Killing weeds with arsenite of soda


Material Information

Killing weeds with arsenite of soda
Series Title:
Press bulletin ;
Physical Description:
15 p. : ; 23 cm.
Wilcox, Earley Vernon, b. 1869
Hawaii Agricultural Experiment Station
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Publication Date:


Subjects / Keywords:
Weeds -- Control -- Hawaii   ( lcsh )
Arsenates   ( lcsh )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )


Statement of Responsibility:
by E.V. Wilcox.
General Note:
Caption title.

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University of Florida
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All applicable rights reserved by the source institution and holding location.
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aleph - 029636014
oclc - 758874858
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. killing Weeds W ith Arseni te of Soda
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Weeds and pests of insect or fungus nature'%jeti if
among the important problems with which the farlr3, ,ji

Contend in all agricultural regions. In controlling these draw-
"~abks to successful production, hand methods were first used
,:ut the use of chemicals was early adopted in combating insect
and fungus disease. Somewhat later, sprays for the destruction
'of weeds received attention and chemicals for weed destruction
-have gradually assumed a greater importance. Many of the

facts which are now known regarding the destruction of weeds
S.byt:means of chemicals were first discovered in connection with
spraying for insects and fungus diseases. In order to destroy
'insects and pathogenic fungi by applications of chemicals to liv-
ing plants it is necessary to use solutions or mixtures of a
strength' sufficient to be fatal to the insects and fungi but not
njmurious to the plants which are to be protected. In the exten-
sive and long-continued spraying experiments which have been
carried on in farm practice, it was soon found that certain forms
. of chemicals used in such operations were more injurious to




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plants than other forms. Attention, therefore, was required on
this point in order to avoid injury to the plants.
In the use of arsenicals for the destruction of insects it is
necessary to get a finely divided condition of the arsenical,
which is at the same time relatively insoluble. The small undis-
solved particles then remain on the surface of the leaves until
washed off or eaten by insects. Soluble arsenicals are extremely
injurious to vegetation and, therefore, have to be avoided in
spraying useful plants. There is thus a complete contrast in the
ideas aimed at in spraying for insects and in spraying to kill
vegetation. Arsenical insecticides must be as insoluble as it is
S esw Tt obtain them, while for killing weeds the most soluble
S :pe.ic is desired.
I :T' In experimei4ts previously carried on at this Station1 carbon
If -,40 bisulpti nws Applied to a number of weeds which grow in the
8 so garden and Belds. This chemical was found to be very effective
*', ttr destruretion of some of our hardiest weeds, both of herba-
~. ^44Iaus Ashrubby nature. When applied on a large scale, how-
ever, and in long-continued operations, there is some danger
from the injurious effects of the fumes of carbon bisulphide upon*
the workmen and the chemical itself is rather expensive. It
seemed, therefore, desirable to carry on experiments with other
chemicals which could be applied more easily and at less ex-
pense. Arsenite of soda has been extensively used on the main-
land of the United States, in Australia and elsewhere for the
destruction of a variety of weed plants. Stone2 found arsenite
of soda exceedingly effective against herbaceous weeds when used
at the rate of one part in 66 parts of water. Gillette3 in using
arsenicals against insects found that the soluble portion of the
insecticides exercised a much greater burning effect upon the
foliage in the presence of dew and direct sunlight. Kilgore4

1 Haw. Sta. Press Bul. No. 25.
2 Mass. Rept. 1908, pt. I, pp. 62-72.
3 Iowa Sta. Bul. 10, p. 419.
4 N. C. Sta. Bul. 77b.

observed that arsenites are more soluble in solutions containing
sulphate of copper and sulphate of iron than in water alone.
Jones1 used arsenite of soda on herbaceous weeds and found the
effect produced by this chemical to be slow but lasting. The
formula used called for one pound sal soda and two pounds of
water diluted before using so as to make nine gallons. In Aus-
tralia the common practice is to buy arsenite of soda already pre-
pared and simply dilute in water at the rate of one pound to five
to ten gallons of water. This solution has proven effective in the
destruction of the prickly-pear, wild blackberry and various her-
baceous and semi-shrubby weeds.
Asenate of soda has in experiments proven even more effect-
ive than the arsenite. For example, Stone in the article cited
above found that the mixture of arsenate of soda and corrosive
sublimate in equal parts caused a very rapid destruction of the
foliage and stems of weeds. Likewise, Morgan2 found that arse-
nate of soda alone caused a rapid and destructive burning on
foliage upon which this chemical was applied, and Jones in the
article referred to above reports arsenate of soda when used at
the rate of one pound to eight gallons of water, to be rather
quicker and more effective in its action than arsenite of soda.
Iron sulphate. In various processes involved in the commer-
cial handling of iron ores, iron sulphate is obtained as a by-
product and costs about one cent per pound in most cities on the
mainland. This chemical has been widely tested in Wisconsin,
Iowa, Maine, South Dakota, Rhode Island and other states, as
well as in foreign countries, and upon a large variety of weeds,
but chiefly upon wild mustard. For this purpose it has been
found particularly effective and has the further advantage of not
destroying cereal grains. For this reason it is commonly sprayed
over grain fields infested with wild mustard, and when thus used
gives excellent results. Iron sulphate has been used in different
strengths, but where the herbage is quite tender a 20 per cent
solution is the one commonly recommended to kill weeds and
not injure cereals. Iron sulphate is readily soluble in water,

