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U. S. DEPARTMENT OF ACxRICULTURE,
BUREAU OF ENTOMOLOGY -BULLETIN No. 76.

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

FUMIGATION FOR THE CITRUS
WHITE FLY,

AS ADAPTED TO FLORIDA CONDITIONS.

A. W. MORRILL, Ph; D.

Special Field Agent.

Issued October 31, 1908.

WASHINGTON:

GOVERNMENT PRINTING OFFICE,

1908.

I'. S. DEPARTMENT OF AGRICULTUR]

BUREAU OF ENTOMOLOGY BULLETIN No. 76.

I.. C). I IOWARD, Entomologist and Chief ol Bureau.

FUMIGATION FOR THE CITRUS
WHITE FLY,

AS ADAPTED TO FLORIDA CONDITIONS.

BY

A. W. MORRILL, Ph. D.

Special Field Agent,

I ssi i i) October 31, L908.

WASHINGTON:

GOVERNMENT PRINTING OFFICE.

L90 8.

BUREAU OF ENTOMOLOGY.

L. 0. Howard, Entomologist and Chief of Bun au .
C. L. Marlatt, Entomologist and Acting Chief in absence of Chief.
R. S. Clifton, Chief Clerk.

F. H. Chittenden, in charge of truck crop and special insect investigations.

A. D. Hopkins, in charge of forest insect investigations.

W. D. Hunter, in charge of southern field crop insect investigations.

F. M. Webster, in charge of cereal and forage plant insect investigations.

A. L. Quaintance, in charge of deciduous fruit insect investigations.

E. F. Philld?s, in charge of apiculture.

D. M. Rogers, in charge of gipsy moth and brown-tail moth work.

W. F. Fiske, in charge of gipsy moth laboratory.

W. A. Hooker, engaged in cattle tick life history investigations.

A. C. Morgan, engaged in tobacco insect investigations.

R. S. "Woglum, engaged in hydrocyanic acid gas investigations.

R. P. Currie, assistant in charge of editorial work.

Mabel Colcord, librarian.

White Fly Investigations.

C. L. Marlatt, in charge.

A. W. Morrill, E. A. Back, W. W. Yothers. special field agents.

2

iTTER OF TRANSMITTAL.

U. s. Department of Agriculture,

Bureau of Entomology,

Washington, J). C, June 11, 1908.

Sir: I transmit herewith, for publication as Bulletin No. 76 of this
Bureau, a reporl on fumigation for the while fly, as adapted to Florida
conditions, by Dr. A.W. Morrill, special field agent.

The investigation of the white fly problem in Florida is now in its
second year, and the results gained of immediate practical importance
are those which indicate host methods of control. Fumigation with
hydrocyanic-acid gas during the short dormant period in winter, when
there are no winged insects, seems to afford the greatest measure4 of
control orpossible extermination. Gas fumigation under the horticul-
tural conditions obtaining in Florida orange groves and the peculiari-
ties of climate presents rather a distinct problem. This bulletin gives
the results of the fumigation experiments of two winters in Florida,
and demonstrates the entire applicability of this method of control to
the white fly. This investigation has been under the general direc-
tion of Mr. C. L. Marlatt, Assistant Chief of this Bureau, with Doctor
Morrill in field charge. The latter was aided during the winter of
1906-7 by Mr. Stephen Strong, formerly horticultural commissioner
of Los Angeles, Cal., and an experienced fumigator, and Mr. A. 0.
Morgan, and during the winter of 1907-8 by Messrs. E. A. Back,
W. W. Yothers, and R. S. Woglum.

The white fly is the big insect problem of Florida and other citrus
districts on the Gulf coast, and the information given in this bulletin
will be of immediate practical value to all citrus growers of the region
indicated.

Respectfully, L. O. Howard,

Entomologist and Chief of Bureau.

Hon. JAMES Wilson,

Secretary <>J\ [gricu/ture.

3

CONTENTS

[ntroduction 7

Condi! ions favoring or necessary to good results 9

[solal ion of grove 9

Concerted action 9

Absence or elimination of food plants oil mm- than citrus 9

Season of the year LO

Meteorological elements 11

Size of i rees and regularil y of setl ing ' IT

Equipment .' 14

Tents 14

Poles and uprights 20

M iscellaneous requirements 22

Chemicals 25

Degree of puril y required 25

Handling, and aecessil y for protect ion from moist lire 25

Proporl ion of water and acid 25

Procedure 27

Methods of handling tents 27

Measuring trees 30

Method of generating the gas 35

Work roni ine 3G

Est i nun ion of time required for fumigation of grove 38

Methods of computing approximate diihensions and cubic contents 39

Dosage requirements for the white fly 40

Experiments with sheet tent . 40

Experiments with bell or hoop tenl 49

Miscellaneous experiments and observations 50

Appearance of Iarvse and pupae of the white fly when destroyed by fumiga-
tion 50

Density of the gas at various heights a hove the ground 51

Effect of himigation on the trees 51

Sugge.-t ions for the fumigation of small trees 54

In the grove 54

In the nnr.-ery 54

Nursery stock for shipment 54

Precautions 55

Expense of fumigation 56

For equipment 56

For chemicals 58

For labor 58

Economy of treatmenl by fumigation 59

Losses prevented 59

( lost of fumigat ion compared wil li spraying 62

Fumigation versus nat ural control 63

Appendix 66

Table of dosage for the citrus white fly 66

Index nit

ILLUSTRATIONS.

Page.

Plate I. Figs. 1-3. — Method of covering small tree with bell or hoop tent 14

II. Figs. 1-3. — Method of covering small tree with sheet tent by means of

poles 20

III. Figs. 1-5. — Successive stages in the operation of shifting a sheet tent

from one tree to the next in the row. Fig. 6. — First tent ready for
introduction of chemicals; "tent men" shifting the second tent
in the series 20

IV. Fig. 1. — Commissary tray: Open compartment (tin lined) for cyanid

at right, balances and torch in the middle, compartment for acid
pitchers and glass graduate at left. Fig. 2. — Top of derrick, show-
ing method of attaching pulley and guy rope. Fig. 3. — Base of

derrick, showing method of constructing braces 22

V. Fig. 1. — Raising 33-foot derricks to an upright position. Fig. 2. — Der-
ricks in position (one on each side of tree), supported by guy ropes;

pulleys hooked to catch-rings in the tent 28

VI. Fig. 1. — Front edge of sheet tent raised to tops of derricks, ready to be
pulled over tree. Fig. 2. — Sheet tent ready for introduction of

chemicals 28

VII. Fig. 1. — Eighty-foot tent covering large seedling orange tree, showing
tent graduated for the purpose of enabling operators to use dosage
table given in the appendix. Fig. 2. — Carrying 5-gallon crocks con-
taining acid and water under the tent, preparatory to introducing
the cyanid 32

TEXT FIGURES.

Fig. 1. Plan for construction of octagonal sheet tent 50 feet across, showing lines

used in constructing octagon 16

2. Method of attaching hooks to tent when covering trees with aid of der-

ricks 18

3. Plan for schedule board, showing convenient arrangement 22

4. Diagram of regularly set grove in process of fumigation with an outfit of

four tents 23

5. Diagram of grove with alternating trees; first four rows in process of

fumigation with four tents; three sets of trees fumigated, the tents
being moved from south to north 24

6. Diagram showing method of marking tents to aid in obtaining dimen-

sions of inclosed space when covering tree 32

7. Tent marked to aid in estimating dosage, in position for fumigation. ... 33

8. White fly (Aleyrodcs titri) : Stages and details 59

9. White fly (Aleyrodes titri): Adult male and female and details 59

10. Florida red scale ( Chrysomphahis ficus) : Stages 61

11. Purple scale (Lepidosaphes bechii) : Stages 62

6

FUMIGATION FOR THE CITRUS WHITE FLY, AS ADAPTED
TO FLORIDA CONDITIONS.

INTRODUCTION.

The discovery of tlio value of hydrocyanic-acid gas as an insecticide
against citrus pests is properly considered one of the most important
advances in economic entomology. This gas was first used by Mr. D.
W. Coquillett, who in 1SSG was detailed by Dr. C. V. Kiley, the Ento-
mologist of the U. S. Department of Agriculture, to experiment with
insecticides against the cottony cushion scale (Icerya purchasi Mask.)
in California. The process was afterwards brought to its present de-
gree of usefulness through the extensive experiments of Mr. Coquillett,
and is now generally recognized in the citrus-growing sections of
California as the most practicable and efficient method of controlling
the black, red, and purple scales. It is now used in combating citrus
scales in South Africa, New South Wales, and elsewhere, with results
so satisfactory that wherever it has once been tested it has proved its
superiority over all other methods.

In the eastern part of the United States Prof. H. A. Morgan
conducted experiments with hydrocyanic -acid gas against citrus
scales in southern Louisiana during the winter of 1892-93. Messrs.
W. T. Swingle and II. J. Webber, of the Department of Agriculture,
were the first to use this treatment against the white fly in Florida,
conducting their experiments in February, 1894. In the winter of
1900-1 901 , Prof. II. A. Gossard, then entomologist at the Agricultural
Experiment Station of Florida, aided during a portion of his experi-
ments by Prof. C. W. Wood worth, of the Agricultural Experiment
Station of the University of California, undertook some experimental
fumigation work against the white fly. The results were sufficiently
satisfactory to lead Professor Gossard to the conclusion that the
efficiency of this treatment against the white fly is such that if a
fumigated grove were segregated from all others, one fumigation would
render it so nearly clean that it would need no additional treatment
for two or three years. It was predicted that a process that has been
found so valuable in other parts of the world is certain eventually
to come into favor in Florida.

7

O FUMIGATION FOR THE CITRUS WHITE FLY.

During the last few years certain nurserymen in Florida have made
use of fumigation against the white fly with good success, treating:,
for the most part, small-sized trees. Other parties have tested fumi-
gation on trees of all sizes, but, for lack of adequate equipment or of
a knowledge of the most economical methods of procedure and dosage
requirements, have not continued.

In January and February, 1907, the writer, aided by Mr. Stephen
Strong, formerly horticultural commissioner of Los Angeles County,
Cal., specially appointed in this Bureau as fumigation expert, and
Mr. A. C. Morgan, special field agent, temporarily transferred from the
cotton boll weevil investigations, conducted careful experiments in
Orange County, Fla., in order that fumigation for the white fly might
be placed upon a practical basis. Modern California methods as
adapted to all sizes of trees were employed and the principal results
are embodied in the present bulletin.

In December, 1907, and January, February, and March, 1908,
fumigation experiments were continued by the Bureau of Entomology
on a larger scale, testing the conclusions drawn from the work of the
previous winter and extending the investigation to cover the ground
more thoroughly. In this work the writer was assisted throughout
the season by Messrs. W. W. Yothers and E. A. Back, and during the
month of January Mr. K. S. Woglum was also engaged in the work.
Altogether nearly 4,000 trees have been fumigated in Florida in
this experimental work, under the immediate supervision of the
agents of the Bureau of Entomology. It is too early to include in
this bulletin more than the general results of the past winter's experi-
mental work, but the text has been made to conform to these
results as far as worked out.

There remain many details concerning the fumigation process which
have demanded investigation, and at the present writing these are
receiving attention by agents of this Bureau who are conducting an
exhaustive study of the matter in California. The present bulletin
aims to give the results of experiments in fumigation for the white fly
and such information and recommendations as are of immediate
value to those who may contemplate the adoption of fumigation as
a practice, or who may desire first to secure a small equipment in order
to become familiar with the methods of procedure. The directions
given herein are believed to be sufficiently detailed to enable any
orange grower to conduct fumigation, after a few preliminary tests,
without the assistance of experienced hands. The recently discovered
occurrence of the white fly in California increases the importance of
definite information concerning the requirements as to dosage.

A new system for the estimation of dosage is recommended herein,
as it is believed that the usual method of judging concerning the dosage
requirements for scale-insects can not give the uniformity of results
which should be obtained inusing this remedy against the white fly.

CONDITIONS FAVORABLE <>i: NECESSARY. 9

CONDITIONS FAVORING OR NECESSARY TO GOOD RESULTS.
isolation OF (;ko\ i:.

[solation in an infested grove is the most favorable condition for the

successful control of the white fl\ by fumigation. A distance of one-
half mile between a given grove and the nearest infested grove ia
sufficient to insure against appreciable interference with the results of
the treatment through the migration of adults between the groves.
In many if not in most cases 300 or 400 yards is sufficient isolation to
prevent the treatment being made unprofitable through such migra-
tions. It i> a common experience in newly infested groves that the
section which first becomes infested may be very noticeably blackened
by sooty mold for two or three years before the white fly multiplies to
an injurious extent in near-by sections of the same grove or in immedi-
ately adjoining groves. The experience mentioned above indicates
that in isolated groves the extermination, or nearly complete extermi-
nation, which can be obtained by carefully conducted fumigation, will
result in a condition of practical immunity over a period of two or
more year--.

CONCERTED ACTION.

Ranking next to isolation as a factor favoring success in fumigation
for the white fly, is concerted action among the owners of groves in
naturally isolated groups, or among all the citrus growers in the various
counties. In California the organization and support of county hor-
ticultural commissions has solved the problems connected with the
alt ainment of the concerted action necessary for the control of various
(it in- pest s in that State. It is predicted that the white fly can never
become a serious pest where such systematic campaigns against citrus
insects have been organized. In Florida, Orange County has already
made a beginning toward the adoption of such measures against the
white fly, having organized a horticultural commission with powers
equivalent to those of similar commissions in California. a The
officials Inning the matter in charge, howrever, have not felt justified
in attempting active field work on a large scale until careful experi-
ments shall have determined what course can be followed with a
certainty of uniform results.

ABSENCE OB ELIMINATION OF FOOD PLANTS OTHER THAN CITRUS.

The presence of food plants of the white fly other than citrus trees,
in citrus fruit growing sections, constitutes a serious menace and in
itself often prevents successful results from remedial work. For-

" For the California lawsee Bui. 61, Bur. Km.. I". s. Dept. Agrici L906), pp. L3-21.

10 FUMIGATION FOR THE CITRUS WHITE FLY.

tunately the list of food plants" is limited, and the greater number
of those thus far recorded is subject to infestation only when located
near or in the midst of heavily infested citrus groves. The food plants
which are of most importance in connection with the white fly control
are the chinaberry trees, privets, and cape jessamine, and these —
except for the last, in certain sections where grown for commer-
cial purposes — can be eradicated readily, or their infestation may
be prevented where community interests precede those of the indi-
vidual in controlling public sentiment. These food plants favor the
rapid dissemination of the white fly from centers of infestation and
their successful establishment in uninfested localities. The}" seriously
interfere with the success of fumigation, as well as of all other remedial
measures, by furnishing a favored breeding place where the white fly
can regain its usual abundance in a much shorter time than would be
the case if it were entirely dependent upon citrus fruit trees for its
food supply. The plants mentioned, together with Citrus trifoliata
(except where used in nurseries), and all abandoned and useless citrus
trees should be condemned as public nuisances and destroyed in all
communities where citrus fruit growing is an important industry.
Where the destruction of chinaberry trees is impracticable for any
reason, they may be rendered innocuous by taking steps to prevent
their becoming heavily infested each year. Tins may be accomplished
by either defoliating each winter or by destroying entirely all privets
and cape jessamines and by thoroughly fumigating each winter all
citrus trees within a distance of 200 or 300 yards of each chinaberry
tree.

SEASON OF THE YEAR.

Fumigation for the white fly should be done during December,
January, and February, beginning not earlier than sixteen to twenty
days after the adults have disappeared, in order that all of the eggs

a The complete list of food plants so far as known is as follows: Citrus (all varieties),
chinaberry (Melia azedarach and Melia azedarach umbraeuliformis), cape jessamine
(Gardenia jasminoides), wild persimmon (Diospyros virginiana), Japan persimmon
(D. Jcahi), privets (Ligustrum spp.), Viburnum nudum, Fieus altissima, prickly ash
(Xanthoxylum clava-herculis) , cultivated pear (Pyrus sp.), cherry laurel (Prim us
laurocerasus), Prunus caroliniana, lilac (Syringa sp.). Water oak (Qjiercus nigra) has
been reported as a food plant of the citrus white fly, but there is no definite record of
the insect reaching maturity on this plant, and the observations made in connection
with the present white fly investigations show that for practical purposes oaks may be
ignored as food plants of this species. Professor Gossard reports having observed
larvae of the citrus white fly on scrub palmetto (Sabal megacarpa I. The author once
ob erved larvae on the banana shrub (Magnolia fuscatum) but apparently none reached
maturity on this plant. Dr. E. A. Back has observed two live larva- of the citrus
white fly on oleander (Nerium oleander). These plants (oaks, scrub palmetto, banana
shrub, and oleander) may be ignored absolutely as food plants unless it is proved
beyond doubt thai ii is possible for the citrus white fly to reach maturity on them.
The cultivated figi Ficus),and thesweel baj I \fagnolia virginiana) have been reported
as food plants, but with little doubt these reports are erroneous.

