Purple loosestrife (Lythrum salicaria)

Invader Type: 

Control

Mechanical Control: 

For small infestations:

  • Hand pull individual plants by grasping each stem at its base and pulling slowly to remove all the root.
  • Break off flower heads before they go to seed.
  • Put the discarded vegetation into a plastic garbage bag to decompose.

For large infestations:

Learn more online at www.watershedmanagement.vt.gov/lakes.htm.

Photos

Description

Pest Overview and Identification: 

Flower: Individual flowers have five or six pink-purple petals surrounding small, yellow centers. Each flower spike is made up of many individual flowers.

Leaves: Leaves are downy, with smooth edges. They are usually arranged opposite each other in pairs which alternate down the stalk at 90 degree angles, however, they may appear in groups of three.

Stalks: Stalks are square, five or six-sided, woody, as tall as 2 meters (over 6 feet) with several stalks on mature plants.

Source: Minnesota Department of Natural Resources.

http://www.dnr.state.mn.us/invasives/aquaticplants/purpleloosestrife/id.html

History: 
Introduced as an ornamental.
Reproductive Strategy / Lifecycle: 

Mature purple loosestrife plants can produce up to 1 million seeds, most of which are viable.

Threat

Ecological Threat: 
  • As the leaves of purple loosestrife (Lythrum salicaria) decompose in water, they secrete high levels of tannic acid. Research shows that American toad (Bufo americanus) tadpoles suffer higher mortality rates in this highly acidic environment.
  • Each purple loosestrife plant can produce 1,000,000 seeds, 97% of which are viable.
  • Wetlands filled with purple loosestrife stands do not contain the grasses, sedges, aquatic vegetation and native shrubs that were once there. Purple loosestrife does not support as many insect species as native plants. Native birds can no longer  find the food sources or quality nesting habitat that they could once find in the wetland.