1 Vt. Sta. Rpt. 1901, p. 248.
2 Agric. Education, 6 (1903) p. 11.

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and no other manipulation is required for the spray than simply
to dissolve the chemical in water. At the Station iron sulphate
has been used upon spurge, cockle-bur, lantana, oi, pig-weed,
Japanese nut-grass and other weeds. When used at the rate of
three pounds per gallon of water, iron sulphate killed all these
weeds except lantana and Japanese nut-grass. The leaves were
destroyed on lantana but the new buds were sent out, showing
that the stems were not killed. The portion of Japanese nut-
grass above ground soon turned brown and died after being
sprayed with iron sulphate, but fresh shoots came up from the-
under-ground bulbs. This chemical can be used effectively.
against most weeds except lantana and Japanese nut-grass, and
has the advantage of not being poisonous or in any way injur-
ious to the soil.
Carbolic Acid. When diluted at the rate of 1 quart in 8
gallons of water, Jones1 observed little effect on common weeds
from spraying with carbolic acid. Qn the other hand, Voelcker2
obtained satisfactory results from spraying wild onion, with a
5 per cent solution of carbolic acid, and the same chemical proved
effective in experiments on miscellaneous weeds at the Massa-
chusetts Experiment Station.
Benzine. This substance has been tested on a small scale in
destroying weeds in gardens in various localities. Stone3 reports.
that a 50 per cent mixture of equal parts benzine and gasoline
in water %,as effective against the less hardy weeds.
Kerosene. In preparing kerosene mixture as a spray for
sucking insects, it is always recommended that care be taken not
to leave any of the kerosene uncombined with the soap in the
mixture, for the reason that if uncombined the kerosene may
burn the foliage. Kerosene has a slight burning effect on the
foliage of various trees. It was tried by Wilson4 as a spray for
weeds at the rate of 610. gallons per square rod. When thus

1 Vt. Sta. Rept. 1901, p. 248.
2 Jour. R. Agr. Soc. Eng. 63 (1902) p. 360.
3 Mass. Rept. 1908, Pt. I. pp. 62-72.
4 Minn. Sta. Bul. 95.

used it was not efficient enough to warrant its application on a
commercial scale.
Salt. The injurious effect of salt upon vegetation is a mat-
ter of common knowledge. Plants show some variation in their
resisting power to salt, but a maximum salt content is soon
reached in the moisture of the soil, after which the plants die or
can not thrive. Salt has been applied for killing weeds, either
dissolved in water or sprinkled upon the ground about the weeds
to be destroyed. Salt is chiefly valuable for this purpose in side-
walks or roadsides where it is not desired to grow cultivated crops
after the weeds are destroyed. In such places there is no harm
from the presence of large quantities of salt in the soil. As a
spray it has been found that salt applied at the rate of 80 bar-
rels is inefficient for the destruction of field weeds. It is, there-
fore, scarcely to be recommended in the list of commercial weed
destroyers in field practice.
Sulphuric acid. On account of its great oxidizing and burn-
ing power, sulphuric acid has frequently been thought of as a
weed destroyer. When used in a 15 per cent solution in water,
Wilson1 found sulphuric acid to be very efficient for destroying
weeds but rather too expensive. Similar results have been ob-
tained in Maine and elsewhere. Sulphuric acid is objectionable
on account of the danger connected with its use by ordinary la-
borers, and its destructive effect on spraying apparatus. At the
Station sulphuric acid was tried as a means of destroying guava,
but without satisfactory results.
Copper sulphate. Copper, both in the form of sulphate and
nitrate, but particularly the former, has been widely used in
killing various kinds of weeds, especially wild mustard. The
effectiveness of copper sulphate for this purpose has been thor-
oughly demonstrated, both in Europe and the United States.
A 3 to 5 per cent solution is commonly recommended to be
applied as a spray. Hitier2 had excellent results in destroying
wild mustard from spraying with a 4 per cent solution of copper

