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Title: USDA Farmers' Bulletin No. 1972: Poison-ivy, Poison-oak and Poison Sumac: Identification, Precautions and Eradication
Author: Crooks, Donald M., Kephart, Leonard W.
Language: English
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Copyright Status: Not copyrighted in the United States. If you live elsewhere check the laws of your country before downloading this ebook. See comments about copyright issues at end of book.

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Transcriber Note

Text emphasis is denoted as: _Italics_ and =Bold=.



                              POISON-_ivy_

                              POISON-_oak_

                                   and

                             POISON _sumac_

                             IDENTIFICATION
                               PRECAUTIONS
                               ERADICATION


                       Farmers' Bulletin No. 1972

                     U. S. DEPARTMENT OF AGRICULTURE


POISON-IVY, poison-oak, and poison sumac remind most people of painful
experiences to be avoided, yet many do not know any one of the offending
plants or their equally poisonous relatives. Learning to recognize them
on sight is relatively easy, especially by examining the distinctive
identifying characters described in the pictures and legends of this
bulletin. There is then a good chance to avoid them or, if one must work
among them, to take preventive measures to escape poisoning.

These plants are very common throughout the United States. They are
found in fields and woods, along fence rows, rock walls, and hedges,
in lawns and gardens, and even sometimes vining on houses. Usually in
any one locality it is necessary to be certain of the identity of only
two or three of them. Maps show at a glance where they are likely to
be found. Frequent observation and recognition of the plants as they
are encountered almost daily is the best way to become poison-oak or
poison-ivy conscious. Nonpoisonous sumacs are easily distinguished from
the poisonous species by the seed heads and leaves.

The old proverb, "an ounce of prevention is worth a pound of cure,"
is good advice to everyone, particularly as regards ivy-poisoning.
Previous escape is not proof of immunity when conditions are right, and
after poisoning occurs there is no quick cure known. Some relief may be
obtained and recovery hastened by use of some of the tested remedies. In
case of severe poisoning a physician should be consulted.

Poison-ivy and other poisonous plants growing in grounds frequented by
people should be eradicated. In some places this can be done by careful
grubbing. In others weed-killing chemicals may be better and more
certainly would avert poisoning for most of us.

This bulletin supersedes Farmers' Bulletin 1166, Poison Ivy and Poison
Sumac and Their Eradication.



Washington, D. C. Issued August 1945



POISON-IVY, POISON-OAK, AND POISON SUMAC: IDENTIFICATION, PRECAUTIONS,
ERADICATION


By Donald M. Crooks, _principal horticulturist, Division of Tobacco,
Medicinal, and Special Crops_, and Leonard W. Kephart, _senior
agronomist, Division of Cereal Crops and Diseases, Bureau of Plant
Industry, Soils and Agricultural Engineering, Agricultural Research
Administration_



Contents


                                                   Page

  A widespread menace to health                       1
  Forms of poison-ivy and poison-oak                  2
    Common poison-ivy                                 2
    Oakleaf poison-ivy                                9
    Western poison-oak                                9
  Poison sumac                                       16
    Confusion of poisonous and harmless sumacs       19
    Introduced poisonous sumac and related species   21
  Poisoning                                          21
    Precautions against poisoning                    22
    Treatment for poisoning                          23
  Eradication of plants                              25
    Chemical weed killers                            25
    Eradication by mechanical means                  25



A WIDESPREAD MENACE TO HEALTH


EVERY year sees many adults, and especially children, accidentally
poisoned from contact with plants that they did not know were harmful.
Had the sufferers known how to detect poisonous plants they could
have avoided them and escaped the painful experience of severe skin
inflammations and water blisters. Very few persons have a sufficient
degree of immunity to protect them from poisonous plants, and many do not
recognize them in the various forms that they assume in different parts
of the country.

One or more kinds of poison-ivy--common poison-ivy, oakleaf poison-ivy,
and western poison-oak--occur in abundance in almost every part of the
United States. Poison sumac is of more limited distribution and occurs
chiefly east of the Mississippi River, usually in swampy regions.

Poisoning by these plants is largely preventable. A knowledge sufficient
to identify them in their various forms is easily gained by anyone who
will make a study of pictures and general descriptions and train himself
by a little diligent practice to observe the plants in his locality. It
is important to become poison-oak or poison-ivy conscious. This can be
accomplished only by learning to know the plants by repeated experience
in observing them in their various forms. Persons who learn both to
know and to avoid the plants can save themselves much inconvenience and
discomfort. The simple means of learning to recognize them will pay big
dividends. It is the first step to the prevention of poisoning and to the
eradication of the pests from private grounds and public places.

The most effective method of prevention is to eradicate the plants, and
wherever possible this should be done. They should not be allowed to grow
in lawns or gardens, with ornamental shrubbery, or on houses. Communities
should not countenance the growth of poison-ivy or poison-oak in school
grounds, on public roadways, or in parks, especially those frequented by
children. The cost of medical aid for one season in treating pupils using
an ivy-infested schoolyard is likely to be more than that of eradicating
the plants, to say nothing of the suffering and inconvenience they may
cause.



FORMS OF POISON-IVY AND POISON-OAK


Poison-ivy and poison-oak are known by a number of local names, and
several different kinds of plants are called by these names. The plants
exhibit a good deal of variation throughout the United States, so much
so that even technical botanists cannot agree on the number of species
and names that should be applied to them. They grow in the form of (1)
woody vines attached to trees or objects for support, (2) trailing shrubs
mostly on the ground, or (3) erect woody shrubs entirely without support.
They may flourish in the deep woods, where soil moisture is plentiful,
or they may be found in very dry soil on the most exposed hillsides. The
plants are most frequently abundant along old fence rows and edges of
paths and roadways, and they ramble over rock walls and climb posts or
trees to considerable heights. They often grow with other shrubs or vines
in such ways as to escape notice.

The leaf forms among plants or even on the same plant are as variable
as the habit of growth; however, the leaves always consist of three
leaflets. The old saying, "Leaflets three, let it be," is a reminder of
this consistent leaf character but may lead to undue suspicion of some
harmless plant. Only one three-parted leaf leads off from each node on
the stem. The leaves never occur in pairs along the stem. The wide range
in habit of growth of plants and leaf types may be noted from a glance at
the several pictures of plants and leaves.

The flowers and fruit are always in clusters on slender stems that
originate in the axis of the leaves along the side of the smaller
branches. The fruits usually have a white, waxy appearance and ordinarily
are not hairy, but may be so in some forms. The plants do not always
flower and bear fruit. The white or cream-colored clusters of fruit, when
they occur, are significant identifying characters, especially at the
season after the leaves have fallen.