CONDITIONS FAVORABLE OB NECESSARY. 11

deposited by these adults may have time4 to hatch. It is impractica-
ble to attempt to destroy t ho egg stage by fumigation, or as a rule by
any other direel means. The scale-like stages, however, technically
known as the larval and pupal stages, are readily destroyed when the
dosage is properly estimated, hi Florida the month of January is,
everything considered, the most favorable month for fumigating for
the white fly. Ordinarily it would probably be undesirable to continue
fumigation after the adults begin to emerge in considerable numbers
in the spring. 'Plus time of emergence, of course, varies according to
the locality and to weather conditions, but in general is between the
middle oi' February and the first of March. It remains for further
experiments to show bow far fumigation may be practiced with profit.
at other seasons of the year. Tt is certain, however, that in cases of
emergency, such as the checking of the spread of the fly in newly
infested groves, fumigation can frequently be used to great advantage
even in midsummer.

M ET E< ) I : ( ) I .( )( ; I ( ! A I . EL E M E NTS .

Light. -Fumigation is conducted in the absence of bright sunlight,

to avoid injury to the foliage which may occur when this precaution is
not observed. With tents treated with oil to make them nearly gas-
tight, damage is almost certain to result from daylight fumigation.
With untreated tents, however, the writer has on several occasions
conducted fumigation experiments with the sun fifteen minutes high
without appreciable injury to the foliage. One orange tree was
fumigated forty minutes, beginning at 3 p. m., with the sun shining,
without any shedding or burning of foliage resulting from the treat-
ment . Tbc tent was placed over the tree twenty-five minutes before
generating the gas, and at the beginning of the forty-minute period
the temperature was 79.5° F., or 4.5° higher than the outside tempera-
ture. Twenty and one-half ounces of potassium cyanid were used,
and 97.7 per cent of the white fly pupae were destroyed. This amount
of cyanid was 4\ ounces less than the amount called for by the
table given in the Appendix. At the time of fumigation, the foliage
on the tree was very much curled by drought and after a few rains
became normal in appearance without the shedding of a single leaf.
The leaves, at the time of the treatment, when torn seemed to be as
dry as paper, alt bough many pupae of the white fly on neighboring
tree- in a similar condition produced adults, as did the nine speci-
men- which were known to survive on the fumigated tree. It is
probable that Future experience will show that trees whose foliage is
curled as a result of drought are not nearly so liable to injury by
daylighl fumigation as are trees whose foliage is in perfect condition.

Fumigation can safely begin with sundown, or, during the fumigat-
ing season in Florida, between \ and 5 o'clock p. in. On dark, cloudy
days fumigation scemsentirely safe at any time with untreated tents.

12

FUMIGATION FOR THE CITRUS WHITE FLY.

Wind. — The effect of wind upon the results is so marked that
fumigation .should not be attempted with anything stronger than
a slight breeze, particularly if the tents have not been rendered
gas-tight or nearby so by the use of a "filler." It has been found,
with an untreated tent, that with a dosage sufficient to destroy 100
per cent of white fly pupae, a brisk breeze renders the results so
uncertain that the effectiveness may be as low as 30 per cent in
some sections of the tree, while in others the destruction of the
insect may be complete.

Atmospheric humidity and dews. — The presence of moisture in the
form of dew does not seem to have any deleterious effect upon the
foliage, although in California it is generally considered necessary to
materially increase the dosage in such cases to insure the effective-
ness of the work against scale insects. Prof. H. A. Gossard a con-
cluded that "moisture did not seem to interfere with the efficiency
of the work, unless the leaves were almost dripping, when it became
a factor of much disturbance, though not as great as we had thought
probable."

The experiments conducted by the writer and assistants during
January and February, 1907, show that moisture on the foliage
during the period of exposure has no marked effect on the foliage
or upon the efficiency of the gas against the white fly. In the six
instances where the leaves were wet with dew, examination showed
that 100 per cent of the insects were destroyed in* aU cases but one,
and in tins only a single specimen out of 102 under observation,
before and after fumigation, survived the treatment.

The results of the tests concerning the effect of atmospheric
moisture on the efficiencv of the fumigation treatment are oriven in
Table I.

Table I. — Effect of atmospheric moisturi on efficiency of fumigation.

Experi-
ment

No. b

Air
humidity.

C end it ir.n- Cc.idition
of tent. of leaves.

Per cent

of insects

killed.

Amount

of evanid

Amount

recom-

of cvaiiid

mended in

used.

tallies: -In

minutes

exposure.

Ounces.

Ounces.

30

24

32

27

I5f

14

9

11

13|

18

33*

32

36*

34

28

19

22

26$

27

26*

30.7

40.2

4.5.12

45.21

15.22

45.25

4.5.27

.50.2

60.2

60.19

Per cent.
100

94+
100

87

s7

96
100

97

64

Wet

. Wet

. Moist

Wet....
Damp. .

.. Wet

Damp..

Damp..
Wet

. M list

. Wet

. Moist

Damp. .
Damp. .

. Drv

. Dry

100
100
100

100
99.

100
100
100

a Bui. 67, Fla. Agr. Exp. Sta., pp. 647-648.

b The number preceding the decimal point indicates the length of exposure.

CONDITIONS FAVORABLE OB NECESSARY.

13

On several occasions it was observed thai the tenl Felt somewhat
damp when being handled, although the humidity recorded 1>\ a
standard sling psychrometer had not reached complete saturation.
On other occasions, as shown l>\ ilic above data, the Foliage was
covered with a dew like a fine mist when the sling psychrometer
indicated as much as 6 per cent below complete saturation. For
practical purposes, however, the moisture on the leaves may be
considered as indicating a condition of 100 per cent atmospheric
moisture. Blank spaces in the table indicate that no note was
made concerning tin's particular point, although the tent was evi-
dently "wet" in experiments t0.2 and 50.2 and the leaves were
evidently "dry" in experiments 45.21 and 45.22. In the experi-
ments summarized in Table I the possibility of reducing the efficiency
oi' the gas through absorption by the moisture on the leaves and
tent had to be taken into consideration. To eliminate this feature
and to determine the effect of the pis on larva1 and pupa1 of the
white1 fly when leaves art1 wet artificially, tests were made by wetting
the leaves both, by dipping and by means of an atomizer. The
results are summarized in Table II.

Table II. Effect of artificially wetting leaves on efficiency of fumigation.

Experi-
ment
No.

Air hu-
midity.

Amount

Of cyanid

used.

Amount
of cyanid
recom-
mended

in table.

Total
number

Of insects
under

observa-
tion.

Per cent

Of insects
killed.

Number

Of insects

on leaves
wet arti-
ficially.

Per cent
Of insects
killed on
leaves
wet arti-
ficially.

Method <>!'
wetting.

Per a rU.

Ounces.

Ounces.

44

20

29

242

71

21

95. 2

Dipped.

4(1...

47

I7j

21

392

88

149

90.6

Sprayed.

10.7

.>.)

8J

13

132

80

40

87.5

Dipped.

in.s

61

1"!

._.,,,

223

96

93

98.9

Sprayed.

40.9

54

12

27

342

93

20

95

Sprayed.

40.13

63

24

28

736

100

567

100

Dipped.

In the above experiments — omitting the last one, in which all
insects were killed — 1,331 insects were under observation. Of these,
323 were on leaves wetted artificially. The weighted average of tin1
insects killed on these leaves is 92.5 per cent. Of the 1,008 insects
on the dry leaves 852, or 84 per cent, were killed. Tins seems to
be of considerable significance in view of the fact that in every
instance where less than 100 per cent of the insects were killed, the
percentage of killed was greater on the artificially wetted leaves
than on the dry leaves.

Taken as a whole the results summarized in the two foregoing
tables show conclusively that moisture on the leaves in the form of
dew does not reduce the edicacy of the gas in destroying the insects,
hut possibly increases it. In the experiments in which moisture was
a factor no injury to the foliage followed, even when the dosage was
increased fully one-half above the amount called for by the table
in the appendix of this bulletin. The results give no justification to

14 FUMIGATION FOR THE CITRUS WHITE FLY.

the practice of some fumigators who, as has been stated, increase the
dosage when the tents and foliage are wet with dew. It seems that
the difficulty in handling wet tents is the only consideration for
winch it is necessary to cease work on foggy nights, everything else
being favorable.

SIZE OF TREES AND REGULARITY OF SETTING.

While it is true that it is possible to place a fumigating tent over
any citrus tree regardless of size, the author strongly recommends
that orange growers make a practice of pruning large seedling trees
so that they will not exceed 28 or 30 feet in extreme height. Such
pruning will greatly reduce the cost of labor in fumigating and will
be of considerable advantage from the standpoint of picking the
fruit. It is probable that the now generally recognized all-around
advantage of low-pruned fruit trees applies squally well to citrus as
to other kinds of fruits. Another consideration of importance is
the regularity in the setting of orange groves and the proper spacing
of trees. In Florida various factors have resulted in many groves
being too crowded or too irregularly set to permit of the easy handling
of fumigating tents. While it is well to bear these things in mind
to the end that all Florida groves may gradually be adapted to
reduce the labor and expense of fumigation, }^et even under present
conditions it is exceedingly rare that fumigation is rendered abso-
lutely impracticable by the size of trees or the irregularity of their
setting.

EQUIPMENT.

TENTS.

Styles of fumigating tents. — Two styles of tents are now in use for
orchard f umigation, the bell or hoop tent (PL I.) and the sheet tent.
The first is bell-shaped and held open at the mouth by a hoop of J -inch
gas pipe. Tents of this style are preferable for use only when the
trees in a grove are uniformly less than 12 feet in extreme height.
Sheet tents are made in the form of flat octagons and, being adapt-
able for trees of all sizes, are in California used almost exclusively.
Plate I, figure 3, shows a tree which is 14 feet in extreme height and
14 feet in extreme expanse, covered by a hoop or bell tent. When the
tent is in position covering the tree the measurements are: Height,
13 feet, and diameter, 12 feet. Hoop tents are not always easily
placed in position over trees of this size, and it is believed that ordi-
narily a sheet tent is more desirable for trees of all sizes. A third
style of tent which will be found useful in fumigating small trees is
the box tent in the form of a rectangular prism. This will probably
prove advantageous for trees 5 feet or less in height. The light
wooden framework supporting the cloth cover gives a form to the

Bui. 76, Bureau of Entomology, U. S. Dept. of Agriculture.

Plate I.

Figs. 1-3.— Method of Covering Small Tree with Bell or Hoop Tent. 'Original.)

1 1 n rs. 1 5

inclosed space which permits of economical use of chemicals with
greater uniformity of results.

( instruction of tints. The const met ion of the box covers such as

suggested in the foregoing paragraph Is a simple matter and con-
venient patterns will suggest themselves at once to anyone desirous
of fumigating small trees. The framework should be lighl hut well
braced, and for a covering either 6J-ounce drill, painted to render it
as nearly gas-tight as possible, or oilcloth is recommended.

Prof. C. W. Woodworth, of the California experiment station,
gives the following directions for cutting the (doth for bell tents:"

All of these tents are made in the same manner, and arc the most economical in
cloth of any tents made. Commonly the tent is made by the " cul and fit" method.
These tents may l>e made with scarcely any loss, if cul according to Hie following
directions: Measure oil' strips <»i" a length equal to twice i he heighl plus one-tenth ! he
diameter of the tent desired. These will make two strips each by marking the exact
middle and measuring off on one edge from the middle line one-quarter of the diameter
of the tent and on \ he ot her one-half 1 he diameter. Now, take a long si rip of molding
and bend it so as to touch these three points and mark off the curve so produced.
This allows lor the seam. In making up. sew the two cut edges together in each pair
of si rips.

As has been stated, sheet tents, or more properly covers, are flat,
regular octagons. The dimensions are sometimes stated in terms of
the true diameter (i. e., the distance between opposite corners),
but for practical purposes the distance between parallel sides should
represent the size of the tent, for the reason that this represents
within about 2 feet (which must be allowed to rest on the ground)
the distance over the tallest tree that a given sheet can cover meas-
uring from the ground on one side to the ground on the other, over
the center of the tree.

Hereafter in this bulletin the size of octagon covers as stated should
be understood to refer to the distance between parallel sides. The
specifications should be carefully worked out before beginning the
construction of a sheet tent as well as of other styles. First, the
dimensions of the tallest tree which the tent is required to cover
should be estimated. This may be accomplished by throwing a tape
attached to a reel over the top of the tree and measuring from ground
to ground. When covered, the weight of the tent will reduce the
extreme height of the tree in most cases by from 2 to 4 feet,
according to the weight of the tent and form of the tree. It will be
well to allow at least 4 feet of the tent to rest on the ground when
covering the largest tree. The desired size having been determined,
a diagram of an octagon should be constructed on paper, as indicated
in figure 1. Each side of the octagon when constructed will be
equal approximately to two-fifths of the distance between the parallel

" Circular No. 11, Cal. Agr. Exp. Sta., pp. 9-10.
mi8— Bull. 7(3—08 2

16

FUMIGATION FOB THE CITRUS WHITE ELY.

sides of the octagon. The number of square yards of cloth required
is about IS per cent, or between one-sixth and one-fifth less than
for a square the sides of which are equal to the distance between
parallel sides of the octagon.

In California S-ounce army duck has been used almost exclusively for
making sheet covers, while in Cape Colony. South Africa, a No. 10
duck ranking in weight between 12-ounce and 15-ounce is commonly
used. The heavier weights are not only more durable but presumably
confine the gas better. A good grade of 6', -ounce drill, however, as
shown later by the results obtained with a bell tent of this material,
seems to be fully equal to the S-ounce duck commonly used in Cali-
fornia. Until careful
experiment- shall
have determined the
relative tightness of
various weights of
duck it is recom-
mended that sheet
tents be constructed
throughout of 8-
ounce duck or of 8-
ounce duck in combi-
nation wit ha "skirt "
of 6^-ounce drill.
The author has seen
a sample of 8-ounce
drill which is no more
expensive than the
best brands of duck
■— -j of this weight, but is

Fig. 1.— Plan for construction of octagonal sheet tent 50 feet across, evidently iai'Slipenor
showing lines used in constructing octagon: A, C, side sections; B,
central section of full-length strips; E, E, so-called "ends " of tent;
S, S, so-called "sides" of tent; B, R, reinforcements; 1-21, strips
of duck 29| inches wide, overlapped \ an inch at the seams.
(Original.)

a

as regards tightness.
Anyone contemplat-
ing the ordering of
a fumigating outfit
should procure as many samples as possible of different brands of
suitable cloth and select the closest woven brand.

The strips when cut should be overlapped three-eighths or one-half
inch and double stitched and all raw edges should be hemmed. In
calculating the number and length of strips the overlapping will
reduce the width of the cloth from three-fourths inch to 1 inch. As
an illustration of the method of calculating the length of the strips
used in making an octagonal tent of S-ounce duck. 50 feel may be
taken as the desired size. This is equal to 600 inches and the width
of the cloth, if 29.5 inches, will be reduced to 28.5 it" overlapped one-
half inch at the seams. By dividing 28.5 inches into 600 inches the

CENTS. 17

nearest multiple is found to be 598.5 inches, or 49 feel and 10J inches,
which is sufficiently close bo the desired width for practical purposes.
The number o( strips in a tent 598.5 inches wide is 21. The middle
section \\ (fig. L) is approximately two-fifths the entire width, or
239.5 inches. Deducting this from 598.5 inches, the entire width,
t In* remainder, 359, equals the sum of the widths of sections A and C.
These sections being equal, the width of each is \7\K~) inches. The
number oi' strips in each section can now be readily calculated. The
21 strips should be numbered on the diagram from left to right.
Section A requires six strips and 8.5 inches of the seventh. Simi-
larly , section C requires six strips, beginning at the right (twenty-firsl
to sixteenth, inclusive), and 8.5 inches of the fifteenth. Section B
requires the remaining 20 inches of strip No. 7, 20 inches of strip
No. 15, and seven entire widths, thus making the total of 21 strips
required.

The cutting of the cloth can bo done without waste if the details
of construction arc well planned. In the above tent seven strips 50
feet long (49 feet 1(U inches) should first be cut for section B. Strips
Nos. 7 and 15 are next cut and the outside corners cut at an angle
of 1") degrees, as indicated in the diagram. Each strip for sections
A and C is cut shorter by its own width outside at each end than the
strip preceding it. Thus the required lengths of the side strips are
found by matching the inner edge of the new one to the outer edge
of the one before it. It is desirable to have the central section, B,
mad*1 up entirely of full-length strips so that the stress will not be
across seams. The stress is so slight, comparatively, in the side
sections A and C, that this is not an important point.

Shrinkage of the goods after being thoroughly wet is an impor-
tant consideration in the economical construction of fumigating
tents. In order that the tents approximate a regular octagon, after
having been used for fumigating purposes, it is necessary either to
have the goods thoroughly shrunk before cutting or to make allow-
ance for subsequent shrinkage by cutting the strips longer. A test
made with a brand of 8-ounce duck commonly used in California for
fumigating tents showed that the shrinkage lengthwise of the goods
amounted to 7.5 per cent, and, crosswise 0.9 per cent; this means
that in a 50-foot tent the shrinkage would result in the full-length
strips shortening 3 1 feet, while the tent would shrinkless than 6 inches
crosswise o]' tin1 strips. Such irregularities might be remedied by a
skirt of ()',-ounce drill, but it is simpler to plan to have each strip
cut longer by a given amount for each 1 per cent of difference in the
lengthwise and crosswise shrinkage. In the case referred to above
this difference is <'>.»; per cent, and each per cent represents an actual
difference of 6 inches. A 50-foot t<vnt constructed in this manner

18

FTMKtATIoX FOR the citrus white fly,

would therefore measure before shrinkage 52J feet (49 feet 10?, inches
+ 3 feet 4 inches) lengthwise of the strips through the middle section.
and 41) feet 10'. inches crosswise of the strips. After shrinking, the
dimensions would be approximately 40 feet 4\ inches in each direc-
tion. The two sides of the octagon which are formed by the ends of
the full-length strips are known as the "ends" of the tent and the
sides of the octagon which are parallel with these strips as the "sides"
of the tent.

