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nearly 100% shoot reduction. In the
following growing season, it was found that
the timing of application also affected the
establishment of purple loosestrife
seedlings. Plants sprayed in the vegetative
stage were able to reinfest with seedlings,
whereas the plots sprayed in early and late
flowering stages were free of purple
loosestrife seedlings.
Biological control has shown promising
results as well. In 1997, Utah State
University Extension and Animal & Plant
Health Inspection Service (APHIS)
introduced Galerucella pusilla, a small
weevil, at Pelican Pond in Cache County,
Utah. By 2000, purple loosestrife was
significantly reduced. Biological controls
are not intended to eradicate purple
loosestrife, but rather reduce it to an
acceptable and sustained threshold. Biocontrol insects remain and work
continuously and are able to move to new
and/or inaccessible areas. However,
insects are subject to population variations
and mortality from flooding.
For updated information on chemical
or biological control of purple loosestrife
contact your local Extension agent, county
weed control supervisor, or search on the
Internet, key word purple loosestrife.
Purple
Loosestrife
References cited:
http://infoweb.magi.com/~ehaber/factpurp.html
www.npwrc.usgs.gov/resource/1999/loosstrf/loosstrf.htm
Designed by Nathan Belliston
07/04
A Wetland Invasion
Produced by
Utah-Idaho CWMA
in cooperation with
Utah State University Cooperative Extension
Impacts
The Invasion
Purple loosestrife (Lythrum salicaria
L.), sometimes referred to as purple
Lythrum, is a native plant of Europe.
Sometime in the early 1800’s Purple
loosestrife was introduced into North
America along the eastern coast of the
United States. There are several likely
sources of seed invasion. It may have been
introduced for use as a healing herb, for
ornamental purposes, on ship ballasts, or
in livestock feed and bedding. Since its
introduction, it has spread to many
wetland areas in the northern half of the
U.S. and southern Canada from the east
to the west coast.
The W
eed
Weed
Purple loosestrife is a
semi-aquatic
bushy
perennial reproducing by
seed and creeping
rootstock. It has been
estimated that a large
healthy plant could
produce up to 2.7 million
seeds. Lance shaped
leaves may be from one to
five inches long. Rosepurple flowers grow in
columns along the upper
end of stems. Bloom
occurs from mid to late
summer.
World
wide
distribution of purple
loosestrife identifies
it as a plant of
temperate climates
with a strong affinity
for moist or saturated
soils of marshy
wetlands. Natural
spread of purple
loosestrife
is
primarily by seed. The continuity and
configuration of a watershed strongly
influence the rate and ease of expansion of
a local infestation. Streams with steep
gradients and narrow canyons are frequently
scoured and have fewer eddies or slackwater areas where purple loosestrife can
take hold. In contrast,
low-gradient
streams with broad
alluvial deposits
offer many sites for
purple loosestrife
infestation. Streams
with a heavy canopy
of trees also reduce
purple loosestrife’s
ability to establish
Environmental
disturbances also
aid in loosestrife
invasion.
In certain habitats,
purple loosestrife may
become so thick so as to
impede water flow. The
proliferation of purple
loosestrife in wetlands
also adversely alters
native plant communities
that may serve as vital
habitat for waterfowl,
furbearers and other
aquatic wildlife.
The spread of purple loosestrife also
has a direct economic impact when plants
clog irrigation or drainage ditches on
farmlands or cause degradation and loss
of forage value of lowland pastures.
Contr
ol
Control
Controlling purple loosestrife can be
done in many ways with varying levels of
success including: hand pulling, cutting,
mowing, cultivation, inundation, fire,
chemical, and biological control. Chemical
and biological control seem to be the most
feasible forms of control.
Tests done in New York used three
rates of glyphosate (Roundup) against
three stages of growth (vegetative, early
flowering, late flowering). There were no
significant differences observed in control
between application rates but a highly
significant difference of control in the
timing of applications. The late flowering
application was the most effective with