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Division of Agricultural Sc i e n c e $
UNIVERSITY OF CALIFORNIA

ALiFORNIA AGRICULTURAL
xperiment Station
xtension Service

POISONOUS
HEMLOCKS

THEIR IDENTIFICATION AND CONTROL

J. M. Tucker • M. E. Fowler • W. A. Harvey • L. J. Berry

CIRCULAR 530

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POISONOUS HEMLOCKS

THEIR IDENTIFICATION AND CONTROL

■ HE poisonous plants referred to in this publica-
tion as "hemlocks" are members of the carrot or
parsley family, Umbelliferae, and should not be
confused with true hemlocks, which are coniferous
trees of the pine family, Pinaceae. Poisonous hem-
locks are of two genera : Conium (Poison Hemlock) ,
and Cicuta (Water Hemlock). They have a general
family resemblance to one another but are not
closely related ; their toxic properties and effects are
different, they present different problems to the live-
stock industry, and they have different diagnostic
features.

THE AUTHORS: J. M. Tucker is Professor of Botany and Botanist in the Experiment
Station, Davis; M. E. Fowler is Assistant Professor of Veterinary
Medicine and Assistant Veterinarian in the Experiment Station,
Davis; W. A. Harvey is Extension Weed Control Specialist, Agri-
cultural Extension Service, Davis; L. J. Berry is Range Manage-
ment Specialist, Agricultural Extension Service, University of
California, Davis.

OCTOBER, 1964

WARNING

2,4-D is classified as an injurious material by the State Department of
Agriculture, and before it can be purchased or used a permit must be
obtained from the County Agricultural Commissioner. It should be used
with care and at a time and in such a manner that it will not drift to other
plants or properties and cause injury to susceptible plants or result in an
illegal residue on other food or feed crops.

THE GROWER IS RESPONSIBLE for residues on his own crops as well
as for problems caused by drift of a chemical from his property to other
properties or crops.

Fig. 1. Mature plants of water hemlock (Cicuta).

General Characteristics of Umbelliferae

The family Umbelliferae, which includes
poison hemlock, also includes carrot, cel-
ery, and parsnip, and herbs such as pars-
ley, anise, dill, caraway, and coriander.
The leaves are usually much divided and
fern-like, and are alternately arranged
along the stem; in some members of the
family (carrot and poison hemlock, for
example) the first year's leaves are in a
basal tuft. The base of the leaf-stalk is
usually somewhat enlarged and partly
surrounds and clasps the stem. The nu-
merous, small flowers are borne in um-
brella-shaped clusters (umbels). A circle
of bracts (small, leaf-like structures)
called an involucre is usually present
around the base of the umbel (fig. lie).
The small, dry fruit of these hemlocks
often shows distinctive features which can

serve as characters for identification. In
order for a botanist to make a positive
identification on an unknown species of *
Umbelliferae it is usually necessary to
have the mature fruit for examination.
Although illustrations of the fruits of all
groups discussed herein are included to
aid the reader, more emphasis is placed
on other identification features for two 4
reasons: most livestock losses from hem-
locks occur long before mature fruits de-
velop and the rancher cannot wait 2 or
3 months for an identification, and be-
cause mature fruits are generally small,
a strong magnifying glass or a good hand-
lens is required in order to study them.
Fortunately, Conium and Cicuta show
good diagnostic features in other organs
much easier to observe. M

WATER HEMLOCK (Cicuta)

How to Recognize Water Hemlock

There are two similar water hemlock
species in California: western water hem-
lock (Cicuta douglasii) and salt-marsh
water hemlock (Cicuta bolanderi) . They
are smooth, erect perennials, 3 to 8 feet
tall, with hollow stems, and short, thick-
ened, basal rootstocks (fig. 1). In large
mature plants, the rootstock is divided in-
ternally into a series of hollow chambers
by cross-partitions which are readily ap-
parent when the rootstock is cut open
lengthwise (fig. 2a). When this is done,
drops of a yellowish, oily liquid ooze out
upon the cut surface, and in a matter of
minutes the liquid turns reddish, and then
reddish-brown. This liquid, which has a
distinctive, aromatic odor, contains the
poison of the plant — a resinous substance
called cicutoxin which is soluble in
organic solvents but not in water.