For convenience, these plants are discussed in this bulletin under three
divisions: (1) Common poison-ivy, (2) oakleaf poison-ivy, and (3) Western
poison-oak. A technical botanist would recognize many species of plants
in what are included as the common poison-ivy, and anyone will recognize
that various forms occur within this grouping.


COMMON POISON-IVY

Some form of the common poison-ivy may be found in almost every part of
the country but the extreme West. The shaded area on the map in figure 1
shows the extensive range where some form of poison-ivy is likely to be
found. The plant is known by various local names--poison-ivy, threeleaf
ivy, poison creeper, climbing sumac, poison-oak, markweed, piery, and
mercury. The most widespread form is classified by botanists under the
botanical name of _Rhus radicans_ or varieties of it; however, many of
the variations are sometimes given other botanical names. The common
poison-ivy may be considered as a vine in its most typical growth habit.

_Figure 1._--The shaded part shows the extensive area where some form of
the common poison-ivy is likely to be found. Other forms also may occur
in parts of the same region.

_Figure 2._--Large poison-ivy vine growing on a tree for support. This is
the usual form of the common poison-ivy in wooded areas.

_Figure 3._--_A_, Common poison-ivy growing in a hedge and on a shade
tree on the edge of a lawn. _B_, Typical vine, showing leaves and the
roots that attach it to the tree.

The vining type most often occurs in wooded areas (fig. 2), where it
depends upon trees for support. Vines often grow for many years, becoming
several inches in diameter and quite woody. Slender vines may run along
the ground, mixed with shrubbery, or take support from a large or
small tree. That a plant growing along the edge of a lawn and into the
shrubbery may be quite inconspicuous as compared with a vine climbing on
a lawn tree is shown in figure 3. The vine readily develops roots when in
contact with the ground or with any object that will support it. When the
vines grow on trees these aerial roots attach the vine securely ( fig. 3.
B). A rank growth of these roots often causes the vines on trees to have
the general appearance of a "fuzzy" rope, which sometimes serves a good
purpose for identification. The vines and roots apparently do not cause
injury to the tree except where growth may be sufficient to cover the
supporting plant and exclude sunlight or break the plant from excessive
weight. The vining nature of the plant makes it well adapted to climbing
over stone walls or on brick and stone houses.

The fact that poison-ivy often becomes mixed in with ornamental shrubbery
and vines often results in its cultivation as an ornamental vine by
people who do not recognize the plant. An ivy plant growing on a house,
as is shown in figure 4, is often prized by an unsuspecting owner. The
vine is attractive and quite effective as an ornamental, but such use
should not be tolerated, as it most certainly will result in cases of
accidental poisoning and serve as propagating stock for more poison-ivy
in the vicinity.

_Figure 4._--Common poison-ivy growing on side of house with ornamental
shrubs. This accidental or intentional use of the attractive vine may
lead to many cases of accidental poisoning.

_Figure 5._--Common poison-ivy growing along fence row. In open sunlight
and over some large areas it is more of a shrub than a vine.

_Figure 4._--Common poison-ivy growing on side of house with ornamental
shrubs. This accidental or intentional use of the attractive vine may
lead to many cases of accidental poisoning.

When poison-ivy becomes mixed in with other vines it is quite difficult
to detect except by one who has carefully trained himself in observing
and recognizing the plant. Also, some other vines and young plants
resemble poison-ivy in many respects. The Virginia creeper and some forms
of the Boston ivy are often confused with it. The Virginia creeper can
always be recognized by its five leaflets radiating from one point of
attachment, as compared with the three leaflets of poison-ivy arranged
in the same manner. The Boston ivy with three leaflets is sometimes
difficult to detect; however, as a rule not all the leaves on the plant
will be divided into three leaflets. By studying a large number of the
leaves it is usually possible to detect on every Boston ivy plant some
leaves that have only one deeply lobed blade or leaflet, while the
poison-ivy always has the three leaflets. A number of other plants are
easily confused with poison-ivy. No specific rule can be observed that
will easily rule out all possibility of confusion. The best policy is to
learn through practiced observation to know poison-ivy on sight and then
to make the determination from observation of all parts of the plant, and
never to judge from a single leaf or part.

_Figure 6._--Leaves of common poison-ivy, about half natural size. These
may occur on the same or different plants: _A_, _B_, _C_ and _F_, less
common; _D_, with even margins, the most common and generally recognized
form; _E_, with lobed margins, nearly nearly as often seen as the shape
in _D_.

_Figure 7._--Common poison-ivy vine with clusters of flowers in the axis
of each leaf.

Common poison-ivy in full sunlight along fence rows or in open fields
grows more in the form of a shrub than a vine. In some localities the
common form is a low-growing shrub from 6 to 30 inches in height.
This form, as well as the vining type, usually has a rather extensive
horizontal system of rootstocks or stems at or just below the ground
level. The vining form under some conditions later becomes a shrub.
Plants of this type are shown in figure 5, where the vine, supported
on the fence, has extended upright stems that are shrublike. In some
localities the growth form over a wide range is consistently either a
vine or a shrub type, while in others what seems to be the same species
may produce either vines or shrubs.

The leaves of the common poison-ivy are extremely variable, the three
leaflets being the only constant character. It is impossible to describe
the great range of variation in the shape or lobing of the leaflets. A
study of the leaf patterns, especially the six shown in figure 6, will
give a fair range of types, although other forms may be found. One plant
may have a large variety of forms of leaves or it may have all leaves of
about the same general character. The most common type of leaf having
leaflets with even margins is shown in figure 6, _D_, and one with
leaflets having slightly lobed margins is shown in figure 6, _E_. The
other forms shown in figure 6 are not quite so widespread, but may be the
usual type throughout some areas.

_Figure 8._--Common poison-ivy, about natural size: _A_, Flowers; _B_,
mature fruit.

Most of the vines or shrubs of poison-ivy produce some flowers that are
always in clusters arising on the side of the stem immediately above a
leaf. The flowers are rather inconspicuous among the leaves, as may be
noted in figure 7, but they are in quite distinct clusters, as shown in
figure 8, _A_. Frequently the flowers do not develop or are abortive and
no fruit is produced. When fruits do develop they serve as a positive way
of identifying the plant. The berries are not easily confused with the
fruits of other plants. They are white and waxy in appearance and have
rather distinct lines marking the outer surface, as the segments appear
in a peeled orange. These lines may be noted in figure 8, _B_, which
shows dense clusters of mature fruit about natural size. Some forms of
the poison-ivy have the fruit covered with fine hair, giving it a kind
of downy appearance; however, in the more common form the fruits are
entirely smooth. The fruit is especially helpful in identifying plants
late in fall, in winter, and early in spring, when the leaves are not
present.

