Purple Loosestrife

Purple loosestrife (Lythrum salicaria) is a perennial wetland plant native to Eurasia. It spreads rapidly in disturbed wetland areas, crowding out native, wildlife-supporting plant species and threatening the health of the Bay ecosystem.

How was purple loosestrife introduced to the Bay watershed?

Purple loosestrife was introduced to the U.S. from Eurasia in the early 1800s for ornamental and medicinal purposes, as well as via dry ballast dumped by foreign ships. It has been well established along the New England coastline since the 1830s.

Purple loosestrife spread throughout the U.S. by:

• Construction of and commerce on inland canals and waterways.
• Increased development and use of roads.
• Commercial sale and distribution of the plant for gardens.
• Regional seed generation for bee forage.

Since 1996, purple loosestrife has been found in nearly every U.S. state (including all Bay watershed states and the District of Columbia) and Canadian province.

Why is purple loosestrife considered to be invasive?

Due to its rapid growth, abundant seed production and lack of natural competitors, purple loosestrife can quickly establish itself in disturbed wetlands, reducing native plant species diversity and quality habitat for wildlife.

• Purple loosestrife dominates native, wildlife-supporting wetland plant species like cattails and bulrushes. In some northern non-tidal wetlands, more than 50 percent of native species have been displaced by purple loosestrife.
• Thick stands of purple loosestrife provide little or low-quality food, shelter, nesting sites and nursery grounds for native wildlife, including muskrats and waterfowl.
• Purple loosestrife threatens some rare and endangered species, such as dwarf spikerush, bog turtles and American bitterns.
• The plant's dense, snarled root system clogs draining and irrigation ditches, impeding water flow and requiring costly dredging.

What is being done to manage purple loosestrife?

Purple loosestrife has been declared a high-priority nuisance species in the Bay watershed because of its ability to spread rapidly and displace native plants. Currently, purple loosestrife regulations and control methods vary from state to state.

Two native European beetle species and two weevil species have been approved by the USDA as biological control agents for purple loosestrife. These species feed on purple loosestrife leaves, stems and buds. Colonies of the beetles and weevils have been shown to reduce purple loosestrife stem height and overall coverage, allowing native plant species to grow back. Other control methods for purple loosestrife include herbicides, burning and manual removal.