NATIVE
RANGE
Eurasia; throughout Great Britain, and across central and southern
Europe to central Russia, Japan, Manchuria China, southeast Asia and northern
India
DESCRIPTION
Purple loosestrife
is an erect perennial herb in the loosestrife family, with a square, woody
stem and opposite or whorled leaves. Leaves are lance-shaped, stalkless,
and heart-shaped or rounded at the base. Plants are usually covered by a
downy pubescence. Loosestrife plants grow from four to ten feet high, depending
upon conditions, and produce a showy display of magenta-colored flower spikes
throughout much of the summer. Flowers have five to seven petals. Mature
plants can have from 30 to 50 stems arising from a single rootstock.
ECOLOGICAL THREAT
Purple
loosestrife adapts readily to natural and disturbed wetlands. As it establishes
and expands, it outcompetes and replaces native grasses, sedges, and other
flowering plants that provide a higher quality source of nutrition for wildlife.
The highly invasive nature of purple loosestrife allows it to form dense,
homogeneous stands that restrict native wetland plant species, including
some federally endangered orchids, and reduce habitat for waterfowl.
DISTRIBUTION
IN THE UNITED STATES
According to the U.S. Fish and Wildlife Service,
purple loosestrife now occurs in every state except Florida.
HABITAT IN THE UNITED STATES
Purple
loosestrife is capable of invading many wetland types, including freshwater
wet meadows, tidal and non-tidal marshes, river and stream banks, pond edges,
reservoirs, and ditches.
BACKGROUND
Purple loosestrife
was introduced to the northeastern U.S. and Canada in the 1800s, for ornamental
and medicinal uses. It is still widely sold as an ornamental, except in states
such as Minnesota, Wisconsin, and Illinois where regulations now prohibit
its sale, purchase and distribution.
BIOLOGY & SPREAD
Purple
loosestrife enjoys an extended flowering season, generally from June to September,
which allows it to produce vast quantities of seed. The flowers require pollination
by insects, for which it supplies an abundant source of nectar. A mature
plant may have as many as thirty flowering stems capable of producing an
estimated two to three million, minute seeds per year.
Purple loosestrife also readily
reproduces vegetatively through underground stems at a rate of about one
foot per year. Many new stems may emerge vegetatively from a single rootstock
of the previous year. "Guaranteed sterile" cultivars of purple loosestrife
are actually highly fertile and able to cross freely with purple loosestrife
and with other native Lythrum species. Therefore, outside of its native range,
purple loosestrife of any form should be avoided.
MANAGEMENT OPTIONS
Small
infestations of young purple loosestrife plants may be pulled by hand, preferably
before seed set. For older plants, spot treating with a glyphosate type herbicide
(e.g., Rodeo® for wetlands, Roundup® for uplands) is recommended. These herbicides
may be most effective when applied late in the season when plant are preparing
for dormancy. However, it may be best to do a mid-summer and a late season
treatment, to reduce the amount of seed produced.
While herbicides and hand removal
may be useful for controlling individual plants or small populations, biological
control is seen as the most likely candidate for effective long term control
of large infestations of purple loosestrife. As of 1997, three insect species
from Europe have been approved by the U.S. Department of Agriculture for
use as biological control agents. These plant-eating insects include a root-mining
weevil (Hylobius transversovittatus), and two leaf-feeding beetles
(Galerucella calmariensis and Galerucella pusilla). Two flower-feeding
beetles (Nanophyes) that feed on various parts of purple loosestrife
plants are still under investigation. Galerucella and Hylobius have
been released experimentally in natural areas in 16 northern states, from
Oregon to New York. Although these beetles have been observed occasionally
feeding on native plant species, their potential impact to non-target species
is considered to be low.
USE PESTICIDES WISELY: ALWAYS READ THE ENTIRE PESTICIDE LABEL CAREFULLY, FOLLOW ALL MIXING AND APPLICATION INSTRUCTIONS AND WEAR ALL RECOMMENDED PERSONAL PROTECTIVE GEAR AND CLOTHING. CONTACT YOUR STATE DEPARTMENT OF AGRICULTURE FOR ANY ADDITIONAL PESTICIDE USE REQUIREMENTS, RESTRICTIONS OR RECOMMENDATIONS.
NOTICE: MENTION OF PESTICIDE PRODUCTS ON THIS WEB SITE DOES NOT CONSTITUTE ENDORSEMENT OF ANY MATERIAL.
CONTACTS
For more information on
the management of purple loosestrife, please contact:
SUGGESTED ALTERNATIVE PLANTS
Native
species of Liatris (blazing star) have showy pink-purple flower spikes
and are an important nectar source for many native species of butterflies and
other insects.
OTHER LINKS
AUTHOR
Jil M. Swearingen, National Park Service, Washington, DC
PHOTOGRAPHS
Barry A. Rice, The Nature Conservancy,
Davis, CA
John M. Randall, The Nature Conservancy, Davis, CA
REFERENCES
Heidorn, R. and B. Anderson.
1991. Vegetation management guideline: purple loosestrife (Lythrum
salicaria L.). Natural Areas Journal 11:172-173.
LaFleur, A. 1996. Invasive
plant information sheet: purple loosestrife. The Nature Conservancy,
Connecticut Chapter.
Malecki, R.A. (et al.).
1993. Biological control of purple loosestrife (Lythrum salicaria).
BioScience 43 (10):680-686.
The Nature Conservancy. Purple
Loosestrife: Element Stewardship Abstract. In: Wildland Weeds
Management & Research Program, Weeds on the Web.
Thompson, Daniel Q.,
Ronald L. Stuckey, Edith B. Thompson. 1987. Spread,
Impact, and Control of Purple Loosestrife (Lythrum salicaria)
in North American Wetlands. U.S. Fish and Wildlife Service. 55
pages.
Virginia Department
of Conservation and Natural Resources. 1995. Invasive Alien Plant
Species of Virginia: Purple Loosestrife (Lythrum salicaria).
Plant Conservation
Alliance, Alien Plant Working Group.
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