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The
Road to Recovery
If ingested by grazing horses or cattle, tansy ragwort
destroys the liver, causing cirrhosis-like lesions and
eventual failure.
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A
relative of the sunflower, the poisonous Eurasian weed, tansy
ragwort, thrives in coastal Washington, Oregon, northern California,
and in the New England States. Likely brought to both coasts
of the United States in ships' ballast, tansy ragwort has
spread eastward from the Pacific coast. First documented in
Oregon in 1922, the ragwort's eastward progression was probably
aided by human transportation of contaminated hay and straw.
Since a single specimen of this prolific weed can produce
up to 150,000 seeds, which can remain viable for three to
fifteen years, tansy ragwort can quickly establish a foothold
in a given pasture.
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Poisonous
tansy ragwort is an enemy to ranchers and beekeepers
alike.
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If
ingested by grazing horses or cattle, tansy ragwort destroys
the liver, causing cirrhosis-like lesions and eventual failure.
By the time symptoms of ragwort poisoning appear, it is too
late to save the animal. It's a drawn-out death that can occur
up to six months after initial consumption. Aside from killing
livestock, the weed displaces native grasses and ruins honey
produced by bees that gather its pollen.
To
control the noxious weed, several of the plant's natural enemies
were released- the cinnabar moth in 1960, the seedhead fly
in 1966 and the flea beetle in the late 1960's. These three
insects work best in concert to control the weed, each feeding
on a different part of the ragwort and at a different time
of the year. In Oregon, a biological control program reduced
the tansy ragwort population by 90% over 17 years. The reduction
has saved an estimated five million dollars per year.
But
tansy ragwort is still a problem in places, including parts
of Idaho, Montana and British Columbia, where the insect species
have not been able to establish populations. In these areas,
people will have to resort to the more labor-intensive and
costly means of control, such as mowing, tilling and applying
herbicides to keep their pastures ragwort-free. 
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Photos:
Nova Scotia
Museum
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