By gathering the cloth around a tightly-rolled wad of burlap and
tying on an iron ring, a convenient arrangement is made for attach-
ing the hooks or poles when covering trees.
(See fig. 2.) In the case of the smaller sizes
of sheet tents, which are to be handled with
simple poles, these rings are unnecessary, at-
tachments being made in the manner here-
after described. For large tents, measuring
more than 42 or 45 feet, it is probably best
to use the rings in all cases. It is most con-
venient to have one of these rings located a
few feet in from each of the four corners of
the middle section of full-length strips (fig. 1 ,
B) . In general, the distance in from the mar-
gin should be from one-twelfth to one-tenth
of the distance between parallel sides of the
tent, and the distance between the two rings
on each side should be from one-third to two-
fifths of the distance between parallel sides.
To the ring mentioned a chain link is some-
times attached (e), called a " jingler," the ob-
ject being to indicate the position of the ring
when the operator shakes the tent, enabling him readily to locate
it at night.

In order to provide for the increased stress on the cloth at the points
where these rings are to be located, a reenforcement should be stitched
on near each of the "ends" of the tent. The main stress in handling
a tent is directly behind the catch rings or places of attachment when
poles are used without rings. There is also considerable stress across
the tent directly between the two rings or places of attachment.
Both of these stresses may be provided for by a reenforcement con=
-Ming of one-half width of the goods used in constructing the tent.
sewed entirely across the full-length strips of the middle section and
extending 2 or 3 feet onto each of the side sections. These reenforce-
ments are located in accordance with the directions given in the
preceding paragraph and as shown in figure 1 (B, R).

Pig. 2. — Method of attaching
hooks to tent when covering
trees with aid of derricks: a,
Tent gathered around ball of
burlap or other suitable ob-
b, stout cord for attach-
ing ring; c. catch-ring; d, hook
on pulley block; e, lap link
or "jingler." (Original.)

TENTS. L9

A skirt of 6J-ounce drill is of considerable advantage in reducing
the weight, especially in the case of the larger sizes of tents. This
drill is usually about 28 inches wide, and when a skirt is to be used
allowance is made for one or two widths in constructing the diagram
and in figuring for the cutting of the 8-ounce duck. Sometimes the
skirt is run all around the margin, hut it is preferable to have the full-
Length strips (section B) extended the entire length of the tent and
the drill sewed to the three sides of seel ion A and of sect ion C. When
the skirl extends all the way around, when shifting the tent by means
of poles or uprights, the rings should always be located on the duck
inside of the skirt, to avoid too greal stress upon the lighter material.

Painting, oiling, mildew-proofing, and <■<!/■< of tents. Various meth-
ods have been used to preserve and to increase1 the tightness of fumi-
gating tents. Linseed oil was one of the, first materials tested for
increasing the tightness of the cloth:' hut experience has shown this
to he undesirable when used either by itself or in combinations, on
account of the deterioration in the strength of the cloth and the lia-
bility to bum or rot when long loft folded. Painting the cloth with
black paint, with an inferior grade of glue, called "size/' and with a
mucilaginous juice of the prickly pear cactus (Opuntia sp.) are three
methods mentioned by Mr. D. W. Coquillett in a report dated in
October, 1890, as in use in California. In recent years these three
methods have all been used more or less, the last the most extensively
of the three. At present the most usual practice of California fumi-
gators is to use untreated tents or tents proofed against mildew by
dipping and boiling in a solution of tannin. This last treatment is not
considered of any value in rendering the tent tighter except by ordi-
nary shrinkage, which would be accomplished as well in due course
after using one or two nights, particularly in Florida, where heavy
dews are usual. The method of treatment with the tannin solution,
a- reported by a committee on fumigation appointed by the Claremont
(California) Horticultural Club and published in various horticultural
and agricultural papers, is as follows:

To preveni ruination by mildew when the tents are damp, they musl lie dipped.
This is done in a large tank, made either of galvanized or boiler iron. These Bhould
lie :; by K) feet and 2! feel deep. The boiler should be^ounded. This must be on

a good arch, so as to permit a fire under it. The smoke pipe <>r chimney of the arch
must he high, to secure a draft. A derrick made by three poles above the tank, sup-
plied with pulleys and a rope, makes dipping easy and permits raising of the icni and
dripping after dipping is completed. It also aids in keeping the tent from i he bottom
of the tank and burning, which must he avoided. The lank is Idled to near the top
with water and made very dark by adding a half barrel of <>ak extract or tannin. This
is well stirred. The tannin should not be added until the water is boiling. The tent
is lowered into the tank of boiling water and extract and hoi led for half an hour. It is

" Report of Commissioner of Agriculture, L887, Report on the Gas Treatment for
& ale [nsects, by I>. W. Coquillett, p. L26.

20 FUMIGATION FOR THE CITRUS WHITE FLY.

now raised from the water and alter dripping ceases it is spread out to dry. The tank
lb idled again and the tannin is added until the color is a reddish brown, and then
another tent may be dipped.

In Florida fumigating tents become thoroughly wet nearly every
night they are in use, but even when untreated will not deteriorate
to any great extent (lining two or three months' use if thoroughly
diied each day, and more especially before being finally rolled up lor
storage during the seasons when not in use. Tents are conveniently
dried each day by simply leaving them on the last tree covered until
dried by the sun. The edges of the tent should be straightened out as
soon after sunrise as possible, and folds in the tent should be arranged
from time to time to facilitate drying. Such work, of course, should
not ordinarily be considered as part of the work of the fumigating crew,
but can be readily attended to by some laborer employed at t he grove.
It is considered by some fumigators that when tents are treated with
oil it is unsafe to leave the trees covered during bright sunlight, but
untreated tents can be safely dried in this manner. Drying is prob-
ably hastened by pulling the tents partly off so as to make an open
space on one side to give circulation of air. Frequently it is a good
practice to pull a tent wholly or partially over two trees in order to
facilitate drying. When tents are dry, to prevent wetting by rain
and subsequent trouble in drying, they should be rolled tip as com-
pactly as possible and arranged to shed water as well as practical >le,
or they may be covered with waterproofed ducking or stored for the
time being in a dry place.

Tents must be kept in repair during the fumigating season and
examined frequently during the daytime for holes which need patch-
ing. If tents are always pulled lengthwise of the strips of the cloth,
there is little danger of tearing, except when there is much dead wood
on the trees. One of the tents used by the agents of the Bureau of
Entomology during the winter of 1906-1907 was used to cover
upward of 100 trees without any injury of this kind.

POLES AND UPRIGHTS.

Poles and uprights are used, as shown in the illustrations (Pis. II,
III), for raising the front edge of the fumigating tents when covering
a tree or pulling the tent from one tree to the next in the row. The
simple poles are as a rule used for tents not exceeding 48 feet in
diameter, and usually vary from 12 to 20 feet in length, according to
the height of the trees to be covered. In California straight-grained
Oregon pine 2 inches in diameter is generally preferred for poles not
exceeding 18 feet in length; for poles longer than IS feet the diameter
should he 2\ inches. In the Gulf regions it is recommended that
seasoned cypress poles he used, as these are much lighter than the
available pine. Although only a single pair need he \\>vi\ with an

Bui. 76, Bureau of Entomology, U. S. Dept. of Agriculture

Plate II.

Figs. 1-3.— Method

if Covering Small Tree with Sheet Tent by Means
of Poles. (Original, i

Bui. 76, Bureau of Entomology, U. S Dept. of Agriculture.

Plate III.

POLES AND UPRIGHTS. 2]

outfit of as many as twenty-five or thirty tents, extra pole-- should
always be on hand as a provision againsl breakage. A one-half inch
rope of either nianila or cotton, about one and one-half times the length
of the poles, Is attached about 3 or 4 inches from the top of each one thai
is in use. The tops of the poles are constructed in various styles for
catching the rings on the tents. The end of the pole may be cul to
allow the ring to slip over the end for a short distance, for instance
1 \ or 2 inches, and to hold the rope in position. Two hardwood pegs
driven through auger holes about 1' inches apart at right angles to
one another will serve this purpose. The most convenient form for
genera] use is the simple rounded top over which the cloth of the tent
i^ doubled and held in place by a hall' hitch of the rope (PI. II, figs.
1. 2). The lower end of the pole should he pointed to prevent it-
slipping on the ground when the tent is being lifted.

For use with sheet tents which are too large lor convenient handling
with the poles described, a pair of uprights or derricks is needed.
These are somewhat heavier poles, with braced crosspieces at the bot-
tom to prevent them from falling sidewise when in an upright posit ion,
and each is provided with a pulley at the top (see PI. TV, fig. 2).
When not attached to the ring in the tent the swinging block is
hooked to a ring bolt or stout staple located on the upright near the
tops of the braces. The poles are 25 feet or more in length, from 3 to 4
inches in diameter at t he base and tapering to from 2 to 3 inches in diam-
eter at the top. They may be made of straight-grained knotless pine or
seasoned cypress. Wherever the latter can be obtained it is preferable
to pine on account of its 'lightness. As shown in Plate IV, figure 3,
crosspieces about 1 by 3 inches in section are spiked or bolted to each
side across the bottom, and brace pieces about 2 by 4 in section extend-
ing from between the ends of the brace pieces to the main pole are
bolted in position. The crosspieces should be 6 feet in length for
derricks 25 or 26 feet high and increasing to about 7V or S feet in
length for 32 or 33 foot derricks. In the writer's experience derricks
are sufficiently long that arc within 2 to 3 feet of the extreme height
of the tree- to be covered, as a consequence of the elasticity of the
citrus branches and the fact that within this distance of the extreme
top the branches are almost invariably slender. A guy rope one-half
or five-eighths inch in diameter and about one and one-half times the
length of the upright is attached to the top of each, just above the
pulley block. It is convenient to have these ropes easily removable
SO that they can be used in tying the tents into compact bales when
rolled up for transportation or storage. The lifting tackle consists of
a rope of the same size as the guy rope and a little less than three
times as long as the upright. One end of this is at t ached to the fixed
pulley block at the top of 1 he upright, passes through the movable
block, then through t he upper fixed block, and t he free end i- usually
t led t » » one of t he brace piece-.

22

FUMIGATION FOIl THE CITRUS WHITE FLY.

.Mis('].i.r.A.\i:ors requirements.

According to the method of procedure hereinafter described and rec-
ommended for use in fumigating for the white fly, when an outfit of
more than four or five tents is in use, a cart or stone drag and a horse
may be desirable for carrying the materials from tree to tree. An
ordinary hand push-cart can be recommended as convenient for use
in some cases. When a horse or a hand push-cart is not available, a
box-like tray (PI. IV, fig. 1) with handles should be constructed.
This should be large enough to contain a supply of acid and cyanid
for all of the trees covered at one time by the set of tents in use. One-
half of the tray should be reserved for as many 3-quart pitchers as

may be needed and for the graduate, and the
other half should be provided with compart-
ments for the bags of cyanid, if weighing is
done by day, or an open box for the loose
cyanid if the weigliing is done as each tree
is fumigated. A torch should be fixed over
the center of the tray, and if the cyanid is
weighed as used there should be a strip of
board across the tray to serve as a platform
for the balances. Balances are preferable to
spring scales for use in weigliing the cyanid.
They should not be larger than necessary for
weigliing 40 ounces of cyanid at once. For
containing the acid temporarily, stoneware
churns of a capacity of 3 or 4 gallons are
much used in California, and can be recom-
mended for use in Florida. Frequently sev-
eral 3-quart.pitchers are more convenient than
the stoneware churns. A measuring glass of
16 ounces capacity is needed for measuring
the acid, and an extra measuring glass should
be provided for use in case of breakage. The
acid is dipped into the measuring glasses by
means of a long-handled enamel-ware dipper, or poured in from a
pitcher. For carrying water a couple of large pails are needed.

The one who measures the acid and generates the gas should be
provided with rubber gloves of good quality and long enough to
cover the wrists well, or even the entire forearm. For generating the
gas, earthernware jars from 1J to 5 gallons capacity are necessary,
according to the size of the trees and dosage required. Extra jars
should be provided to obviate possible inconvenience in case of break-
age. Cylindrical jars are preferable to those which narrow at the to]).
as the chemicals are much more likely to boil over in the latter than in
the former. The cyanid. after being weighed, may be put into paper

Fig. 3.— Plan for schedule board,
showing convenient arrange-
ment: A, space for resting lan-
tern temporarily; B, scratch
pad; C, dosage table; D, dia-
gram of grove. (Original.)

Bui. 76, Bureau of Entomology, U. S. Dept. of Agriculture.

Plate IV,

Fig. 1 .—Commissary Tray: Open Compartment 'Tin Lined' for Cyanid at Right,
Balances and Torch in the Middle, Compartment for Acid Pitchers and
Glass Graduate at Left. Fig. 2.— Top of Derrick, Showing Method of
Attaching Pulley and Guy Rope. Fig. 3.— Base of Derrick, Showing Method
of Constructing Braces. Original.'

M1SCELLAN EOUS REQUIRED i.n I 8.

28

bags or into tin cans, or it may be emptied directly from the scoop
into the generating jar. A spade or shove] should be on hand for
use whenever it is accessary to weighl down the edges of the tent by
b few shovelfuls of earth and also for use in burying the contents of
t he jars. A copy of the table of dosage required for the white llv and
found in the appendix of this bulletin should always be on band. A
convenient arrangement for bandling the diagram of the grove and
the dosage table when fumigating is illustrated by figure 3. This
represents a board upon which, the position for setting the lantern
temporarily, and the positions for attaching diagram of the grove,
dosage table, and scratch pad are indicated. For the board a side
of an orange box is very satisfactory. This should be strengthened
1>\ two laths nailed

across the grain on the rough side. ()

n the

28-36
9

33-40

13

32-39

37-45
17

25-30

7

30-37
10 \

37-48
18

30-36

10'i

40-61
25

33-40
13

38-54
20'yz

38-44
\7

38-50
19

37-51
19

36-40

I4'l

ABCDEF^GHIJKL

Fig. 4.— Diagram ol regularly set grove in process of fumigation with an outfll of four tents: X, X.

trees missing. (Original.)

smooth side at the bottom tb° diagram of a portion of the grove
(fig. 5) should be fastened with thumb lacks. This diagram should
include as much of the grove as can be fumigated in any one nighl
and should be dated and preserved after the work for thenighl has
been checked off on the original diagram (figs. 1. 5) of the grove as a
whole, [mmediately above the diagram the dosage table (fig. 3, C)
should be located. If the board is smooth it may be painted white
and the table copied thereon with pencil. If the table is on card-
board it may be fastened with thumb tacks. Above the dosage
table ,i scratch pad (fig. :;, />') should be fastened in the upper right-

24

FUMIGATION FOR THE CITRUS WHITE FLY.

/V.

hand corner, while the space (fig. 3, A) in the upper left-hand corner
is left for the fumigator to set his lantern while he is writing down on
the diagram the dimensions of the tented tree and the amount of
dosage. It will he found convenient to attach a pencil to this board
with a short string.

The diagrams of the grove are prepared as shown in figures 4 and 5,
representing a small grove set in regular and alternate rows respec-
tively. When set with any form of regularity the individual trees
may be conveniently referred to by numbering the rows in one direc-
tion and lettering
them in the other.
Thus the first tree of
row No. 1 is called
1A, the second IB,
etc., while in the
other direction the
trees are referred to
as 2A, 3A, etc. In
measuring the cir-
cumference of. the
t rees or in checking
the correctness of
the estimates based
on pacing, a 75 or
100 foot tape at-
tached to a reel is
needed. Water-
tight barrels are re-
quired for contain-
ing the stock of wa-
ter for use during

w.

9

8

7

6

e.

X

X

4

42-54

24

43-62
29

3

39-47
20

40-49
21

X

41-51
23

Z

42-50
23

47-60
34

40-47

20

43-48

24

i

32-38
13

42-50
23

i

FlG. 5. Diagram of grove with alternating trees; first four rows in
process of fumigation with four tents: three sets of trees fumigated,
the tents being moved from south to north: X, X, X, trees missing.
(Original.)

the night.

When weighing
the cyanid a tin
scoop is sometimes useful, and leather gloves should be provided
for the one who does the weighing. When weighing of the cyanid
i- to be done during the day five wooden boxes, with hinged covers,
of a size that will conveniently fit into the cart, or one box with
six compartments, should be constructed for use in holding paper
hags of cyanid in doses of 1, 2, 5, 10, and 20 ounces, respectively.
Kxperience will show the number and style of lanterns and torches
required. A hammer, hatchet, and other incidentals can be procured
as found uecessary.

PROPORTION OF WATEB AND Ailh. 25

CHEMICALS.
DEGREE OF PC KIT Y REQUIRED.

The materials used in generating hydrocyanic-acid gas are potas-
sium cyanid (KCN), sulphuric acid (HaS04), and water. The cyanid
and acid should be purchased of a reliable dealer. The cyanid should
be guaranteed to l>e 98 or 99 percent, which is practically chemically
pure. The acid should be guaranteed to he 66°a and, as additional
assurance, it would be well to have a sample tested by a druggist or
by the fumigator himself by using an acid hydrometer. This instru-
ment is inexpensive and can he obtained through any druggist.
A linn or hard cyanid should be obtained rather than a. soft or
porous product .

