1o. 42, SECOND SERIES, FOURTH EDITION.
SB °

= nited States Department of Agriculture,
ENT BUREAU OF ENTOMOLOGY.

L. O. HOWARD, Entomologist and Chief of Bureau.

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HOW TO CONTROL THE SAN JOSE SCALE.
By C. L. Maruatt,
Entomologist and Acting Chief in absence of Chief.
THE SAN JOSE SCALE A PERMANENT FACTOR IN FRUIT GROWING.

The San Jose scale is so widely disseminated and has become so
firmly established in the principal deciduous-fruit regions of this
country that its extermination is now, in most cases, out of the
question. In the main, therefore, the San Jose scale must be recog-
nized as a permanent factor to be regularly dealt with as are other
insect evils or the fungous diseases of plants.

Extermination is possible only where the scale is detected at the
very outset on new or recently planted nursery stock or at least
before any considerable chance of spread has been afforded. It is true
that by the greatest care in the introduction of nursery stock the San
Jose scale may for years, perhaps, be kept out of districts now free
from it, and one is warranted, therefore, in adopting every precaution
to avoid introducing this scale and even to attempt extermination
wherever the conditions are reasonably favorable. There is only one
method of exterminating the scale, and that is by digging up and
burning all infested trees. This is an heroic remedy and is advised
only under the conditions of very recent introduction of nursery
stock—in other words, where the scale is discovered within a few
months after the purchase of the infested trees. If the scale has
passed an entire breeding season in an orchard, it will have spread
much more widely than any inspection will indicate and very likely
will have gained a footing on wild and ornamental plants other than
fruit trees, from which it will reintroduce itself into neighboring
orchards or into new plantings, however thorough may have been the
attempts to eradicate it.

THE SAN JOSE SCALE CAN BE CONTROLLED.

While, therefore, one is undoubtedly justified in asserting that the
San Jose scale is to be a permanency, it by no means follows that the
profitable growth of deciduous fruits is seriously menaced on this
account. The experience in California, covering many years, has
abundantly demonstrated that this scale insect can be controlled, and
the more recent experience in the East points indubitably to the same
conclusion. In other words, by proper repressive and remedial treat-

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ment, the value of which has been demonstrated by much practical
experience, an orchard can be protected from serious injury and kept
in a good paying condition so far as influenced by the San Jose scale.

In view of the above, it is certainly very unwise and wasteful to dig
up and burn a large portion of an orchard because it is infested with
this scale insect, especially since the replanted stock, even if clean
when purchased, would, with little doubt, be in the same condition of
infestation in a very short time.

One of the main objects of this circular, therefore, is to emphasize
the importance and value of honest efforts to control this insect for the
great majority of districts where it has established itself, rather than
efforts at extermination, which will at best rarely prove successful and
will always be accompanied with great immediate loss. The other
principal object is to designate briefly the means of control which
experience has shown to be of practical value.

THE DIFFERENT MEANS OF CONTROLLING THE SAN JOSE SCALE.

The methods of control which have been especially followed in the
Eastern States are (1) the lime-sulphur wash, (2) the soap treatment,
(3) treatment with pure kerosene, (4) treatment with crude petroleum,
(5) treatment with mechanical mixtures of either of the last two oils
with water, and (6) petroleum emulsion with soap. All of these methods
have proved themselves to be successful against the San Jose scale when
properly carried out. As compared with the lime-sulphur wash the next
three mentioned are much more expensive, and the two oils, unless very
carefully applied, are more likely to injure the treated plants. They are,
on the other hand, more certain to effect nearly or quite complete
extermination of the scale. One’s choice of method must therefore be
governed by availability, special needs, and experience. In the main
these remedies, including the lime-sulphur wash, are winter treatments
and may be employed at any time when the trees are in dormant, leaf-
less condition. The weaker oil-water mixtures and the emulsions may,
however, be used in the growing season. The treatments enumerated
are all for trees in the orchard. Nursery stock badly enough infested
to require such treatment is best destroyed. For the general disin-
fection of nursery stock the hydrocyanic-acid-gas treatment is the
standard and only satisfactory means.

