Typical Purple Loosestrife Shoot with Multiple Stems, Each Topped by Inflorescence
Purple loosestrife (Lythrum salicaria
L.) was introduced to North America from Europe and Asia in the early to mid 1800ís. The seeds were carried in ship ballast and on livestock that were brought to this country for trade. Purple loosestrife was widely cultivated for its ornamental and pharmacological values. However, this species can invade wetland habitats and result in negative impacts on the ecosystem. Such ecosystem effects include altered detritus decomposition and nutrient cycling. Also, purple loosestrife may displace native plant species resulting in the formation of dense monotypic stands and the reduction of native plant species richness and diversity. In addition, purple loosestrife has little value for wildlife as few species utilize the plant for a food source or shelter.
Purple loosestrife is not listed as a federal noxious weed. It is listed as a state noxious weed in Arkansas and South Carolina, and a Class B noxious weed in Alabama and North Carolina. It is widely recognized as an invasive weed of wetlands.
Purple loosestrife is a perennial species that over-winters as a stem base. Plants are composed of numerous angled stems that grow to over 6 feet. The leaves are lance shaped with fine hairs, and are attached directly to the stems without petioles. Leaves can be opposite, whorled, or spiraled around the stem.
Purple Loosestrife Flowers with 6 Petals, Occuring in
Axillary Clusters Around the Stem
Purple flowers occur in axillary clusters that form a spike inflorescence. Each flower has 5 to 7 narrow, wrinkled purple petals. Flowering begins in late June and continues through September. It has been suggested that purple loosestrife can draw pollinators away from native plants, which may aid in this plants prolific seed production. A mature multi-stemmed plant, 1.5-6 feet in height, may produce between two and three million seeds that can remain viable in the soil for many years. It takes approximately eight weeks from germination for purple loosestrife to flower.
Seed dispersal is largely by drift in moving water; however, long distance transport occurs when seeds become embedded in mud adhering to wildlife, livestock, humans, and vehicles. Purple loosestrife can spread vegetatively by detached shoot and rootstock fragments.
Natural spread is through seed transport in water or animals. Purple loosestrife is a highly prized ornamental plant, and its spread has largely been through the ornamental trade.
Purple loosestrife grows in a variety of moist soil habitats including wet meadows, marshes, floodplains, river margins, and lakeshores. The plant can tolerate shallow water depths, but optimal growth is attained in moist soil habitats. Disturbed sites create excellent opportunities for seed germination and expansion of new purple loosestrife infestations.
Purple loosestrife has spread without natural herbivores or human assistance establishing plant communities in native wetlands. Purple loosestrife distribution in North America ranges in the east from New Brunswick to North Carolina and British Columbia to California in the west. Purple loosestrife occupies more than 300,000 acres of North American wetlands
Purple loosestrife has been reported for AR, AL, MS, and TN.
In recent years three species of insects, Galerucella pusilla
(a leaf-feeding beetle), Galerucella calmariensis
(a leaf-feeding beetle), and Hylobius transversovittatus
(a root-mining weevil), have been used to control infested sites. Of the three species, the two leaf-feeding species have the greatest success in controlling purple loosestrife populations. The beetles over-winters as adults and lay their eggs on the leaves of purple loosestrife plants in the spring. Subsequent larvae feed on the leaves and the flowers of purple loosestrife plants. However, this method tends to take many growing seasons to observe control of infestations.
Herbicide Recommendations for Purple Loosestrife
||DMA 4 IVM
Herbicides offer more efficient control of purple loosestrife populations greater than one acre, as well as spot-treating small colonies. Many formulations of glyphosate and triclopyr have been used extensively to control infestations. Glyphosate and imazapyr are non-selective herbicides; therefore, treatment may affect other plant species such as cattails and rushes. Triclopyr and 2,4-D formulations are selective broadleaf herbicides and may not affect other desirable monocot species nearby. However, only formulations labeled for aquatic use can be applied to plants in or near water. For all of these herbicides, use 0.25% to 1% v/v of a nonionic surfactant for foliar applications.
Small infestations, less than 100 plants, can be controlled by hand pulling plants, digging up the stem bases, or flower removal. These methods should not be used when seed production is occurring as this will aid in seed dispersal and new infestations of purple loosestrife. Care must be taken to remove all seeds and plant material from clothes and equipment as small plant fragments can result in new infestations. All plant material should be dried and burned to ensure that purple loosestrife plants and fragments are not viable. Techniques such as cutting, mowing, and controlled burns have been used in an attempt to control purple loosestrife populations. The deployment of these techniques has largely been ineffective and can promote new plant growth.
Flooding or inundation has been reported to control colonies of purple loosestrife. Plants must be inundated by at least 2 ft of water for at least one month. Controlled burns have also been employed, alone or in combination with broadcast herbicide treatments.
Nonchemical Management Techniques for Purple Loosestrife
|Has shown success, however, effective control takes many years.
|Not proven to be effective.
||Effective but feasible only for infestations of 100 plants or less. Care must be taken to avoid spreading seeds. Plants must be dried and burned.
||Effective but feasible only on small infestations. Must remove all roots and fragments to prevent regrowth.
||Feasible on larger infestations where hand pulling and digging are not. Care must be taken to remove flowers before seed has set to avoid spreading seeds.
||In some instances infestations have been perpetuated and new populations established from plant fragments.
||These methods have been largely ineffective in controlling infestations and are generally not recommended.
Mitich, W.L. 1999. Purple loosestrife, Lythrum salicaria
L. Weed Technology 13:843-846.
Mullin, B.G. 1998. The biology and management of purple loosestrife (Lythrum salicaria
). Weed Technology 12:397-401.
Thompson, D.Q., Stuckey, R.L., and Thompson, E.B. 1987. Spread, impact, and control of purple loosestrife (Lythrum salicaria
) in North America wetlands. U.S. Fish and Wildlife Service.
Thompson, D.Q. 1991. History of purple loosestrife (Lythrum salicaria
) biological control efforts. Natural Areas Journal 11:148-150.
Stuckey, R.L. 1980. Distributional history of Lythrum salicaria
(purple loosestrife) in North America. Bartonia 47:3-20.
Geosystems Research Institute, Mississippi State University
North Dakota State University
United States Department of Agriculture
United States Geological Survey
Wisconsin Department of Natural Resources
Dr. John D. Madsen
Ryan M. Wersal, Geosystems Research Institute, Mississippi State University
Mississippi State University
Geosystems Research Institute
Mississippi State, MS 39762-9652