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Poison Hemlock
Apiaceae (=
Umbelliferae), the parsnip family
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Background
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 Poison
hemlock is native to Europe. It contains highly poisonous alkaloids toxic to
all classes of livestock and humans. It has poisoned many who have mistaken
it for parsley. Poison hemlock is often found on poorly drained soils,
particularly near streams, ditches, and surface water.
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Description
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 Poison
hemlock is a biennial that grows up to 10 feet
tall. Stems are stout, hollow, ridged, and mottled with purple spots. Leaves
are shiny green, 3 to 4 times pinnately compound, and
clasp the stem at the
obvious nodes. Crushed foliage has a disagreeable, mousey odor. Flowers are
small, white, and borne in umbrella-shaped clusters about 3 inches across
in early summer. Seeds are ridged and flattened, with 2 seeds borne
together. The plant has a thick, white
taproot.
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Distribution
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 It
grows throughout the U.S. except from eastern Montana to northeastern
Minnesota and south to Nebraska. It has an extensive presence in Idaho. |
Control
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A biological control agent (a
defoliating moth) provides good to excellent but inconsistent control.
Herbicides are also available.
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© 1999 University of Idaho:
Text and photographs for these pages from Idaho's Noxious Weeds, by
Robert H. Callihan and Timothy W. Miller (revised by Don W. Morishita
and Larry W. Lass).
Please contact: Ag Publishing, University of Idaho, Moscow,
Idaho 83844-2240; 208 882-7982 visit the Resources for Idaho website at
http://info.ag.uidaho.edu, for more information about this or other
publications.
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Scotch Thistle (cotton
thistle)
Asteraceae (= Compositae), the aster family
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Background
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 Scotch
thistle is a native of Europe and eastern Asia and is probably an escaped
ornamental. Scotch thistle stands are dense and practically impenetrable due
to the weed's spiny nature and large size. It spreads by seed and generally
inhabits moist sites or drainages in dry locations.
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Description
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 Scotch
thistle is a biennial that grows up to 8 feet
tall. The plant forms a rosette of leaves the first year, and produces a
seed stalk the second year. Leaves are large (up to 2 feet long and 1 foot
wide) and strongly armed with spines, and the blades form conspicuous
fringelike extensions along the stem. The entire plant is finely hairy to
woolly, giving it a silvery-gray color. Flower heads develop in midsummer in
groups of 2 or 3 on branch tips. Flower heads are globe shaped, upright,
intensely spiny, and up to 2 inches in diameter; flowers are purple. Seeds
are slender, smooth, and plumed.
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Distribution
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 Scotch
thistle is widely but sparsely distributed in the U.S. and throughout Idaho.
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Control
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Biological control agents are not available, but herbicides can provide
excellent control of this weed if applied to very small plants.
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© 1999 University of Idaho:
Text and photographs for these pages from Idaho's Noxious Weeds, by
Robert H. Callihan and Timothy W. Miller (revised by Don W. Morishita
and Larry W. Lass).
Please contact: Ag Publishing, University of Idaho, Moscow,
Idaho 83844-2240; 208 882-7982 visit the Resources for Idaho website at
http://info.ag.uidaho.edu, for more information about this or other
publications.
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