HANOI. INC., AND NECESSITY FOR PROTECTION FROM MOISTURE.

Potassium cyanid can be purchased in boxes of 200 pounds each.
The cyanid readily absorbs moisture, and for this reason after a box
is opened it should he kept constantly covered with burlap sacks and
protected against rain when necessary. When only a few trees are
to be treated and the box of cyanid is not to be completely used,
within a few days at t he most, it is recommended that it be stored
in large-sized tin cans with covers made practically air-tight by means
of cheese cloth or muslin. The acid when used in large quantities is
purchased in drums containing about 1,500 pounds. In smaller quan-
tities it i^ sold in carboys containing a little less than 200 pounds.
The carboys make convenient receptacles for handling in the groves.
In emptying from a drum into carboys a large funnel of glass or
sheet lead is useful. When the carboys are boxed and not other-
wise provided with handles, strips of wood may be nailed along paral-
lel sides projecting at each end, so as to make convenient handles
For t wo men. If carboys can not be obtained or the quantity of acid
used does not require temporary containers for such amounts, large
jugs may he used. In all cases the containers, except when in use,
should he stoppered. For this purpose wooden plugs, made tight
w ith asbestos, such as can be bought in sheets from hardware dealers,
may be used. When the acid is to be stored in carboys for more
than a few days the plugs should be made extra tight by means of
plaster of Paris. For water required in the generation of the gas
anything that is reasonably clean will answer the requirements.

PROPORTION OF WATER AND ACID.

The proportion of the materials theorel ically required for a complete
chemical reaction is I part of potassium cyanid, 1 part of acid, and 2
parts of w ater. In pract ice3 however, an excess of acid up to one-fourth

a Sixty-six degrees sulphuric acid Is 93 per cent strength.

26

PUMIGATIOK FOB THE CITRUS WHITE FLY.

more than the actual requiremenl is ordinarily used, while it is gen-
erally considered that the use of three or four times as much water
as acid reduces the danger of shedding of the leaves from excessive
dosage. The experiments conducted by the writer relating to this
point have thus far given only negative results by failing to show
any relation between the proportion of -the water and acid and the
ellcct of the gas upon the insects or the foliage. In 66 of the experi-
ments summarized hereafter a record was made of the proportion
of 1 lie water and acid. In nearly every case the object was to
determine the minimum dosage required, and while the record
included the proportions of the water and acid no effect of the varia-
tion in tins regard was looked for until the results were summarized.
The chances, therefore, were equal in regard to the selection of a dose
of the required amount for greatest utility in the various tests. The
results in connection with the proportion of water and acid used
are eriven in the Table III:

Tablk III. — Results obtained with varying proportions of water and arid.

Tarts of water to one
part of acid.

mei?ts in ments ta

Shri£nfL°,f Per cenfof

warned h^e flies
were killed. were killed.

Total.

9

3
14

<>'

3.

3*

4

5

10
0

11
0

17 27
1 1
9 20
1 1

Total

31 a.-) 66

10
21

7
2S

17

49

It will be observed from the table that the result- seem to favor the
smaller amounts of water in proportion to the acid rather than the
larger amounts. The data are not extensive enough to establish this
conclusively, and it is not improbable that the difference in the
percentage of white flies killed has no connection with the propor-
tion of water and acid. It is at least evident, however, that there
is no marked difference in favor of the use of water in a proportion
greater than necessary for the complete chemical reaction. The
Association of Horticultural Inspectors in 1903 adopted the formula
usually expressed 1-2-4, meaning 1 part of cyanid, 2- of acid, and
I of water. Mr. Wilmon Newell's laboratory experiments0 lead
him to conclude that this formula permits the1 volatilization of an
apparently maximum amount of prussic (hydrocyanic) acid.

«Bul. 15, Georgia State li-.ar.l of Entomology, pp. 21-24, L905..

METHODS OF HANDLING CE1 2 \

The element of beat due to the mixing of the acid and water is rec-
ognized as an important factor in generating the gas. According to
('. P. Lounsbury0 very nearly the maximum amount of heal is evolved
when equal volumes of acid and water arc used, and he advises against
the use of more than 2 volumes of water to i of acid.

The point in question is one of those now under* investigation in
California l>\ agents of this Bureau. Until conclusions are reached
the writer would recommend that the chemicals he used in the propor-
t ion of 1 part of cyanid, 1 part of acid, and :\ parts of water, or l-l-.'5.
'Phis formula i^ recommended for the present on account of results of
experiments reported herein and upon which the table given in the
appendix is based, being obtained with an average of 3 parts of water
to 1 of acid. Future experiments may justify the California prac-
tice from the standpoint of danger to the foliage from the use of the
smaller amounts <A' water. In the experience of t tie writer as reported
herein, the injury to the foliage has been too slight to show tiny rela-
tion to the proportion of the chemicals,

PROCEDURE.
METHODS OK HANDLING TENTS.

Sheet tents. — Octagonal sheet tents, or covers, are placed in position
over trees by means of the changing poles and derricks which have
been described. A tree which measures in extreme height between
30 and 35 feet can be covered and made entirely ready for the genera-
tion of the gas in less than two minutes if the work is not interfered
with by the too close planting of trees. Smaller trees usually require
from one to two minutes, according to size. When the changing poles
are used (Plate II, figs. 1, 2; Plate III, figs. 1-5) in covering small
trees, one man on each side of the tree places the ring over the end of
his pole if catch rings are used, or if not, makes a double fold of the
cloth over the end of the pole and makes a half-hitch over it with the
rope to prevent it from slipping off. With the pointed end of the
pole on each side about opposite the center of the tree they then raise
the end of the pole and attached tent about 8 feet, or until the poinlcd
ends hold without slipping, and, holding on to the rope, step forward
and away from the tree and pull the tent into position. Some opera-
tor^ prefer,after attaching the tent to the end of t he pole, to stand with
one foot on the pointed end and raise the pole entirely by means of the
rope. Knots tied in the ro pes at convenient intervals near the end
are of great assistance in pulling. If the trees are so large that they
require tents too large and heavy for handling by two men and yet
not large enough to require the use of derricks, a third man maybe
employe.d to advantage. The edge of the tent is made fast to the

a Agricultural Journal (Cape Town), L902, p. 4.

28 FUMIGATION FOB THE CITRUS WHITE FLY.

end of each pole as before, but the two operators station themselves
with t he rope in hand at the foot of their respective poles while the
helper raises the end of each pole in turn, so that the operators can
use their ropes to advantage. The committee of the Clermont Horti-
cultural Club, of California, in their report heretofore referred to, rec-
ommended that four men, or two for each pole, be regularly employed.
When trees are close planted or there is fear of breaking branches by
changing the tent from one tree to the next, or there is dead wood
threatening to tear the tent if simply dragged oil*, the practice of
"skinning it off" will be found to be useful. In this method the
attachments of the poles are made at the far side of the tent and the
cloth slides over itself as the tent is pulled from one tree to the next.
In handling sheet tents by means of derricks (PI. V, figs. 1, 2; PI.
VI, fig. 1) four to six men can work to best advantage. The writer
has, however, with one assistant successfully handled a sheet with
26-foot derricks. After placing one of the derricks in the posil ion for
raising the tent the guy rope was fastened to a tree while the second
derrick was raised. Each operator then held the guy rope by means
of a loop through which the elbow was placed, giving the use of both
hands while raising the tent with the tackle. Ordinarily two men
should not attempt to cover a tree by themselves, particularly if there
is a slight breeze. When four men are available for handling sheet
tents with derricks, they proceed as follows: The sheet is pulled into
position back of the tree to be covered, with the rings located one on
each side. The derricks are placed one on each side of the tree, flat
on the ground and their bases parallel, either directly opposite the
center of the tree or within a distance of 3 or 4 feet back, whichever
experience with trees of various sizes and widths of rows may show to
be best. Two men station themselves, one at the base of each der-
rick with guy rope in hand. The other two men go to the opposite
ends of their uprights and raise them to a vertical position with the
assistance of the men at the bases, who pull with the guy ropes, stand-
ing on the cross pieces as long as necessary to prevent slipping. The
second two men now steady the derricks while the first two walk for-
ward and take a position for holding them in place by means of the
guy ropes. The derricks are now brought to a position where the
tops are 3 or 4 feet beyond the vertical in order to prevent the weight
of the guy rope from causing them to fall forward prematurely.
The two men at the bases of the derricks now attach the hooks of the
swinging blocks to the rings of the tent and by means of the tackle
raise the front edge of the tent to the tops of the derrick-. These
men may now tie their hoisting ropes to the braces or hold them
tightly by band while the other men pull on the guyropes, causing
the derricks to fall forward, pulling the tent oxer the tree. Five or
six men may he needed to cover ver\ large seedling trees such as are

Bui. 76, Bureau of Entomology, U. S. Dopt. of Agriculture.

Plate V.

Fig. 1.— Raising 33-Foot Derricks to an Upright Position. (Original.j

Fig. 2. — Derricks in Position One on Each Side of Tree) Supported by Guy
Ropes; Pulleys Hooked to Catch-Rings in the Tent. (.Original.'

Bui. 76, Bureau o' Entomology. U. S. Dept. of Agriculture.

Plate VI.

Fig. 1.— Front Edge of Sheet Tent Raised to Tops of Derricks, Ready to be
Pulled Over Tree. ^Original.)

Fig. 2.— Sheet Tent Ready for Introduction of Chemicals. ^Original

\l I. r lions OF HANDLING rENTS. 29

common in Florida, especially when the trees are closely set. After
adjusting or "kicking in" the edges, the tent is ready for the intro-

diict ion oi' i be chemicals.

Whether simple polos or derricks are used, tents are usually
changed from one tree to the next in the row by making the attach-
ment as described and pulling the tent directly off From one onto
the other. When there are only a. few large trees to fumigate and
the tents at hand are singly not sufficiently Large to cover, two can
l>e frequently used to advantage, placing them in position from oppo-
site >ides and having them overlap as much as possible without inter-
fering with tightness at the ground.

It i^ hest to have the tents large enough so that not less than 2 feet
o( the edge will rest on the ground at any point when adjusted and
ready for fumigation. Sometimes it may be accessary to weight
down the tents at certain points by means of a few shovelfuls of
earth. Carelessness of the workmen charged with adjusting the
tents at the ground would result in seriously curtailing the benefits
from fumigating a grove. When arriving at the end of a row, or on
other occasions when it is desired to uncover a tree without at the
same4 time pulling the tent in position over another, the tent is usually
dragged off by hand. If there is dead wood present, however, to
avoid the possibility of injuring the tent, removal with the poles or
derricks may be advisable. It is well to call attention again to the
desirability of always pulling the tent lengthwise with the strips,
whet her in changing the tent from tree to tree or in dragging off from
a t ree after t reat ment.

Bell tents. — The method of covering trees with hell or hoop tents is
so plainly shown by Plate I as to require but few words of explanation.
The cloth should fall over the hoop on the side farthest from the tree,
in order to bring the center of the tent about over the center of the
tree in covering. Usually two men, one on each side, can easily
throw the tent entirely over the tree, hut if the tree to be covered re-
quires nearly the full capacity of the tent it will be necessary to pass
around to the front of the tree and pull the tent down into position
with the hoop resting on the ground. Ordinarily the cloth which ex-
tends below the hoop makes the tent sufficiently tight at the bottom
when the hoop is resting flat on the ground. An extra man with a
pole or rope may be necessary to assist in handling the largest sizes of
hoop tents, when they are used to cover the largest trees possible. In
changing from one tree to the next in the row a little experience will
show what is the quickest and easiest method. Tents of this pattern
an- at present little used in California, the sheet tent being greatly
preferred even for small trees.

30 FUMIGATION FOE THE CITRUS WHITE ELY.

MEASURING TBEES.

Xu-fssity for measurements. — The rule followed by some California
fumigators in estimating the dosage for scale insects is to give an
amount which in the manager's judgment is as large as each tree will
stand without injury to well-matured growth. Tender growth is
almost invariably injured by a proper dosage, but this loss is not con-
sidered of consequence. In Florida, however, there is usually little or
no new growth until toward the close of the season to which fumi-
gation for the white fly should be limited. It is obviously impos-
sible, even for an experienced fumigator, without measuring, to
judge of the size of trees so accurately as to avoid overdoses, on
the one hand, wasting a small percentage of the chemicals, and, on
the other hand, underestimates with the consequent lack of effec-
tiveness. The difference between an effective dosage as a treat-
ment for the white fly and one which would produce injury to the
tree is not large in many cases, a and careful estimation of dosage
seems essential for economy and success in fumigation for this insect.
Even among fumigators considered most successful in California, there
is a Ancle diversity of opinion as to the quantity of chemicals required
for trees of the same size, as shown by the observations of Mr. S. J.
Hunter, reported by Professor Woodworth, and by the published rec-
ommendations as to dosage by various writers. The significance of
this in California is that there is a great difference between efficiency
against the scale insects treated and danger to the trees; and the prac-
tice of basing dosage on guesses as to the dimensions, either before or
after covering, necessarily results in the danger of underestimation of
the dosage requirement on the one hand and a needless waste of
chemicals on the other. A study of the table given in the appendix,
showing the dosage recommended for successful work against the white
fly with untreated tents,6 proves the physical impossibility of a fumi-
gator approximating such dosage without a definite knowledge of the
size of the space inclosed and of the ratio of the number of cubic feet of
contents to the square feet of surface through which the gas gradually
escapes. This can be obtained only by actual measurements. The
only two dimensions which it is at all practicable to obtain are the
circumference of the tented tree at the base and the distance over the
top from ground to ground. The system here recommended will, by
insuring satisfactory results, prove the most economical for adoption

« The experimental work conducted in Florida during the winter of 1907-8 has
shown that the liability of injuring citrus trees from overdosingis frequently depend-
ent upon the physiological condition of the trees as affected by the nature of the
soil, the soil moisture, and the chemical fertilizers used in the' grove.

& Water-shrunk or its equivalent asregards tightness, li should be home in mind
thai mildew-proofing with tannin, etc., is not supposed to increase t ightness more than
does the normal shrinking.

MEASURING TREES. 31

by any citrus grower contemplating the use of fumigation for the
white fly, This has been thoroughly demonstrated by the experi-
mental work conducted in the winter of 1907-8, when, as has been

stated, approximately 4,000 trees were fumigated.

Methods followed in experimental work. — The measurements of

tented trees in the experiments conducted in January and February,
1907, were made by means of a tape measure attached to a reel. In
obtaining the distance over in each case the end of the tape was held
in one hand while the reel was thrown over the center of the tent and
the measurement made from ground to ground. For the purposes of
the experiments, accuracy being desired as far as possible, measure-
ments were made in two directions, from east to west and from north to
south. In each case care was used to have the tape pass as nearly as
possible over the center of the tree regardless of the highest point. Of
72 tented trees measured in two directions, 70 per cent were found to
vary 12 inches or less in the two measurements, 15 per cent to vary
from 1 3 inches to 24 inches, and 1 1 per cent from 25 inches to 50 inches.
The average variation was 12 inches and the maximum 50 inches.
Inasmuch as it is recommended that in • using the table appended
hereto the number in the first column next above the actual measure-
ment (when the actual measurement is more than 6 inches above an
even number) be selected in estimating the dosage, it is evident that in
nearly all cases a measurement over the top of the tented tree in one
direction, together with the circumference, wall show the dosage with
sufficient accuracy for practical purposes. A fumigator should, how-
ever, in using the table and knowing the measurement over in one
direction, make allowances in case the irregular shape of the tree
makes the single measurement over the top fall short of indicating the
true size.

A new scheme for obtaining measurements. — The measuring of the
tented tree by means of the tape, as described, requires two men,
owing to the difficulty of getting the tape over the center of the
tree. Ordinarily it requires only one or two minutes at the most to
obtain these measurements, but when more than a few trees are to be
treated a simpler and quicker process is necessary. One man can
quickly obtain the circumference by using a tape provided at the end
with means for attaching to the tent, while he walks once around the
tree to the starting point, unreeling the tape as needed. For attach-
ing the tape to the tent some form of metal clamp, such as is usually
found in stock at gentlemen's furnishing stores, is suggested. In
fumigating on a large scale the use of a tape causes considerable
trouble, owing to unavoidable tangling and misplacing, especially
when used at night. One of the operators, however, should always
estimate the circumference of the tented tree by pacing. This cannot
be done with sufficient accuracy without considerable preliminary
49918— Bull. 76— 08 3

H2

FUMIGATION FOK THE CITRUS WHITE FLY

experience — obtained l>v measuring the first ten or fifteen trees
covered, both with the tape and by pacing, and comparing the
results. In pacing, the actual distance traveled will of course always
be greater than the circumference as measured by the tape. With a
little experience the proper allowance can be estimated with sufficient
accuracy.

For obtaining the distance over the top of the tented tree the author
has devised a plan which will so simplify the careful estimation of
dosage in conjunction with tables such as the one presented in the
appendix that a far greater uniformity of results and important sav-
ing of materials will
follow its adoption.
This method consists
in marking the tent
as shown in figures 6
and 7 and in Plate
VII. The tent isfirst
t hor oughly w a t e r -
shrunk, after which
from one to three en-
tire conspicuous lines
are painted length-
wise of the tent for
the length of the
full-length strips,
and one line at right
angles to longitudi-
nal line or lines.

