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.=