Purple Loosestrife Management Program

Purple loosestrife plant.

Purple loosestrife (Lythrum salicaria, L. virgatum and their hybrids) is a wetland plant from Europe and Asia that invades marshes and lakeshores, replacing cattails and other wetland plants. The DNR and other agencies and organizations manage purple loosestrife because it harms ecosystems and reduces biodiversity.

Purple Loosestrife Program

The Purple Loosestrife Management Program was established in the Minnesota DNR in 1987. State statutes direct the DNR to coordinate a control program to curb the growth of purple loosestrife (M.S. 84D.02) and a significant amount of progress has been made toward the development of a sound approach to manage this invasive species. This management program integrates chemical and biological control approaches and cooperates closely with local, state and federal groups involved in purple loosestrife management.

Chemical control of purple loosestrife

Chemical spraying of purple loosestrife.

Attempts by the DNR to control purple loosestrife have included the use of herbicides. A statewide prioritization plan was developed for selecting control sites in public waters and wetlands. This plan was implemented because DNR personnel observed that herbicides do not result in long lasting reductions of loosestrife when applied to large populations that have been established for a number of years. Consequently, small and recently established populations of loosestrife, which are likely to have small seed banks, are given the highest priority for treatment. Priority is also given to watersheds in the state that have little or no loosestrife present. Since 1990, the average number of purple loosestrife infestations treated each year was 150. The number of sites treated with herbicides is declining due the introduction of biological control agents.

Biological control of purple loosestrife

Insects used for biological control of purple loosestrife.

When a plant from one continent is introduced to another, it usually leaves behind the natural enemies that help prevent population explosions where it normally grows. The purpose of biological control is to reunite a plant with its natural enemies. Complete eradication is unlikely; the goal of biological control is to reduce numbers of the target plant to lessen its ability to displace native vegetation. Since 1992, biological control has been used a to control purple loosestrife statewide. Biological control is now one of the main methods used to manage purple loosestrife in Minnesota. Purple loosestrife eating insects have been released on more than 800 of the 2000 known purple loosestrife infestations in Minnesota. To date, many of the release sites are experiencing exceptional control by the purple loosestrife eating insects. More details on biological control of purple loosestrife.

What you can do to control purple loosestrife on your property or shoreline.