_Figure 9._--The shaded area is the region where the eastern oakleaf form
of poison-ivy is likely to occur. Other forms also may be in the same
region.


OAKLEAF POISON-IVY

Of the several kinds of poison-ivy, the oakleaf form occurring in the
Eastern and Southern States is more distinctive than some other types.
Some people know it as oakleaf ivy while others call it poison-oak,
a name more commonly used for the western species discussed later.
Botanists have not always agreed upon the scientific name to be applied
to this form; however, they now use the name _Rhus toxicodendron_. Some
botanists have used the Latin names _R. quercifolia_, while others used
the name _Toxicodendron quercifolium_, both of which are more descriptive
of the oakleaf form, as the generic name of the oak is _Quercus_. The
area where the oakleaf form may occur, from New Jersey to Texas, is
outlined in the map shown in figure 9. The common poison-ivy also occurs
in some form throughout many parts of this same area.

The oakleaf poison-ivy usually does not climb as a vine, but occurs as
a low-growing shrub. Stems are usually upright in their general growth
habit, as they appear in figure 10. The shrubs usually have rather
slender branches, often covered with a fine pubescence that gives the
plant a kind of downy appearance. The leaflets occur in threes, as in
other ivy, but are lobed, somewhat on the general plan of the leaves of
some kinds of oak. The middle leaflet usually is lobed somewhat alike
on both margins and very much resembles a small oak leaf, while the two
lateral leaflets are often irregularly lobed. The leaves shown in figure
11 are a common form. The lighter color on the under side of one of the
leaves (fig. 11, _A_) is due to the pubescence, or fine hairs, on the
surface. The range in size of leaves varies considerably, even on the
same plant; the leaf shown in figure 11, _B_, however, is about natural
size.

The fruit of oakleaf poison-ivy has the same general appearance as the
fruit of common poison-ivy shown in figure 8, although the individual
fruits and stems are often pubescent, while most of the other forms have
a waxy, smooth, cream-colored fruit.

_Figure 10._--Eastern oakleaf poison-ivy shrub. The upright growth as
a low shrub is common. The three parts of each leaf somewhat resembles
an oak leaf. The gall formations that cause wartlike protuberances are
common on all species.

_Figure 11._--Eastern oakleaf poison-ivy: _A_, Leaves, showing upper deep
green surface and lower lighter colored surface. _B_, Single leaf, about
natural size. The terminal leaflet more nearly resembles an oak leaf than
the two lateral leaflets.


WESTERN POISON-OAK

The western poison-oak (_Rhus diversiloba_) of the Pacific Coast States
is usually known as poison-oak, but is occasionally referred to as
poison-ivy or yeara. It is likely to be found in the region designated
by shading in figure 12, and from central Oregon northward through
Washington may be growing intermixed with common poison-ivy. The term
"poison-oak" is a misnomer, as this species is in no way related to the
oak but is related to poison-ivy. Anyone familiar with either of these
plants in their several forms will likely recognize the other, both as
plants to be avoided.

_Figure 12._--The shaded area is the region where the western poison-oak
is likely to occur. Other forms may also be in the same region.

The most common growth habit of the western poison-oak is in the form of
a rank upright shrub with many small woody stems rising from the ground.
It frequently grows in great abundance along roadsides (see fig. 16) and
in uncultivated fields or on abandoned land.

Sometimes western poison-oak attaches itself to upright objects for
support and takes more or less the form of a vine. A plant of this type
is shown in figure 13, where it is growing on a telephone pole by the
roadside. It may be noted even in this case that the tendency is for
individual branches to continue an upright growth rather than become
entirely dependent upon other objects for support. In some areas,
especially in woodland, poison-oak may grow principally as a vine. Areas
have been noted where 70 to 80 percent of the trees leaves and flowers.
in a wooded area support vines running more than 25 or 30 feet in height,
although the most common form of the plant is the shrub.

_Figure 13._--Western poison-oak on a telephone pole. This vine form is
not uncommon, especially on trees in woods.

_Figure 14._--Western poison-oak: Upright shrub, with fruit, growing in
open pasture field.

_Figure 15._--Western poison-oak, showing common leaf types: _A_, The
more common leaves with irregular margins; _B_, less typical, although
not uncommon, leaves with even margins.

_Figure 16._--Western poison-oak growing alongside roadside. This rank
shrubby growth is typical for most localities.

_Figure 17._--Western poison-oak, showing common leaf types: _A_, Leaves
with thick leathery appearance; _B_, leaves irregular in shape with
much-curled or distorted surfaces; _C_, branch, with leaves and flowers.

In open pasture fields western poison-oak usually grows in spreading
clumps from a few feet to several feet tall (figs. 14 and 16). Where it
develops extensively it greatly reduces the area for grazing and becomes
a serious menace to most people who frequent the area or attend cattle
that come in contact with the plants while grazing.

_Figure 18._--Western poison-oak: _A_, Top of shrub, with leaves and
fruit; _B_, clusters of fruit after leaves have fallen.

Low-growing plants, especially those exposed to full sunlight, are often
quite woody and show no tendency for vining. Low-growing plants with
woody stems are common in pasture areas or along roadsides. Livestock in
grazing do not invade the poison-ivy shrub, and as a rule these plants
continue to spread both by root-stock and seed.

As in other ivy the leaves consist of three leaflets with much
irregularity in the manner of lobing, especially of the two lateral
leaflets. The Latin name _dirersiloba_ refers to the irregularity
occurring in the shapes of the leaves on different plants and on the same
plant or even irregularity in the lobing of leaflets of the same leaf.
Sometimes lobes occur on both sides of a leaflet, thus giving it somewhat
the semblance of an oak leaf. The middle or terminal leaflet is more
likely to be lobed on both sides and resembles an oak leaf more than the
other two. A study of the leaves shown in figures 15 and 17 shows the
variation in lobing. Some plants may have leaflets with an even margin
and no lobing whatsoever, as those in figure 15, _B_. The surface of the
leaves is usually glossy and uneven, so that they have a thick leathery
appearance.

_Figure 19._--A large poison sumac shrub about 15 feet tall, growing on
the edge of a swamp.

