Purple loosestrife

Lythrum salicaria

Background

Identification

• Multiple stems rise typically less than 5 feet tall, occasionally up to 9 feet tall, leaves spear-shaped 2 to 6 in. long with smooth edges.
• Flowering stems end in a 4 to 14 in. spike of purple flowers, each with a small yellow center.

Identification key in: Hickman, J. ed. 1993. The Jepson Manual: Higher Plants of California. University of California Press.

Growth and spread

• Reproduces primarily from seed, occasionally from stem fragments.

Habitat and local distribution

• Native to Europe, introduced in US by early 1880s (Grossinger et al. 1998).
• Common in disturbed wetland habitats, such as stream and river banks, edges of ponds, lakes, and reservoirs, flooded areas, ditches and roadsides, but can colonize fairly pristine wetland areas, including marshes, wet prairies, meadows, pastures, and bogs (Benefield 2000).
• Found in several places in the freshwater marshes of Bay-Delta area, generally at a low density.

Impacts

• Competes with cattails and other native marsh plants.
• Degrades habitat for waterfowl and other wildlife.
• Obstructs boating and other waterway recreation.
• Clogs irrigation systems.

Prevention and Control

Prevention

• Plant natives or spread native seed in disturbed areas.
• Search threatened areas regularly (at least annually) to look for newly arrived plants.

General control notes

• Follow-up monitoring of treated areas suggested for three years to ensure reinfestation does not occur (Benefield 2000).

Manual or mechanical control

(Monheit, pers. comm.)

• Hand digging and cutting—CDFA hand removes plant's root ball, and prior to blooming, cut and bag the flower head to prevent dispersal of seeds.
• Mowing—tests conducted in other states have shown this method to further spread rather than control purple loosestrife since plant fragments left behind can root.

Biological control

• Biological control agents—two leaf-eating beetles (Galerucella spp.), a root-mining weevil (Hylobuius transversovittatus), and a seed-eating beetle (Nanophyes marmoratus) are permitted for release in California; however, low density of purple loosestrife in the San Francisco Bay-Delta may not be able to maintain insect population (Monheit, pers. comm.).

Chemical control

• Application of herbicide—CDFA applies glyphosate (Rodeo®) with a R11 surfactant from a hand-held sprayer to minimize drift of herbicide (Monheit, pers. comm.).
• Estimated costs: costs for materials and application by a contractor are approximately $250 per acre for glyphosate, depending on size of treatment area, scale of treatment, and herbicide dosage. It is recommended to contract a licensed professional for herbicide applications (Gibbons et al. 1999).

References and more information