The leaves are large and much divided,
and are once, twice, or three times pin-

nately compound. The individual leaflets
(the ultimate divisions of the leaf) are
lance-shaped, and have regularly serrate
margins (fig. 26) . Also, the leaflets show
a distinctive venation pattern: the sec-
ondary veins usually extend from the mid- "
rib out to the notches between the mar-
ginal teeth (fig. 2c), whereas in most
other genera in the family the secondary 4-
veins run out to the tips of the teeth.
Water hemlock does not have a circle of
bracts surrounding the base of the umbel
as in most members of the family; only
one or two small bracts may sometimes
be found. The numerous, small, white
flowers are grouped in compound umbels.
The fruits, which are about %" to 3/16"
long, are dry when fully ripe and each
splits readily into two halves (a charac- 4
teristic of the whole family). Fruits are
broadly oval, or roundish and slightly
flattened (fig. 2d). *

[4]

J BR

Fig. 2. Water hemlock (Cicuta). A — rootstock cut lengthwise, 80 per cent actual size;
>. B — leaf, 25 per cent actual size; C — leaflets, showing distinctive venation pattern, 80

per cent actual size; D — fruit, 7 times actual size. Inset is actual size.

Where Water Hemlocks Grow

Water hemlocks are restricted to wet
habitats — marshy areas, the borders of
streams, lakes, etc. Salt-marsh water hem-
lock is found in salt marshes along the
coast in central and southern California,
or in brackish marshes around the var-
ious arms of San Francisco Bay. Western
water hemlock occurs throughout most
of the state from sea level to elevations of
7.500 feet or more.

Poisonous Properties

The rootstocks of these plants are ex-
tremely poisonous: two to six rootstocks
CY2 to 1 pound) can kill a mature cow
in as little as an hour. Dried rootstocks
are as poisonous as fresh ones. All animals
(including man) are poisoned if they eat
enough Cicuta, but cattle are most often
grazed in areas where Cicuta grows and
are more likely to pull up the rootstocks
from wet ground. The young leaves of
Cicuta also contain cicutoxin, and early
in the growing season may cause livestock
losses. As the leaves expand, however, the
poison becomes less concentrated, and
consequently mature leaves rarely cause
poisoning.

Cases of livestock loss from eating
Cicuta have been fairly common in Cali-
fornia. The most serious occurrence to
come to our attention in recent years was
during the winter of 1961-62, when twen-
ty-seven cattle died on a ranch in Del
Norte County. These animals had been
feeding on swampy land which had been
cleared and seeded to grass; it is probable
that Cicuta was the cause of death, as the
area was found to be heavily infested with
the plant and pieces of its rootstock were
found in the rumen of two of the dead
animals.

Signs of Poisoning

Cicuta produces such a rapid death that
in most cases illness will not be observed.
Animals may be found dead near the
source of the plant, and diagnosis is based

on finding that the plant has been eaten
and perhaps finding parts of the root-
stocks in the rumen or paunch.

The first signs of poisoning may be
seen from 10 to 60 minutes after the plant
is eaten. The animal walks stiffly and acts
uneasy. The eyelids may begin to twitch.
In a few minutes the muscles of the neck
begin to twitch and may cause the head
to jerk; soon many muscles are twitching,
and the animal may appear to be jumping
up and down. As the muscles continue to
contract the animal falls down, goes into
violent convulsions, and fights for its
breath. The legs are flung about wildly,
the neck may be arched down between
the legs or pulled backwards, and the
third eyelid is frequently pulled over the
eyeball. The mouth and face become con-
torted and violent chewing motions occur
with frothing at the mouth. Periodically,
the animal will relax and lie quietly for
a moment, but a slight noise or touch will
start the convulsions again.

If the animal falls down and goes
into convulsions it will die within 15 to
30 minutes after it has shown marked
signs of poisoning. An autopsy of the dead
animal will not give much help unless
parts of Cicuta are found in the rumen —
the poison affects the brain so quickly that
no lesions are produced. Animals that
have eaten only small amounts of Cicuta
may show mild signs and live.

Treatment

Because there is no specific antidote for
Cicuta poisoning, and because death
usually occurs too quickly for anyone to
treat the animal, prevention is the only
hope in controlling losses from poisoning.
The rancher must recognize the plant and
eliminate it, or keep livestock away
from it.

