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Species Management Plan Purple Loosestrife Lythrum salicaria L. Life History/Identification

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Species Management Plan

Purple Loosestrife

Lythrum salicaria L.

Life History/Identification: Purple Loosestrife is a native of Eurasia. The species was introduced to the northeastern U.S. and Canada in the 1800’s. It has been planted in many areas as an ornamental. It has also been used as a medicinal plant, which might contribute to its spread. It is a perennial plant with a square woody stem. The leaves are opposite in arrangement and are lance to heart shaped. The plants are covered with a fine pubescence and can grow from four to ten feet tall. Flowers form in spike-like inflorescences at the ends of stems and are five to seven petaled, magenta colored and showy. An individual plant can have up to 50 stems and produce several million seeds. The plant has a woody rootstalk from which plants regenerate in the spring or can form new stems during the growing season if the plant is damaged.
Status: Purple loosestrife is a prohibited noxious weed on the Arizona Noxious Weed List. Prohibited plants as defined by Arizona State Law are invasive exotic plant species not known to exist within the state (see below). Importing them into the state is illegal and any areas found to be infested within the state are subject to quarantine.
Known Locations: The only populations known to exist within the state are on the Apache-Sitgreaves NF. There are currently no known populations of purple loosestrife on the Coconino, Kaibab and Prescott National Forests, however it has the potential to invade N. Arizona. This plant is an aggressive invader in Colorado and New Mexico.
Impacts: Purple loosestrife is a pernicious aquatic weed. It is extremely aggressive. It drastically alters the character of a wetland, replacing native emergent plant communities by forming dense monocultures. Large plants with multiple stems can dominate the canopy in the wetland. Seeds are dispersed in mud, which adheres to animals and people. Plants can also regenerate vegetatively from underground stems, spreading as much as one foot per year. Many new stems emerge from woody rootstalks each year. Cultivars of purple loosestrife are able to cross freely with some of the native species of the genus Lythrum. For this reason, planting of purple loosestrife as an ornamental within the range of native Lythrum spp. should be discouraged. Selling purple loosestrife is prohibited in many states but it is still sold in wildflower mixtures and as nursery stock in some areas.
Purple loosestrife can destroy aquatic wildlife habitat including the nesting habitat of ducks and marsh birds. It out competes native emergent vegetation and replaces native wetland communities. The species is capable of invading many types of wetland areas including wet meadows, tidal zones, river and stream banks, reservoirs, ponds and backwaters.

  1. Cultural control:

Due to the pernicious nature of purple loosestrife it is difficult to control once it has become established in an area. Prevention should be used to keep this species out of native wetlands. Transporting or planting this species in Arizona is prohibited. However, seeds may be present in some wildflower mixes. The content of these mixes should always be checked before they are planted. Education is needed to discourage use of this species as a wildflower. There are several local natives that could provide equally showy flowers without risk to the environment.
2. Mechanical Control:

Hand pulling can be used on young, small populations. However, once the root system has become established on older plants or if the plants produce seeds, pulling will not provide effective removal. Pulling can leave fragments of roots in the ground, allowing regeneration of additional plants on the site. Purple loosestrife is a prolific producer of seeds. These seeds are available in the soil for regeneration on the site or can be transported to other areas in mud that adheres to animals and people. Mowing or cutting will remove the top portion of the plant and help to reduce seed production if done before seeds form. However, the plants on the site regenerate from roots. Tools used for mowing or cutting should be cleaned before leaving the area to ensure that purple loosestrife is not transported to other areas. All of the above methods may help to control the population but may not eradicate it from the site. A pry tool, which removes the entire plant including the roots, has been used. It was used on a newly established population and scattered plants. This was an effective method on that population (TNC Listserve Digest #55). Fire is not an effective control method for purple loosestrife. Fire may kill the top portion of the plant but the woody caudex of the root is below the ground surface and is insulated from the effects of fire. Due to the height of the plants, there is little concentration of fuel on the surface of the soil. Therefore, fire within a population of purple loosestrife is probably not intense enough to destroy seeds that may be present on the soil surface. Burning during the early of the year may favor purple loosestrife over native emergent aquatic vegetation.

  1. Chemical Control: Noted here are chemical control techniques in use in other areas. Always check with weed specialists or chemical suppliers to ensure correct dosage and application. Mention of these products does not imply endorsement by the Northern Arizona Weed Council, San Francisco Peaks Weed Management Area, the USDA Forest Service, nor the Nature Conservancy. Currently the use of herbicides is not allowed on lands administered by the Coconino, Kaibab and Prescott National Forests. Always check with your local land manager before using herbicides on public lands.

Glycophosphate has been used to control purple loosestrife. Several treatments are needed to control the plant. This herbicide is a broad-spectrum herbicide, which kills both broadleaf plants and grasses. It cannot be used with ½ mile of a potable water source. 2,4-D has also been used. This herbicide kills all broadleaf plants. Care should be taken to ensure non- target plants are not sprayed. Triclopyr can be used for purple loosestrife control. However, it cannot be used in aquatic settings. Seasonally dry wetlands infested with purple loosestrife can be treated with triclopyr during dry periods.
4. Biological Control:

Five insects have been approved by APHIS for control of purple loosestrife. All of these insects are beetles. This includes a root-mining beetle (Hylobius transversovittatus), two flower feeding beetles (Nanophytes marmoratus), a seed-feeding beetle (N. brevis), and two leaf-eating weevils (Galerucella calmariensis and G. pusilla) (APHIS). There is some concern over Nanophtyes brevis. Individuals have been found to be infected with a nematode that may spread to native insects. For this reason, the Purple Loosestrife Project has stopped work with this species and used the other species mentioned above instead.

5. Integrated Control:

Treatment of noxious weeds with more than one method increases the chance of successful control. Cutting the plants then treating the stumps with glycophosphate provides better control than cutting or hand pulling. If using this method, the cut plants should be placed in an area where the cut stems will not form new roots and start new plants. Stems that are cut then placed on wet soil can form roots and begin new plants.


Arizona Noxious Weed List, Plant Services Division, Arizona Department of Agriculture, Phoenix, AZ

Colorado Weed Management Association, CWMA Office: PO Box 1910 Granby, CO 80446. Purple Loosestrife
Cornell University, Purple Loosestrife Project Page [online]. Available: (3/16/2001)
Phillips, B.G, Daevid Lutz and Debra Crisp. 1997. Noxious Weed List for Coconino, Kaibab and Prescott National Forests. On file at Forest Supervisors Office, Coconino National Forest.
Sheley, R.L.; Petroff, J.K; editors 1999. Biology and Management of Noxious Rangeland Weeds. Oregon State University. Press; 438 pp.
Swearingen, Jil M., Plant Conservation Alliance, Alien Plant Working Group- Purple Loosestrife [online]. Available: (3/16/2001)
The Nature Conservancy TNC Weed Listserve Digest #55 & #56

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (2001, February). Fire Effects Information System, [Online]. Available: (3/16/2001)

USDA Animal and Plant Health Inspection Service, Plant Protection Quarantine, Insects, Mites an Nematodes Introducted for Bio Control [online]. Available
U.S. Department of Interior, Bureau of Land Management, Surprise Field Office Purple Loosestrife [online]. Available: (3/16/2001)
Photo from Colorado BLM website

Debra Crisp Page 6/25/2016
Created 3/16/2000 Last printed 3/13/2002 02:46:00 PM

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