Purple loosestrife (Lythrum salicaria) is a perennial wetland herb that grows in sunny wetlands, ditches, around farm ponds and in other disturbed habitat. It is native to Europe and was accidentally introduced into North America in the mid-1800s. Because it has no natural enemies here, it has spread aggressively into wetlands throughout the northeast and the upper Midwest. In 1963 only two wild populations of purple loosestrife were known in Missouri. By 1985, however, we had more than 40 wild populations.
Purple loosestrife has showy purple spikes of flowers, making it an attractive garden flower. The use of purple loosestrife in landscape plantings and flower gardens has added to its spread in Missouri. Seven hybrids that are considered nonaggressive are now commercially available: Morden Pink, The Rocket, Rose Queen, Dropmore Purple, Columbia Pink, Morden Rose, and Morden Gleam.
Why It's a Problem
Purple loosestrife is aggressive and will crowd out native plants that are used by wildlife for food and shelter. Purple loosestrife has almost no value for wildlife food or shelter. Once established it can destroy marshes, wet prairies and clog up waterways.
When and Where to Find It
Purple loosestrife now occurs primarily in the northern half of the state with higher concentrations along the Missouri and Mississippi Rivers. However, the plant can be found scattered anywhere throughout Missouri. The purple spikes are showy from late June or early July through late August. Look for it in marshes, wet prairies, along streams, around farm ponds, and in moist fields, pastures, and roadside ditches.
How To Control It
Purple loosestrife spreads rapidly by the very numerous seeds (300,000 per plant or more) produced annually. Prevention and early detection is key. For this reason it is very important to locate and eradicate the first plants to invade a wetland basin or habitat.
Hand-pull small infestations
Small infestations of up to 100 plants are best eliminated by hand pulling. Pull all or as much as possible of the root system out. If the plants are simply broken off at the soil surface, the "root crown" will sprout new stems. Pull plants before they flower if possible to avoid scattering seeds in the removal process. Remove all stems from the wetland area as discarded stems will sprout and create new plants.
Try herbicides for large infestations
Clusters in excess of 100 plants, up to 3 acres, and plants too large to pull out, are best controlled by herbicides. Currently, loosestrife can be controlled with Roundup on terrestrial sites and Rodeo in wetlands and over water. These are U.S. Environmental Protection Agency registered herbicides that should be applied by licensed herbicide applicators following label instructions.
Larger infestations are not presently controllable but may be contained in some situations by pulling and/or herbicide treatment of individual plants as they spread around the periphery of dense stands. Effective control of large infestations is dependent on future research. Present action is aimed at containing the spread of this weed.
Report Purple Loosestrife
Report sightings of purple loosestrife to MDC:
Purple Loosestrife Alert
Missouri Department of Conservation
P.O. Box 180 J
Jefferson City, MO 65102