Controlling Water Hemlock

It is often possible to reduce water hem-
lock infestation and improve growth of
more desirable forage species by drying

[6]

the soil. This may be done by levelling,
improving drainage, and realigning
ditches; rootstocks brought to the surface
should be removed before they can be
eaten by livestock.

Hand-grubbing of scattered plants,
mechanical cultivation, and chemical
sprays, can control the pest. Hand-grub-
bing or digging is usually done in small
areas in the spring when soil is moist;
plants can often be pulled from moist soil
with a minimum of digging. Care should
be taken to remove all the rootstocks in
the soil, as remaining pieces can sprout
and form new plants; rootstocks should
be placed in bags or boxes and carried
from the field to be dried and burned.
Larger infestations may be plowed and
thoroughly harrowed several times with
a spring-tooth harrow to drag the root-
stocks to the surface. The exposed root-

stocks should be collected, dried, and
burned as described above.

2,4-D sprays have given good control,
using 2 pounds of 2,4-D per acre in suf-
ficient water to give complete wetting of
the water hemlock's foliage ; a low- volatile
ester of 2,4-D, or an amine formulation
with an added wetting agent, can be used.
Spraying should be done in late spring
or early summer when the plant is grow-
ing vigorously but before its seeds ma-
ture. Grasses are not damaged by 2,4-D —
they will usually fill in spaces occupied by
the hemlock and so help prevent regrowth
and reinfestation. A follow-up treatment
on regrowth in the fall or the following
spring should be planned; spot spraying
of any water hemlock appearing in sub-
sequent years should keep the area free
of this pest.

Other Umbelliferae Which May Be Confused With Water Hemlocks

The following plants, which commonly
occur in wet habitats, may be confused
with water hemlock. However, none of
them has the same combination of char-
acteristics so distinctive of Cicuta: the
chambered rootstock in large, mature
plants ; the oily, aromatic liquid exuding
from cut surfaces of the rootstock; the
secondary veins of the leaflets running to
the notches between the teeth rather than
into the teeth; and the lack of a circle
of bracts at the base of the umbel.

Water parsnip, Sium suave (fig. 3) .
This plant is more similar to water hem-
lock and can be more readily confused
with it than can any of the others listed
below. Its leaves are only once pinnately
compound (fig. 3a), however, while
water hemlock leaves are usually two or
three times pinnately compound (fig.
26). The venation pattern of the leaflets
is quite different; the secondaries are
rather weak and irregular and do not
extend directly to the margin (as in

Cicuta) but become lost in a network of
small veinlets (fig. 36). Unlike Cicuta, a
definite circle of small bracts occurs at
the base of the umbel.

Water parsnip grows in marshes and
along sloughs from central California
northward into British Columbia. Al-
though reportedly toxic to livestock, there
appear to be no authentic cases of its hav-
ing caused livestock loss.

Water parsley, Oenanthe sarmentosa
(fig. 4) . Water parsley is a lower- growing
plant than water hemlock, and is com-
monly 2 to 4 feet tall. The stems are softer
and more succulent than those of water
hemlock; the leaflets are more coarsely
toothed and often deeply cleft or divided
(fig. 46) , unlike the evenly serrate leaflets
of water hemlock. Mature fruit is %6 of
an inch or less in length, barrel-shaped
to cylindrical, and has conspicuous
elongated styles (fig. 4c).

Water parsley grows mainly along the
coast from southern California into

[7]

Fig. 3. Water parsnip (Slum suave). A — leaf, 25 per cent actual size; B — leaflet, showing
venation pattern, 80 per cent actual size; C — fruit, 14 times actual size.

Canada, and in the northern Sierra
Nevada.

Cut-leaved water parsnip, Berida
erecta (fig. 5) . This plant is 10 inches to
30 inches tall, and has leaves only once
pinnately compound, whereas those of
water hemlock are two or three times
pinnately compound. A circle of small
bracts occurs at the base of the umbel.

further distinguishing it from water hem-
lock.

Cut-leaved water parsnip grows in
marshes and along sluggish streams
throughout most of California.

