Native to: Europe and Asia
The introduction of purple loosestrife into North America occurred in the early 1800s with the importation of wool containing seeds, as a favorite herb in flower gardens and from released ship ballast water. It has become one of North America’s most widely dispersed and dominant nonnatives in habitats ranging from dry soils to inundated marsh areas or lakes. Many sources consider it to be present in every state in the contiguous Unites States except for Florida.
Habit: Perennial and shrub-like, up to 10 feet tall.
Stem: A recognizable feature is the square-shaped stem, which is generally four to six-sided.
Leaves: Lance-shaped with smooth edges and grow up to four inches long. Usually arranged in pairs opposite each other on the stem, and rotated 90 degrees from the pair below, sometimes appear whorled.
Flowers: Individual flowers have five or six pink-purple petals surrounding small, yellow centers. Single flowers make up flower spikes, which can be up to one foot tall.
Fruit/Seeds: Tan capsules contain many tiny seeds.
Distribution in Florida: Not present.
Primarily spread by seed, each mature plant can produce up to 2.7 million seeds annually. The plants also produce extensive roots that can send out 30-50 shoots. Root and stem fragments can produce new plants. It causes problems in wetland ecosystems by forming dense monocultures, outcompeting native plants, altering hydrology and changing water chemistry. The dense stands can also limit recreational access to water and are unsuitable habitat for native wildlife.
Do not plant. Clean boats and equipment and drain live wells before leaving a waterbody.
Small infestations can be dug out, taking care to remove all root material.
Mowing is not recommended as plants will likely re-sprout and seeds may be spread.
4 insects have been introduced and proven quite effective at reducing plant populations. These include two leaf-feeding beetles (Galerucella calmariensis and G. pusilla), a rootmining weevil (Hylobius transversovittatus) and a flower-feeding weevil (Nanophyes marmoratus).
Control rates of greater than 90% can be realized with applications of glyphosate and imazapyr; also, triclopyr (alone or mixed with 2,4-D) provides control for purple loosestrife. Single applications of registered herbicides generally do not provide satisfactory control for more than one season, but the use of imazapyr and glyphosate can result in multiseason control. Herbicides used to control purple loosestrife have very different selectivity spectrums for nontarget plants and application rate affects selectivity. When selecting an herbicide, it is important to consider potential negative impacts on the many important nontarget wetland species from overspray or exposure to high concentrations of herbicides needed to effectively control purple loosestrife. Consult your local UF IFAS Extension Office for management recommendations.