The lime-sulphur wash.—-In California, where this scale insect first
occurred, the standard remedy for it is the lime, sulphur, and salt wash,
a mixture formerly used as a sheep dip in Australia and employed with
little change against the San Jose scale and, by a lucky chance, proving
effective. This wash was naturally first thought of on the discovery of the
San Jose scale ineastern orchards. The earlier tests, however, conducted
by this office in 1894, were unfavorable, and the experimentation which
followed resulted in the demonstration by ourselvesand others of several

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distinct and valuable methods of control noted below. Later studies of
the action of this wash in California led the writer, in 1900, to give it
a further careful trial in the East, with most successful results, demon-
strating that, with favoring conditions, i. e., absence of dashing rains
for a few days subsequent to the application, it would give just as good
results in the Eastern States as on the Pacific coast. A year later
(1901-2) very elaborate tests conducted by Dr. Forbes in Illinois showed
that fairly hard rains will not always invalidate spraying with this mix-
ture. A vast amount of experience of the most practical kind since
gained, contributed to by all the eastern experiment stations and by
the big commercial fruit growers of the Middle and Eastern States,
has fully demonstrated the practical merit of this wash and its supe-
riority to others in point of safety to trees and in cheapness. The
wash is furthermore a valuable fungicide and is notably useful against
the peach leaf curl, sprayed trees being practically immune from this
disease, so that the cost of treatment is often more than made good
by the fungicidal benefit alone. Its disadvantages are the difficulty
of preparation and the heavy wear which it entails on apparatus—
objections, however, which do not offset its notable advantages, par-
ticularly for commercial-orchard work or where the number of trees
to be treated is sufficient to warrant the trouble of its preparation.
It is, in fact, the standard spray now used in commercial orchards for
the San Jose scale.

In the matter of composition of the wash, scarcely any two experi-
mentersagree. Salt was a part of the original composition of the sheep
dip and has long been retained, with the idea that it added, perhaps, to
the caustic qualities, and particularly to the adhesive nature of the wash.
For the latter purpose a very small amount only, 1 or 2 pounds to the
bushel of lime, need be added, following the custom in the prepara-
tion of whitewash mixtures. In practical experience, however, the salt
seems to have been of very little benefit and is therefore omitted in the
formula now given. The proportion of lime and sulphur is a matter of
some indifference. The mixture obtained 1s sulphide of lime, and if an
excess of lime 1s used it simply remains undissolved in the mixture and
adds to the whitewashing character of the application. Too much lime
is distinctly objectionable, however, because of the greater difficulty of
spraying and harder wear on the pump and nozzles. The formula here
given is substantially the one which has been hitherto recommended by
this Bureau, reduced to the 45 or 50 gallon basis, or the capacity of the
ordinary kerosene barrel commonly used in its preparation by the steam
method.

lWinslalkediplitmemere es ft ey ee ee! & pounds. . 20
TEL tHrnS| (007 SoU) 1 oe ea a eo dossss 15
WHAteninOnnNaKenerte po Ae 2 of os wees ese els oes gallons.. 45 to 50

The flowers of sulphur, although requiring somewhat longer cooking,
seems to make a better wash than ground sulphur, but the latter may

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be employed. Good quality stone lime should be secured and slaked
ina small quantity of water, say one-third the full dilution. The sul-
phur, previously mixed up into a stiff paste, should be added at once
to the slaking lime. The whole mixture should be boiled for at least
one hour, either in an iron kettle over a fire out of doors or in barrels
by steam. Prolonged boiling increases the percentage of the higher
sulphides, but the practical end is obtained with a boiling of the time
indicated. In the process of making, the color changes from yellow
to the clear brown of sulphide of lime, except for the excess of lime
floating in it. After an hour’s boiling the full quantity of cold water
ean be added, and the mixture should then be promptly applied in
order to get its full strength before the higher sulphides are lost by
cooling and crystallizing out. In transferring to the spray tank it
should be passed through an iron screen or strainer, and the tank itself
should be provided with an effective agitator.

The wash is a winter application and can not be applied to trees in
leaf. It may be applied at any time after the falling of foliage in
early winter and prior to the swelling of the buds in spring. It will
probably be necessary also to make this application every year, or at
least as often as the San Jose scale develops in any numbers. The
wash kills the San Jose scale not only by direct caustic action, but also
by leaving a limy coating on the trees, which remains in evidence until
midsummer or later and kills or prevents the settling of any young
scale insects which may come from parents escaping the winter action.

The wear on pumps and nozzles can be kept to a minimum by care-
fully washing the apparatus promptly after use. The Vermorel nozzle
is the best one for the wash, and additional caps may be secured to re-
place wornones. The use of an air or other gas pressure pump instead
of the ordinary liquid pump will save the wear of the lime on the pump.
In spraying with this wash clothing is ruined, and only the oldest gar-
ments should be worn. Care should be taken also to protect the eyes
to avoid unnecessary inflammation.

