|
|
Introduction
|
|
Purple loosestrife, Lythrum salicaria, is one
of 35 species of Lythrum in the world. Purple loosestrife is the most
popular of the ten common names in America and Great Britain. The plant
is most easily identified in the summer from late June to early
September when the flower is in bloom. In North America the Purple
loosestrife can be confused with fireweed, blue vervain, blazing stars,
and spira. Purple loosestrife is used as an ornamental and also used as
a medicinal herb for diarrhea, ulcers, and dysentery.
|
Weed Description
|
|
Purple loosestrife is an erect perennial herb with a
square woody stem that spans 4-10 feet high. The leaves are opposite or
whorled and are sessile. The plant also displays a downy pubescence and
can be glabrous. The flowers usually contain 5-7 petals and are
displayed in a magenta color. The flowers also contain 12 stamens.
In late autumn the leaves can become dehydrated and turn bright
red. This can last up to 10 days. In winter the plants can be
identified by its brownish dead stocks it leaves.
|
Invasion History
|
|
Purple loosestrife is originally from Eurasia. Much
of the plants native distribution is located in Central and Southern
Europe, Russia, Japan, Southeast Asia, and Northern India. Loosestrife
was introduced to North America in the 1800s through ship ballast and
was used as an ornamental and for medicinal purposes. The invasion of
purple loosestrife started in Northeast United States and spread
through the temperate regions of the United States and Canada. Today
Purple loosestrife is documented in 43 states and is
labeled invasive in 27 states . It has been estimated that
Purple loosestrife covers about 400,000 acres of federal lands
alone.
|
Habitat and Distribution
|
|
Purple loosestrife is found in a narrow
range of habitats.
The plant usually prefers the saturated soils of wetlands, marshes, and
riparian meadows. Purple loosestrife is also found to be spread along
road
ditches. The plant is also still found in gardens although many states
are banning
the purchase of the seed due to its invasive nature. The distribution
of the
plant in the United
States
is heavily in the temperate regions.
|
|
|
Biology and Ecology
|
|
Purple loosestrife has an
extended flowering season from June to September that allows 30-50
flowering stems to produce up to 3 millions seeds annually. Flowers are
pollinated by insects and fall to the ground when seed is ripe and
ready for dispersal. These floating seeds or propagules are dispersed
by water until they are lodged into moist soil were germination and
establishment can begin. Purple loosestrife seeds germinate at an
optimum temperature of 15-20 C with no germination below 14 C. Purple
loosestrife seeds have been known to germinate on substrates with a pH
as low as 4.0 and as high as 9.1. Purple loosestrife grows best in full
sunlight and will dramatically decrease seed production in 40% less
sunlight. Purple loosestrife can also reproduce vegetativley through
underground stems, although most of the reproduction comes from seeds. Purple loosestrife is a long lived perennial. Most of the seedling
establishment occurs in the late spring to early summer when
temperatures are warm. Seedling emergence is usually seen within 13-17
days and can be a vigorous plant in 10 years. Purple loosestrife is
highly competitive and will invade, overtake and create monospecies
stands in aquatic environments. This dominance is due to its
reproductive advantages of variable seed dispersal techniques and
having no native natural enemies in the U.S.
|
Ecological and Environmental Impacts
|
|
Purple loosestrife ecologically affects plant
and animal communities by displacing native plants with a monotypic
stand of its species. The wetland areas that are being infested are the
most diverse and productive of our ecosystem. This native vegetation
being replaced is critical habitat for many aquatic species of animals
such as waterfowl, fish, mammals, reptiles, and amphibians .These
stands can also affect the water flow of streams which can cause
increased erosion and deposition in water systems.
|
Economic and Human Impacts
|
|
Purple loosestrife impacts humans both
socially and economically.
Purple loosestrife currently threatens fields of wild rice and hay
which can have a significant economic impact for agriculture both
present and in the
future. Also, purple loosestrife is less palatable than the native
vegetation, so forage values of pastures used for livestock are
decreasing in areas of infestation. Purple loosestrife can also have
social impacts by creating barriers to riparian zones used for
recreation due to the dense stands in creates. Also the
infestation can cause different management agencies, groups or private
landowners to fight over management objectives and goals.
The estimated economic impact of purple loosestrife is in the millions.
|
Management Options
|
|
There are many ways to control the spread of
Purple loosestrife, including mechanical, chemical, and biological.
Small stands can be controlled mechanically by removing all above and
below ground portions of the plant before it seeds by digging or hand
pulling. Chemical control can be achieved by applying herbicides early
in the growing season before seed and especially late in the year
before dormancy. Effective herbicides include Glyphosate, Garlon 3A,
and 2, 4-D. Herbicides and mechanical control are good for smaller
populations but the most effective control method for long term large
stands is biological control. There are currently four insects listed
and approved by the U.S. Department of Agriculture for bio-control
agents. The four insects are the leaf feeding beetles, Galerucella
pusilla and Galerucella calmariences, the root-mining weevil,
Hylobius transversovittatus, and the seed-feeding beetle,
Nanophyes. The Galerucella beetles are the most effective for
bio-control agent.
Preventing establishment of new infestations and preventing the spread
of existing infestations is important to manage loosestrife. One
prevention method is to make sure to wash equipment or clothing when
leaving an infested area. Also continuous monitoring, especially in
areas downstream from a site of infestation is particularly important to
management of purple loosestrife.
|
Additional Resources
|
|
Heidorn, R. and B.
Anderson. 1991. Vegetation management guideline: purple loosestrife
(Lythrum salicaria L.). Natural Areas Journal 11:172-173.
Thompson, D.Q., R.L. Stuckey, E.B. Thompson.
1987. Spread, Impact, and Control of Purple Loosestrife (Lythrum
salicaria) in North American Wetlands. U.S. Fish and Wildlife
Service. 55 pages. Jamestown, ND: Northern Prairie Wildlife
Research Center Online.
http://www.npwrc.usgs.gov/resource/plants/loosstrf/index.htm (Version
04JUN1999).
Wilson, M.A., M. Schwarzlaender, B. Blossey and C. B. Randall. 2004.
Biology and Biological Control of Purple Loosestrife. Morgantown, WV:
Forest Health Technology Enterprise Team, USDA.
USDA, NRCS. 2007. The PLANTS Database (http://plants.usda.gov, 25 April
2007). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
|