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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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Perennial Sowthistle (field
milk-thistle)
Asteraceae (=Compositae), the aster family
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Background
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 Perennial sowthistle is native to western Asia and
Europe. It spreads both by seed and creeping roots, and it grows under a
many conditions. Plants produce from root buds as deep as 2 feet, often
resulting in large, dense colonies.
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Description
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Perennial sowthistle has
crowded, spatula-shaped to deeply lobed, dandelion-like leaves up to 10
inches long near the base of the plant. Stem leaves are much reduced,
usually unlobed,
 and scarce; all leaves are prickly toothed along the
margins. Stems are hollow, sparsely branched, and up to 6 feet tall. Both
leaves and stems exude a milky latex when broken. Yellow, dandelion-like
flower heads are 2 inches wide and bloom from June until frost. The flower
heads and their stems bear coarse, spreading, gland-tipped hairs. Seeds are
reddish brown, 1/8 inch long, flattened, ribbed, and tipped with white
plumes. The plant has extensive horizontal roots.
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Distribution
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 Perennial sowthistle is present in the northern U.S.,
and in California, Texas, Missouri, and North Carolina.
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Control
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No biological control agents are available, but herbicides are. |
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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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