1 Minn. Sta. Bul. 95.
2 Jour. Agr. Prat. 5 (1905) pp. 65-8.

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sulphate or a 3 per cent solution of copper nitrate. Copper
sulphate may be added with a slight advantage to a solution of
arsenite of soda, since, when thus used, it increases the solubil-
ity and burning effect of the arsenite.
Ammonia. Ammonia has also been used as a spray for the
destruction of weeds but cannot be recommended for general use
on account of its slight burning power and the disagreeable
fumes which annoy the laborers.
Arsenite of soda. This chemical is usually prepared by boil-
ing together common white arsenic and washing soda or sal soda.
Theoretically these chemicals combine in such a proportion that
if about 11, pounds of soda be used for each pound of white
arsenic, the proper combination will take place to render all of
the arsenic soluble by the formation of arsenite of soda. In
practice a considerably larger proportion of soda has been used,
up to 4 pounds per pound of white arsenic. It seems unneces-
sary, however, to use more than 2 pounds of soda per pound of
white arsenic. In preparing arsenite of soda we have had good
results from boiling a mixture of one pound white arsenic and
two pounds sal soda per gallon of water for from 15 to 20 min-
utes. The exact length of time to continue the boiling can hot
be stated beforehand with any certainty but the boiling should
be continued until the solution becomes clear. The clearing of
the solution indicates that the proper chemical combination has
taken place. In Australia, where arsenite of soda has been
widely used for killing weeds, the common practice is to buy the
arsenite of soda as such on the market, but in. the spraying thus
far done in Hawaii with arsenite of soda, it has been prepared
by boiling white arsenic and sal soda as just described. The
stock solution obtained by boiling together the sal soda and white
arsenic is to be diluted before spraying with 15 to 24 parts of
water, depending on the hardiness of the weeds to be destroyed.
Arsenate of soda. This chemical is about equally soluble
with arsenite and where obtainable on the market at a reason-
able price may be substituted for the latter. In experiments
with miscellaneous weeds, Jones' found arsenate of soda very

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effective when used at the rate of 1 pound to 8 gallons of water.
Similarly in Massachusetts arsenate of soda gave good results
as a weed destroyer, either when used alone or when mixed with
corrosive sublimate in equal parts.
Before giving an account of the experiments with arsenite of
soda at this Station and elsewhere in Hawaii, it may be well to
refer briefly to other experiments with the same chemical. In
Australia this spray has been widely used for the destruction of
prickly-pear, wild blackberry and other shrubby and herbaceous
weeds. For this purpose it has proven so effective as to make a
wide field for itself in the programme of weed destruction.
Maiden,2 on the basis of a number of experiments, recommends
for destroying prickly-pear a solution of arsenite of soda con-
taining 1 pound to from 5 to 9 gallons of water. In other exper-
iments more concentrated solutions were used, particularly for
the destruction of wild blackberry and other shrubby weeds.
Likewise in Iowa, North Carolina, Vermont, Massachusetts and
elsewhere on the mainland, as well as in Europe, arsenite of
soda has been used with good success in destroying miscellaneous
herbaceous weeds. In Massachusetts it proved effective when
used at the rate of 1 part to 66 parts of water. Kilgore3 found
that when an attempt was made to combine arsenical insecticides
containing soluble arsenic with fungicides containing copperas,
copper sulphate or iron chloride, the burning effect of the arse-
nite was considerably increased by the presence of the other min-
eral salts. In spraying experiments for the destruction of insects
Gillette4 observed that soluble arsenites in arsenical sprays pro-
duced a greater burning effect in the presence of dew and direct
sunlight. These points are worth considering as indicating the
conditions under which applications of arsenite of soda should
be made in order to obtain a maximum effect.

