Part 6

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.