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giant horsetail
giant horsetail (Equisetum telmateia)
ODA rating: B
Perennial; grows six inches to several feet tall. Aerial stems jointed and hollow except at nodes. Fertile stems tan with brown leaves, unbranched, and terminate in elongated, spore-bearing cones. Sterile stems green with many whorls of slender, jointed branches. Sterile stems arise after fertile ones and persist longer.
It generally grows in moist areas and is found west of the Cascade Mountains in Oregon. The plant spreads rapidly by rootstocks and often invades pastures and cropland from infested stream courses and ditch banks. It is not uncommon for topsoil used in landscaping and new construction to contain rootstocks for horsetail.  Horsetail is a difficult plant to control once it has become established.
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Images courtesy of Western Society of Weed Science
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Known hazards
Several species of horsetail are poisonous to livestock, especially horses; problems usually arise when dry plants are fed to stock in hay.
A native of Europe and northern Africa, giant horsetail rush is now common from Alaska to southern California.
Distribution in Oregon
First documented site in Oregon was 1881 in Multnomah County.

Map legend
Yellow:  limited distribution
Red:     abundant
Grey:    not known to be present
Biological controls
No approved biological control agent is available at this time.