Purple Loosestrife (Lythrum salicaria) is a perennial featuring long spikes of colorful purple-pink flowers that begins blooming in July.
How did purple loosestrife arrive in North America?
Records show that Purple Loosestrife has been in North America since the 1830’s. The plant came to North America in the ballast of ships from Europe and was also introduced as a medicinal and ornamental plant. In Minnesota, records show that in the 1920’s several garden clubs actually introduced purple loosestrife into wetlands for “beautification” purposes. By the latter part of the century it had multiplied to the point of invasiveness.
Purple Loosestrife in Full Bloom - July
Why is purple loosestrife a problem species?
Purple loosestrife is found in 68 of Minnesota’s 87 counties. Purple loosestrife invades wetland and lakeshore habitats, displacing native plant communities and destroying habitat and food sources for waterfowl and other wetland wildlife. Producing half a million seeds per square meter allows purple loosestrife to easily re-establish itself.
How is purple loosestrife managed in Minneapolis’ Parks?
Since the late 1990’s the Minneapolis Park and Recreation Board has collaborated with the Minnesota Department of Natural Resources to use a biocontrol method on purple loosestrife. The biocontrol is a leaf feeding beetle that feeds on the leaves of the plant. After several years of defoliation the plant declines and dies.
Using biocontrol methods for controlling invasive plants is not a quick control method. Extremely cold winters, wet spring/summers and seasonally flooded areas do not favor establishment of leaf-feeding beetles. Fluctuations in temperature and flooding may reduce beetle populations.
How you can help
In Minnesota, Purple loosestrife (Lythrum salicaria, L. virgatum and any combination thereof) is listed as a noxious weed and a prohibited exotic species in Minnesota. It is illegal to possess, plant, transport, or sell purple loosestrife in Minnesota. You can help by removing any purple loosestrife plants you grow in your garden so that the seed is not transported to nearby wetlands and shorelines.