The flowers are borne in clusters on slender stems diverging from the
axis of the leaf, as may be noted in figure 17, _C_. The individual
flowers are greenish white and about one-fourth inch across. The cluster
of flowers matures into greenish or creamy-white berrylike fruits about
mid-October. These are about the size of small currants and are much like
other poison-ivy fruits, having a smooth greenish-white glossy surface
striped somewhat like the segments of a peeled orange. Many plants bear
no fruit, although others produce it in abundance, as shown in figure 18,
_A_. The fruits are not always spherical, but sometimes have a somewhat
flattened appearance, as is shown in figure 18, _B_. They remain on the
plants throughout fall and winter and are quite helpful in identifying
poison-oak in seasons after the leaves have fallen.

_Figure 20._--The shaded area shows the region where poison sumac is
likely to occur in bogs or swamps, although isolated plants are sometimes
found in dry soil.



POISON SUMAC


Poison sumac grows as a coarse woody shrub or small tree (fig. 19) and
never in the vinelike form of its poison-ivy relatives. This plant is
known also as swamp sumac, poison elder, poison ash, poison dogwood, and
thunderwood. It does not have variable forms, such as occur in poison-oak
or poison-ivy, and botanists agree to call it _Rhus vernix_. The area in
the Eastern States where it is likely to be found is chiefly eastward
from eastern Minnesota, northeastern Illinois, Indiana, central Kentucky
and Tennessee, and southeastern Texas, as shown on the shaded area of the
map, figure 20. This shrub is usually associated with swamps and bogs,
and the most typical growth occurs along the margin of an area of wet
acid soil.

_Figure 21._--Small branch of poison sumac with six compound leaves.

_Figure 22._--Fruit of poison sumac, one-third natural size. These fruits
somewhat resemble those of poison-ivy. They are always on drooping
slender stems attached at the side of the small branches and are never
terminal as in the species of sumac that are not poisonous.

The plants range in height from 5 or 6 feet to small trees that may
attain a height of 25 feet. The poison sumac shrub shown in figure 19
is growing on the edge of a swamp and is quite typical of the general
appearance of the larger shrubs, which approach a treelike form. As a
rule the shrubs do not have a symmetrical upright treelike appearance.
They are more or less inclined to lean and have branched stems with about
the same diameter from the ground level to the middle height of the shrub.

Occasional isolated plants are found outside of swampy regions.
Apparently these plants are started from seed distributed by birds. The
plants in dry soil usually do not become more than a few feet tall. They
are likely to cause poisoning to unsuspecting individuals, as single
isolated plants are not readily recognized, especially out of their usual
region.

The leaves of the poison sumac are divided into 7 to 13 leaflets,
arranged in pairs with a single leaflet at the end of the midrib (fig.
21).

_Figure 23._--_A_, Smooth sumac and dwarf sumac growing in a mixed stand.
These plants are not poisonous. _B_, Terminal fruiting spike of smooth
sumac, about one-seventh natural size. This form of terminal fruiting
spike is typical of all the species of sumac that are not poisonous.

The leaflets are an elongated oval shape without teeth or serrations on
the margins. They are 3 to 4 inches long and 1 to 2 inches wide, with a
smooth velvetlike texture and bright orange color when they first appear
in spring. Later they become dark green and glossy on the upper surface
and pale green on the lower and have scarlet midribs. Early in fall they
turn to a brilliant red-orange or russet shade.

The small yellowish-green flowers are borne in clusters in slender stems
arising from the axis of leaves along the smaller branches. The slender
clusters of flowers have much the general appearance of the poison-ivy
flower, but hang in much longer clusters. The flowers mature into
ivory-white or green-colored fruits resembling those of poison-oak or
poison-ivy, except that they are usually less compact and hang in loose
clusters that may be 10 to 12 inches in length (fig. 22).


CONFUSION OF POISONOUS AND HARMLESS SUMACS

Because of the same general appearance of several common species of
sumac and the poison sumac, considerable confusion has occurred as to
which one is poisonous. Throughout most of the range where poison sumac
grows, three other species are the only ones that are likely to be
confused. These are the smooth sumac (_Rhus glabra_), staghorn sumac (_R.
typhina_), and dwarf sumac (_R. copallina_). All the nonpoisonous species
have red fruits that together form a distinctive terminal seed head,
as shown in figure 23. These are easily distinguished from the slender
hanging clusters of white fruit of the poison sumac, as shown in figure
22. Sometimes more than one species of the harmless sumac grow together,
as shown in figure 23, _A_.

When seed heads or flower heads occur on the plants it is easy to
distinguish the poisonous from the harmless plants; however, in many
clumps of either kind, flowers or fruit may not develop. Fortunately,
the leaves have some rather distinct characteristics, which can be
easily observed. Figure 24 shows leaves of the three harmless species as
compared with poison sumac.

The leaves of the smooth sumac (fig. 24, _A_) and of the staghorn sumac
(fig. 24, _B_) have many leaflets, which are slender lance-shaped with a
toothed margin. In these species there are usually more than 13 leaflets.
The leaves of the dwarf sumac (fig. 24, _C_) and the poison sumac (fig.
24, _D_) have fewer leaflets, and these are more oval-shaped, with smooth
or even margins.

The dwarf sumac, however, may be readily distinguished from the poisonous
sumac by the winged midrib of the leaf (fig. 24, _E_). There is
considerable variation in the size of the wing margin along the midrib,
which in some cases may be reduced almost to a line between the leaflets.
The winged midrib is more prominent near the terminal leaflet and can
always be detected. The midrib of the poison sumac is never winged. A
little study of the fruit and the leaf characteristics of the poisonous
and harmless species will make it possible to avoid the poisonous one and
utilize the other, which has considerable value as an ornamental plant,
as a source of commercial tannin, and for controlling erosion on waste
hillsides.

_Figure 24._--Leaves of species of sumac that are often confused: _A_,
Smooth sumac; _B_, staghorn sumac; _C_, dwarf sumac; _D_, poison sumac;
_E_, enlarged portion of dwarf sumac leaf from _C_, showing the wing
margin of the midrib. Poison sumac does not have the winged midrib.


INTRODUCED POISONOUS SUMAC AND RELATED SPECIES

The small Japanese lacquer-tree, although uncommon in the United States,
is an introduced species of sumac (_Rhus verniciflua_) that is quite
similar to the native poison sumac. It is native to Japan and China and
is the source of Japanese black lacquer. Cases of poisoning hare been
traced to contact with lacquered articles. Because of its poisonous
properties, this tree should never be planted.

