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diff --git a/59555-0.txt b/59555-0.txt new file mode 100644 index 0000000..5ba0d27 --- /dev/null +++ b/59555-0.txt @@ -0,0 +1,1160 @@ +*** START OF THE PROJECT GUTENBERG EBOOK 59555 *** + + + + + + + + + + + + +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. + + + + + + + +End of the Project Gutenberg EBook of USDA Farmers' Bulletin No. 1972: +Poison-ivy, Poison-oak and Poison Sumac: Identification, Precautions and Eradication, by Donald M. Crooks and Leonard W. Kephart + +*** END OF THE PROJECT GUTENBERG EBOOK 59555 *** |