White heads, Sphenosciadium capi-
tellatum (fig. 6). An erect plant 3 to 5
feet tall. Similar in a general way to water
hemlock, it differs in a number of re-

[8]

Fig. 4. Water parsley (Oenanthe sarmentosa). A — leaf, one-third actual size; B — leaflets,
75 per cent actual size; C — fruit, 12 times actual size.

spects. The base of the leafstalk of the
upper leaves is enlarged, and has an in-
flated appearance ; the leaflets are usually
more irregularly toothed than those of
water hemlock, and the inconspicuous
secondary veins run into the teeth rather
than to the notches between the teeth.

The umbel is finely woolly, unlike water
hemlock, and the flowers are in dense
ball-like heads (fig. 6c). The fruit is
flattened, and has a narrow marginal
wing on either side (fig. 6c?).

White heads occurs along streams and
in swampy places in the mountains of

[9]

Fig. 5. Cut-leaved water parsnip (Berula erecta). A — leaf, 60 per cent actual size; B —
leaflet, slightly enlarged; C — upper leaf, 60 per cent actual size; D — fruit, 18 times
actual size.

California, at altitudes ranging from
3,000 to 10,000 feet.

Angelica, Angelica species (fig. 7).
Some species are somewhat similar to
water hemlock, and a few occur in wet

habitats. Individually, they differ from
water hemlock in various ways, but in all
of them the fruit is conspicuously differ-
ent, having thin flattened margins on
either side (fig. 7c) .

[10]

®

A

Fig. 6. White heads (Sphenosciadium capitellatum). A — leaf, 25 per cent actual size;
B — leaflets, 80 per cent actual size; C — flower cluster, two-thirds actual size; D — fruit,
9 times actual size.

[ii]

Fig. 7. Angelica (Angelica). A — leaf, 25 per cent actual size; B — leaflets, half size;

C — fruit, 7 times actual size.

[12]

POISON HEMLOCK (Conium)

How to Recognize Poison Hemlock

There is only one species of poison hem-
lock in California, Conium maculatum
(fig. 8), a branching biennial commonly
4 to 6 feet tall, but sometimes attaining a
height of 10 feet. It has a long, white,
often-branched tap root ; the stem is stout,
hollow, smooth, erect, and marked with
reddish-purple spots (fig. 9) — the spotted
stem is one of its most distinctive features.
Lower leaves are 1 to 2 feet long or more,
much dissected, and fern-like. The small,
white flowers are arranged in open, com-
pound umbels, 3 inches or less across. A
circle of small, simple bracts surrounds
the base of the umbel (fig. 10c). The
small fruits are oval, and when dry have
ribs that are minutely but distinctly
(under a magnifying glass) wavy or un-
dulating (fig. 10c?). Like water hemlock,
the fruit splits into two halves when fully
ripe.

Where Poison Hemlock Grows

Poison hemlock, a native of Europe,
occurs at lower elevations throughout
much of California. Unlike the water
hemlocks it is not semi-aquatic, and al-
though frequently found in moist ground
it may thrive in fairly dry soil.

Poisonous Properties

Conium has been recognized as a poi-
sonous plant for many centuries. Its
poisonous principle (consisting of several
alkaloids) is found in the green leaves
and stems and the fruit of the plant.
Owing to the volatile character of the
poisons this hemlock largely loses its
toxicity on drying. Thus, hay containing
Conium is not dangerous.

The plant is rarely eaten, but if whole-
some forage is lacking livestock may eat
the young foliage with fatal results. In
rare instances, the small seed-like fruits
may occur as an impurity in grain in
sufficient quantity to poison livestock fed

on it. Conium is not nearly as dangerous
as Cicuta because the animal must eat 1
to 2 per cent of its body weight to produce
poisoning, and even then the animal may
recover if given proper care.

Signs of Poisoning

Poisoning signs appear 2 to 4 hours
after eating the plant. Conium affects the
animal's brain ; the animal loses strength,
its hind legs buckle beneath it, and it
staggers and falls. It may get up again
with difficulty, or it may stay down. The
front legs soon become paralyzed and the
animal appears drowsy and goes into a
coma. An animal may be down and
paralyzed for a day or two and still re-
cover. Death can occur in 5 to 10 hours
after these signs are noted, and autopsies
reveal nothing significant.

