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Purple loosestrife is on the loose


by: SUBMITTED PHOTO: OREGON DEPARTMENT OF AGRICULTURE - Purple loosestrife is the weed of the month for July. This invasive species grows to heights of 10 feet.July’s weed of the month is an invasive species that is completely un-American: purple loosestrife.

Purple loosestrife is native to Europe, Asia, northwest Africa and southeastern Australia but has spread around the world with the rise of marine commerce. In its native lands, purple loosestrife is controlled by both climate and natural pests such as beetles and weevils. Elsewhere around the world, though, culture and climate have favored its spread far beyond these arid lands.

You will find purple loosestrife in wet soils, often those that have been disturbed. It appears in massive thickets in shallow standing water or other moist areas. It can grow to heights of 10 feet and has a broad appearance on the landscape due the nearly 50 stems per plant. The stems are squared or hexagonal, similar to the stem of a mint plant.

Flowers are very showy, a bright pink to purple with five to seven petals on an long, upright stalk, quite visible from a distance from July through September.

The leaves are less distinctive, although with practice, identifiable by their downy surface and lance-shape toward the top of the plant; lower down, they appear more rounded or heart shaped. They are arranged in whorl or opposite formation with smooth margins.

The showy purple flowers of purple loosestrife crown a vigorous plant that crowds out marsh vegetation required by wildlife for food, reproduction and shelter. Decreased waterfowl and songbird production have been well documented in heavily infested marshes, where loosestrife can displace more than half of the native vegetation. Both waterfowl and mammals can be impacted by changes wrought by loosestrife to the wetland’s structure and function. This former ornamental species can be found along wetlands, stream banks and shorelines of shallow ponds as well as more recently in agricultural areas, adding direct economic impact to its ecological effects. For these reasons, Oregon has classified it as a class B weed, requiring quarantine.

As with all invasive species, prevention is still the best medicine. Integrated control is needed in many areas, and early detection of the species allows for rapid response by government agencies charged with preventing a population explosion.

Tualatin Soil and Water Conservation District encourages the public to be on the lookout for noxious and invasive weeds and to report them to the Oregon Invasive Species Hotline online at oregoninvasiveshotline.org or by calling their offices at 503-648-3174, ext. 5. Contact Tualatin SWCD for advice on eradication, restoring native vegetation or assistance with other resource conservation concerns.