UNIVERSITY OF CALIFORNIA.

AGRICULTURAL EXPERIMENT STATION.

BULLETIN NO. 71.

The Use of Gases Against Scale Insects, the bottom of the tent and run through

a lL Z " , _ at tne upper corners of the scaffold. T

as insecticides— with special reference to the j scaffolding, one tent being left over the tree
white scale, Icerya Purchasi. The following is while the scaffolding is moved to the next
a summary of results, of which a full report! In adjusting the tent, the bottomiis placed on
will be published hereafter. the ground about three feet from the tree and

The use of gases for this purpose has been covered with earth. This brings the gas to
long contemplated, and various appliances have bear upon the base of the tree and the surround-
been suggested for the ready application of any ing soil.

efficacious gas. The ease with which gas pene- The generator in which the gases were pro-
trates to all parts of the tree naturally suggests duced consists of a,heavy sheet-iron cylinder, 11
its use as preferable to washes, which at best inches in diameter and 13 inches high. Thebot
leave many parts of the foliage and infested torn rests on a plank, and to the top is fitted a
branches untouched, even when sprayed with movable cover suspended in a frame by a
the greatest care. In order that the gas may bench-screw. Into the cover are fitted two
be an efficient insecticide, it must be so poison- pieces of gas-pipe — one for the exit of the gas
ous that even when applied in small quantities toward the tent, and the other, connected with
it produces fatal results; for in the application a pump, carries the gas which returns from the
the air confined in the tent covering the tree tent. Two small reservoirs are also inserted in
dilutes the gas to a great extent. Again, the the cover; in these are contained the solutions
gas must be capable of being generated quickly which are to flow into the generator for the
in sufficient volume. The record below shows production of the gas.

that only one of the gases employed fulfilled In order to establish circulation and to force
these conditions to a satisfactory extent. Pre- the gas into the tent, a pump is used, which
liminary experiments with some others hav- also serves to exhaust the gas from the upper
ing shown their unfitness for the purpose, part of the tent and to force it again through
either on account of expense or because of in- the generator. It is proposed to replace the
jury to the foliage, or imperfect action on the pump by a small fan-blower, which is much
in8ec ts, their study was not pursued further. more expeditious than the common pump which

Appliances for Application. wa8 U8e <**

TJie tent for covering the tree is made of The Ga898 Experimented With.

heavy bed-ticking, thoroughly oiled with linseed Among the gases used were chlorine, sul-
oil. This cloth serves the purpose best, as it is phuretted hydrogen, ammonia, carbon bisul-
very closely woven, is pliable and easily phide, carbon monoxide, carbonic acid, hydro-
folded, cyanic acid, and carbolic acid vaporized by

The support of the tent, devised by Mr. heat.
Titus, is a very ingeniously contrived scaffold- Chlorine. — Some preliminary experiments
ing mounted on wheels, which serve to move it were made in small vessels into which this gas
from one tree to another. Its dimensions had been introduced. Some infested branches
are 26 feet high, with a base 20x20 feet, were allowed to remain in them for times vary-
Its upper part is 20x12, and carries upon ing from 5 to 35 minutes, without any notice
the top a roller made of galvanized iron (6 able effect being produced on the insect. At-
taches in diameter and 12 feet long), upon mospheres more strongly saturated with the
which the tent is rolled when taken from gas proved fatal to the insect in a short time,
the tree. Side guy-ropes are attached to In other treatments extending over 18 hours,

with leas saturated atmospheres, only a smal
percentage of the insects was killed. No decided|
effects were noticeable on the foliage unless the)
gas was very concentrated.

Carbon Bisulphide.— A lime tree, 12 feet inj
diameter of top, was treated with the vapor of!
2£ pounds of sulphide of carbon for 45 minutes.!
At the end of this time the insects were lively,
and during the treatment had crawled up and
collected around a rope surrounding thar tree,
at the point where the gas was being injected
from the hose. It proved that the gas thus
used injures neither the insects nor the foliage.
It is upon record, however, that in cases where
the vapor has not been thoroughly diffused,
but was allowed to flow down from an open
vessel placed in the top of the tent, serious
injury was done to the foliage at points where
the undiluted vapor flowed down.

