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Purple loosestrife


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PURPLE LOOSESTRIFE



(Lythrum salicaria))


  • P
    urple loosestrife can be ten feet tall at maturity.

  • The multiple stems are squarish with four to six sides.

Look-a-likes:




Fireweed, (Epilobium angustifolium), commonly grows in drier ground than purple loosestrife, and does not have a square stem.

C
ooley’s hedgenettle,
(Stachys cooleyae) seldom grows taller than four feet, and the plants are not branched or bushy. The leaves are nettle-like, with toothed edges.




Butterfly bush, (Buddleia spp.), is a garden ornamental which sometimes grows in the wild. It has a round stem, and the bright purple flowers grow in a tightly packed flower head.





Hardhack, (Spiraea douglasii), has a round stem and fluffy, pinkish flowers arranged in tight clusters.

Distribution:

We are currently aware of only four or five purple loosestrife sites in Clallam County.




WHY BE CONCERNED?


  • Purple loosestrife invades wetlands and displaces native vegetation.

  • It supplies little food or habitat to wildlife; native plants do.


Purple loosestrife is a Class B designate weed.

Control is required in Clallam County.



Ecology:

  • Purple loosestrife grows in wet sites, especially ones that have been disturbed by human activity.

  • It is a perennial with a spreading root system. The stems die down each year but the woody root system remains in the ground.

  • A mature plant can produce 2.7 million seeds which can be dispersed by wind, water, humans or animals. Purple loosestrife reproduces by seed or by sprouting from underground stems or root fragments.

CONTROL


Prevention and early detection are the best means of control.

  • Do not buy or plant purple loosestrife or any of its cultivars.

  • Avoid introducing soil or gravel from areas known to have purple loosestrife.

  • Remove seedlings when young because they can usually be pulled easily and they have not had an opportunity to reproduce.

  • Replant newly weeded areas with a desirable (preferably native) plant species, to discourage reinfestation.

  • Dispose of weeds properly, bag or burn seed pods (carefully!) or fragments that may sprout.

  • Monitor the site for several years; promptly remove new seedlings.





HANDPULLING is recommended for small populations and isolated stems. The plants should be pulled out before they have set seed. The entire rootstock must be pulled since regrowth from root fragments is possible. Minimize disturbance to soil and native plants. Remove uprooted plants and broken stems, since they can resprout.
MOWING may be effective if done frequently and if the cut stems dry rapidly. Otherwise, cut stem pieces can send out roots and establish new plants.
FLOODING has been used as a control strategy, but is recommended only for large populations because of the problems with maintaining high water levels, and the fact that other plants are also killed.
BIOLOGICAL CONTROL:

Several species of European flies, weevils or beetles have been released in Washington as biological controls for purple loosestrife. Galerucella spp seem to be especially effective and are available for release.


Herbicides can be effective, but should always be applied with care. Do not apply herbicides over or near water bodies. Read the label to check that you are applying an herbicide in the right place, to the right plant, at the right time, and in the right amount. For perennial weeds, long term control requires stopping seed production and attacking the weed’s root system. Translocated herbicides, (ones that move throughout a plant’s system) are recommended. These are most effective on young, actively growing plants.

  • RoundupTM (glyphosate) is effective on purple loosestrife, but is non-selective and can damage all types of vegetation, possibly allowing purple loosestrife to reinvade. Spot application is advised.

  • WeedmasterTM (2,4-D and dicamba) is also effective, and will not kill established grasses or grass-like plants.

Warning: Purple loosestrife usually grows close to water and any herbicide application near or over water requires a permit from the Department of Ecology and a specially licensed applicator.


Call if you see this plant.
Prepared by the Clallam County Noxious Weed Control Board; revised 11/2000

For more information call: (360) 417-2442



or see www.clallam.net/weed


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