A native shrub or small tree called poison-wood, doctor gum, or coral
sumac is commonly found in the pinelands and hummocks of extreme southern
Florida, the Keys, and the West Indies. It is much like the poison sumac
and closely related to it. Most botanists name it _Metopium toxiferum_,
although previously it was named _Rhus metopium_, and sometimes metopium
is used as its common name. The small tree, or shrub, has the same
general appearance as poison sumac. The leaves have the same general
appearance, except that there are usually only three to seven leaflets,
which are more rounded. The fruits are borne in clusters in the same
manner as those of poison sumac (fig. 22), but individual fruits are
two or three times as large and orange-colored. All parts of the plant
are exceedingly poisonous to the touch and cause the same kind of skin
irritation as poison-ivy or poison sumac.



POISONING


Through experience, many people know that they are susceptible to
poisoning by poison-ivy, poison-oak, or poison sumac, while some others
either have escaped contamination or have a certain degree of immunity.
The extent of immunity appears only relative, and absolute immunity to
the toxic principle apparently does not exist. Persons who have shown
a degree of immunity upon repeated contact with the plants may develop
poisoning on subsequent exposure.

The skin irritant of poison-ivy, poison-oak, and poison sumac is the same
toxic agent. It is a nonvolatile phenolic substance called urushiol and
is found in all parts of the plant, including roots and fruit. It occurs
in great abundance in the plant sap. The danger of poisoning is greatest
in spring and summer, when the sap is abundant, and least late in fall or
in winter.

Poisoning is usually caused by contact with some part of the plant. A
very small quantity of the poisonous substance is capable of producing
severe inflammation of the skin and can easily be transferred from one
object to another. Clothing may become contaminated and is often a source
of such prolonged infection that it is likely to be judged as a case of
poisoning difficult to cure. Dogs and cats frequently touch the plants
and transmit the poison to unsuspecting persons. The poison may remain on
the fur of animals for a considerable period after they have walked or
run through poison-ivy plants. Smoke from burning plants will carry the
toxin and has been reported to cause severe cases of poisoning. Cases of
poisoning of children from eating the fruit have been reported. A local
belief that eating a few leaves of these plants will develop immunity in
the individual is unfounded. It never should be attempted. No part of the
plant should ever be taken internally, as it is a violent irritant and
poisonous to man.

Cattle, horses, sheep, hogs, and other livestock apparently do not suffer
from skin irritation caused by these plants, although they have been
observed to graze upon the foliage occasionally. Bees collect honey from
the flowers, though no reports are on record of any ill effects from the
use of the honey.

The time between contamination of the skin and the first symptoms
varies greatly with individuals and probably with conditions. The first
symptoms of itching or burning sensation may develop in a few hours
or after 5 days or even more. The delay in development of symptoms
is often confusing in attempting to determine the time or location
when contamination occurred. The itching sensation and subsequent
inflammation, which usually develops into water blisters under the skin,
may continue for several days from a single contamination. Persistence
of symptoms over a long period is likely to be due to new contacts with
plants or with previously contaminated clothing or animals. Severe
infection may produce more serious symptoms, which result in much pain
through abscesses, enlarged glands, fever, or complicated constitutional
malfunction. Secondary infections are always a possibility in any break
in the skin, such as is produced by breaking vesicles that have formed as
large water blisters.


PRECAUTIONS AGAINST POISONING

The most effective way to prevent poisoning from the plants is to avoid
contact with them. If it is necessary to work among them, some measure
of prevention can be gained by wearing protective clothing, but it is
necessary to remember that the active poisonous principle can easily be
transferred. Some protection also may be obtained in advance by the use
of protective creams or lotions. They prevent the poison from touching
the skin, or make the active principle easily removed, or neutralize it
to a certain degree.

Various formulas containing ferric chloride and glycerin have been used
more or less effectively as a preventive measure, although there may
be some danger of pigmentation of the skin from the ferric chloride. A
common formula is ferric chloride, 5 parts; glycerin, 25 parts; alcohol,
25 parts; water. 50 parts.

A lotion of this formula applied to the exposed skin prior to contact
with poisonous plants gives effective protection for many people. It
is especially effective if followed by thorough washing with soap and
water. Such washing, even if no protective lotion has been used, is often
effective in preventing poisoning. Proper precaution should be taken
by repeated lathering with a strong alkali soap, followed by thorough
rinsing and repeating the process several times. The water should be
frequently changed, and a shower or flowing water bath is preferable. The
soap probably only emulsifies the active principle, and thorough rinsing
is necessary to avoid spreading the poison to other parts of the body.

The United States Public Health Service reports successful chemical
protection against ivy poisoning by use of an oxidizing agent--sodium
perborate prepared and used fresh as an ointment. Following is a formula
given for the ointment: Cetyl alcohol, 35.1 percent; stearyl alcohol,
5.3; ceresin, 3.5; castor oil. 20.8; mineral oil, 21.9; Duponol WA pure,
1.7; sodium perborate. 10.0; and boric acid, 1.7 percent.

A more recent less oily formula recommended for both mechanical and
chemical protection is given as follows: Shellac, 13 parts; isopropanol,
31; linseed oil, 4; titanium oxide, 12; sodium perborate, 13; talcum, 20;
and carbitol, 3 parts.

Sometimes cottonseed oil, olive oil, or petrolatum is applied as a
protective ointment when contamination is anticipated. Later the oil must
be completely removed by repeated washing.

Clothing, wearing apparel, and tools that have been contaminated are
often difficult to handle without further danger of poisoning. Some
who are more or less immune to poisoning often contaminate others by
carelessness. Contamination on automobile door handles or on a steering
wheel after a trip to the woods often causes prolonged cases of poisoning
of persons who have not been near the plants. One of the most effective
ways for decontaminating articles is by thorough washing through several
changes of strong soap and water. Contaminated clothing should not be
worn again until thoroughly washed. It should not be washed with other
clothes, and care should be taken to rinse thoroughly any implements used
in washing.

Dogs and cats can be decontaminated in the same manner; precaution should
be taken, however, to avoid being poisoned in doing the washing. It is
likely that most "dry cleaning" processes will remove any contaminant;
but there is always danger that clothing sent to commercial cleaners may
cause poisoning to unsuspecting employees.

Certain prophylactic inoculations for the prevention of ivy poisoning
have been developed and used with limited success; such treatment,
however, should be administered by a physician only. The theory that
eating a few leaves of these poisonous plants will confer immunity is
without foundation; it should not be attempted even as an experiment,
because very serious poisoning is likely to result.


