Purple Loosestrife

Purple Loosestrife
		by *Richard Malecki* National Biological Service
Purple loosestrife (Lythrum salicaria) is an exotic wetland perennial introduced to North America from Europe in the early 19th century (Stuckey 1980). By the 1930's, the plant was well established along the New England seaboard. The construction of inland canals and waterways in the 1880's favored the expansion of purple loosestrife into interior New York and the St. Lawrence River Valley (Thompson et al. 1987). The continued expansion of loosestrife has coincided with increased development and use of road systems (Thompson et al. 1987), commercial distribution of the plant for horticultural purposes, and regional propagation of seed for bee forage (Pellet 1977). The plant now occurs in dense stands throughout the northeastern United States, southeastern Canada, the Midwest, and in scattered locations in the western United States and southwestern Canada. Newly created irrigation systems in many of the western states have supported its further spread.

Purple loosestrife is a classic example of an introduced species whose distribution and spread have been enhanced by the absence of natural enemies and the disturbance of natural systems, primarily by human activity. Although noted for the beauty of its late summer flowers, which also provide a nectar source for bees, loosestrife has few other redeeming qualities. Its invasion into a wetland system results in suppression of the native plant community and the eventual alteration of the wetland's structure and function (Thompson et al. 1987). Large, monotypic stands not only jeopardize various threatened and endangered plants and wildlife, such as Long's bulrush (Scirpus longii) in Massachusetts (Coddington and Field 1978), small spikerush (Eleocharis parvula) in New York (Rawinski 1982), and the bog turtle (Clemmys muhlenbergii) in the northeastern United States (Bury 1979), but they also eliminate natural foods and cover essential to many wildlife, including waterfowl (Rawinski and Malecki 1984).

Purple loosestrife (Lythrum salicaria). Courtesy R. Malecki, NBS

Purple loosestrife has many traits that enabled it to become a nuisance in North America. A single, mature plant can produce more than 2.5 million seeds annually; these seeds are long-lived (Welling and Becker 1990) and easily dispersed by water and in mud, adhering to aquatic wildlife, livestock, and people (Thompson et al. 1987). Established plants are tall (about 2 m or 6.5 ft) with 30-50 stems forming wide-topped crowns that dominate the herbaceous canopy. A strong rootstock serves as a storage organ, providing resources for growth in spring and regrowth if the aboveground shoots are cut, burned, or killed by application of foliar herbicides. No native herbivores or pathogens in North America are known to suppress purple loosestrife (Hight 1990).
No effective method is available to control loosestrife, except in small localized stands that can be intensively managed. In such isolated areas, the plant can be eliminated by uprooting by hand and ensuring that all vegetative parts are removed. Other control techniques include water-level manipulation, mowing or cutting, burning, and herbicide application (Malecki and Rawinski 1985). Although these controls can eliminate small and young stands, they are costly, require continued long-term maintenance, and in the case of herbicides, are nonselective and environmentally degrading.
The most promising control measure for purple loosestrife is the application of classical biological weed-control procedures that use natural enemies like insects, mites, nematodes, and pathogens to reduce weed densities to tolerable levels. Results of insect surveys and screening tests conducted with the U.S. Department of Agriculture's Agriculture Research Service and the International Institute of Biological Control in Europe have identified five beetle species as potential control agents for purple loosestrife. Each species showed enough host specificity for purple loosestrife to be introduced with no ill effects to native North American plants.
Efforts are under way to rear large numbers of these insect species for further distribution and establishment in other states and provinces. A petition to introduce two of these beetles is under review by the USDA's Animal and Plant Health Inspection Service. Initial collection of these insects in Europe for release into the United States is planned for 1994.
A cooperative state and federal program for the biological control of purple loosestrife focuses on an international environmental weed problem that cannot be controlled by conventional means. With support from federal and state agencies we have brought together an international scientific advisory staff to participate in and oversee the selection, screening, and introduction of an insect predator community that will provide a long-lasting biological control mechanism for loosestrife, and which will also develop a corresponding program of research and evaluation.
Purple loosestrife is now a naturalized weed that always will be a part of most North American wetlands. Researchers hope that introducing select insects will result in replacing monotypic stands of loosestrife by native vegetation and an overall decrease in the occurrence of the plant. We predict a reduction of purple loosestrife abundance over the next 15-20 years to about 10% of its current level over about 90% of its North American range (Malecki et al. 1993).
		For further information: Richard Malecki National Biological Service New York Cooperative Fish and Wildlife Research Unit Fernow Hall Cornell University Ithaca, NY 14853