Treatment

There is no specific antidote for
Conium poisoning, but keeping prostrate
animals shaded or warm and providing
feed and water will save most of them.
Laxatives may help to remove the
material from the rumen; do not drench
an animal in a coma, as a fatal pneumonia
may be produced.

Controlling Poison Hemlock

Poison hemlock occurs in wet and in
drier portions of fields. If the area is wet,
improved drainage may help the growth
of desirable pasture plants but will not
eradicate the poison hemlock. However,
frequent close mowing will eliminate an
infestation by preventing seed formation.
Close mowing also reduces the amount of
green vegetation available for grazing,
and the dried mowed material rapidly
loses its toxicity.

Poison hemlock can also be controlled
by spraying with 2,4-D in late spring
while the plants are growing vigorously

[13]

fi

4)

Fig. 8. Mature plants of poison hemlock (Conium maculatum).

.....

■ ■ - //

Fig. 9. Spotted stem of poison hemlock (Conium maculatum).

(old, dry plants are not controlled by this
treatment) . Ester or amine formulations
of 2,4-D, at 2 pounds per acre in sufficient
water to give thorough wetting, will give
control. Some re-treatment is usually
necessary because of missed plants, new
seedlings, or regrowth; in heavy infesta-

tions, treatment each spring for several
years is necessary for complete eradica-
tion. Improvement of desirable forage
plants through pasture management, fer-
tilization, irrigation, or drainage will help
to prevent reinfestation.

Fig. 10. Poison hemlock (Conium maculatum). A — leaf, 20 per cent actual size; B —
portion of leaf, one-third actual size; C — flower cluster, actual size; D — fruit, 6 times
actual size.

[16]

®

rtftv,

Fig. II. Wild carrot (Daucus carota). A — leaf, half size; B— portion of leaf, two-
thirds actual size; C — flower cluster with involucre at its base, two-thirds actual size;
D — fruit, 7 times actual size.

[17]

Fig. 12. Bishop's weed (Ammi ma jus). A — lower leaf, 60 per cent actual size; B — leaf
midway up the stem, 60 per cent actual size; C — upper leaf, 80 per cent actual size; D —
flower cluster showing involucre, actual size; E — fruit, 11 times actual size.

Other Umbelliferae Which May Be Confused With Poison Hemlock

The following plants could be confused
with poison hemlock, although they do
not possess the combination of characters
distinctive of poison hemlock: the red-
dish-purple spotting on the stems, the
circle of small, simple bracts, and the
wavy ribs on the fruit.

Wild carrot, Daucus carota (fig. 11) .
A biennial with finely dissected, fern-like
leaves. The stems are usually finely
bristly-hairy and the leaves sparsely
hairy, whereas poison hemlock is quite
smooth, lacking pubescence altogether.
The umbel is surrounded by a circle of
conspicuous, pinnately divided bracts
with elongated, narrow divisions (fig.
lie) . The small fruits bear conspicuous
rows of bristles (fig. lie?).

Wild carrot, a native of Europe, has
become widespread as a weed in this
country. In California, it is sparingly
established at scattered localities.

Bishop's weed, Ammi ma jus (fig.
12) . An erect biennial, 1 to 2% feet tall,
with smooth, branched stems. The lower
leaves (fig. 12a) are pinnately compound
with lance-shaped leaflets having very
finely and sharply serrate margins, quite
unlike the leaves of poison hemlock. The
leaflets become progressively narrower up
the stem (fig. 126), however, and the
smaller upper leaves are much more
similar to Couium, being two or three
times pinnately dissected, with narrow
divisions (fig. 12c). The umbel is sur-
rounded by a circle of conspicuous bracts
which are divided into narrow, elongated
segments (fig. 12a7) ; this feature is quite
different from Conium.

Bishop's weed, a native of Eurasia, has
become sparingly established in Cali-
fornia, mainly in Napa and Sonoma
counties.

Co-operative Extension work in Agriculture and Home Economics, College of Agriculture, University of California, and United States Department of Agriculture
cooperating. Distributed in furtherance of the Acts of Congress of May 8, and June 30, J914. George B. Alcorn, Director, California Agricultural Extension Service.

12Jm-10.,64(E6416)V.L.

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