Sulphuretted Hydrogen.— Several treatments
with this gas were made on a small scale, the
application lasting from 5 to 35 minutes. The
effects produced either with diluted or concen-
trated gas were similar to those produced by
ohlorine, except that even the concentrated sul-
phuretted hydrogen did not injuriously affect
the foliage. An experiment in which a whole
tree was treated in the tent for 45 minutes, with
quite concentrated sulphuretted hydrogen gas,
showed clearly that the effect was far from be-
ing satisfactory; the insects for the moment
were stupefied, but in the course of an hour and
a half the majority of them were again moving
about.

Ammonia. — The vapor from one pound and
a half of strong ammonia water was applied to
an 11 -foot lime tree for 30 minutes. The re-
sults were disastrous to the foliage; the leaves
were all scalded, and in a few days all dropped
from the tree, and even the newer growth of
wood was injured. The insects, however, were
not perceptibly harmed.

Carbon Monoxide. — Very strong hopes have
been entertained by many for the successful ap-
plication of this gas. Its apparent cheapness
and easy production, when the necessary plant
is once erected, would recommend it. Unfor-
tunately our experiments show that it is not
sufficiently effective to warrant its use. The
gas was obtained by forcing air through a small
furnace filled with red-hot charcoal, care being
taken to cool and to measure the gas before ap-
plying it. No appreciable effect was noticeable
after 40 minutes. In a duplicate experiment, in
which the charcoal was more strongly ignited
and continuously introduced into the barrel for
30 minutes, only slightly better results were ob-
tained.

Oxalic Acid. — It was thought that the pro-
duction of carbon monoxide by decomposition
of oxalic acid by heat might be substituted for
the previous method of generating this gas.
One-quarter of a pound of oxalic acid was
ignited, and the gases applied in a manner sim-
ilar to that of the preceding experiment.
Neither the insects nor the foliage were harmed
in the least. This experiment has incidentally
shown that the vapor of formic and oxalic acids,
also produced during the heating of the latter
is likewise ineffective.

Carbolic Acid. — It had been suggested that

carbolic acid vaporized by heat would prove
fatal to the insect. A dose of half a pound of
liquid acid was volatilized in the furnace, and
the vapor blown in the vessel containing the
infected branch. At the end of 20 minutes all
the old insects were still alive, and some of the
young ones, just molted, were moving about.
An hour later the foliage appeared as if scalded.

Hydrocyanic Acid.— -It was only with hydro-
I cyanic, or prussic acid (generated by the action
i of sulphuric acid on potassium cyanide), that
sufficiently fatal effects were secured to war-
rant a more thorough determination of the time
of exposure and quantities of material which
would produce the best resultB. Numerous ex-
periments were carried on for this purpose, and
it was shown that even small amounts were ef-
fective. It was also shown that even in these
8m all quantities an injurious effect upon the
foliage was produced. In the beginning of the
experiments, 11 mining cyanide" of potassium
was used. It is a very impure material and
contains along with the cyanide a considerable
amount of carbonate of potassium. For this
reason many of the first treatments were prac-
tically ineffective.

Later treatments with pure cyanide were
more successful in destroying the insects, but
the foliage was proportionally injured. Treat-
ments varying in dose from 4 to 12 ounces
of cyanide, and in time from 15 to 60 minutes,
showed that the effect produced on the foliage
by longer treatment was not proportionally
greater than that produced by short treatment.
Neither was the effect of longer treatments
proportionally more fatal to the insects. It
was thus clearly shown that the gas mixture
should be of considerable strength in order to
insure rapid action.

The effect of the gas was so disastrous to the
foliage that it became necessary to find some
means of remedying this trouble. This was
sought in applying a second gas, which might
preserve the foliage. Sulphuretted hydrogen
was therefore injected into the tent, together
with the cyanide gas, both from the same gen-
erator; a portion of the sulphuretted hydro-
gen being introduced before the cyanide was
generated. It was found that the insects ap-
peared stupefied when the tent was raised, but
large numbers revived in a few hours. The
effect of the cyanide seemed therefore to have
been decreased by the sulphuretted hydrogen.
The foliage was not preserved, although not
so badly affected as by treatments with cyanide
alone.

Carbonic acid gas was next tried. Trees
were treated with larger doses of cyanide than
heretofore used, and the carbonic acid from
1£ pounds of carbonate of soda was at the same
time introduced with these doses. The insects
were killed and the foliage of a 12-ft. tree remain-
ed unharmed, while that of a 14-ft. tree with the
the same amount of carbonio acid was slightly
injured. Thus it was shown that it would re-
quire 1£ pounds of bicarbonate of soda to pre-
serve tree-tops 12 feet in diameter, and that
with this protection the deadly cyanide could be
successfully used.

