Description:
Because purple loosestrife has a showy flowering spike which often exceeds 2 feet in length, is hardy in northern climates, and tolerates saturated soils, purple loosestrife has been a popular garden plant. Beekeepers were even encouraged to plant purple loosestrife to provide honey bees with flowers to visit in wetlands since most wet meadows and swamps are considered unproductive as bee forage. Lythrum virgatum or 'wand loosestrife' is believed by some to be a separate species, but North American taxonomists don't recognize this as a valid species. Horticultural selections of Lythrum spp. such as 'Morden Pink' and 'Dropmore Purple' were thought to be sterile, but recent research at the University of Minnesota and elsewhere showed that cultivars are not sterile and they can serve as pollen sources for L. salicaria and will hybridize with winged loosestrife, Lythrum alatum, a native species (Anderson and Ascher 1994). Because these cultivars can hybridize with purple loosestrife or become weeds themselves, most states now consider all loosestrife (cultivars, L. virgatum and L. salicaria) as primary noxious weeds. Noxious weed laws vary from state to state but in general they prohibit the cultivation, propagation, transportation and sale of these plants.

• Control: Conventional control practices range from herbicides to hand removal of plants and manipulation of water levels. If the infestation is relatively small (from 1-100 plants) hand removal and herbicide application has a greater chance of eliminating the problem, especially if disturbance of the site is minimal and if sufficient numbers of native plants are able to shade out purple loosestrife seedlings. In large infestations where purple loosestrife has formed dense monotypic stands, or where the extent of the infestation covers large areas with purple loosestrife at low to moderate density, conventional control is far less effective and suppression rarely lasts for more than a few growing seasons. In general, using nonselective herbicides in large expanses of purple loosestrife is not recommended. As an alternative to conventional control methods, Minnesota, in conjunction with several northern states, began a purple loosestrife biological control program in 1992. Building on the basic findings of Malecki et al. (1993) where natural enemies of purple loosestrife were studied in Europe, insects that are implicated in control of purple loosestrife in Europe have been imported to North America.
• Biological: Using insects to control exotic weed species is not a new concept and there are many examples where weeds have been successfully controlled by importing insects from the weed's native range. However, there are strict guidelines to follow before an exotic insect is approved for release in the U.S. For purple loosestrife biological control, extensive feeding studies were conducted in Europe to assure that the candidate insects were sufficiently host specific. Currently, there are five species approved for release in the U.S. and Canada, two leaf feeding beetles, Galerucella calmariensis and G. pusilla, a root feeding weevil, Hylobius transversovittatus, and two seed feeding weevils, Nanophyes marmoratus and N. brevis. With the exception of N. brevis all species have been released in North America. The current focus of most purple loosestrife biological control programs in North America is the rearing and release of the leaf feeding beetles. These insects are easy to rear and handle. However, it may take all species or different insects yet to be released to control purple loosestrife in all locations.
• Herbicide: Refer to the State Noxious Weed Control Board site