For bell tents and
sheet tents up to
about 35 feet in di-
ameter, one line
running lengthwise
of the strips will be
sufficient, although
three are preferable.
For larger sheet tents three lines should always be made. The tent
may be water-shrunk, if not already so, by allowing it to become
wet with dew or other means, after which it should be thoroughly
dried in the sun. The entire tent, or at least the central section
of full-length strips, is spread flat on the ground, and the middle
strip with the proper location for a median line is located. This
line should be painted with a good quality of black paint a (flexible
paint preferable) about 2\ or 3 inches wide. If three lines are

j.

A

e

c

/

8

1

8

T 8

1 \

/

^

I

I

1 <L

1 N

/

9

I

9

1 9

1

/

S

i

S

1 £

1

\

/

*

I

V

1 V

1

\

/

e

i

£

i e

1

\

z

i

Z

1 z

1

D

|_L_|_|_|_|_

-

CNJicOC'd-l'OiVOiKicOi

lODlNIOMCnl-MaJ

to

-l-l-l-

-l-l-l-l

I

2

i

2 1

2

k

i

I

3

4

1

1

3 1

4 1

3
4

\^

I

5

1

5 1

5

\.

l

6

1

6 1

6

\.

i

7

T

7 1

7 y

\

I

8

i

8 1

8 /

ABC

Fig. 6.— Diagram showing method of marking tents to aid in obtaining
dimensions of inclosed space when covering tree: A A, BB, CC, par-
allel lines painted lengthwise with the strips of cloth from one "end"
of the tent to the other; DD, cross-line passing through center of
tent at right angles to other three. [Figures on lines AA, BB, and
CC represent the distances in feet from the line DD and figures on
DD represent distances from line BB. For the purposes of the dia-
gram these distances are not proportional to the size of the tent.]
(Original.)

a Paints containing linseed nil should be avoided.

Bui. 76, Bureau of Entomology. U. S. Dept. of Agriculture.

Plate VII.

MEASURING I R] ES.

83

Deeded, another one is painted on each side of this line ai a
distance of about :>() inches For tents 60 feel or less in diameter

and from 12 to 48 inches for tents of larger size. These two lines

should not be more than l inch is width, so thai they can be

readily distinguished from the wider median line. The cx-,\c\ cen-
ter o\' the tent is now located by measurement on the median line
and the corresponding points on the two outside lines are marked.
Taking into consideration the smallest tree that the tent probably
will ever be used to cover, distances are measured on these three
lines, in both directions from the center, so that parallel lines about
I indies long, \ inch wide, and 1 foot apart can he made across
each longitudinal line, beginning 1 fool from the edge of the tent

FlG. 7. — Tent marked to aid in estimating dosage, in position for fumigation. (Adapted from

Marian.,

and making the lines in succession toward the center. After making
a given number of these cross lines on each longitudinal line, the
number in each case equal to the distance from the middle point to
the cross line is painted on with conspicuous figures. (PL III, figs.
3, 4, 5, and 6; PI. IV, fig. 1; PI. VII, figs. 1 and 2.) If properly
marked according to these directions, the corresponding cross lines
on the three parallel longitudinal lines should be marked with the
same number, as shown in figure 6. When the tent is exactly cen-
tered over a tree the reading at the ground on both sides of the tent
will be the same. Ordinarily, however, when the tent is so placed
that this line passes as nearly over the center of the tree as it is

34 FUMIGATION FOE THE CITRUS WHITE FLY.

possible to estimate, the readings will differ by 2 or 3 feet, often
more. As the tent should always be pulled lengthwise of the strips,
the central line will most often lie over the center of the tree, and
hence be most useful in obtaining the distance over from ground
to ground. Frequently, however, this measurement of the tented
tree can be best obtained by selecting for the purpose one or the
other of the outside lines. The distance over the top in all cases is
the sum of the two readings on the line selected. The fourth line,
painted at right angles to the three running lengthwise, passing
through the middle point of each, extending to the sides of the tent
and marked with the distances corresponding to those on the first
three lines, will be of advantage when a tree is so irregular in form
that one line passing over the center of the tree seems to fail to give
the measurement with sufficient accuracy. When it is necessary to
use this line the tent can be readily pulled directly forward or back-
ward whatever distance is necessary to bring this line as nearly as
possible over the center of the tree, leaving the longitudinal line
(previously selected as the one passing most nearly over the center)
in the same relative position as before. The average of the read-
ings on the two lines will give the desired dimension as nearly cor-
rect as is necessary. Measurements of a few such irregular trees
will assist the operator's judgment until his experience is sufficient
to enable him to estimate the allowance in ordinary cases when
necessary. The tables appended, however, give a margin above the
average requirements which will cover ordinary cases of variation
from the regular forms.

When a single longitudinal line is used on the smaller sized tents
this line can be readily brought to any desired position by pulling
sidewise on the tent, without the risk of damage by ripping at the
seams, as with the larger sizes. The lines, in addition to their use-
fulness in estimating the dosage, will be found of considerable assist-
ance in locating the catch rings, and in other ways, when handling
the tent.

Previously proposed schemes for marking tents to aid in estimating
dosage. — The idea of marking the tents to aid in determining the dose
is not a new one, for in California several years ago a tent was in-
vented which was marked with concentric rings, at each of which
a dose was indicated. This failed to take into consideration the
variation in circumference of tented trees whose distance over is the
same. Professor Woodworth has suggested a system of marking
tents, concerning which he says : a

It consists in making a series of parallel lines near two opposite edges of the tent,
which are so distanced from the center point that they shall correspond with the
dosage of a tree of the average shape. Upon these lines will be placed numerals,

a Bui. 152, Cal. Agr. Exp. Sta., p. 15.

METUOD «'l CT.N KHATINi; THE CAS. 35

indicating the dose, the circumference in yards (paces), and the difference (thai is,
the amount the dose must be varied) should the distance around be more or less
than the amount indicated for an average tent.

This suggestioD in regard to the marking of bents with the dosage

to obviate the use of printed tables seems to the writer to be of con-
siderable value under some circumstances. One objection to the use
of differentials in this manner is that the cubic capacity and dosage

does not increase in direct proportion to the increase in circumfer-
ence with a given distance4 over the top. To illustrate the method
of marking the tents with the dosage, when desired, a tent meas-
uring 30 feet over from ground to ground will serve as an example.

The tabic4 in the appendix shows that for every 5 feet of difference
in the measurement of the circumference of a tent measuring 30 feet
over the top. the amount of cyanid is increased or decreased one-
half ounce, or 0.1 ounce for each foot. With the figure 30 on the tent,
we would place the dosage of a tented tree measuring 30 feet in cir-
cumference. The dosage called for by the table for a tent of this
size (30 by 30) is 9\ ounces. Following this the differential, or 0.1
ounce, is placed. The entire directions for obtaining the dosage4
would read 30 — 94 — 0.1. A tented tree measuring 30 feet over and
38 feet in circumference would require 9-i ounces plus 0.8 ounce or,
for practical purposes, 10J ounces. If the measurement was 30 feet
over and 25 feet in circumference, the dosage would be 94 less 0.5
ounce, or 9 ounces.

When tables are worked out in detail, as they should be where
accurate1 work is desired, reference to them is undoubtedly by far
the quickest and safest method under ordinary circumstances.

METHOD OF GENERATING THE GAS.

In order to permit of making the measurements of tents and esti-
mating the dosage with the care hereafter recommended and with
the least possible delay, it is sometimes advisable, in operations on
a large scale, that the cyanid be weighed during the day or at other
times when it is not advisable to fumigate, or, if done at night, that
an additional helper be employed. Such a helper, in addition to
weighing the cvanid, might look after the replenishing of the stock
of cvanid and acid at the cart as needed and assist in measuring the
tents and emptying the generating jars. The cyanid should be
weighed up in lots of \, 1, 2, 5, 10, and 20 ounces, put into paper
bags of convenient size, and protected from dampness. When the
tented trees all measure less than 34 feet over the to]) from ground
to ground, the doses of 20 ounces each will not be required, and
when measuring more than this the lots of one-half ounce may be
dispensed with. At the cart, drag, or tray these bags of cyanid
should be kept in separate boxes, or in separate compartments of a

36 FUMIGATION FOR THE CITRUS WHITE FLY.

large box, and selected as needed to make up the proper dosage for
the trees as they are fumigated. It has been the writer's experi-
ence that the better plan is to weigh up the chemicals in the
field as fast as the dosage for the successive trees is determined.
Three times as many ounces of water (liquid measure) as of cyanid
is first poured into the jar. It is unnecessary to be exact in this
measurement, and a long-handled dipper of 16 ounces or 1 pint
capacity is preferable to the glass graduate. If, for example, 30 ounces
of water are required, two and one-fourth dipperfuls are poured into
the jar, dipping from the pail carried with the commissary tray. As
many ounces of acid as cyanid to be used is measured in the graduate,
being poured from one of the pitchers which are carried in one end
of the commissary tray (Plate IV, fig. 1).

Another member of the crew in the meantime arranges for the
proper dose of the cyanid and, with a lantern in hand when neces-
sary, raises the edge of the tent while the one who measures the acid
and water pours the acid into the jar containing the water, carries
the cyanid and generating j ar under the tent (Plate VII, fig. 2), and at
arm's length empties in the cyanid. The' jar should be placed about
halfway between the base of the tree and the edge of the tent. For
each 8 or 10 ounces of cyanid the generating jar should have a capacity
of 1 gallon. For very large seedling trees two 3-gallon, 4-gallon, or
even 5-gallon jars may sometimes be needed, while at other times one
3-gallon jar and one 2-gallon jar will be required for single trees,
although to avoid errors it is preferable to divide the dose evenly
between the jars when more than one are used. When two jars are
used, they should be placed one on each side of the tree. The
operator holds his breath, as soon as the cyanid is dropped into the
generator, and as soon as he is outside the edge of the tent is dropped
into place, while the violent boiling of the chemicals, as the gas is
generated, can be distinctly heard for several minutes. The cyanid
should be added as soon as possible after adding the acid, for the
heat evolved by the acid and water at the time of mixing is neces-
sary for the rapid generation of the gas. The man who measures the
acid and generates the gas should have his hands protected by loose-
fitting rubber gloves and should avoid being too close to the jar
when pouring in the acid. He should never touch the tent while
wearing the gloves unless they have been thoroughly rinsed in water.

WORK ROUTINE.

The systematic arrangement of the details of the procedure is of
great importance in fumigation. The plans of work vary consider-
ably with different fumigators, but it is the purpose in all cases to fol-
low Mich work routine1 as will keep all hands constantly employed.
In California from two to six men are employed in each outfit accord-

WORK ROUTINE, 87

ing to the size and number of the trees. For medium-sized trees
requiring tents not larger than ! l feei in diameter, five men can work
to advantage. This crew can handle 30 tents every forty-five
minutes and can treat from 350 to 400 trees in a night's work of ten
hours. For trees requiring Larger tents, which are shifted hy means of

Uprights, a crew of five or six men is needed to handle about 12 or 1 5

tents every forty-five minutes, or between LOO and L50 trees in a full

night's work. This rapidity is attained when the trees are regularly
set and properly spaced and when the schedules showing the dosage
for each tree to be fumigated are prepared during the day, or when the
dose Is based upon the judgment of the fumigator after the tent has
been placed in position. As has been stated, the plan of work com-
monly followed in California in treating scale insects, as far as the
estimation of dosage is concerned, can not he recommended for use
against the white1 fly in Florida. The method of estimating the
dosage herein recommended at the most affects the schemes of routine
previously followed in fumigating only by adding an extra man to
the crew. One1 man can calculate1 the dosage faster than two men can
weigh out the chemicals and generate the gas. The extra expense- of an
additional man is entirely negligible considering the increase in effi-
cieicy on the one hand and the check on unnecessary waste of the
chemicals on the other.

I itds of water should be placed during the day at convenient
points in the grove, as should also carboys or large jugs containing
tin .cid. The tents are taken to the end of the rows, unrolled, and
pla< ,l in position for covering the first trees. The cart with its sup-
ply <V acid and cyanid is located near the end of the row of tents, and
even thing is put in readiness to start work by sundown if the wind
is not m) strong as to interfere. Each man in the crew has definitely
assigned duties. The men who handle the poles or derricks are com-
monly mown in California as "tent pullers," or "tent men." These
men, w th their one or more assistants, proceed to pull each tent in
success] >n over the first treesof the row. If one tree should be missing,
the tent is left unused during the first period rather than to break the
line by moving it at once to the second tree. As each tree is covered,
each oneof the tent men, a ft er disconnecting his pole or derrick, walks
halfway tround the tent, pulling in the edges so that it will not
spread on. to inclose unnecessary space. A tent after being pulled
in at the bottom is shown in Plate VI. After reaching the end of the
row the tern men return to the eart or commissary tray and assist in
generating (he gas. As soon as the first tent is in position the fore-
man with a antern in hand, except when the light from the moon is
sufficient, notes the position of the tent with respect to the center of
the tree, using as guides the lines heretofore described. The reading
LS made where the selected line touches the ground.

88 FUMIGATION FOR THE CITRUS WHITE FLY.

He notes on the scratch pad the first reading and paces around the
tent, noting on the pad the reading on the opposite end of the selected
line. Upon reaching the starting point the distance over and the
circumference — as, for example, 38-44 — are noted at once upon the
diagram (fig. 3, D; figs. 4, 5). The dosage table is referred to and the
amount of cyanid to be given is noted in the diagram below the figures
noting the dimensions. The foreman or the man who determines
the amount of chemicals then assists in measuring and introducing
the chemicals, or if two other men are available for this work he pro-
ceeds to the next tree and determines the dosage as before.

The supply of water and chemicals for the set of tents is moved
ahead as fast as the generating of the gas is started under each tree.
The assistant, when working on the second set of trees, picks up the
generating jars beneath the first trees recently fumigated and midway
between the rows scoops out a hole with his foot or with a spade ana
buries the contents of the jar. The foreman should never trust anr
responsible part of the operation to an assistant whom he does not
know to be reliable. He should thoroughly systematize the work so
that no unnecessary hands will be employed while at the same time
his entire outfit of tents will be utilized to the best advantage.

ESTIMATION OF TIME REQUIRED FOR FUMIGATION OF GROVE.

When two men can conveniently shift the tents, they can eoV;»'..a
tree, take the measurements, and generate the gas without difficulty
in about five minutes when not hampered by irregularities in 'the
location of trees. This means that two men should be able to ha' idle
9 or 10 tents in forty-five minutes with the methods herein recom-
mended. Allowing fifteen minutes each hour for rest and restock-
ing of the commissary tray with chemicals, two men begiming
at 4 p. m. could fumigate about 75 trees by midnight. Tkrep men
in the same time could easily fumigate 100 or 115 trees somewhat
larger in size, or at the rate of 13 or 14 tents every hour. Four or five
men should be able to fumigate each hour from 20 to 25 trees as large
as can conveniently be covered by means of changing poles. When
uprights are used a crew of six men, or possibly in some casesas many
as eight, can work to best advantage. Such a crew shouLl handle
from 10 to 15 tents 50 feet in diameter, or larger, every hour, including
time for rest and restocking cart or tray with the chemicals

With three men attending to determining the dosage andgenerating
the gas and two men shifting t he tents, the trees being 1- to 15 feet
high, the author with other agents of the Bureau in experimental
work on one occasion fumigated 19 trees in thirty-live (oinutes. In
one night a crew of six men have fumigated 221 budded/trees varying
from 12 to 16 feet in height. In this case certain irregularities in
the plan of setting the grove prevented a much better record.

APPROXIMATING DIMENSIONS LND CUBIC CONTENTS. 39

In undertaking the Fumigation of a large grove the citrus growers
should avoid underestimating t ho hindrance to the work through winds
and rains. Fortunately during the season for Fumigating in Florida

there is comparatively lit i le rainfall in ordinary years. In the central
Section of Florida winds at night w ill ordinarily interfere very lit t le, hut
in sections Dear the coast interference from this source may be more
frequent. From the middle of December until the middle4 of Febru-
ary it is well to make allowance for an average of two nights each week
when Fumigation work will have to he suspended.

In fumigating seedling trees 30 feel or more in height one could
expect to fumigate from 300 to 400 trees a week with an outfit of s or K)
tents. En fumigating trees from 15to20fee1 high with an outfit of 20
tents one could expect to fumigate from 800 to 1 ,000 trees a week. In
the cases of both the large and the small trees these estimates can fre-
quently be exceeded when conditions are favorable, but as the period
for fumigating is so limited it is advisable to avoid underestimating
the time required to complete the fumigation of a grove. In plan-
ningfor the necessary equipment it is safe to calculate that with one
tent for each 100 trees the work of fumigation can be completed in
between ten and fourteen nights' work. In many cases it is neces-
sary to have two complete outfits at work in the same grove when
the work is started late in the season and there is danger of new
growth appearing on the trees before one outfit could finish the

METHODS OF COMPUTING APPROXIMATE DIMENSIONS AND
CUBIC CONTENTS.

