Adams County
CO Noxious Weeds

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  Purple Loosestrife

(Lythrum salicaria L.)

Loosestrife Infestation

Purple loosestrife is a native forb of Europe. It is a taprooted perennial; short rhizomes also exist. This plant is considered a noxious weed and is included on the Colorado and the Adams County Noxious Weed Lists. Purple loosestrife has escaped from ornamental plantings to aquatic sites such as riverbanks, ditches, shorelines, and wet meadows. Infestations rapidly replace native vegetation, can impede water flow in canals and ditches, and have little wildlife habitat value.

This noxious weed spreads primarily by seeds carried in water, in fur of feather of animals, and from human activities. One mature plant can produce up to 3 million seeds per year! Seeds survive in the soil for 5 to 20 years. Pieces of roots or stems also can produce new plants. Purple loosestrife produces multiple stems, 2 to 8 feet tall and 4-sided. They can either be smooth or hairy. Leaves are opposite or whorled on stems, 2 to 5 inches long, tongue-shaped with pointed tips and attached directly to the stem (no petiole). Flowers are reddish-purple in color and have 5 to 7 petals.


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