE CHARACTERISTICS: Above ground parts of purple loosestrife typically die in late fall. Senescing foliage often turns red. Dead brown stems often persist through winter, are oppositely branched, and may retain a few capsules.

HABITAT:

• purple loosestrife: Perennial and seasonal wetlands, including marsh and pond edges, streambanks, canals, and ditches. Especially invasive on disturbed sites. Tolerates some shade and most soil types, including infertile soils. Grows best in slightly acid to neutral soils. Does not tolerate being submerged during the growing season.
• hyssop loosestrife: Seasonal wetlands, ditches, cultivated fields, especially rice fields. Often grows on exposed mud. Tolerates some salinity. Sensitive to heavy frost.

DISTRIBUTION:

• purple loosestrife: Scattered in the western North Coast Ranges, southern North Coast, northwestern Modoc Plateau, northern and southern Sierra Nevada foothills, Central Valley, San Francisco Bay region. Much of temperate North America, especially Northeastern U.S. To 1000 m (3300 ft). Expanding range.
• hyssop loosestrife: Throughout California, except deserts and Great Basin. To 1600 m (5250 ft).

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PROPAGATION/PHENOLOGY: Reproduce primarily by seed. Stem fragments can develop roots under favorable conditions. Seeds disperse with water, mud, human activities, and by clinging to feathers, fur, and feet of animals.

• purple loosestrife: A large plant can produce more than 2 million viable seeds in one season. Most seeds sink in water. Seeds typically germinate mid-spring through early summer. Upon germination, seedlings float to the surface. Optimal temperature range for germination is between 15-20º C. Light appears to increase germination. Seeds under cold dry storage remain highly viable for at least 3 years, but longevity under field conditions is unknown. Seedlings can mature and flower within 8-10 weeks.
• hyssop loosestrife: Plants produce an estimated average of 3,200 seeds per plant. Seeds lack a dormancy period. Seeds stored in dry soil at room temperature can survive for at least 14 years, but longevity under field conditions is unknown. Most seeds germinate in spring when conditions become favorable. Fall-germinated seedlings may overwinter under mild conditions. Seedlings typically emerge after water levels subside.

MANAGEMENT FAVORING/DISCOURAGING SURVIVAL:purple loosestrife: Monitoring uninfested areas and hand-pulling newly discovered seedlings before seed is produced can help prevent the spread of purple loosestrife. Cutting flowering stems followed by flooding can help control but not eliminate dense infestations. Cut stems can re-root under certain conditions. Plants are most susceptible to systemic herbicide effects during the late flowering stage.

SIMILAR SPECIES: Spatulaleaf loosestrife [Lythrum portula (L.) D. Webb, synonym Peplis portula L.][Bayer code: none] and threebract loosestrife [Lythrum tribracteatum Salzm. ex Spreng.][Bayer code: none] are wetland plants introduced from Europe that resemble hyssop loosestrife. Spatulaleaf loosestrife is a creeping summer annual that roots at the nodes and has inconspicuous white to pink flowers ~ 2-3 mm long. Unlike hyssop loosestrife, spatulaleaf loosestrife has bell-shaped calyx tubes 1-2 mm long and fleshy spoon-shaped leaves that gradually tapered to a narrow base. Northern Sierra Nevada, to 2200 m (7200 ft). Threebract loosestrife is a summer annual to short-lived perennial with +/- obovate leaves. Unlike hyssop loosestrife, threebract loosestrife has triangular calyx tube appendages that resemble the sepal lobes and are covered with red glands. Central Valley, San Francisco Bay region, and northern Modoc Plateau, to 1500 m (4900 ft). California loosestrife [Lythrum californicum Torrey & A. Gray] is a native perennial that may be mistaken for purple loosestrife. However, under most circumstances California loosestrife is not considered a weed. Unlike purple loosestrife, California loosestrife has glabrous stems, petals mostly 4-8 mm long, and linear inflorescence bracts with acute or rounded tips. California loosestrife occurs on wetland sites in the southeastern North Coast Ranges, Sierra Nevada foothills and high regions of the southern Sierra Nevada, Central Valley, Central- and Southwestern regions, and Desert regions, to 2200 m (7200 ft).

CONTROL METHODS:

Mechanical: includes mowing or cutting, pulling, and digging. While mowing is generally ineffective, mowing timed at the bud stage may reduce seed production. Cutting earlier may increase stem densities and mowing after seed production only serves to spread the infestation. Mowing is frequently not an option in most wetland areas, drainages, or along water courses. Hand pulling or digging results in more disturbance, but may be successful on small infestations. Young plants are most easily pulled, while older plants may require digging. New plants may emerge from missed roots or from stems left lying in contact with moist soil.

Biological: Biocontrol is probably the most viable option for long-term control of large purple loosestrife infestations. At least four insects are currently being tested in California, but none are currently available for release. Two species of leaf-eating beetles (Galerucella calmariensis and G. pusilla) have had considerable success in reducing purple loosestrife in other states and may be promising here in California.

Chemical: Spot applications of glyphosate at 1.5% v/v timed at the early flowering stage have been effective. Fall applications are also recommended. Glyphosate can also be successfully integrated with mowing and applied directly to the tops of cut stems in a 20-30% solution with a wick applicator. One important issue with glyphosate is injury to desirable vegetation. Purple loosestrife is highly competitive and will rapidly reinfest open areas. Therefore, it is important to minimize injury to desirable vegetation surrounding infestations. It may not be necessary to completely wet all of the foliage to kill the plant. However, wetting at least 25% of the foliage is recommended.

References:
Bender, J. and J. Randall. 1987. Lythrum salicaria. The Nature Conservancy Element
Stewardship Abstract. 8 pp.
Heidorn, R. and B. Anderson. 1991. Vegetation management guideline: purple loosestrife (Lythrum salicaria L.). Natural Areas Journal 11:172-173.
Hight, S. D. and J. J. Drea, Jr. 1991. Prospects for classical biological control project against purple loosestrife (Lythrum salicaria L.). Natural Areas Journal 1: 151-157.
Kok, L.T., T.J. McAvoy, R.A. Malecki, S.D. Hight, JJ. Drea, and J.R. Coulson. 1992.
Host specificity test of Hylohius transversovittatus Goeze (Coleopera: Curculionidae), A potential biological control agent of purple loosestrife, Lythrum salicaria L. (Lythraceae). Biological Control 2: 1-8.
Kok, L. T., T. J. McAvoy, R. A. Malecki, S. D. Hight, J. J. Drea, and J. R. Coulson. 1992. Host specificity tests of Galerucella calmareinsis (L.) and G. pusilla (Dutt.) (Coleoptera: Chrysomelidae), potential biological control agents of purple loosestrife, Lythrum salicaria L. (Lythraceae). Biological Control 2:282-290.
Mal, T. K., J. Lovett-Doust, L. Lovett-Doust, and G. A. Mulligan. 1992. The biology of Canadian weeds. 100. Lythrum salicaria L. Canadian Journal of Plant Science 72:1305-1330.
Malecki, R.A., B. Blossey, S.D. Hight, D. Schroeder, L.T. Kok, and J.R. Coulson. 1993. Biological control of purple loosestrife. BioScience 43:680-686.
Thompson, D.Q. 1991. History of purple loosestrife (Lythrum salicaria L.) biological control effects. Natural Areas Journal I 1: 148- 150.
Thompson, D.Q., R. L. Stuckey and E.B. Thompson. 1987. Spread, impact and control of purple loosestrife (Lythrum salicaria) in North American wetlands. Fish and Wildlife Research 2. 55 pp.

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