TREATMENT FOR POISONING[1]

[1] For a fuller description of treatments for poisoning see: United
States Public Health Service, ivy and sumac poisoning. Pub. Health
Rpts. Sup. 161 (rev.), 8 pp., 1943. For sale by the Superintendent of
Documents, Government Printing Office, Washington 25, D. C. Price, 10
cents.

There seems to be no absolute quick cure for ivy poisoning for all
individuals, even though many studies have been made to devise
effective remedies. Remedies may be helpful in removing the poisonous
principle or rendering it inactive and for giving some relief from the
irritation. Mild poisoning usually subsides within a few days, but if
the inflammation is severe or extensive a physician should be consulted.
Self-treatment also has other dangers, as the symptoms of ivy poisoning
may be confused with those of other conditions and harm may be done by
improper treatment. In all cases the safest procedure is to consult a
physician.

Some tried remedies are effective on certain individuals and ineffective
on others. Sometimes a person will find one remedy effective and later,
to his surprise, get very little relief from it. A large number of patent
medicine remedies of doubtful value are commonly offered for sale. The
following are more or less standard measures that have been advocated by
different individuals and found helpful in certain cases.

The United States Public Health Service recommends a 10 percent alcoholic
solution of tannic acid applied as a lotion. It is stated that in using
it the tops of the blisters should be rubbed off with sterile gauze
saturated with the solution and that any large blisters should be opened
with a sterile instrument. The treatment should be repeated three or four
times at 6-hour intervals. A modified form of this treatment recommends
vigorous rubbing of the lesions with alcohol-soaked gauze to remove
the tops of blisters, followed by application of a 10 percent aqueous
solution of tannic acid as a lotion. Any treatment involving opening
of blisters and the application of alcohol is severe, and many cases
requiring such treatment should be handled by physicians.

One of the oldest well-established remedies is a fresh solution of
one 5-grain tablet of potassium permanganate dissolved in 1 quart of
water; concentrations as much as 5 percent, however, have been used. The
potassium permanganate is apparently active in neutralizing any poison
that may remain on the surface of the skin and it has some therapeutic
properties. This solution may be applied freely to the irritated or
contaminated skin, but the skin should be rinsed with water a few
minutes after the stronger solutions are used. Applications should be
repeated every hour or two. The brown stain it causes on the skin will
in time wear off, or it may be removed with lemon juice. It more or less
permanently stains clothing.

Ferric chloride in combination with several other substances has been
used effectively by many people. One of the most common formulas is that
given under the discussion of precautions against poisoning (p. 22). To
this formula 1 to 3 percent of phenol is frequently added to reduce the
itching; however, not more than 1 percent of phenol should ever be used
without the advice of a physician, on account of the danger of systemic
absorption and poisoning. The solution should be freely applied to the
irritated or contaminated skin every hour or two. Some instances of
persistence of the brown discoloration of the skin have been reported.
For this reason its use is limited, but for most individuals the
discoloration completely disappears after a few days. Stain on clothing
is usually permanent.

Photographer's hypo solution has been used with good results in many
cases. This is a 10-percent solution of sodium thiosulfate in water. The
irritated or contaminated skin should be bathed in it every hour or two.
It does not stain skin or clothing.

A calamine lotion with the addition of about 2 percent of phenol is often
used and in many cases is effective. Frequent applications are necessary.
For some people it is effective in relieving the itching. The pink stain
is not permanent.

It is better to leave inflamed areas exposed to the air rather than cover
them with dressings. If poisoning is so severe that dressings appear
necessary, a physician should be consulted before any home remedies are
applied.



ERADICATION OF PLANTS


Poison-ivy[2] can be killed either by mechanical means, such as digging,
or by applying chemical herbicides. The best modern herbicides are so
deadly to plants that a single treatment kills all the leaves and 90
percent or more of the roots. This is the easiest and least dangerous
way to destroy these poisonous pests. There are places, however,
where chemicals cannot be used, as in hedges and shrubbery where the
poison-ivy is closely mixed with the valuable plants. In such situations,
hand-pulling is the only satisfactory method. At times also chemicals and
spraying equipment are not available, and then the mattock, scythe, or
plow must be resorted to. Even with these simple tools some timing and
handling methods are better than others.

[2] For brevity, the single designation poison-ivy is used under this
heading to apply equally to all poison-ivies and to poison sumac.


CHEMICAL WEED KILLERS

By using care poison-ivy can be destroyed with chemicals without danger
of poisoning to the operator. Except in very heavy growth, one may stand
at a distance from the plants and apply the herbicide without touching
the leaves. Most chemicals are applied as a spray solution, and many
sprayers can be equipped with extension nozzles 2 feet or more in length.
The greatest danger of ivy poisoning occurs from careless handling of
gloves, shoes, and clothing after finishing the work. Garments should be
worn that can either be destroyed after use or washed thoroughly in hot
soda solution and soapsuds.

The chemicals thus far found most satisfactory on poison-ivy are,
in approximate order of effectiveness, ammonium sulfamate, 2,4-D
(2,4-dichlorophenoxyacetic acid), ammonium thiocyanate, borax, carbon
disulfide, coal-tar creosote oil, fuel oil and similar petroleum
distillates, sodium chlorate, and sodium arsenite. Less effective
chemicals include common salt, kerosene, gasoline, calcium cyanamide,
ammonium sulfate, and iron sulfate.

Chemicals other than borax are best applied as a spray to the foliage.
Borax is scattered dry on the soil around the plants. Any field or
garden spray machine or even a sprinkling can is useful for applying
the liquids, but a common knapsack sprayer holding about 2 gallons is
convenient and does not waste the solution, application should be as a
fine spray under moderate pressure rather than a driving mist, since
the object is to wet the leaves of the poison-ivy and avoid wetting the
leaves of desirable plants.

Most chemicals used on poison-ivy are injurious to the foliage of all
kinds of plants and must be applied with caution if the surrounding
vegetation is valuable. During the early part of the growing season the
leaves of the poisonous plants usually tend to stand conspicuously apart
from those of adjacent plants and can be treated separately if sprayed
with care. Later the leaves become intermingled and injury to adjacent
species is unavoidable. Chemicals other than oil are not injurious to the
thick bark of an old tree, and poison-ivy clinging to the trunk can be
safely sprayed with them.

