Seasonal Cycle: This aggressive weed not only re-seeds
prolifically, but also reproduces vegetatively from underground stems called rhizomes that
spread at a rate of about one foot per year. Purple loosestrife flowers in July and August
in most of Connecticut. The seeds mature in August and September, and germinate the
following season as long as the soil is not too wet, and soil surface temperatures are
optimum. Dead stalks remain standing through winter.
Distribution: Originally a native of Europe, loosestrife was
introduced to the northeastern United States and Canada in the 1800's and has since spread
westward to Minnesota and southward to Virginia. Although not native, it can occur
"naturally" in any freshwater wetland area, particularly in an area that has
been disturbed. It is also sold commercially for perennial gardens. Two cultivated species
widely available are Lythrum salicaria and Lythrum virgatum. Cultivars of these species
are supposedly self-infertile, but can become quite fertile and widespread when crossed
with wild purple loosestrife and should not be used for home gardens.
Other points of interest: Purple loosestrife has a long
history of use in herbal medicine. It has been used to stop both internal and external
bleeding, and sap extracted from the leaves can be taken to control dysentery. Although it
is now seldom used, L. saIicaria was highly recommended in early herbals.
Control: In spite of its spectacular beauty, often covering
acres of wetland areas, purple loosestrife is a particularly troublesome invasive species
with low wildlife value. It can grow as dense monocultures, crowding out sedges, grasses,
rushes, and other aquatic plants more valuable to wildlife. In Minnesota, where purple
loosestrife has spread at an alarming rate, it is illegal to plant or sell either L. salicaria or L. virgatum. Purple loosestrife is listed as a noxious weed in 12 other
states, where its importation and distribution is prohibited.
Control techniques include early detection of purple
loosestrife, hand-pulling of small infestations of one to two year-old plants before they
set seed, and spot treatment of older plants with non-selective herbicides such as Rodeo
for aquatic communities or Roundup on terrestrial sites. A DEP permit is required for the
use of Rodeo in aquatic communities, however. If herbicides are used, they are most
effective when sprayed in the late summer or early fall, but repeated use is costly, and
the long-term effects on natural systems are not fully understood. Due to a
strongly-developed tap root, removal by digging is not recommended since the disturbance
may encourage proliferation.
Biological control, in this case using insects from the
plant's natural environment, is being studied by the U.S. Department of Agriculture. The
species include a root-mining weevil, Hylobius transversovitta, and two leaf-eating
beetles, Galerucella calmariensis and Galerucella pusilla. Release of these insects
occurred in 1992 in New York, Pennsylvania, Maryland, Virginia, Minnesota, Oregon and
Washington state. Their impact should be noticeable by 1997,
Additional Information Sources: A Field Guide to Coastal
Wetland Plants of the Northeastern United States. Ralph W. Tiner, Jr. The University of
Massachusetts Press, Amherst 1987.
Wetlands - Audubon Society Nature Guide. William A. Niering.
Chanticleer Press, New York 1985.
Diagnostic Information: Flowers: July to September; small,
purplish-pink with five to seven petals, clustered in the axils of reduced leaves, forming
long dense terminal spikes (4-16 inches long). Leaves: sessile (without stalks), up to
four inches long, lance-shaped, with heart-shaped bases, somewhat clasping stem,
oppositely arranged, sometimes in whorls of three, turn red at the end of the growing
season. Stems: four-angled, almost woody, glabrous to pubescent. Fruits: small capsule.
This fact sheet has been prepared by The
Nature Conservancy