1 Vt. Sta. Rept. 1901, p. 248.
2Agr. Gaz. N. S. W. 9 (1898), p. 984.
3 N. C. Bul. 77b.
4 Iowa Sta. Bul. 10, p. 419.

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At this Station experiments have been carried on with arse-
nite of soda in testing the effect of this chemical upon a number
of weeds, including oi (Stachytarpheta dichotoma); lantana,
spurge (Euphorbia peplus), pualele or sow thistle, pig-weed,
purslane, cockle-bur (Xanthium strumarium), glue (Acacia far-
nesiana), dodder, Japanese nut-grass, honohono (Commelina.
nudiflora), crotalaria and other weeds. In these experiments
the stock solution, as described above, was dissolved in from 15
to 20 parts of water. The effect of the spray was manifest in
most instances within 2 or 3 hours, but on Japanese nut-grass
the leaves did not turn brown until the second day. On all of
these weeds the leaves and stems ultimately died as a result of
a single application.
In spraying alfalfa infested with dodder the alfalfa was
killed as well as the dodder. In this respect the results were the
same as those obtained with spraying with iron sulphate. The
leaves and small stems of lantana were destroyed by a single
application, but for the complete destruction of the plant a sec-
ond, third or even fourth treatment was found necessary. With
sow thistle, although apparently destroyed, it seemed to recover
rather promptly and grew up again from the base of the plant.
Similar results have been had in Nahiku in spraying this plant.
Some difficulty is likely to be experienced in destroying hono-
hono on account of the fact that in dense patches it is hard to
reach all portions of the plant with the spray and two or three
applications may be necessary. Japanese nut-grass, although
entirely destroyed above ground by the arsenite of soda spray,
promptly grew up again from the underground bulbs without
showing any serious diminution of vigor. In previous experi-
ments of the Station it was found possible to destroy this plant
with carbon bisulphide, but this chemical is too expensive for
use on a large scale. Judging from the experiments which have
thus far been made, the best way to destroy this weed economi-
cally is to shade it out by using pigeon-peas and allowing them
to occupy the ground for a year or more.
In the practical application of arsenite of soda on a large

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scale in Hawaii, the chief credit is due to Mr. W. A. Anderson,
Manager of the Nahiku Rubber Company. In consequence of
the satisfactory results which he has obtained, the method has
been generally adopted by all of the other rubber companies.
More than 500 acres of land covered with miscellaneous shrubby
and herbaceous weeds have already been cleaned by means of the
spray, and ultimately the whole area now planted to rubber will
be treated in this way. Some of the experience of Mr. Anderson
is stated as follows in a letter from him:

"We use it for all troublesome grasses according to the following
formula: 2 pounds crystal sal soda, 1 pound arsenic, boiled in 1 gal.
water until clear. This is diluted in about 24 gals. of water in the
field and applied at the rate, roughly, of about 100 gals. of the diluted
mixture per acre, more or less according to the length and thickness of
the growth.
"We find this effective for all the grasses we have to deal with, and
for the Hitchcock berry and for the general run of weeds, excepting
pualele (milkweed), ginger, and wild taro. For best results on hono-
hono a little stronger solution, perhaps one gallon of stock mixture to
20 of water, is necessary. Diluted 1 to 24, it is partially effective with
the three exceptions given above, and I feel sure that used slightly
stronger, it would dry them up, as it does the grasses and ordinary
"In a complete list of the plants affected, lantana could not be
omitted, as it burns the leaves off, and I have in mind a patch treated
over a year ago which has not grown yet. It is unquestionably safe
to say lantana can be kept in check with it, the fact having been dem-
onstrated that the growth above ground can be killed, the conclusion
would be natural that by keeping at it, the roots in time might be
starved out.
"Hilo grass is actually disappearing from our fields that have been
plowed, and thereafter treated with the spray. Considerable areas are
entirely free from it, and it has been thinned out everywhere."

For several years the Hitchcock berry or thimble berry, and
German ivy (Sen.ecio mikanioides) have been encroaching on the
grass lands of some of the ranches on Hawaii, particularly the
Parker Ranch. The method of eradication at first adopted was
that of digging out by hand. In this way about $1500 per
month was being expended on these weeds and the financial bur-
den seemed an excessively heavy one for the single item of weed
eradication. As soon as the experiments with arsenite of soda
had been carried far enough to warrant a specific recommenda-