The soap treatment.—Whale-oil or fish-oil soap, preferably made
with potash lye, is dissolved in water by boiling at the rate of 2 pounds
of soap to the gallon of water. If applied hot and on a comparatively
warm day in winter, it can be easily put on trees with an ordinary
spray pump. On avery cold day, or with a cold solution, the mixture
will clog the pump, and difficulty will be experienced in getting it on the
trees. Treesshould be thoroughly coated with this soap wash. Pear trees
and apple trees may be sprayed at any time during the winter. Peach
trees and plum trees are best sprayed in the spring, shortly before the
buds swell. If sprayed in midwinter or earlier, the soap solution seems
to prevent the development of the fruit buds, and a loss of fruit for one
year is apt to be experienced, the trees leafing out and growing, how-
ever, perhaps more vigorously on this account. ‘The soap treatment is

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perfectly safe for all kinds of trees and is very effective against the
seale. With large trees or badly infested trees, preliminary to treat-
ment it is desirable, with this as well as other applications, to prune
them back very rigorously. This results in an economy of spray and
makes much more thorough and effective work possible. The soap
can be secured in large quantities at from 33 cents to 4 cents a pound,
making the mixture cost, as applied to the trees, from 7 cents to 8
cents a gallon. The success of the soap treatment is largely influenced
by the quality of the soap used. Many brands are on the market,
mostly made with soda lye. A potash soap should be insisted on, and
one that does not contain more than 30 per cent of water. The soda
soap washes are apt to be gelatinous when cold and difficult or impossi-
ble to spray except when kept at a very high temperature.

Kerosene treatment. —This consists in spraying the trees with ordinary
illuminating oil (coal oil or kerosene). The application is made at any
time during the winter, preferably in the latter part, and by means of a
spray pump making a fine mist spray. The application should be made
with the greatest care, merely enough spray being put on the plant to
moisten the trunk and branches without causing the oil to flow down
the trunk and collect about the base. With the use of this substance
it must be constantly borne in mind that careless or excessive applica-
tion of the oil will be very apt to kill the treated plant. The application
should be made ona bright, dry day, so that the oil will evaporate as
quickly as possible. Ona moist, cloudy day the evaporation is slow,
and injury to the plant is more apt to result. If the kerosene treatment
be adopted, therefore, it must be witha full appreciation of the fact that
the death of the tree may follow. This oil has been used, however, a
great many times and very extensively without consequent injury of
any kind. On the other hand, its careless use has frequently killed
valuable trees. Its advantages are its effectiveness, its availability,
and its cheapness, kerosene spreading very rapidly and much less of it
being required to wet the tree than of a soap and water spray. Pure
kerosene is more apt to be injurious to peach and plum than to pear
and apple trees, and the treatment of the former, as with the soap
wash, should be deferred until spring, just before the buds swell.
With young trees especially it is well to mound up about the trunk a
few inches of earth to catch the overflow of oil, removing the oil-
soaked earth immediately after treatment.

The crude-petroleum treatment.—Crude petroleum is used in exactly
the same way as 1s the common illuminating oil referred to above. Its
advantage over kerosene is that, as 1t contains a very large percentage
of the heavy oils, it does not penetrate the bark so readily, and, on the
other hand, only the light oils evaporate, leaving a coating of the heavy
oils on the bark, which remains in evidence for months and prevents
any young scale which may come from the chance individuals that were

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not reached by the spray from getting a foothold. Crude petroleum
comes in a great many different forms, depending upon the locality,
the grade successfully experimented with in the work of this Bureau
showing 43° Baumé. Crude oil showing a lower Baumé than 48° is
unsafe, and more than 45° is unnecessarily high. The lower specific
gravity indicated (43°) is substantially that of the refined product, the
removal of the lighter oils in refining practically offsetting the removal
of the paraffin and vaseline. The same cautions and warnings apply
to the crude as to tbe refined oil.

The oil-water treatment.—Various pump manufacturers have now
placed on the market spraying machines which mechanically mix kero-
sene or crude petroleum with water in the act of spraying. The attempt
is to regulate the proportion of kerosene so that any desired percentage
of oil can be thrown out with the water and be broken up by the nozzle
into a sort of emulsion. Some of these machines, when everything is
in good working order, give fairly satisfactory results, but absolute reli-
ability is far from assured. The best outlook for good apparatus of this
sort seems to be in carrying the oil and water in separate lines of hose
to the nozzle, uniting them in the latter, and in maintaining an abso-
lute equality of pressure on both the oil and the water tanks by employ-
ing compressed air as the motive force, kept up by an air pump, the
air chamber communicating with both of the liquid receptacles. One
or more manufacturers are now working on apparatus of this general
description. A 10-per-cent-strength kerosene can be used for a sum-
mer spray on trees where the San Jose scale is multiplying rapidly and
where it is not desirable to let it go unchecked until the time for the
winter treatment. The winter treatment with the water-kerosene
sprays may be made at a streneth of 20 per cent of the oil. Applica-
tions of the oil-water spray should be attended with the same precau-
tions as with the pure oil, and there is even somewhat greater risk, owing
to the natural tendency one has to apply the dilute mixture much more
freely than the pure oil. The application should be merely enough to
wet the bark and should not, to any extent, at least, run down the
trunk. The collection of water and oil about the trunk is just as dan-
gerous to the tree as the pure oil.

