NATIVE WOODY PLANTS OF THE UNITED STATES 
9 
POISONOUS PLANTS 
Plants clermatitically poisonous to man ordinarily will not be 
planted, because collection of seed or cuttings cannot be made with- 
out exposure to the irritants. In many places such plants may be 
spontaneous. If they are of value in erosion control or as wildlife 
food or cover and particularly if they are sufficiently removed from 
habitations, they may often be left to perform a useful function. 
The subject of livestock poisoning has been admirably treated by 
Chesnut and Wilcox {119) and by Marsh {392). Their authoritative 
generalizations are paraphrased here. 
It may be stated as a general fact that the popular idea that range 
animals will voluntarily seek out poisonous plants and eat them from 
preference is not true. Animals seldom eat poisonous plants except 
as they are driven to do so by lack of other food. Almost all poison- 
ous plants are distasteful to livestock and under ordinary circum- 
stances will be avoided. Loco plants, which are herbaceous, are an 
exception to this rule. 
The state of the local vegetation as affected by weather conditions 
ordinarily exercises considerable influence on the occurrence or non- 
occurrence of poisoning. In the early spring certain poisonous plants 
may start to grow before the native grasses. If these poisonous 
plants are at all conspicuous or offer any considerable amount of 
succulent material, livestock may be tempted to eat them. The acrid, 
bitter, or otherwise disagreeable taste of such plants seems not to 
deter livestock. Sheep and cattle may often eat large quantities of 
plants that are extremely distasteful to the human palate. 
In seasons of unusual drought, grasses on the range may become 
thoroughly dry while other plants remain green and tempting. It 
is obvious that livestock will be more apt to eat poisonous plants 
when such plants offer more tempting forage than the grasses. It 
is equally obvious that when grasses and other harmless forage plants 
are present in abundance and in good condition, sheep and cattle less 
often make tlie mistake of eating poisonous plants. 
To prevent poisoning of livestock, reliance should be placed on 
prevention rather than remedies. Animals must be so well cared for 
that they will not be tempted to eat poisonous plants. They must be 
prevented from eating such plants by careful handling of the herds. 
It must always be borne in mind that animals seldom eat poisonous 
plants by preference, but that under starvation conditions they may 
be driven to do so with disastrous results. 
Usually, in selecting stock for planting, nontoxic species can be 
chosen. In rare instances, however, certain toxic forms may be the 
only ones capable of doing the job. In such event, great care should 
be exercised to see that plantings will not be available to livestock. 
This can be accomplished either by fencing or by proper management 
of the herd. 
AGGRESSIVE PLANTS 
Whether to include or exclude a species that may become a pest 
is often a difficult decision to make. Extreme aggressiveness may be 
the character necessary for successfully controlling a given site, but 
if such aggressive species spread and become a nuisance because they 
are difficult to eradicate, the planter may often regret having used 
them. 
