Stevens County Noxious Weed Control Board
This web site will help you identify & control noxious weed with information and photographs to aid you.

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Purple loosestrife
Lythrum salicaria L.     
Loosestrife Family

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


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

pl1.jpg (36711 bytes)
shoreline plants

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browning plants due to
biocontrol damage

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cutting flowering heads
prior to herbicide treatment

Where found
Infestations at Waitts Lake, Loon Lake and Lake Spokane; a few other minor infestations have been located in pastures and along ditches elsewhere in Stevens County.

MS.doc     PDF

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Last Edit: March 25, 2015

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