In the use of the oil sprays noted above, one wao has not had expe-
rience with them is advised to make some careful preliminary tests to
fully master the process, preferably waiting two or three weeks to
determine the results before entering on the general treatment of the
orchard. It is well, also, with the oil-water mixtures to test the pump
from time to time, spraying into a glass jar or bottle to determine by
actual measurement whether the correct percentages of oil and water
are being maintained.

Petroleum-soap emulsions.—The kerosene-soap emulsion, following
chiefly the Riley-Hubbard formula, has been one of the standard means

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against scale insects for twenty years. The distillate emulsion gener-
ally employed in California for spraying citrus trees, on which the lime,
sulphur, and salt wash can not be used, is substantially the same thing,
except that it is made with the California distillate or petroleum oil.
Crude petroleum of any kind, as well as the refined product, may also
be used in making thisemulsion. The use of the soap emulsion against
the San Jose scale in the East has not been very general on account of
the greater facility with which the pure oil or oil-water mixtures can
be applied. The difficulty of obtaining uniform results with the latter
has led to a return to the use of emulsions to some extent, and there
can be no doubt about their superior merit when it is desired to dilute
the pure oils. Emulsions may be applied atany strength with absolute
confidence that there will be no variation. Where the emulsion can be
prepared wholesale by steam power, its employment is attended with
no difficulties. In California it is prepared by oil companies and sold
at very slightly more than the cost of the oil and soap ingredients. It
is made after the following formula:

IPEUROIGWTIN SE 6 eae oa ee eee enn yrs Oa gallons.- 2
Wanale-olisoapy (or I quart soft soap) 22-222. J22222--22- eee pound... 3
Wy enuere: (Stove) oo Ske et ee lps ee ee Reem LOD rh i | | gallon.. 1

The soap, first finely divided, is dissolved in the water by boiling
and immediately added boiling hot, away from the fire, to the oil. The
whole mixture is then agitated violently while hot by being pumped
back upon itself with a force pump and direct discharge nozzle throw-
ing a strong stream, preferably one-eighth inch in diameter. After
from three to five minutes’ pumping the emulsion should be perfect,
and the mixture will have increased from one-third to one-half in bulk
and assumed the consistency of cream. Well made, the emulsion will
keep indefinitely and should be diluted only as wanted for use.

In limestone regions, or where the water is very hard, some of the
soap will combine with the lime or magnesia in the water, and more
or less of the oil will be freed, especially when the emulsion is diluted.
Before use, such water should be broken with lye, or rain water should
be employed.

For winter sprays dilute the emulsion with either 3, 4, or 5 parts of
water, giving a percentage of oil of approximately 17, 13, and 11 per
cent. The strength in oil of this application on trees as compared
with the oil-water sprays is the equivalent of 25, 20, and 15 per cent
oil, because relatively more of the heavier oil-soap emulsion ts held
by the bark. The two stronger mixtures may be used on the apple
and pear and the weaker one on peach and plum.

For summer applications dilute with 7, 10, or 15 parts of water,
giving approximately 8, 6, and 4 percent of oil. The weaker strengths
may be used on trees with tender foliage, such as that of peach, and
the greater strength for strong foliage plants, like the apple and pear.

ONIAN INSTITUTION LIBRARIES

All nursery stock which is under the least suspicion of contamination
with the San Jose scale should be fumigated; and it is perhaps worth
while to fumigate in any case to give the utmost assurance of safety to
the purchaser. The hydrocyanic-acid-gas fumigation is the one to use.
This gas is generated by combining monies cyanide, sulphuric acid,
and water. The proportions of the chemicals are as follows: Refined
potassium cyanide (98 per cent), 1 ounce; commercial sulphuric acid,
1 ounce; water, 3 fluid ounces—to every 100 cubic feet of space in the
fumigating room or house. The latter should be as nearly air-tight as
possible and provided with means of ventilation above and at the side,
operated from without, so that at the end of the treatment the poison-
ous gases can be allowed to escape without the necessity of anyone
entering the chamber. The generator of the gas may be any glazed
earthenware vessel of 1 or 2 gallons capacity, and should be placed
on the floor of the fumigating room and the water and acid necessary
to generate the gas added to it. The cyanide should be added last,
preferably in lumps the size of a walnut. Promptly after adding the
cyanide the room should be vacated and the door made fast. The
treatment should continue forty minutes. It must be borne in mind
that the gas is extremely poisonous and must under no circumstances
be inhaled. The gas treatment is effective against the scale on grow-
ing trees in the orchard also; but the difficulty and expense of the
treatment, except for nursery stock, make it prohibitive in the case of
deciduous fruits.

WI

3 9088 01272 701

FUMIGATION OF NURSERY STOCK.

Approved:
JAMES WILSON,
Secretary of Agriculture.

WasuHineton, D. C., March 10, 1906.

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