Purple Loosestrife

Purple Loosestrife (spiked willow-herb, long-purples, purple Iythrum) Lythraceae, the loosestrife family

Purple LoosestrifeBACKGROUND: Purple loosestrife is a semi-aquatic plant native to Europe, probably introduced as an ornamental. Valuable riparian habitat is degraded, and food species are rapidly displaced by this weed, which has no wildlife value. Purple loosestrife spreads both by seed and spreading rhizomes that form dense, woody mats.

DESCRIPTION: Purple loosestrife is a semi-aquatic, hardy perennial that can grow over 8 feet tall. Stems are usually 4 sided and much branched, bearing opposite or whorled, 4-inch long, lance-shaped leaves. Crowded flower spikes develop at the stem tips in midsummer. Flowers are 1-inch in diameter with 5 to 7 reddish purple, wrinkled petals that appear as if they have been crushed. A single plant may produce over 2.5 million tiny seeds per year.

Purple LoosestrifeDISTRIBUTION: Purple loosestrife is found throughout the northeastern U.S. and in some western states and in Idaho.

CONTROL: Biological control agents are available and include 2 leaf beetles that have worked well in Idaho. Herbicides are available, but effectiveness on purple loosestrife is inconsistent and application is difficult.

Purple Loosestrife Distribution Map - Grey Area

 

© 1999 University of Idaho: Text and photographs for these pages from Idaho’s Noxious Weeds, by Robert H. Callihan and Timothy W. Miller (revised by Don W. Morishita and Larry W. Lass).

Please contact: Ag Publishing, University of Idaho, Moscow, Idaho 83844-2240; (208) 882-7982; cking@uidaho.edu; or visit the UI Extension/CALS Publications and Multimedia Catalog website at www.cals.uidaho.edu/edComm/catalog.asp, for more information about this or other publications.