Transcript Lythrum salicaria

Purple Loosestrife: An Insidious Invader in the United States
Ecology and Management of Invasive Plants
NRES 641
By
Brian R. Wright
In Blossey (1995), purple Loosestrife (Lythrum salicaria) is a:
– Invasive emergent wetland perennial plant that has been
introduced worldwide.
– Plant that is native to Europe and Asia
– Plant also has been introduced into Australia, New Zealand,
Peru, Chile, and Canada
– Plant that has been introduced into the lower 48 states, except
Florida, in the United States
– Plant that has been designated as a noxious weed in at least 19
states
In Anderson (1995), purple loosestrife is a plant that has infested
approximately 300,000 acres of wetlands, and approximately
100,000 acres of riparian pasture causing an estimated $45
million dollars in damage in the United States each year
The success of this plant species in the United States is due
mainly by the lack of North American insect predators
Further, continued expansion of the range of this species
coincides with increased development and use of road
systems, commercial distribution for horticultural purposes,
and regional propagation of seeds for bee forage
Purple loosestrife was introduced in the United States in the early
1800’s
Purple loosestrife was a plant that was brought to the United
States by settlers for their flower gardens, and seeds were
present in the ballast holds of European ships that used soil to
weigh down ships for stability on the ocean (University of
Minnesota 2006).
Purple loosestrife was also used as a treatment for diarrhea,
dysentery, bleeding, wounds, ulcers, and sores (Blossey
et. al 2001). This species is an aggressive weed that rapidly
displaces wildlife-supporting indigenous plant species in
wetland communities while offering no value to many animal
species
Purple loosestrife is in the family Lythraceae
This species is rhizomatous and can invade wetland
habitats by roots, root fragments, and stems as well as
seeds (Lym 2004).
Leaves of purple loosestrife are classifed as simple and are small
linear to lancelate. Further, the leaves are from 0.75 to 4
inches long, 0.2 to 0.5 inches wide and can be opposite or
whorled (Lym 2004).
Leaves attach directly to the stems at their bases and are oblong
with heart-shaped bases (University of Maine Cooperative
Extension 2008).
According to the University of Maine Cooperative Extension
(2008), the most identifiable characteristic of purple loosestrife is
the rose to purple to white colored flowers.
Flowers have 5 to 7 pink purple petals surrounding small, yellow
centers and are clustered on spike-like stems.
The size of the spikes can range from a few inches to 3 feet (Lym
2004). The stems of this species are square and can be smooth
to somewhat fuzzy. Flowers open in July and continue to
bloom through September or October. These plants can reach
a height of 2 meters, and one mature plant can produce more
than 2.5 million seeds annually (Blossey 2002;
Wisconsin Department of Natural Resources
2004).
Seeds of purple loosestrife can remain viable for more than 20
years and seed survival can range from 60 to 70% resulting in an
extensive seed bank (Wisconsin Department of Natural
Resources 2004).
Under natural conditions, seedling density can approach 10,000
to 20,000 plants/meter squared.
The fruit of this plant is composed of a dry capsule generally
containing 100 or more tiny, dark-colored seeds (University of
Maine Cooperative Extension 2008). These seeds are one
millimeter or less in size (Lym 2004). This plant species has a
characteristically large taproot
Purple loosestrife seeds are dispersed by water and in mud
adhered to aquatic wildlife, livestock, and people (Blossey 2002).
This species can be very opportunistic in areas where recent soil
disturbances have occurred.
This plant species are commonly are found growing in man-made
storm-water retention ponds, ditches, next to parking lots, and
roads (University of Maine Cooperative Extension 2008).
Further, this invasive wetland plant’s seeds fall near the parent
plant and are transported long distances by water, animals,
boats, and humans (Wisconsin Department of natural
Resources 2004).
Additionally, this species follows a pattern of establishing
populations on disturbed sites, maintaining low population
numbers, and then dramatically increasing populations when
conditions are optimal (University of Maine Cooperative
Extension 2008).
In Malecki 1993, monotypic purple loosestrife stands reduce
biodiversity of wetland systems by replacing native plant
species, thereby eliminating the natural foods and cover that
affect many wetland wildlife species.
Purple loosestrife plants need soil temperatures above 20
degrees centigrade for successful germination (Blossey
2002).
Control measures are broken down into four categories,
including prevention, mechanical, chemical, and
biological. These measures are used to combat purple
loosestrife infestations (Blossey 2002; Lym 2004;
University of Minnesota 2006).
Prevention of infestations of purple loosestrife is by far
the best and most effective control measure available to land
managers, government agencies, state agencies, and the general
public (Wisconsin Department of Natural Resources 2004).
Mechanical control measures include: cutting, pulling, digging,
mowing, and burning (Wisconsin Department of Natural
Resources 2004)
.
The best time to cut purple loosestrife down is before the
plant flowers. Cutting too early encourages more
flower stems to grow, and cutting too late may mean
that seeds may have already fallen (Wisconsin
Department of Natural Resources 2004).
Pulling and digging can be effective in controlling purple
loosestrife infestations, but this measure may create
disturbed bare spots that may allow for re-growth, or
infestations by a different species of invasive plant.
Pulling and digging are recommended for small
populations (3 acres or less), low density situations,
and for isolated stems.
Pulling and digging is recommended for young plants (up to 2
years old) or in loose soils.
Mowing has not been shown to be effective in controlling purple
loosestrife infestations due to the fact that this species can
reproduce vegetatively. Further, mowing needs to be
combined with flooding in order to be effective against purple
loosestrife. Mowing and flooding are not recommended
because this method could contribute to dispersal of the
species by disseminating seeds and stems (Wisconsin
Department of Natural Resources 2004).
Burning is also ineffective in controlling purple loosestrife
infestations.
Chemical control methods can be effective and are perhaps the
best way to eliminate purple loosestrife infestations; however,
chemical control methods have limited utility when large areas
are to be treated due to: the high cost of herbicides, the
potential for environmental contamination, and the potential
impact on aquatic organisms. Currently, glyphosate
herbicides (Round-up, Rodeo, and Glyfos) are the most
commonly used chemicals to kill purple loosestrife.
Glyphosate must be applied in late July or August prior to
flowering and seed drop in order to be most effective.
Triclopyr (Garlon 3A) is another herbicide used to control purple
loosestrife, is formulated to be used around water, and does not
Multi-year chemical treatments are required for residual control of
seedlings and vegetative re-growth.
Biological control methods are another effective treatment to combat
purple loosestrife infestations. Three biocontrol species have been
released in 25 states and 7 Canadian provinces. These species
include a root-boring weevil (Hylobius transversovittatus) and two
leaf-feeding beetles (Galerucella pusilla) and Galerucella
calmariensis) (Blossey 1995; Lym 2004).
Adult and larvae of the Galerucella insect species feed on leaves and
flowers (Lym 2004). These insects over-winter as adults and lay
eggs in June (Lym 2004).