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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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Purple Loosestrife (spiked
willow-herb, long-purples, purple Iythrum)
Lythraceae, the loosestrife
family
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Background
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 Purple
loosestrife is a semi-aquatic plant native to Europe, probably introduced as
an ornamental. Valuable riparian habitat is degraded, and food species are
rapidly displaced by this weed, which has no wildlife value. Purple
loosestrife spreads both by seed and spreading
rhizomes that form dense, woody mats.
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Description
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Purple loosestrife is a semi-aqua tic, hardy
perennial that can grow over 8 feet
tall. Stems are usually 4 sided and much branched, bearing opposite or
whorled, 4-inch long, lance-shaped leaves. Crowded flower
spikes develop at
the stem tips in midsummer. Flowers are 1-inch in diameter with 5 to 7
reddish purple, wrinkled petals that appear as if they have been crushed. A
single plant may produce over 2.5 million tiny seeds per year. |
Distribution
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 Purple
loosestrife is found throughout the northeastern U.S. and in some western
states and in Idaho.
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Control
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Biological control agents are
available and include 2 leaf beetles that have worked well in Idaho.
Herbicides are available, but effectiveness on purple loosestrife is
inconsistent and application is difficult.
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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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