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

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

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


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.

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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.

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.



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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.

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).


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.

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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