tion it was urged that this spray be adopted for the weeds on
ranch land. An extensive test was at once begun with results
which have justified the general application of arsenite of soda.
Not only the Hitchcock berry and German ivy are destroyed by
this spray but also the nettle (Hesperocnide sandwichensis).
These are the very worst weeds on ranch land. The use of arse-
nite of soda as a spray seems to be a practical solution of the
problem of their eradication. Large bushes of Hitchcock berry
are destroyed by a single application. At any rate the roots
have been found to be dead for a distance of 18 inches from the
base of the trunk and, of course, the leaves and the stems were
all killed by the same treatment.
The method of application of arsenite of soda on rough ranch
land or in rubber plantations is a simple one. The most of these
lands do not admit of horse-drawn spraying apparatus on account
of the junglelike nature of the weeds and the roughness of the
lands. A knapsack spray holding about 5 gallons of solution
may be carried on the backs of laborers, who can readily make
their way through the bushes and grass, covering the vegetation
with the spray as they walk along. One laborer can spray from
one to two acres per day, depending upon the height and density
of the weeds to be sprayed and the character of the land. The
total cost of a single application, including materials and labor,
varies from $1.25 to $2.25 per acre. The flowers and tender
foliage of all weeds are destroyed by a single application and
this effectively prevents the immediate spread of the weeds. As
a rule the stems and roots of the weeds are destroyed by the
first application. Hilo grass, however, lantana and certain other
of the hardy weeds may require two or three applications for
their complete destruction. About 100 gallons of the diluted
spray is usually sufficient for an acre of ground.
In spraying with arsenite of soda it should be remembered
that the effect is produced by contact with the aerial portions of
the plant. The spray should be applied in the form of a fine
mist so as merely to cover the surface of the leaves and the
stems. Care should be exercised not to drench the plants, since

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no more effect would be thus obtained, and the risk would be run
of introducing too much arsenic into the soil.
At Ulupalakua some losses have been experienced in the
death of cattle from eating a poisonous passion vine which has
gradually spread over a small area of the ranch land. The arse-
nite of soda is now being used for destruction of this plant and
also to kill the air plant (Bryophlyllum calycinum), a useless
weed which covers some of the range and prevents other plants
from growing. It is commonly considered that red sage (Salvia
coccinea) causes abortion in cows and mares. The evidence for
this belief is quite conclusive and has come from a number of
ranches. The arsenite of soda is now being used on Lanai for
the destruction of this weed.
The chemical method for the destruction of weeds as de-
scribed in this bulletin is capable of a much wider application,
particularly for killing weeds along roadways and in waste
places where cultivation is at present out of the question. It
should, of course, be remembered that the arsenite is poisonous
and stock animals should not be allowed to browse upon
sprayed vegetation until after sufficient rain has fallen to wash
off what may remain on the foliage. As a rule the effect of the
spray begins to be manifested within a few hours in the wither-
ing and browning in the leaves of sprayed plants. They are
thus rendered unpalatable as feed for animals. The spray must
remain in contact with the foliage for at least two hours, in
order to have the desired effect. In applying arsenite, therefore,
a clear day should be chosen, or at least one in which it is not
likely to rain soon after the application of the pray.


In addition to the danger of stock becoming poisoned from
grazing on sprayed vegetation, it seems desirable to consider the
possible injurious effect of arsenic upon the soil and cultivated
crops which may be growing in the soil at the time, or which may


be subsequently planted in it. This matter has already received
some attention, particularly by the Colorado Experiment Sta-
tion. There is still some difference of opinion as to the possible
harmfulness of continued spraying with arsenic. Bishop1 made
analyses of potatoes after the vines had been sprayed with Paris
green and found that they-contained .0002 per cent of arsenic.
Breteau2 made an examination of wine obtained from grapes
picked from vines which had been sprayed with arsenicals and
found .003 to .2 mg of arsenic per liter of wine. Comere3 cul-
tivated algae in solutions of potasium arsenate. This investiga-
tor found that algse not only grew well in nutritive solutions con-
taining arsenate but that arsenic acid could replace phosphoric
acid in such plants. Hyslop4 found that in cattle which had been
sprayed with arsenical solutions, arsenic was present in urine
but not in meat or milk. Collins5 made cultures with barley in
which arsenic was added at the rate of 11 pounds per acre nor-
mally. The grain of barley grown in the pots contained arsenic
to the extent only of 4 oz. per acre and the straw 110 oz. per
acre. Arsenic has been found in minute quantities in the fruit
and in all parts of fruit trees which have been continuously
sprayed with arsenic. It is well known that plants readily ab-
sorb arsenic from the soil but a considerable variation exists in
their sensitiveness to this chemical. In the long-continued liti-
gation between the smelters.and cattlemen in Deer Lodge Val-
ley, Montana, an excellent opportunity was had of studying the
effect of arsenic upon vegetation and live stock. Unfortunately,
too little attention was given in this extensive investigation to
the effect of arsenic upon plants when absorbed into their tissues.
The arsenic in this case was deposited largely upon the surface
of the plants in dust which settled from smelter fumes and
which contained arsenic in large quantities. In all cases, how-

1 Jour. Am. Chem. Soc. 28 (1906), p. 184.
2 Jour. Pharm. Cbim. 28 (1908), p. 156.
3 Bul. Soc. Bot. France 56 (1909), p. 147.
4 Natal Agr. Jour. 15 (1910), pp. 693-697.
5 Jour. Soc. Chem. Ind. 21 (1902), pp. 221-222.