References
Bury, R.B. 1979. Review of the ecology and conservation of the bog turtle, Clemmys muhlenbergii. U.S. Fish and Wildlife Service Spec. Sci. Rep. Wildlife 219. 9 pp. Coddington, J., and K.G. Field. 1978. Rare and endangered vascular plant species in Massachusetts. U.S Fish and Wildlife Service, Washington, DC. 62 pp. Hight, S.D. 1990. Available feeding niches in populations of Lythrum salicaria L. (purple loosestrife) in the northeastern United States. Proceedings of the International Symposium of Biological Control of Weeds 7:269-278. Malecki, R., B. Blossey, S. Hight, D. Schroeder, L. Kok, and J. Drea. 1993. Biological control of purple loosestrife. BioScience 43:680-686. Malecki, R., and T.J. Rawinski. 1985. New methods for controlling purple loosestrife. New York Fish and Game Journal 32:9-19.	Pellet, M. 1977. Purple loosestrife spreads down river. American Bee Journal 117:214-215. Rawinski, T.J. 1982. The ecology and management of purple loosestrife (Lythrum salicaria) in central New York. M.S. thesis, Cornell University, Ithaca, NY. 88 pp. Rawinski, T.J., and R.A. Malecki. 1984. Ecological relationships among purple loosestrife, cattail, and wildlife at the Montezuma National Wildlife Refuge. New York Fish and Game Journal 31:81-87. Stuckey, R.L. 1980. Distributional history of Lythrum salicaria (purple loosestrife) in North America. Bartonia 47:3-20. Thompson, D.Q., R.L. Stuckey, and E.B. Thompson. 1987. Spread, impact, and control of purple loosestrife (Lythrum salicaria) in North American wetlands. U.S. Fish and Wildlife Service Res. Rep. 2. 55 pp. Welling, C.H., and R.L. Becker. 1990. Seed bank dynamics of Lythrum salicaria L.: implications for control of this species in North America. Aquatic Botany 38:303-309.

References

Bury, R.B. 1979. Review of the ecology and conservation of the bog turtle, Clemmys muhlenbergii. U.S. Fish and Wildlife Service Spec. Sci. Rep. Wildlife 219. 9 pp.

Coddington, J., and K.G. Field. 1978. Rare and endangered vascular plant species in Massachusetts. U.S Fish and Wildlife Service, Washington, DC. 62 pp.

Hight, S.D. 1990. Available feeding niches in populations of Lythrum salicaria L. (purple loosestrife) in the northeastern United States. Proceedings of the International Symposium of Biological Control of Weeds 7:269-278.

Malecki, R., B. Blossey, S. Hight, D. Schroeder, L. Kok, and J. Drea. 1993. Biological control of purple loosestrife. BioScience 43:680-686.

Malecki, R., and T.J. Rawinski. 1985. New methods for controlling purple loosestrife. New York Fish and Game Journal 32:9-19.

Pellet, M. 1977. Purple loosestrife spreads down river. American Bee Journal 117:214-215.

Rawinski, T.J. 1982. The ecology and management of purple loosestrife (Lythrum salicaria) in central New York. M.S. thesis, Cornell University, Ithaca, NY. 88 pp.

Rawinski, T.J., and R.A. Malecki. 1984. Ecological relationships among purple loosestrife, cattail, and wildlife at the Montezuma National Wildlife Refuge. New York Fish and Game Journal 31:81-87.

Stuckey, R.L. 1980. Distributional history of Lythrum salicaria (purple loosestrife) in North America. Bartonia 47:3-20.

Thompson, D.Q., R.L. Stuckey, and E.B. Thompson. 1987. Spread, impact, and control of purple loosestrife (Lythrum salicaria) in North American wetlands. U.S. Fish and Wildlife Service Res. Rep. 2. 55 pp.

Welling, C.H., and R.L. Becker. 1990. Seed bank dynamics of Lythrum salicaria L.: implications for control of this species in North America. Aquatic Botany 38:303-309.