The dosage recommended in the table given in the appendix is based
upon detailed records of 100 trees fumigated by the writer and his
assistants during January and February, 1907. Heretofore tables of
this kind have been based on the height and diameter of the trees,
with the exception of one prepared by Prof. C. W. Woodworth, who
firsl recommended a dosage system based on the dimensions of the
tented tree-. The two dimensions of practical importance are the
circumference and the distance over the top from ground to ground.
The method for obtaining these dimensions has been described. In
Professor Woodworth's table of dosage referred to above, the amount
of cyanid was directly proportional to the cubic contents. The table
of dosage here recommended is based upon actual experience and is,
as far as known to the writer, the first to take into consideration the
effect of leakage. Tented trees are always more or less irregular and
any attempt to calculate the volume of the space inclosed can give
only approximate figure-. A cylinder surmounted by a hemisphere
is the regular figure that is nearest to the form of a tented tree. The
leakage surf ace of a flal octagonal tent covering a tree obviously is not

40 FUMIGATION FOR THE CITRUS WHITE FLY.

the same as the surface area of such a figure, but rather the area of a
circle with a diameter equal to the distance over the top of the tent
from ground to ground. To a certain extent the folds in a tent when
in position over a tree reduce this surface, but this is a factor of little
consequence, as it i> present in all cases, and the portion of the tent
folded so a- to prevent all leakage represents only a small percentage of
the whole. For practical purposes, therefore, the leakage surface is
calculated from the mathematical formula o.l416 multiplied by the
square of the radius or 7tR2. The approximate height of the tented
tree can be calculated from the following formula, in which C repre-
sents the circumference of the tent at the base and O represents the

distance over the top : H = - 9 + 9 —'

The diameter is found by dividing the circumference by 3.141(3.
The height and diameter having been obtained, the cubic contents of
the regular figure mentioned can be calculated by the following for-
mula : 7tll2 I H — -5- )• The actual cubic inclosure of a tented tree will

obviously always be more or less smaller than the regular figure to
which this formula applies, although irregularities in shape will have
a tendency to counteract one another.

DOSAGE REQUIREMENTS FOR THE WHITE FLY.
EXPERIMENTS WITH SHEET TEXT.

Summary of results with regard to dosage. — In experiments to
determine the dosage requirements for the white fly when using
sheet tents, detailed records were made concerning each tree fumi-
gated during the first season's work,0 including every factor which
might influence the results. The main objects in view hi conducting
the experiments were to determine the minimum dosage require-
ments for destroying the white fly larvae and pupae, the rate of leakage
of the gas through the cloth, the effect of moisture on efficiency of the
treatment, the effect of the treatment upon the foliage under various
conditions of moisture, the margin as to dosage between effective
treatment for the insect and danger to the tree, and the effect of
different proportions of water and acid. Observations on other
points, such as effect of wind, sunlight, condition of foliage as
affected by drought, etc., were made as opportunity afforded. All
the experiments were conducted between January 12 and March
1, 1907, inclusive, but observations as to results were continued for
several weeks after the latter date. During this period practically

" The results of the experimental work during the winter of L907 8 substantiate the
conclusions derived from the work of the firsl season so far as the data up to this time
completed show.

DOSAGE REQUIREMENTS. 41

all the immature white flies were in the pupal stage. Of the many
thousands of specimens examined in the course of the experiments,
less than five were in earlier stages. The principal experiments
were conducted in the grove at the laboratory in Orlando. Fla.,
but cooperative experiments were conducted on a larger scale in an
extensive grove in the western portion of Orange County. The
detailed records concerning the efficiency of fumigation against
the white fly refer to experiments conducted at Orlando. A group
<>!* trees was selected for treatment on account of the comparative
abundance of the live insects. As it was considered desirable to
examine t ho insects both before and after treatment, leaves were
selected at various distances from the ground, and in various sections
of the tree, and the number of live and apparently normal pupae
was aoted on a tag which was left attached to each leaf. After
fumigation examinations were made at intervals of a lew days until
the appearance of the pupae on the tagged leaves showed, beyond
doubt, that the insects were dead or, if unaffected, • until the evidences
of normal vitality were unmistakable or the adult insects had emerged.

The acid used in the experiments, with the exception of experiments
Nos. 45.37, 60.21 , X.7, and X.8, was tested with a Beaume hydrometer
and found to be 66°, as guaranteed by the manufacturers. The
potassium cyanid was guaranteed to be 99 per cent pure. A sample
was analyzed in the Bureau of Chemistry of the Department of
Agriculture and it was reported to contain 40.59 per cent cyanogen,
a little more than 0.5 of 1 per cent more than that theoretically
present in chemically pure potassium cyanid, the excess being due
to a trace of sodium cyanid.

As has been previously stated, the sheet tent used was made of the
brand of S-ounce duck which is most used in California for fumigat-
ing tents. The tent was untreated but was thoroughly shrunk by
exposure to heavy dews and therefore as tight as those ordinarily
used.

A system of numbering the experiments was adopted which
indicates the length of exposure and consecutive number of the tree
treated for the particular duration of time. The number before the
decimal point indicates this exposure for sixty minutes and less.
Exposures ranging from one and a half to three hours are indicated by
the letter X preceding the decimal point.

'Fable IV summarizes the data based upon the experiments of
January and February, 1907, concerning dosage for the white fly,
including for convenience the dosage called for by the tables found in
the appendix.

42

FUMIGATION FOR THE CITRUS WHITE FLY.

Table IV. — Summary of dosagt experiments uith sheet tent constructed of S-ounce duck.

Measurements of

Amount of

tented tree.

cyanid

recom-

Experi-
ment No.

Amount of

Per cent of

mended in

cyanid

white flies

table friven

Distance

( in- n infer-

used.

destroyed.

in appen-

over.

ence.

dix; 45
minutes'
exposure.

Feet.

Feet.

Ounces.

Ounces.

20.1

45

57

16*

91.9

-•

30. 1

50

60

7

31

35}

30.2

44

584

11

66

28

30.4

47

62"

18

92

33

30.5

39

50

16*

98.6

20

30.6

46

56

20

71

29

30.7

40*

56

30

100

24

30.8

38

48

251

100

18*

40.1

44

53

5

31

254

40.2

m

59

10

84

26

40.3

42\

60

15

85

27

40.4

45

56

21

80

28*

40.6

39

54

17*

88

21

40.8

444

58*

17J

97

29*

40.9

431

56

12

93

27

40.10

38

46

134

95.7

17*

40.11

45*

63

25"

99.2

32*

40.12

51*

64

30§

98.4

41*

40.13

444

57

24

100

28

40.14

43*

54

26 i

100

26

40.15

37"

48

21

100

18

40.18

43

54

32

100

25

40.20

43

60

32

100

27

40.21

474.

56

38

100

31

45.1

37

47

21

100

17*

45.3

47

51*

22

99.5

28

45.4

45

57*

23

100

28

45.5

464

604

26*

98.9

32

45.6

43*

56"

22*

100

26*

4.'). 7

50*

56

36

100

34

45.8

44i

58

27

100

28

45.9

364

48

21

100

17

45.10

45*

67

35

100

34

45.12

344

43

15|

100

14

45.13

314

38

in

100

11*

45.15

404

50

26i

+99. 6(?)

21

45. 17

37"

45

21

100

164

45.19

314

39

14}

100

Hi

45. 20

33

50

12*

99.5

15

45.21

31

42

9

89.3

11

45.22

38

46

13f

99.8

IS

45.23

464

56

294

100

294

45.24

34|

47

154

100

15

45.25

484

57

334

100

32

45.26

33

46

13"

100

14

45.27

464

65

364

+99. 7(?)

34

45.28

46*

50

244

99.5

-

45.30

294

30

6"

100

9*

45.33

:^V.

36

10

100

14

45.34

40*

44

21

100

194

45.35

40*

47

20

100

194

45.36

45

50

204

97.7

25"

45.37

35

50

19j

92

16* i

50.1

44

58

23

66

28

50.2

394

46*

28

100

19

50.5

52"

56

37

100

354

60.1

51

60*

30*

98.6

38

60.2

43

56

22

100

26*

60.4

44*

58

234

100

29

60.5

384

50

16*

100

20

60.6

33*

38

8*

97

13

60.7

38*

56

18

94

22"

60.19

41*

584

27

100

26*

60.20

29

374

8*

66

L0

60.21

41

55"

25

97.6

24

X.l

43*

56

-_

?

26*

X.3

47|

54

>.

99.6

30

X. 4

34

49

15

99.8

l.V.

x .:.

47*

54

24*

99.7

30

X 6

45*

53

171

98.8

27*

X.7

49

62

40

«99.8

37

X .8

524

64

35*

f'94

42

a One pupa apparently alive 24 days after fumieatint:: 7:n dead.
'- 200 examined : 188killed, 12 alive.

DOSAGE REQUIRED l-.\ I B.

48

Deductioris concerning effectivi dosage. In formulating a definite
table of dosage requirements from the above experiments the most
significant results are (hose in which the amount of cyanid used was
sufficient to destroy all but a very small percentage of the insects.
Table Vgives more complete data concerning the foregoing experi-
ments, in which from 95 to 99.9 per ccn! of the insects were killed;
also, for comparison, it gives the dosage called for by tables pre-
pared by t he author.

Table V. Data concerning dosage in those experiments in which 95 to 99.9 per cent of

white flies were destroyed.

Measurement a

of tented 1 pee.

Approx-

Experi-
ment

No.

imate

Dis

Cir-

capacity

oi in

tance

cumfer

closed

over.

ence.

space.

Feet.

Feet.

Ou. ft.

30.5

:,(i

2, lis

■in. in

18

46

2.080

in. 8

:■

58j

;;.:,si

li >. ll

63

4,290

40. 12

514

.a

5,338

15.20

33

50

1 . 862

15. 22

as

46

2.0S0

45

50

3,046

4.".. 28

46 J

50

3,194

4.".. :,

till'.

4.238

4:.. 3

47

50*

3,397

33*

38

1.297

6a 21

41"

55

3,027

BO. 1

51

60*

4,867

6X.4

34

40"

1.890

■X. 1

43*

56

3.412

i rfX.H

a

53

3.272

«X. 5

54

3.713

;x. 3

m

54

3,713

Approx-
imate

leakage
surface

Sq.ft.

1.II7.".
1,134
1,554
1,625
2,082
855
1,134
1,590
1,697

1,'734

881
1.320
2, 042

908
1,485
1,625
1.771
1,771

Ratio of

leakage

Amount

surface

cyanid

to cubic

use.!.

contents.

Ov/nces.

L:2.28

Hi',

1:1. 83

13*

1:2.30

m

1:2.65

25

1:2.56

30?

1:2. 17

12*

1:1.83

13*

1:1.88

20*

1:1.88

24',

1:2.49

26*

L:l. 95

22

1:1.47

8*

1:2.29

1:2.38

30*

1:2.08

15

1:2.29

22*

1:2.01

17*

1:2.09

24*

1:2.09

28*

Rate:
Number
cubic feel

per ounce

cyanid.

lis
1 54
207
171
171
I 40
154
lis
130
160
154
152
121
160
126
156

IS'I

151
130

\moiinl

Kale:

c\ anid

Number

recom-

cubic i <•«■ t.

mended

per ounce

in table

cyanid

given in

recom-

appendix

mended.

Ounces.

20

122

171-

119

29

123

32*

131

41

130

15

124

17*

119

25

122

26*

120

32

132

28

121

13

Kin

24

126

38

128

15*

122

26*

129

27*

110

30

123

30

\i:\

a One of several trees fumigated on night of March 1, 1907. Unsatisfactory results supposed to be due
to poor quality of acid.
6 Exposure, l hour and 45 minutes,
e Exposure, 2 hours and 50 minutes.
d Exposure, 1 hour and 30 minutes.
e Exposure, l hour and 35 minutes.
/Exposure, 1 hour and 55 minutes.

For purposes of comparison with Table V, the data on the dosage
experiments in which all of the insects were believed to have been
killed in forty-five-minute exposures are given in Table VI, which,
like the preceding, includes the rate and amount of dosage calculated

according to the dosage recommendations hereinafter given.

44

FUMIGATION FOR THE CITRUS WHITE FLY.

Table VI. — Data concerning dosage in those experiments in which 100 per cent of white

' Jties were destroyed.

Experi-
ment

No.
(series

45).

Measurements
of tented tree.

Approx-
imate

Approx-
imate
leakage
surface

Ratio of
leakage
surface

to cubic
contents.

Rate:

Number
cubic feet
per ounce

cyanid.

Amount

cyanid

Rate:

Number

Dis-
tance

over.

Cir-
cumfer-
ence.

capacity
of in-"
closed
space.

Amount

cyanid

recom-
mended

in table
given in
appendix

cubic feet

per ounce

cyanid

recom-
mended.

Feet.

Feet.

Cu. ft.

Sq.ft.

Ounces.

Ounces.

30

m

30

735

683

1:1. (is

6

118

9*

77

13

31

38

1,149

754

1:1. 52

11 1

100

11

1(14

19

31|

39

1,219

779

1:1.56

14*

84

11*

106

26

33

46

1,656

855

1:1. 93

13

127

14

118

33

34*

36

1,224

935

1:1.31

10

122

13

94

12

:uT.

43

1,620

935

L: 1. 73

I5f

103

14

116

24

34*

47

1,855

935

1:1.98

15*

119

15*

119

17

364

45*

1,888

1.043

1:1.81

21

90

17

111

9

;;.;■.

48

2,049

1,043

1:1.96

21

98

17

120

1

37

47

2,075

1,075

1:1.93

21

99

17

122

34

40

44

2,092

L.256

1:1.66

21

100

18*

113

35

40

47

2,341

1,256

1:1.86

20

117

20

117

6

43i

56

3,412

1,482

1:2.35

::

151

26|

129

8

44*

58

3.691

1.554

1:2.37

27"

136

2'.tT,

125

4

45"

57*

3,732

1.589

1:2.34

23

162

28*

131

10

45*

67

4,665

1.625

1:2.87

35

133

344

132

23

46*

56

3,556 •

1.697

1:2.15

29i

124

30"

118

25

48*

57

4,095

1.846

1:2.21

33^

122

33

124

7

50*

56

4,275

2,002

1:2.13

36

119

34

125

These tables show that with tents of 8-oimce duck and untreated
with paint or sizing there is little or no advantage in exposures of
more than 40 minutes. The results with exposures of 30 and 40
minutes compare favorably with those ranging from 45 minutes to
2 hours and 50 minutes. It is evident that the gas escapes rapidly
and that in the course of a period of 30 to 40 minutes at the most
the gas from a dosage of maximum utility is so diluted as to be
practically ineffective. On the other hand, the table shows con-
clusively that the experiments afford no justification for reducing the
dosage on account of lengthening the exposure from 45 to 60 minutes
or longer. Everything considered, the writer adopted the 40-minute
period of exposure as probably affording the greatest benefit from a
given amount of cyanid.

As an aid in determining the rates of dosage which could be safely
recommended for the various ratios of leakage surface to cubic eon-
tents, the experiments referred to in Table V were arranged in accord-
ance with the ratio, and in each case the writer estimated the amount
of potassium cyanid which it seemed evident would have been ample
for the destruction of all the insects. The degree of success obtained
with the amount of potassium cyanid actually used was taken into
consideration in estimating the amount needed. The data thus
arranged, together with calculations of the rate, or number of cubic
feet of space per ounce of potassium cyanid, are given in Table VII.

DOSAGE REQUIREMEH rS.
Table VII. Study of doaagt rates.

\:>

i: ktio of

\lllotlllt

Rate Number oubio

square feet

CJ :iliul BSl i-

(eel •■!"

space per

in leakage

Amount of

Percenl of

mated :is

ounce ol

yanid.

.surface to

cyanid

w hlte tin s

necessary

cubic feel

used.

deal royed.

for

Esl imated

of

successful

i ed.

;is

contents.

results.

necessarj .

0 liners.

Ouna 8.

i :2.6fi

'_'.")

<>'.>. 2

■ii

171

l.V.t

1:2.66

301

98. l

34

171

17.7

1:_*. 49

-V.!

98. 9

29

L60

IK,

1:2.38

30j

98.6

x\

L80

1 11

1:2.30

17;

97

20

•JUT

L79

1 : 2. 29

ok

97.6

28

127

L08

1 : 2. 28

1M

98.6

lit

1 is

128

1:2. 17

12 J

99. 7.

11

11'. t

133

1:2.09

•_'lT.

99. 7

27

l.M

138

U2.09

28J

99. 6

30

130

L24

1:2.08

1.")

99. s

L6

126

lis

1:2.01

17',

98.8

•jo

IS!)

L83

L:1.96

■ >■>

99.5

24

154

ill

1 : 1 . ss

24j

99.5

27

l.iii

IIS

1:1. ss

20l

97.7

•.'•I

lis

127

1:1. 83

13*

99.8

15

154

L38

1:1.83

i;u

95.7

17

l 16

L22

1:1. 17

Si

97

11

152

118

From a study of the data in the Table VII the writer concluded
that lor a ratio of 1:1.5 the cyanid should be used at a rate very
near to 1 ounce to 110 cubic feet of space. Owing to the fact that
in all cases tented trees include less inclosed space than would a
regular figure which for purposes of approximate calculations has
been considered as equivalent, this rate would be higher for a reg-
ularly shaped inclosure whose cubic contents could be definitely cal-
culated. Probably 1 ounce to 100 cubic feet of space is nearer the
actual rate which the experiments indicate is necessary with the ratio
mentioned. This, however, is of little consequence in dealing with
sheet tents, for only the comparative volumes and dosage rates for
trees of different dimensions are required for practical purposes.
Having decided upon the adoption of 1 ounce of potassium cyanid
per 1 10 cubic feet of space with the ratio of 1:1.5, calculations were
made for tents with different ratios up to 1:3.6. Professor Gossard
reports0 that 1 ounce to 170 cubic feet of space destroys all white
fly pupa1 in an air-tight fumigatorium. Considering that this rate
i- approximately correct, an equivalent rate for the volume inclosed
by a sheet tent covering a tree would be more than 170 cubic fed in
the ideal form of inclosure upon which the calculations are based.
Experiments numbered X.3 and X.4, however, show that a rate not
Less than 1 ounce for \H\ cubic feet of space should be used when
the ratio is 1 : 2. When the ratio is increased from 1:1.5 to I: infinity6
and the rate of dosage for this latter ratio is considered as 1 ounce

a Fla. Exp. Sta. Bui. 67, p. 652.

b It i< evident that if the aumbei of cubic feel of space were infinitely greater titan
the number <>i" square feel of leakage surface, the rate "t" dosage required for an air-
tight fumigatorium would be sufficient.

