Purple Loosestrife

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Houndstongue
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Poison Hemlock
Purple Loosestrife
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Purple Loosestrife (Lythrum salicaria)

Purple loosestrife is a member of the Loosestrife family. It is a perennial introduced from Europe. The erect, square stem can reach 1 ½ to 8 feet tall with magenta-colored flowers. Purple loosestrife is a highly aggressive invader species that can be found in most wetland sites throughout the state. If left unchecked, a wetland will eventually become a monoculture of loosestrife, posing a severe threat to waterfowl habitat and impeding water flow in irrigation ditches. This escaped ornamental is also a prolific seed producer, able to produce over 10,000 seeds per square yard.  

Comments: At this time the plant is found occasionally in Pitkin County in horticultural settings. We have not seen evidence that it has spread to native habitat, however it should be a future concern. The US Fish and Wildlife Service and the Colorado Division of Wildlife are extremely alarmed about the proliferation of purple loosestrife in wetland and riparian habitats.

Biological controls: Biological control may eventually bring weed populations under control, but it will not eliminate or prevent the spread of noxious weeds. A survey of loosestrife populations in Europe has resulted in the selection of five insects which may have potential as biocontrols. Three of these species have completed initial screening tests conducted by the International Institute of Biological Control in Switzerland, and one, Hylobius transverovittatus, a root mining weevil which attacks the vascular tissue of the plant, was subsequently released in New York in 1991.

Chemical controls: Chemical control has been effective. The choice of chemicals depends on the location of the infestation. Since most purple loosestrife infestations are in wetland or aquatic habitats, herbicide choices are limited. Before herbicides are utilized in a riparian/wetland situation, all other possible management alternatives should be investigated. Herbicides should be used only as a last resort and with extreme caution in wetlands or riparian areas. For additional information contact your local city, county or town natural resource office. (See section VII for phone numbers.)

Cultural controls: None available.

Mechanical controls: Mechanical methods include hand pulling, mowing, and flooding. Hand pulling is effective when infestations are detected early. The root system must be completely removed, since the root sections can sprout and form new plants. For this reason hand pulling is only effective on small plants.

Education: The key to purple loosestrife management and other escaped ornamentals is to create an awareness among homeowners, nurseries, landscapers, and landscape architects that purple loosestrife is a noxious weed and therefore should not be specified in plantings, sold in nurseries or planted in home gardens or large-scale landscape projects.

Locations of Infestations of Purple Loosestrife on Roads and Open Space in Pitkin County:

Purple loosestrife can be found as an ornamental plant throughout Pitkin County, Aspen and Snowmass Village.