Weed Watch- Poisonous Plants
D. L. Ace, L. J.
Hutchinson, Pennsylvania State U., University Park; G. F. W. Haenlein, U. of
Delaware, Newark (Modified and updated by J-M. Luginbuhl, August 11) Submitted by Eve H. Honeycutt, Livestock Agent,
Lenoir and Greene Counties
This time of year,
pastures are growing too fast to keep the weeds grazed or mowed. Many times you may encounter weeds you
can't identify. How do you know if
it's poisonous? Below is an
excellent article from an NCSU specialist about the symptoms of poisonous plant
ingestion. For help identifying
weeds, contact your Extension office.
Factors contributing to
plant poisoning are starvation, accidental eating and browsing habits of
animals. Starvation is the most common reason. Most woodland or swampy-ground
pastures contain many species of poisonous plants. These are usually eaten only
when animals have nothing else to eat.
Animals accidentally eat
certain plants as they graze. A notable example of this is water hemlock. This
plant emerges in wet areas, which are the first to become green in early
spring. Animals eager to eat the fresh young grass may accidentally bite off
the crown of this plant with fatal results. Another type of accidental
poisoning occurs when large amounts of cockle are present in wheat, which is
fed as grain.
Some animals on good
feed in a dry lot or excellent pasture become bored with the same regular diet.
They may eat unpalatable weeds or ornamental plants growing along fences. Goats
and cattle like to vary the best kind of diet with a little ''browse''. Many
ornamental or wild shrubs may be consumed, not because they are palatable but
because the animal craves variation in its diet.
The severity of
poisoning is related to the quantity of material eaten, the specie of animal eating
the plant, portion of the plant and condition of the plant eaten, level of
ground moisture, general health of the animal prior to ingesting the substance
and the age and size of the animal. Therefore some livestock can eat some of
the bad plants and under several of the mentioned conditions, fail to show
symptoms of injury or poisoning. At other times death may occur.
Scores of plants contain
material toxic to animals if eaten in sufficient quantity. Some of the plants
are well known, some quite rare, some are useful, others are valued
ornamentals. They may be grouped by the type of poison contained, the effect of
their toxins or the part of the plant containing the poison. Some plants may
contain several poisonous principles.
Cyanogenetic Plants
These contain under
certain conditions, prussic acid (hydrocyanic acid), a deadly poison which
interferes with the oxygen-carrying ability of the blood. Death in these cases
is usually rapid and with little outward symptoms. Members of the prunus family
of plants, especially wild cherries, are dangerous. Peaches, plums, wild
cherry, and other stone fruits belong to this group of plants. Wilting of
the green leaves caused by frost, storm damage, or by cutting, changes a
glucoside (glycoside) found in the leaves to hydrocyanic acid (HCN) and sugar.
The sweet, wilted leaves are thus more attractive to animals than normal
foliage. Hydrocyanic acid content varies widely, but under some conditions a
few handfuls of leaves may be enough to kill a horse or cow. This type of
poisoning should be suspected when sudden death of animals follows windstorms
or early sharp frosts. These leaves apparently lose their poison after they
have become dry; the limp, green or partially yellowed leaves are the most
dangerous. Sudan grass and sorghums are also cyanogenetic plants. These
plants are usually deadly when damaged or frozen. Aftermath sprouts following
an early frost are particularly dangerous. Very little sudan grass poisoning
occurs from animals trampling down plants and later eating them although this
is often listed as dangerous. In dry weather, sudan grass is often pastured to
the ground without ill effects. After sudan grass has been repeatedly frozen
and the plants are completely dead, it is safe but not very valuable for
pasture.
Once frozen, sorghum,
sorghum sudan hybrids, or their aftermath should never be pastured. As long as
the plants show any green color they may be very poisonous. Both frosted
sorghum and sudan grass can be best and most safely utilized by ensiling them
for at least two weeks before feeding. Normal ensilage fermentation safely
eliminates the poisonous principle.
Common milkweed, a perennial that grows three or four feet high,
has a heavy stem and leaves and is frequently found in pastures. The milky
white sap is sticky and has a bitter taste but livestock eat the topmost,
tender leaves if good forage isn't abundant. Remove plants by spading, pulling,
cutting or plowing extensive areas and planting to cultivated crops for a year
or two.
Horse nettle is a perennial plant, two-feet-high, with spiny
stems and leaves, and smooth, orange-yellow berries. Fruits are more toxic than
the foliage. It's a common plant in grasslands and fields and is a member of
the nightshade family.
Black nightshade is an annual plant, two-feet high, with many
branches. Leaves are variably smooth or hairy. The stems are angled in
cross-section and sometimes spiny. Clusters of white flowers, one-fourth inch
across, bloom in midsummer and are followed by small, black fruits. Both the
foliage and green berries are toxic. The ripe berries are not poisonous. Black
nightshade is widely distributed.
The following are
excellent websites for more information:
Plants Poisonous to
Livestock and Pets in North Carolina,
Bulletin No. 414 (revised), by James W. Hardin and Cecil F. Brownie.
Poisonous Plants of
North Carolina
Cornell University
Poisonous Plants Informational Database