The regulation of the doses for the different
sized trees so as to produce uniform treatments

is calculated on the basis of the results of thej liage is protected by the carbonic acid gas.

experiments which determined the amount of
each constituent for a 12-foot tree. The fol
lowing table indicates the amounts for trees of
different dimensions of top, based upon the
rates of cubical contents:

oize 01
Tree,
feet.

Cyanide of
Potassium,
fluid ozs.

tSi-Carbonate
of Soda,
pounds.

bulpnunc

Acid,
fluid ozs.

•7

•05

•4

1.6

.11

•3

2-5

.20

4.0

.29

2.1

6.o

.44

3.1

8-5

.63

4-5

"•5

.87

6.2

15-5

1.14

8.2

20.0

1.50

11,6

25-4

1.90

13-5

31.6

2.50

16.6

39-2

2 92

20.7

47-5

3-55

25.2

57-5

4-23

30.1

67.7

5.o5

35-8

70.9

5-93

42.1

90-5

6.93

49.2

In order to apply the doses easily they are
prepared so that the required amounts of each
ingredient can be directly measured. The cyan-
ide solution is prepared by dissolving say 10
pounds of the solid salt in about 2£ gallons of
water, warmed nearly to the boiling point, stir-
ring at intervals, cooling, and then diluting to 2J
gallons. This solution will contain about one

It is advisable that the treatments should
follow cultivation after about four days, so that
all weeds and places where the insect may find
lodgment would be destroyed. The insect will
then be on, or very near, the tree; the fitting of
the tent to the ground is thus also much easier.

The eggs of the insect remained apparently
uninjured, wherever protected by the woolly
covering. A second treatment, to destroy such
as may afterward hatch, will therefore be nec-
essary.

It must not be understood that these experi-
ments definitely settle the mode of operation
and the Bize of the doses to be used. They are
merely suggestive of a general plan which can
be so perfected in the future that the applica-
tion of this remedy to other kinds of trees and
insects must be attended with good results.
It simply remains for the ingenious cultivator
to devise the necessary appliances for its use,
on a small scale, on all sorts of fruit trees,
shrubs and plants.

It must not be forgotten that extreme care
in the handling both of this deadly gas and of
the cyanide itself is necessary. To inhale the
one, or to taste or touch a wound with the
other, may lead to serious consequences.

Berkeley, June 12, F. W. Morse.

Aotion of the Los Angeles Supervisors.

Just after the foregoing was written, the fol-
lowing letter was received from A. Scott Chap-

ounce of cyanide of potassium to 2J fluid ouncea ™ an .> ° f Sa ° G /{l rie !'. m f. mber of the California
of the liquid. State Board of Horticulture:

The bicarbonate of soda is pulverized finely rr %M San Gacriel, June 8, 1887.

and measured off in a vessel marked, so as to e F > -Morse, University of Cah/ornia-DEAR
designate pounds and fractions of a pound of SlR: ™e Board of Horticulture of Los Angeles
, , 6 ,. , r . . , T . . , i • au county nave been out to examine the work done by

the solid material. It is then placed in the gen- J Ml , Titus> lace and bave pronounced it th £

erator and the dose of cyanide mixed best .. killing - that they have ever seen>
with it, and, if necessary, a little water added They asked my father (Mr. A. B. Chapman) to go
to make it into a thin paste. ^ After before the Board of Supervisors and make a state-
adding the measured dose of sulphuric acid, ment of your work. He went before the board and
the pump is worked slowly at first, and more explained things to tnem. .They then agreed to pay
rapidly after the gas has passed into the tent, all the expenses incurred by him and Mr. Titus;
The time for each treatment must be deter- the y further agreed to ask you to come down again
mined by future experiments; 15 minutes a J? d carr y y° ur P Ian *° completion, agreeing to pay
seemed to be quite sufficient when the cyanide a11 your expenses and salary, the same as was done
i i 1 t. si u a • ui 1 by Mr. Titus and my father, during your previous

alone was used but it may be desirable to ex- ^ " v ^spectrally yours,

tend the treatment to 30 minutes when the fo- A. Scott Chapman.