Chemical sprays can be used at any time when poison-ivy is in full leaf,
June and July being perhaps the best months. Ordinarily treatments should
begin not later than August 15, as poison-ivy then begins to go dormant
and sprays are ineffective.

Best results are obtained both with sprays and with dry chemicals when
the soil is moist but not wet at time of treatment. Borax can well be
applied just before a rain, but sprayed chemicals are likely to be washed
off if rain falls within 24 hours. One gallon of spray solution is
sufficient to cover all the leaves on 1 square rod (272 square feet) of
dense poison-ivy, or 2 to 4 square rods of a scattered stand.

Sprays give best results when applied in early morning or late afternoon
when the air is cool and moist. Spraying in the middle of a dry, hot day
is likely to be disappointing unless the plants are in deep shade.

No method of chemical eradication can be depended upon to kill all the
plants in a stand of poison-ivy with one application. Three to four light
retreatments made as soon as the new leaves are fully expanded are always
necessary (1) to destroy plants missed the first time, (2) to treat new
growth from the old roots, and (3) to destroy seedlings. At least three
and sometimes four treatments at intervals of 2 to 8 weeks are necessary
before all plants are dead. These followup treatments do not require
much time or material, but neglect of them may easily lead to serious
reinfestation.

Poison-ivy has an annoying habit of "playing possum." Plants believed
dead sometimes revive after many months. Thus an area under treatment
must be watched closely for at least a year if complete eradication is to
be assured.

Dead foliage and steins remaining after the plants have been killed with
chemicals are only slightly poisonous, but to avoid difficulty the dead
stems should be cut off and burned.

=Ammonium sulfamate.=--This chemical, under a proprietory name, has come
on the market recently as a weed killer and has proved especially useful
against poison-ivy. Ammonium sulfamate is not dangerous to use under
ordinary conditions, is not harmful to the soil, and is not flammable.
It is slowly corrosive to metals, and spray equipment should be washed
thoroughly with a solution of lime or soda immediately after use. Like
salt, ammonium sulfamate absorbs moisture from the air and must be stored
in a dry place.

Ammonium sulfamate is dissolved in water at the rate of 12 ounces per
gallon and sprayed on the leaves until they are wet but not dripping.
The foliage begins to wilt within 21 hours, but the action is slow,
and a week or more may elapse before the leaves die. Some new growth
may be expected after 4 to 8 weeks, and this should be sprayed as soon
as the new leaves are fully expanded. Two or occasionally three such
retreatments are needed before the kill is complete.

=2,4-D (2,4-dichlorophenoxyacetic acid).=--This chemical under the
abbreviated name 2,4-D, or DCP, is a recent addition to the list of
effective weed killers and may become an important weapon for use against
poison-ivy. It should not be confused with DDT or DD, two other new
agricultural chemicals, the first an insecticide and the second used as
a soil fumigant. Under wartime restrictions the use of 2,4-D was very
limited, but its prospective value is so great that those interested in
the control of poison-ivy should be informed about it.

The chemical 2,4-D is one of the so-called "plant hormones," or
"growth regulators." In minute quantities it stimulates some of the
plant functions, but in slightly larger dosage it is toxic. A solution
consisting of one-seventh ounce in 1 gallon of water sprayed on
poison-ivy foliage kills all leaves hit and may kill the roots. In the
concentration used in weed killing 2,4-D is not believed to be harmful
to animal life, but until this point can be thoroughly clarified the
chemical should be used with reasonable caution to avoid poisoning.
2,4-D is not flammable and is not corrosive to spray machinery. If the
sprayer is used also for insecticides and fungicides it must be washed
very thoroughly to remove the slightest trace of the 2,4-D. This is very
difficult, however; it is safer to use another sprayer.

To make a spray solution 2,4-D must be combined with other chemicals,
as it is not soluble in water. A number of substances, including
polyethelene glycols and naphthenic soaps, have been used for this
purpose, but the best solvent has not yet been determined. Commercial
weed killers containing 2,4-D are of varying composition.

=Ammonium thiocyanate.=--This byproduct of the coal-gas industry is one
of the newer herbicides. The crude commercial chemical is a pink or
reddish salt, very soluble in water. It does not keep well, tends to
disintegrate into a red, sludgy mass, and is difficult and disagreeable
to handle. A purer form in clean white crystals is available and is well
worth the slight extra cost. In either form ammonium thiocyanate is
injurious to the skin and to leather articles, and in time it corrodes
metals. The spray solution is made by dissolving 1 to 1½ pounds of
ammonium thiocyanate in 1 gallon of water.

Most annual, plants and some perennials are killed by a single
application of ammonium thiocyanate. Poison-ivy usually requires three
or four treatments. Ammonium thiocyanate has a high content of nitrogen,
much of which remains in the soil and eventually becomes a fertilizer.
Thus an area treated with this chemical is likely to produce a profuse
growth of annual weeds a month or two after treatment.

=Borax.=--Common borax scattered on the soil is deadly to the roots of
many plants. Spread dry at the rate of 10 to 15 pounds per square rod, it
kills poison-ivy slowly over a period of 6 to 8 weeks. A second somewhat
lighter treatment 3 to 5 months later is usually necessary to kill all
plants completely.

Borax is easy to handle, nonpoisonous, and nonflammable, readily
obtainable, and not expensive. It is one of the best chemicals to use
around stone walls, rocky ledges, fences, and other inaccessible places.

Plants differ greatly in their resistance to borax. Some species, as
Virginia creeper and deep-rooted trees, do not seem to be injured, but
others, notably dogwood, are very sensitive to it. Until more complete
information is available as to the effect of borax on other plants,
it should be employed on poison-ivy only where possible damage to
surrounding vegetation is not objectionable.

=Carbon disulfide.=--The fumes of this pungent, volatile liquid are very
poisonous to plants, and the chemical is widely used in the West to kill
deep-rooted perennial weeds. When poison-oak, particularly, is growing
in a mixture with wild morning-glory (bind-weed) or similar noxious
weeds, both plants may often be killed at one operation by treating the
soil with carbon disulfide. Holes ordinarily 6 inches deep and 18 inches
apart in all directions are punched in the soil with a 1-inch iron bar,
and 2 ounces of carbon disulfide are poured in each hole. The openings
are closed immediately with a wooden club. This dosage equals 20 pounds
of the chemical per square rod. Carbon disulfide is likely to be less
effective on shallow-rooted than on deep-rooted plants and is therefore
of limited value against poison-ivy, which is surface-rooted.

