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Key identifying traits
Has long, showy, rose-purple flower spikes
Flowers are small, numerous & have 5-7 petals
Usually associated with moist or marshy areas
Leaves are simple, entire, and opposite or whorled
Forms substantial root wads with many stems
Has erect stems, often growing 6 to 10 feet tall
Stems are stiff and four-sided
Develops root rhizomes and abundant seeds
Has both a woody tap root and fibrous root system
Biology and ecology
An attractive rhizomatous perennial; reproduces by seed, roots and
vegetative growth
Forms up to 2.5 million, pepper-size seeds per plant; seeds float on
water and stick to animals
Commonly displaces desirable wildlife habitat
Only bees make good use of infested habitat
Dense infestations can impede water flow
Infestations often arise from ornamental use
Sometimes confused with fireweed and spiraea
Control
Prevention – Learn to identify
plants; beware of ornamental varieties & contaminated boats/motors
Biological – Several released in our county with unusually rapid
and substantial impact on plant vigor and reproduction (Galerucella
& Hylobius)
Cultural – Competitive vegetation helps although plants can
invade healthy native as well as managed introduced plant habitats
Mechanical – Small infestations can be dug, bagged and disposed
of taking care not to disperse seeds
Chemical – Non-selective or broad leaf herbicides can be
effectively used depending on site; if plants are in bloom, clip/bag
flowers prior to spray; special care, permits and licenses
may be required if plants are growing in or very near water.
Refer to the
PNW Weed Management Handbook for specific chemical recommendations |
shoreline plants
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