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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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Yellow Starthistle (St.
Barnaby's thistle, cotton-tip thistle)
Asteraceae (=Compositae), the aster
family
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Background
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 Yellow starthistle originated in the Mediterranean area
and Asia. It spreads exclusively by seed, which may lie dormant for as long
as 10 years. It causes "chewing disease" and death in horses. Yellow
starthistle will grow wherever downy brome (cheat-grass) grows.
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Description
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Yellow starthistle is a winter
annual maturing from 2 to
72 inches tall. A rosette of deeply lobed leaves up to 8 inches long forms
after seed germination in the fall. Stem leaves up to 4 inches long develop
in early spring, their blades forming fringelike extensions on the stem.
Yellow flower heads develop at the tips of branched stems from late spring
until fall. Flower head bracts bear stiff, sharp thorns 3/4 inch long. Seeds
are tan with white and brown mottling, 1/8 inch long; both
plumed and unplumed seeds develop in each flower head. Plumed seeds are not highly
windborne; unplumed seeds not at all.
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Distribution
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Y ellow starthistle is widely scattered throughout the
U.S., but is a severe problem only in the West. |
Control
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Three seed head weevils and 2 seed head flies have been good to excellent
biological control agents in Idaho.
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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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