  =Carbon disulfide is poisonous, and as it is also highly flammable it
  should be handled as carefully as gasoline.=

=Coal-tar creosote oil.=--In the fractional distillation of coal, many
oils and oillike substances are obtained, some of which are very toxic to
plants. The most common and usually the cheapest is the creosote used for
wood preservation. This substance has great penetrating power and is an
excellent herbicide on woody plants like poison-ivy. Ordinarily creosote
oil is too expensive to use alone and is therefore mixed with some
kind of petroleum oil. A mixture of 75 percent fuel oil and 25 percent
creosote oil is almost as effective as straight creosote and is made at
one-third the cost. Two applications of this mixture at an interval of
about 6 weeks usually kill a high percentage of poison-ivy. Creosote is
not selective and kills all plants alike.

_Fuel oil (Diesel and similar oils)._--Crude petroleum is refined into
many kinds of oil, and those corresponding to fuel oil. Diesel oil,
stovetop oil, and orchard-heating oil are more injurious to plants
than crude oil itself or the higher distillates, such as gasoline
and kerosene. Fuel oils are widely used for destroying vegetation,
particularly by highway departments in States having oil resources. When
sprayed on poison-ivy, fuel oil brings about a slow but fairly sure death
of the plants. Two or three applications may be necessary before the
roots are killed. Fuel oil, like creosote, must be used with care around
valuable trees and shrubs because it penetrates the bark and kills or
injures all species. As used for poison-ivy spraying there is no injury
to the soil. The oil-soaked vegetation is flammable.

=Sodium chlorate.=--Sodium chlorate is the standard herbicide for killing
deep-rooted perennial weeds like bindweed, but when used as a spray, it
is a dangerous fire hazard, and when applied dry, it sterilizes the soil
for 2 to 4 years. Where sterilization of the soil is desirable or not
objectionable, one application of the dry chemical, evenly at the rate of
3 to 4 pounds per square rod, is sufficient for a complete kill.

If used as a foliage spray on poison-ivy, the chemical is dissolved in
water at the rate of 8 to 12 ounces per gallon. The leaves are killed
within a few hours, but the plants are likely to make a strong new growth
and may require as many as six treatments before they cease to produce
new leaves.

  =Sodium chlorate mixed with wood, cloth, or other organic materials
  is highly combustible and easily ignited. Shoes and clothing on which
  chlorate solution has been allowed to dry are especially dangerous,
  for they will ignite and burn with explosive fury. Contaminated
  clothing should be kept wet until thoroughly washed in a large
  volume of water. Chlorate should be stored only in original metal
  containers, as any admixture of chlorate, wet or dry, with straw,
  wood, dust, cloth, or leather has properties similar to those of
  gunpowder or matches.=

=Sodium arsenite.=--Sodium arsenite is one of the most powerful plant
poisons known and is widely used for sterilizing soil on railroads,
roadways, and other places where no vegetation of any kind is desired. It
is relatively inexpensive. In normal times sodium arsenite is obtainable
in both powder and liquid form. In weak solution (4 to 6 ounces per
gallon of water) the chemical can be used as a spray to destroy
poison-ivy. Like sodium chlorate spray, it kills the leaves but not the
roots, and five or six treatments may be required. The solution kills the
leaves of all plants impartially and will also kill the young tender bark
of shrubs and trees. This may be either an advantage or a disadvantage,
depending upon circumstances.

  =All compounds containing arsenic are deadly poisons if taken
  internally. Arsenical sprays and chemicals should not be used where
  there is any possibility that materials sprayed with them will be
  eaten by animals or man. In some communities special permission must
  be obtained before arsenical weed killers may be used.=


ERADICATION BY MECHANICAL MEANS

Poison-ivy can be grubbed out by hand quite readily early in spring and
late in fall. When the ground is soft after rains the roots come out in
long pieces. Grubbing when the soil is dry and hard is almost futile,
since the roots break off in the ground, leaving large pieces that later
sprout vigorously. Eradication by grubbing is permanent if well done.
Because of his close contact with the plants, the person doing the
grubbing should have a high degree of immunity to ivy-poisoning. Many
people are not so immune as they believe, and it is common sense to wear
leather gloves with gauntlets and a shirt with long sleeves. If care
is taken to prevent the poison-ivy from touching the face, and if the
clothes, including the gloves, are burned or thoroughly washed after use,
severe poisoning may be avoided.

Poison-ivy vines climbing on trees should be severed at the base and as
much of the vine as possible pulled away from the tree. Often the roots
of the tree and weed are so intertwined that grubbing is impossible
without injury to the tree. Close mowing of the poison-ivy shoots at
frequent intervals is the only remedy. Roots and stems removed in
grubbing should be burned or otherwise destroyed, since the dry material
is almost as poisonous as the fresh. Care must be taken to keep out of
the smoke.

Old plants of poison-ivy produce an abundance of seeds, and these are
freely disseminated, especially by birds. A poison-ivy seedling 2 months
old usually has a root that one mowing will not kill. Seedling plants at
the end of the first year have well-established underground runners that
only grubbing or chemicals will kill. Seedlings are a constant threat as
long as old poison-ivy is in the neighborhood.

Plowing is of little value in combating poison-ivy unless followed by
persistent stirring with a cultivator or harrow, to keep all roots
loosened from the soil. Otherwise plowing merely propagates the weed.

Mowing with a scythe or sickle is a common method of attacking
poison-ivy, but it has little effect on the roots unless frequently
repeated. The number of cuttings required to kill depends upon the age of
the plants and the size of the roots, but is seldom less than four. New
shoots should be cut as soon as the first leaf on each stem is full size.
Cutting either earlier or later delays eradication.

Weed burners are implements resembling oversize blowtorches. Two types
are manufactured, one producing a short, hot, blue flame and the other a
long smoky-yellow flame. Both are useful for destroying foliage. Neither
is likely to kill perennial plants like poison-ivy at one operation, even
though the flame is held on the weeds for a minute or more until leaves
and stems are completely incinerated. The roots are not injured by this,
and new leafy shoots soon develop. A better plan is to "sear" the plants
by passing the flame slowly over the vines just long enough to sear or
wilt the leaves, but not long enough to burn them. The roots appear to
be injured more by "searing" than completely burning the leaves, and the
operation is quicker and cheaper. Three to four searings when the leaves
reach full size usually kill the roots.



                        U. S. Government Printing Office: 1945--652512


For sale by the Superintendent of Documents, U. S. Government Printing
Office, Washington 25, D. C.



       *       *       *       *       *


Transcriber Notes


All illustrations were moved so as to not split paragraphs.





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