Ecology and Management of Purple Loosestrife (Lythrum salicaria L.)

Invasive Species Technical Note Number MT-21

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Invasive Species Technical Note Number MT-21 (PDF; 225 KB)

By Jim Jacobs, Invasive Species Specialist, NRCS, Bozeman, Montana

Abstract

Purple loosestrife, also commonly referred to as lythrum, is a robust, perennial forb invasive in riparian areas and wetlands (see Figure 1).

Figure 1. Purple loosestrife growing along an irrigation ditch during July in Washoe County, Nevada

Purple loosestrife reproduces both by seed and buds on spreading roots. It can grow to over 6 feet tall (2 m); has square stems; opposite or whorled, lance-shaped leaves with heart-shaped bases; and reddish-purple flowers that grow at stem tips in a spikelike inflorescence. Native to Europe and Asia and a member of the Litheraceae family, it was transported from Europe to North America in the early 1800s intentionally as an ornamental and accidentally as a contaminant of soil used for ship ballast. Initial spread across North America is believed to be mainly by waterborne commerce. Its spread to Montana was first reported in Toole County in 1980 as a wet roadside ruderal, and, as of 2008, it has been reported in 16 counties across the state. In Montana, it has been found in gardens, gravel pits, wetlands, and potholes and along roads, railroads, irrigation ditches, creeks, and lakes. It is listed as a Montana Category 2 noxious weed. Currently, known infestations in Montana are being contained to about 300 acres.

The aggressive, clonal growth habit of purple loosestrife crowds out native riparian plants important to wildlife and channel stability. Its stout spreading roots and prolific seed production make purple loosestrife difficult to control and eradicate. Because it is a pest in wetland environments, herbicidal control is often limited to chemicals with an aquatic label, including triclopyr, glyphosate, 2,4-D, and imazapyr. Five insect species have been approved for release in North America to manage purple loosestrife. Hand pulling and digging are effective on early establishing plants. However, individuals can regenerate from stems, rootstocks, and the seed bank. Stems and roots should be disposed of by burning or placing in the trash.

Plant Biology

• Identification
• Life History
• Habitat, Spread and Impacts

 Management

• Herbicide
• Biological Control
• Physical Control
• Revegetation
• Integrated Pest Management

References

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Last Modified: 08/19/2008