S "

ever, in which careful analyses were made, arsenic was found
to have been absorbed into the substance of grasses.0
The most extensive study of the effect of the absorption of
arsenic upon plants has been carried out by Headden.1 Many
fruit trees, both apple and pear, were observed to be in a sickly
condition or dying in the orchards of Colorado which had re-
ceived arsenical sprays for from 20 to 40 years. An examina-
tion of the soil under such trees showed the presence of arsenic
in varying quantities, the highest being 138 parts per million.
In some cases where sickness or death of the trees was observed
the arsenic content of the soil was at least ten times that of nor-
mal soils in that locality. The orchardists were found to have
been applying for years what must be considered as excessive
amounts of arsenic. In some cases as much as 0.9 of a pound per
tree. In a period of six years this would amount to 432 pounds
per acre or about 108 parts per million in the first foot of soil.
The first symptom of poisoning in the orchard trees was a pre-
mature yellowing of the leaves. If the application of the arseni-
cals was repeated the next year the trees died the second year.
Serious injuries were also produced in these orchards from the
corrosive effect of the arsenic which ran down the trunks of the
trees. The bad effects were most noticeable at the collar of the
trunk near the surface of the ground.
In view of the somewhat divergent opinions which have thus
far been expressed relative to the effect of arsenic upon plants,
we may well inquire what may be considered the outlook from
the continued use of arsenite of soda as a weed destroyer in
Hawaii. The results announced by Headden and referred to
above have been called in question by other writers but without
substantial evidence to disprove his position. Our experience in
Hawaii is of only two years' duration. In a letter from Mr. W.
A. Anderson of Nahiku, Maui, the following statement is made
on the point under consideration:
"As you know, we have been using the spray for nearly two years

6 Jour. Am. Chem. Soc. 30 (1908), pp. 915-946.
1 Colo. Sta. Buls. 131 and 157.


now, in quantities, and have not been able yet to observe any injurious
effects on the trees. Where it has been applied frequently enough to
keep the ground in a measure free from weeds, a marked improve-
ment is noticed in the appearance of the soil, as I suppose might be
expected from exposing it to the air."

In applying the arsenite spray on the rubber plantation of
the Pacific Development Company a considerable quantity of
the solution was accidentally upset near two rubber trees and
the leaves fell from these trees within two days apparently from
the poisonous effects of the arsenite. The trees, however, are
The conditions under which arsenite of soda has been applied
in Hawaii differ greatly from those which prevail in apple or-
chards in Colorado. In the first place we are applying only
five pounds of arsenic per acre and to soils which normally con-
tain no arsenic. Then, too, the rainfall in rubber plantations is
very high (160 to 200 inches per year). In the spraying exper-
iments in the Colorado apple orchards the most insoluble form
of arsenic was used. When washed down into the soil it, there-
fore, remains for a long time, gradually becoming soluble and
being absorbed by the roots of the trees. Arsenite of soda is an
extremely soluble form of arsenic. It is not known whether a
considerable quantity of the arsenite of soda may subsequently
be fixed in the soil by interaction with other chemicals found in
the soil. The soils in the rubber plantations, however, are ex-
tremely porous and are underlaid with a-a to such an extent that
running streams are rare. It is highly probable, therefore, that
the most of the arsenite of soda washed into the soil by rains is
carried away by the water passing through the soil. It seems
very doubtful whether any serious accumulation of arsenic can
take place in the soils of the rubber plantations so long as the
conditions remain as at present. It can not be questioned, how-
ever, that arsenic in excessive quantities in the soil is injurious
to nearly all forms of vegetation, and, therefore, some care
should be observed in not using unnecessarily large quantities of
the arsenical spray. No harmful results have thus far been ob-
served upon rubber or other cultivated plants in Hawaii from

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arsenicals and it is not likely that harm will result, at least in
porous soils such as prevail in rubber plantations, particularly
with the very small quantities of arsenic which are being used.
The effects of arsenic will be closely observed and if any injury
should manifest itself in years to come, the danger may be
avoided by adopting for a year or so the harmless but somewhat
less effective method of spraying with sulphate of iron.

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