46

FUMIGATION FOR THE CITRUS WHITE FLY.

for 170 cubic feet of space, all of the rates are more or less greater
than those used in the experiments in which from 95 per cent to
99.9 per cent of the insects were killed. It is evident that the increase
in number of cubic feet per ounce of potassium cyanid from 110 to
170 must be calculated at a rate which is in direct proportion to the
percentage of increase in cubic contents. The method employed in
these calculations is shown in Table VIII, which gives the figures
with the ratios ranging from 1:1.0 up to 1:3.6.

Table VIII. — Rates of dosagi as affected by ratio of number of squart feet in surfact to
th number of cubic /'<< t m volunu .

Per cent

Number

Differ-
ence be-

Increase

Number

Differ-
ence be-

of in-

of cubic

tween

in num-
ber cubic
feet per

of i n-

of cubic

tween

in num-
ber cubic

Ratio.

crease in

feet per

number

Ratio.

crease in

number

cubic con-

ounce

cubic feet

cubic con-

ounce

cubic feel

tents.

cyanid.

per ounce
and 170.

ounce
cyanid.

1:2.4

tents.

cyanid.

per ounce

and 170.

ounce
cyanid.

1:1

------

76.8

93.2

....„„..

4.34

133.5

36.5

1.7

1:1.1

86.1

83.9

1:2.5

4.16

135

35

1.5

1:1.2

9.09

93.7

76.3

7.6

1:2.6

4

136.4

33. 6

1.4

1:1.3

8.33

100.1

69.9

6.4

1:2.7

3.85

137.7

32.3

1.3

1:1.4

7.69

105.4

64.6

5.3

1:2.8

3.7

138.9

31.1

1.2

1:1.5

7.14

110

60

4.6

1:2.9

3.6

140

30

1. 1

1:1.6

6.66

114

56

4

1:3.0

3.44

141

29

1.03

1:1.7

6.25

117.5

52.5

3.5

1:3.1

3.33

142

-N

.97

1:1.8

5.88

120.6

49.4

3.1

1:3.2

3.26

142.9

27.1

.91

1:1.9

5.55

123. 3

46.7

2.7

1:3.3

3.12

143.8

26

1:2.0

5.26

125.8

44.2

2.5

1:3.4

3.03

144.5

25.4

.79

1:2.1

5

128

42

2.2

1:3.5

2.94

145.3

24.7

.75

1:2.2

4.76

130

40

2

1:3.6

2.86

146

24

.71

1:2.3

4.54

131.8

38.2

1.8

In Table VIII the number of cubic feet of space per ounce of potas-
sium cyanid increases toward 170, representing the rate when the
ratio is 1 to infinity, and the dosage increases in rate (= decrease in
the number of cubic feet per ounce of potassium cyanid ) as the units
of cubic contents become infinitely small in number as compared
with the units of square measure of leakage surface. Using the
above rates as a basis, the doses for trees measuring from 10 to 76
feet over the top have been calculated. The dimensions of the tented
trees and volumes of the inclosed spaces have been calculated in
accordance with the formula? given in the preceding pages. Table IX
gives the original calculations, while in the appendix the recommended
doses alone are given, in a form more convenient for practical use in
the field.

DOSAGE REQUIREMENTS. 4?

Table IX. Recommended dosage, with ^5-w/inuU. exposures.

Measurements of

Heighl

Diameter

Ra1 '

tented trees.

of regular of regular

Ratio <>i

\ 1 IK Mill 1

viva Of

figure

ngure

leakage

number

of cyanid

leakage

with

Willi

Volume.

surface

cubic feel

Distance

Circum-
ference.

surface.

foregoing
measure

foregoing
measure-

i<> oubio
contents.

space per
ounce

I'l'CI l| II

mended.

over.

incuts.

ments.

cyanid

Feet.

Star, feet.

Feet.

Feet.

Cu. i>>t.

Ouna i.

10

12

16
20
L5

7s

78

113

3.0
3. 2
4.0

4.7

0. I

4.8

IS

69

Cm

L:0 61
1:0.89

1:0.57

1.0
1.0
2.(1

it

20

2i
2o

113

l.Vl

i.M
154

4. 2

5.1,

5. 2
4.7

... i

4.8

6.4
8.0

101

85
L33

171

1:0.89
L:0.55
1:0.86

1:1. 11

2.(1

2. 5
2. 5

'"*76"

it;

20

201

0.2

0.4

105

1:0.82

02

3.0

25

201

5. 7

8.0

221

1:1. 10

ss

3.0

30

201

5. 3

o. 5

270

L:l. 37

100

3.0

is

20

254

7.2

0.4

107

1:0.77

50

1.0

25

254

0.7

8.0

27!

1:1.00

71

4.0

30

254

0.3

9.5

347

1:1.36

1 1 12

l.(i

35

254

5. 8

11.1

406

1:1.00

11 1

4.0

20

20

314

8.2

0.4

220

1:0.73

54

1.2

25

314

7.7

8.0

321

1:1.02

4.2

30

314

7.3

9. 5

418

1:1.33

loo

4.2

35

314

o.s

11. 1

500

1:1.50

112

4.4

22

25

380

8.7

8.0

372

1:0.97

75

4.9

30

380

8.3

9.5

489

1:1.28

96

5.1

35

380

7.8

11. 1

594

1:1.50

111

5.3

40

380

7.4

12.7

670

1:1.78

118

5.9

24

30

452

9.3

0. 5

550

1:1.21

93

5.9

35

452

8.8

11. 1

688

1:1.52

110

6.2

40

452

• 8.4

12.7

797

1:1.70

117

6.8

4.")

452

7.9

14.3

927

1:2.05

128

7.2

26

30

531

10.3

9.5

621

1:1.17

89

7.0

35

531

9.8

11.1

782

1:1.47

107

7.3

40

531

9.4

12.7

924

1:1.74

118

7.8

45

531

8.9

14.3

1,046

1:1.97

124

8.4

28

30

615

11.3

9.5

692

1:1.12

86

8.1

35

615

10.8

11.1

876

1:1.42

105

8.3

40

615

10.4

12.7

1,051

1:1.70

117

8.9

45

615

9.9

14.3

1,206

1:1.96

124

9.7

30

30

707

12.3

9.5

763

1:1.08

80

9.0

35

707

11.8

11.1

970

1:1.37

100

9.7

40

707

11.4

12.7

1,178

1:1.66

114

10. 3

45

707

10.9

14.3

1.364

1:1.93

123

11. 1

32

30

804

13.3

9.5

834

1:1.03

79

10.5

35

804

12.8

11.1

1,067

1:1.32

100

10.7

40

804

12.4

12.7

1,305

1:1.02

114

11.4

4o

804

11.9

14.3

1,527

1:1.90

1 23

12.4

50

804

11.5

15.9

1, 750

1:2.17

129

13.6*

34

30

908

14.3

9.5

906

1 : 1. 00

7o

4.9

35

908

13.8

11.1

1,161

1:1.28

95

12.0

40

908

13.4

12.7

1,433

1:1.58

112

12.8

45

908

12.9

14.3

1,684

1:1.85

121

13.9

50

908

12.5

15.9

1,951

1:2.14

128

15.2

3G

35

1,018

14.8

11.1

1,265

1:1.24

95

13.3

40

1,018

14.4

12.7

1,560

1:1.53

110

14.2

45

1,018

13.9

14.3

1,844

1:1.81

120

15.3

50

1,018

13.4

15.9

2,149

1:2.11

128

10.7

55

1,018

13. 0

17.5

2,428

1:2.38

132

18.4

38

35

1,134

15.8

11.1

1,360

1:1.20

93

1 1.0

40

1,134

15. 4

12.7

1,688

1:1.48

107

L5.7

45

1.134

14.9

14.3

2,005

1:1.76

118

17.0

50

1.134

14.4

15.0

2.:: is

1:2.07

120

18.7

55

1,134

14.0

17. 5

2.00S

1:2.35

132

2D. 2

40

40

1,256

10.4

12.7

1,816

1:1.44

100

17.0

45

1.250

15.0

14.3

2,165

1:1.72

117

1 8. 5

50

1,256

15.4

15.lt

2.. MO

1:2.02

125

20.3

55

1.250

15.0

1 7. 5

2,909

L.-2.31

131

00

1.250

1 1. 5

10. 1

3.250

l 2 59

135

21. 1

42

40

1 . 385

17.4

12.7

1,943

1:1.40

1(15

1 8. 5

45

1 . 385

it;.!)

14.3

2,326

1:1.68

115

20.2

50

1 . 385

10.4

15.9

2,745

1:1.98

121

22. 1

:..-.

I . :',x5

16.0

17.5

3,149

1:2.27

130

24.2

60

1 . 385

15.5

19.1

3,542

1:2.55

L35

26.2

44

45

1 . 520

17.9

14.3

2, 186

1:1. OS

II I

21.8

50

1,520

17.4

15.0

2.011

1:1. 93

123

23. 0

.",.-,

1.520

17.0

17.5

3.3S0

1:2.22

130

26.1

60

1.520

10.5

10. 1

:',. sin

1:2.52

L35

28.3

66

1,520

16.1

20.7

4,254

1:2. so

L38

30. B

49918— Bull. 76— 08-

48 FUMIGATION FOR THE CITRUS WHITE FLY.

Table IX. -Recommended dosage, with 45-minute exposures — Continued.

Measurements of

Height

Diameter

Rate of

tented trees.

of regular of regular

Ratio of

dosage.

Amount

of cyanid

Area of

figure

figure

leakage

number

leakage

with

with

Volume.

surface

cubic feet

Distance.

over.

Circum-
ference.

surface.

foregoing
measure-
ments.

foregoing
measure-
ments.

to cubic

contents.

space per
ounce
cyanid.

recom-
mended.

Feet.

Feet.

Sq. feet.

Feet.

Feet.

Cu.feet.

Ounces.

46

50

L, 61 12

18.4

15.9

3,133

1:1.88

121

25. y

55

1.662

17.9

17.5

3.(130

1:2.18

129

28.1

60

1,662

17.5

19.1

4,115

1:2.47

134

30.7

65

1,662

17.0

20.7

4,591

1:2.76

138

33.2

70

1,662

16.6

22.3

5,038

1:3.03

141

35. 7

48

50

1,810

19.4

15. 9

3. 332

1:1.84

121

27. 5

55

1,810

18.9

17.5

3,870

1:2.13

128

30.2

60

1,810

18.5

19.1

4,401

1:2.43

133

33. 1

65

1,810

18.0

20.7

4,927

1:2.72

137

35.9

70

1,810

17. 6

22.3

5,428

1:3.00

141

38.5

50

55

1,964

19.9

17.5

4.111

1:2.09

127

32. 4

60

1,964

19.5

19.1

4,687

1:2.38

132

35. 5

65

1,964

19.0

20.7

5, 264

1:2.63

13(1

38.7

70

1,964

18.6

22.3

5,828

1:2.96

140

41.6

75

1,964

18.2

23.9

6,358

1:3.24

142

44.7

52

55

2,123

20.9

17.5

4, 351

1:2.05

126

34. 5

60

2,123

20.5

19.1

4,974

1:2.34

132

37.6

65

2,123

20.0

20.7

5.600

1:2.63

136

41.1

70

2,123

19.6

22.3

6,217

1:2.92

140

44.4

75

2,123

19.2

23.9

1,. Ml.",

1:3.20

142

47.9

54

55

2,289

21.9

17.5

4,591

1:2.00

125

3d. 7

60

2,289

21.5

19.1

5,261

1:2.30

131

40.1 !

65

2,289

21.0

20.7

5, 936

1:2.60

136

43.6

70

2,289

20.6

22.3

6,607

1:2.88

138

47.8

75

2,289

20.2

23.9

7,252

1:3.16

142

51.1 ,

56

60

2,462

22.5

19.1

5,547

1:2.25

130

42.6 |

65

2,462

22.0

20.7

6,273

1:2.54

135

46.4

70

2,462

21.6

22.3

6,997

1:2.84

138

50.7

75

2,462

21.2

23.9

7,700

1:3.12

142

54.2

80

2,462

20.8

2.5.5

8,459

1:3.43

144

5S. 7

58

60

2V641

23.5

19.1

5.834

1:2.20

130

44.8

65

2,641

23.0

20.7

6,609

1:2.50

135

48.8

70

2.641

22.6

22.3

7. 396

1:2.80

138

53.6

75

2,641

22.2

23.9

8,147

1:3.09

141

57. 7

80

2,641

21. S

25.5

8,971

1:3.39

144

62.3

60

60

2,826

24.5

19.1

6,120

1:2.16

128

47.8

65

2.826

24.0

20.7

6, 945

1:2.45

134

51.8

70

2,826

23.6

22.3

7,786

1:2.75

138

56.4

75

2,826

23.2

23.9

8,595

1:3.04

141

60.9

80

L'.SL'ti

22.8

25. 5

9, 483

1:3.35

144

65. 4

62

60

3,018

25.5

19.1

6. 406

1:2. 12

128

50.0

65

3.018

25.0

20.7

7,282

1:2.-11

133

54. 7

70

3.018

24.6

22.3

8,176

1:2.71

137

.V.I. 0

75

3,018

24.2

23.9

9,042

1:3.00

141

64. 1

80

3,018

23.8

25. 5

9,995

1:3.31

143

69 2

64

60

3.215

26.5

19.1

6. 693

1:2.08

126

53: i

65

3, 215

26.0

20.7

7,618

1:2.37

132

57. 7

70

3. 215

25.6

22.3

8. 565

1:2.66

136

63.0

75

3. 215

25.2

23.9

9.4S9

1:2.95

140

67. 7

80

3,215

24.8

25. 5

10,507

1:3.2(1

143

73. 4

66

60

3,419

27. 5

19. 1

6,979

1:2.04

12(1

55. 4

65

3,419

27.0

20.7

7.955

1:2.33

131

60.7

70

3,419

26.6

22.3

8,955

1:2.61

134

66. 8

75

3,419

26.2

23.9

9.937

1:2.90

140

70.9

80

3.419

25.8

25. 5

11.019

1:3.22

142

77.(1

85

3,419

25.3

27.1

11.939

1:3.49

144

82. 9

68

60

3, 630

28.5

19.1

7,266

1:2 "ii

125

58.1

65

3, 630

28.0

20.7

8,290

1:2.28

130

63. ;

70

3,630

27.6

22.3

9, 345

1:2.57

135

69.2

75

3. 630

27.2

23.9

I0..--M

1:2.86

139

74. 6

80

3, 630

26. 8

2.5.5

11.531

1:3.17

142

81. 1

85 ■

3,630

26.3

27.1

12.513

1:3.45

144

87. 5

70

60

3,848

29.5

19.1

7,552

1:1.9(1

123

-1. 1

65

3. sis

29.0

20.7

8,627

1:2.24

130

(1(1. 3

70

3,848

28.6

22.3

9, 731

1 :2.5a

135

72. 1

75

3,848

28.2

23.9

10,831

1:2.81

138

7s. :,

80

3,848

27.8

25. 5

12,043

1:3.10

142

84.8

85

3,848

27.3

27. 1

13,088

1:3.40

144

90.9

72

60

1,069

30.5

19.1

7,838

1:1.92

123

63.7

65

4.069

30.0

20.7

8,963

1:2.20

130

68.9

70

1,069

29.6

22. 3

in. 12 1

1:2.49

131

75. 5

75

1,069

29.2

23.9

1 1 . 278

1:2.77

137

82. 3

80

4,069

28.8

25. 5

12,555

i::: 08

ill

89.0

85

J, 069

28. 3

27.0

13,662

1:3.35

114

94.8

90

1,069

27. 8

28.6

L4,829

1:3.64

146

101.5

DOSAGE REQUIREMENTS.

49

Table IX. Recommended dosage, with 15-minute exposures Continued.

trements oi
tented I reea.

Distance

i\,t.

71

Circum-
ference.

F,,l.
60
65

70

80
85

<H>
t><)

65

70

7.".
SO

85

on

Area of
leakage
surface.

Beighl Diameter
o\ regularol regular

figure figure

wilh wiili

foregoing foregoing
measure- measure
aents.

incuts.

Sq. feet.

Feet.

1,299

31.5

1,299

81.0

4,299

3ft 6

1,299

30.2

4,299

29. 8

4,299

29. 3

4,299

2S. S

1,534

32. ."»

4,534

32 0

4,534

31.6

4,534

31,2

4,534

30. 8

1,534

30. 3

4,534

29.8

Feet.

i '.i. i

20. 7

22. 3

23. 9

L'7. (I
28.6
L9. 1
20.7
22 3
23. 9
25. 5
27.0
28.6

Volume

Cu. feet.

