Britt Slattery, USFWS
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Purple Loosestrife
Lythrum salicaria
Origin: Eurasia
Background
Purple loosestrife was introduced to the northeastern
United States 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. Purple loosestrife adapts readily to natural
and disturbed wetlands.
Distribution and Ecological Threat
According to the U.S. Fish and Wildlife Service, purple
loosestrife now occurs in every state except Florida.
Purple loosestrife is capable of invading many wetlands,
including wet freshwater meadows, tidal and non-tidal
marshes, river and stream banks, pond edges, reservoirs
and ditches. Under favorable conditions, loosestrife is
able to rapidly establish and replace native vegetation
with a dense, homogeneous stand that reduces local
biodiversity, endangers rare species and provides little
value to wildlife.
Description and Biology
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Plant: erect perennial herb in the loosestrife family
(Lythraceae); have a square, woody stem usually covered
by downy hair; grow from 4 to 10 feet high, depending
upon conditions.
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Leaves: lance-shaped, stalk-less and rounded to
heart-shaped at the base; arranged in pairs or whorls
around the stem.
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Flowers, fruits and seeds: produces a showy display of
magenta-colored flower spikes throughout much of the
summer. Individual flowers have five to seven petals. A
single mature plant can have 30 to 50 stems arising
from one rootstock, and can produce an estimated two to
three million seeds per year. The flowering season
extends from June to September; flowers require
pollination by insects, for which they supply an
abundant source of nectar.
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Spreads: through the vast quantity of seeds, dispersed
by wind and water. It also readily reproduces
vegetatively through underground stems at a rate of
about one foot per year.
Prevention and Control
Small infestations of young purple loosestrife plants may
be pulled by hand, preferably before seed set. For older
plants, spot treatment with a glyphosate type herbicide
(Rodeo® for wetlands or near water, Roundup® for
uplands) may be effective. Biological control, using
several imported beetle species approved by the USDA for
release, is the most effective method for long-term
control of large infestations. Although these beetles
occasionally feed on native plant species, their potential
impact to non-target plants is considered to be minimal.
Native Alternatives
Joe Pye weed (Eupatorium
fistulosum)
Chris Miller, NRCS
|
cardinal flower (Lobelia
cardinalis)
USFWS
|
blue vervain (Verbena hastata)
R. Harrison Wiegand
|
blazing star or gayfeather (Liatris
spicata)
Randy Loftus, USFWS
|
New York ironweed (Vernonia
noveboracensis)
Britt Slattery, USFWS
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obedient plant
(Physostegia virginiana)
Britt Slattery, USFWS
|
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