| Walla
Walla County Noxious Weed Control Board
Weed
of the Month
Purple
Loosestrife
Purple loosestrife (Lythrum
salicaria) is an erect, much-branched perennial, often growing 6
to 8 feet tall, usually associated with moist or marshy sites. It
has a large woody taproot with fibrous rhizomes which spread rapidly
to form a dense mat. Leaves are lance-shaped, rounded or heart-shaped
at the base, and opposite or whorled. Rose-purple flowers having
5 to 7 petals are arranged in long vertical racemes. Flowering begins
in late May and continues through August.
Purple loosestrife is
an introduced European ornamental species that often escapes to
aquatic sites such as streambanks or shorelines of shallow ponds.
A single plant may produce up to 300,000 seeds. Infestations can
become dense and impede water flow in canals and ditches. Reports
of reduced habitat for wildlife are common.
Control: Small infestations
can be pulled out by hand but it will resprout from the root crown
if broken off at the soil surface.
Aquatic labeled glyphosate
or triclopyr is applied to actively growing plants at full to late
flowering stage. Seedlings may be effectively treated early in the
season after a fall application to mature plants. Follow pesticide
label instructions and precautions.
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