8, 125
9,300
10,513
11,726
13,067
14,237
15, 171
8, in
9,635
10,903
12. L73
13,579
14,812
It,. L13

Ratio <>i
leakage
Burface
to cubic
contents,

1.89

2. 18
2. 45
2. 72
3.03
3.31
3.60

1 . 85

2. 12
2. II)
2.66

2 99
3.26

3 55

Rate ol

fix j

cubic tasi "' '"'•"",|

Tsar -ssb

cyanld.

121
129
134
137
Ml
143
146
120
128
133
136
no
143
145

Oil II, ,

r.7. 1
71.3
78. I
85.6
92. 7
99. 5
106.0
70.0
7.-, •_>

82.0

89 i
07. 0
103.5

ill l

EXPERIMENTS WITH BELL OR HOOT TENT.

The boll or hoop tent used in these experiments was one constructed
of 6J-ounce drill of the brand most commonly used in California.
Owing to the form of the tent the leakage surface is far less in propor-
tion to the volume than in the sheet tent. The data concerning the
experiments and the recommended dosage based upon the experi-
ments with the sheet tent are given in Table X.

Table X. — Experiments in fumigation v:ith bell-shaped tent of 6\-ounee drill.

Measurements of

Amount of

Ex-

tented trees.

Amount of

Number of
white

Per cent of

cyanid

recom-

peri-
ment
No.

cyanid

flies un-

white (lies

mended in

Distance

Circumfer-

used.

der obser-

killed.

table for

over.

ence.

vation.

•4.1 minutes'

exposure.

Feet.

Feet.

Ounces.

Ounces.

30.3

2S!

35

4

555

88

9

40.5

27"

38

4

138

88

8*

40.7

33*

38

8*

132

80

13

40.10

20

23

4

300

100

•}',

40.17

2.5J

27

7

47G

100

7"

40.19

24"

20

4

209

100

5*

40.22

20

22

2

162

97.4

4*

45.2

28

29

7

427

100

8*

45. 1 1

20

31*

4*

284

100

1\

15. 1 i

31

35

■a

289

100

10*

45.16

27*

29

431

100

8*

45.18

27

34*

9}

595

LOO

8

45.29

29*

30

6

530

100

91

45.31

23

24

31

376

98.7

6

50.3

24*

31 J

4

128

97. 6

7

50.4

34*

37

8*

990

llll)

14

60.8

26

31

4*

42

85. 7

7j

X.2

33

35

11

200

LOO

121

In these experiments a dosage sufficient to destroy all pup?p was
used in eleven instances. The total amount of cyanid used in the
eleven experiments was 7<S:> ounces, whereas the doses recommended
in the tables, based upon the experiments with the sheet tents of
8-ounce duck, together amounted to 96 ounce's. The average of the
amounts used in the eleven tests was 7.2 as against 8.7 recommended

50 FUMIGATION FOR THE CITRUS WHITE FLY.

in the tables. It is evident from the results summarized in the fore-
going table that prolongation of the period of exposure beyond 40
minutes produces no noticeable increase in effectiveness. It is also
evident that the dosage recommended for use with sheet tents of
a good quality of 8-ounce duck is ample for bell tents of a good quality
of 6^-ounce drill. The smaller amount of leakage surface with bell
tents as compared with sheet tents may be entirely responsible for the
apparently wide margin between the recommended dosage and the
dosage actually required for efficiency, but it seems safe to conclude
that the 6^-ounce drill used in the bell tent held the gas approxi-
mately as well as the 8-ounce duck, the difference in leakage surface
considered.

MISCELLANEOUS EXPERIMENTS AND OBSERVATIONS.

APPEARANCE OF LARV.E AND PUP^E OF THE WHITE FLY WHEN DE-
STROYED BY FUMIGATION.

The opportunities for studying the efficiency of the gas against
citrus pests are far superior with the white fly as compared with
the true scale insects. While it requires considerable skill in the
examinations, the vital conditions of the larvae and pupae, both
before and after treatment, can be recognized with practical cer-
tainty without removing the specimens from the leaves. When in a
normal condition the insects in the stages mentioned appear green,
owing to their translucence, and paired yellowish spots, due to inter-
nal organs, are sometimes visible in the abdominal region. As the
pupa reaches maturity the reddish eyes of the adult become conspicuous
and the location of the developing adult wings is indicated by whitish
patches on either side of the body. T\ Tien destroyed by fumigation
with hydrocyanic-acid gas the larvae and pupae usually turn more or
less brownish in the course of a few days. This brownish discolora-
tion is most pronounced along the middle of the body. Frequently,
however, two or three weeks may elapse before they can be positively
determined as dead. In the first examinations made by the author,
pupae on fumigated trees were classed as alive, doubtful, and dead.
It was afterwards determined that in practically every case those
classed as doubtful were in reality dead. Examinations under a
compound microscope were found to be of some assistance at times,
but on the whole unsatisfactory. In such cases movements of the
internal organs furnish positive proof that the insect is alive, but
when these movements can not be detected there may still be doubt
concerning the condition of the specimen unless granulation or dis-
coloration of the body contents is evident. The most satisfactory
method of observing the results of fumigation is to examine the
insects with a hand lens of 1 or 1J inch focal distance without dis-

APPEAKANVK OF LARV2E AND IM I'.l. \\ 1 1 I . N DESTROYED.

51

turbing the insect or detaching the leaf from the tree. String tags
attached to leaves upon which are specimens classed as doubtful

will enable examinations of such specimens from time to time until

their condition is positively determined. A careful examination of
normal specimens and direct comparisons of these with those on
leaves of Fumigated trees will assist in the ready identification of the

dead insects.

DENSITY OF THE GAS AT VARIOUS HEIGHTS ABOVE THE GROUND.

It is natural to presume that owing to the fact that hydrocyanic-
acid gas is lighter than air, its density during the process of fumiga-
tion is greater toward the top of the tree. In four of the nine obser-
vations on the comparative effect of the gas at different heights
above ground the results of this variation in density are not evident.
In the other five observations the results are quite striking. In the
six experiments in which observations were made 10 feet or more
from the ground, the average percentage of insects killed up to 6
feet above the ground was 04, while from 10 to 18 feet above ground
the average percentage killed was 71. The data concerning the
effectiveness of the gas at various distances from the ground is sum-
marized in Table XL

Table XI. — Efficiency of gas as affected by height above ground.

Ex-
peri-

Distance
above
ground.

Number of
white fly

Per cent

Ex-
peri-

Distance

Number of
white fly

Per cent

ment
No.

pupae ex-
amined.

killed.

ment
No.

ground.

pupae ex-
amined.

killed.

Feet.

Feet.

30.4

4-G

427

89

30.1

4-0

74

21

14-15

244

98.3

12-14

909

36

18

120

100

40.3

4-6

822

80

20.1

4-fi

087

91.9

12-14

445

90.8

12-14

1,000

90.8

30.3

2

396

92.8

20.7

4-5i

222

77

3i-7

159

78

10

300

60

40.7

2

93

80.6

40.12

2
3§-5
4-6

112
728
541

64

98.4

26.4

4-0

139

79.2

14-10

136

50

The results show that when examining for the results of fumigation,
the most significant effects are those within a few feet of the ground.
The observations concerning the results of the experiments upon
which the recommendations in this bulletin are based were made in
all cases within 7 feet of the ground, and included examinations of
insects on leaves closest to the ground in all cases.

EFFECT OF FUMIGATION ON Tl IK TREES.

During the months of December, January, and February, until the
appearance of the new spring growth, fumigation for the white fly
with the dosage herein recommended will rarely occasion appreciable

52 FUMIGATION FOR THE CITRUS WHITE FLY.

injury to orange trees and apparently never to tangerine and grape-
fruit trees. The liability of injuring trees through the emptying of the
contents of the jars after fumigation close to or upon the base of the
trees will be referred to under the subject of precautions. The injury
to orange trees from the gas itself has never in the writer's experience
been sufficient to offset the benefits of destroying the white fly and
scale insect pests. Nevertheless the subject is one of considerable
importance. The experiments conducted in January and February,
1907, demonstrated the practicability of destroying the white fly
with hydrocyanic-acid gas without injury to citrus trees.

The fumigation of nearly 4,000 trees in the winter of 1907-8 has
greatly extended our knowledge of the effect of fumigation upon the
trees, but there remain several unsolved problems in this connection
which it is hoped will be elucidated by future experience. The work
of fumigating a grove should be completed if possible before the new
growth appears in the spring. Under certain temperature conditions
successful fumigations may occasion no injury to new growth, but
there is danger of destroying the first spring shoots which normally
produce the greater part of the blooms. When affected by the gas
new shoots wilt and turn dark, appearing as though affected by frost.

Under certain conditions there is more or less shedding of the old
leaves following fumigation. The loss of 10 or 15 per cent of the old
foliage can not be considered an injury, inasmuch as even more than
this proportion is usually shed during the winter or in the spring. In
fact, it has been demonstrated b}r experiments conducted by Mr.
Yothers and the writer in February, 1908, that the leaves shed by
fumigation when the percentage of the whole does not exceed 15 per
cent are among the leaves which would normally drop in the course
of a few wreeks.

In the experiments with the sheet tent of 8-ounce duck summarized
in Table IV, the most extensive shedding occurred in experiments
40.14. In this it was estimated that about 50 per cent of the leaves
were shed. The tree was fumigated on January 29, beginning at
4.07 p. m., about one-half hour before sunset. No shedding was
observed until the morning of February 2, when it was estimated that
from 15 to 20 per cent of the leaves dropped. On February 4 it was
estimated that 50 per cent of the leaves had fallen, after which date
the amount of the shedding was inappreciable. The winged petioles
of the leaves remained attached to the tree in most cases and the
fallen leaf blades showed distinct brownish areas due to burning by
the gas. The tree consisted of five steins growing from the roots of a
tree frozen to the ground in 1895. One of these stems was affected
by foot rot or mal-di-gomma , and the defoliation of this was nearly
complete, materially increasing the percentage of shedding from the

EFFECT OF PUM IGA DION <»N TREES. ,r).S

tree as a whole. This tree was observed in Full bloom od April 1, and
ten months after the treatment appeared as vigorous as any tree in
the grove and bore more than the average crop of fruit. In the
experiments with the bell tent of 6$-ounce drill, shedding of conse-
quence occurred only in the case of experiment X.2. This tree was
fumigated on January 29, beginning at 4.41 and ending at 7.50 p. m.
It was estimated that the shedding amounted to about 30 per cent
in tins case.

In experiment 45.36 the exposure began at 3.07 p. m. in bright sun-
Light with the temperature at 7.")° F. The tent had been in position
for thirty minutes preceding the introduction of the chemicals, and
the inside temperature was 4£° higher at the beginning than the out-
side temperature mentioned above. The tent was in direct sunlight
during the entire forty-five minutes of exposure, and doubtless the
inside temperature rose to S2J or 83°. As shown in Table IV, the
amount of potassium cyanid used was 4\ ounces less than the
amount recommended in the table given in the appendix. The
leaves were curled as a result of drought at the time of the fumiga-
tion and no shedding of leaves or injury of any kind to the tree could
be detected by subsequent examinations.

An overdose is indicated by the scorching of the foliage on entire
twigs. This is more likely to occur near the tops of the trees. In
such cases several twigs, each 6 inches or a foot in length, may be
entirely killed, the leaves, instead of dropping within a few days,
turning brown and remaining attached to the dead twig. This is
not necessarily accompanied by excessive shedding of the foliage.
The physiological condition of the trees seems to have a marked
effect on their liability to shed foliage, Vigorous trees are less
susceptible than weak, poorly nourished ones. Trees in the same
grove but growing under different conditions as regards the nature
of the soil and the amount of soil moisture showr differences in this
respect. In most groves trees will not shed leaves excessively if
the dosage is increased 25 per cent above the recommended amounts.
Frequently there will be no shedding at all following such a course.
In other citrus groves the recommended dose is as large as the trees
will stand without shedding to an injurious extent.

The likelihood of damaging citrus fruits by fumigation is such that
it is strongly advisable to pick the crop before starting to fumigate.
In January, 1908, many seedling trees were fumigated which held
from five to eight boxes of oranges per tree, without any injury
whatever following the treatment. In other cases a small percent-
age of the fruit developed sunken areas or "pits" which turned dark
and ruined the affected fruit for shipping purposes. Fumigation
in midwinter, using the dosage table given in the appendix, does not
seem to affect the fruit of Hart's Lake, Lamb's Summer, or Valencia

54 FUMIGATION FOR THE CITRUS WHITE ELY.

varieties. Grapefruits are slightly susceptible to this injury, while
tangerines appear not at all susceptible, although considerable shed-
ding of the fruit occurred in one instance when the recommended
dosage was doubled.

SUGGESTIONS FOR THE FUMIGATION OF SMALL TREES.

IN THE GROVE.

In discussing the style of fumigating tents desirable for use against
the white fly the author has referred to the advantages of the use of
box covers for small trees. In many cases complete defoliation of
the trees during the winter months would be the best method of
checking the pest, but fumigation is preferable under most circum-
stances. The dosage with box covers will depend upon the tightness
of the cloth used. It has been recommended that the cloth be made
as nearly air-tight as possible by means of paint, or that air-tight
oilcloth be used. The rate of dosage can be readily determined by
means of a series of tests, beginning with 1 ounce of potassium
cyanid for each 170 cubic feet of space (0.00588 ounce per cubic
foot) and decreasing the number of cubic feet per ounce 10 feet for
each experiment until the results are satisfactory and uniform. Xo
experiments have thus far been conducted by the author along these
lines, but it is expected that in the course of the investigations of
the white fly now under way in Florida this phase of white fly con-
trol will be given consideration.

IN THE NURSERY.

Several square yards, including many trees, can be covered in the
nursery by a single tent. If the cloth is unpainted, the dosage for a
first trial can be calculated by first determining the ratio of the leak-
age surface to the cubic contents and referring to Table VIII in this
bulletin, where the recommended rate of dosage will be found for the
various ratios. The results of the preliminary tests should be care-
fully observed before fumigating on a large scale, in order that the
rate of dosage may be adjusted to suit the tightness of the cloth used
as a cover.

NURSERY STOCK FOR SHIPMENT.

Prof. H. A. Gossard, formerly of the Florida experiment station,
has determined that in an air-tight fumigatorium 1 ounce of potas-
sium cyanid for each 170 cubic feet of space/' is sufficient to destroy all

« "One gram to 6 cubic feet of space," lie reports, "seemed sufficient to kill every-
thing, but to make the dose more certain 1 gram to 5f cubic feet was adopted as the
standard dose and has been repeatedly tried, always giving the uniform resull of kill-
ing all larvae pupa'' and adults." Bui. 67, Fla. Exp. Sta., p. 652. One ounce is
equal to 28.35 grams, from which it is calculated thai 1 gram for <i cubic feet of space
i- equal to 1 ounce for 170 cubic feet and 1 gram for 5} cubic feet is equal to 1 ounce
for 163 cubic feet.

NUIM.KY STOCK FOB SHIPMENT. 55

larvae and pupa1 of thr while fly. To destroy the eggs, however, he
found that a larger dose was necessary. The author fully concurs
with Professor Gossard in his recommendation to defoliate completely

all white fly infested nursery stock before shipping, and, as an extra
precaution, to fumigate. The almost invariable experience of Florida
nurserymen, however, shows that citrus trees should not he fumigated

with roots bare. The Fumigation is far less necessary than when the
insects concerned are true scale insects and are at t ached to the stems.
White flic's have never been known to reach maturity except on the
leaves, although eggs and crawling larvae may occasionally he found
on young growing shoots. It is safe to presume (hat there are no
unhatched eggs of the white fly on anything other than leaves and
young succulent growth of stems. When these are completely re-
moved there need he no fear that the pest will he carried by means
of the trees. The entire leaves, including the winged had' petioles,
must he removed, and when large shipments are concerned careful
attention must he given to this. A greater danger than the trees
themselves is found in the packing. This, as Professor Gossard
points out, might be a possible source of danger if infested citrus
leaves were allowed to get into the moss or other material used in
packing. The danger is, of course, slight, but should nevertheless
be borne in mind by shippers and buyers of nursery stock.

PRECAUTIONS.

As is customary in publications on entomology in which the use of
potassium cyanid is recommended in combating insect pests, atten-
tion is directed to the extremely poisonous nature of this substance.
There are on record no fatalities due to the use of potassium cyanid
a- an insect icicle against orchard pests, but this is because the danger
from careless use was well known and simple precautions were
observed. In weighing the doses it is recommended that the hands
he protected by leather gloves, and after starting the generation of
the gas the operator should avoid breathing until he is outside in the
open air. A slight choking sensation experienced when standing
close to the tents during the fumigation acts as a danger signal, and
one should not persist in remaining where4 the gas is dense enough to
produce this result. The acid should always be handled with great
care. In addition to precautions necessary for the safety of the
operators, care should betaken to avoid the scattering of small parti-
cles of the cyanid where fowls or other animals might become poisoned.
As this substance is readily soluble in water and is deliquescent, or
capable of liquefying through the absorption of moisture from the
aii-. -mall particles accidentally dropped soon disappear.

50

FUMIGATION FOR THE CITRUS WHITE FLY

Other precautions which it seems desirable to emphasize at this
time concern the avoidance of damage to the tents and trees. Tents
should never be dragged over the ground where the residue of the
jars has been poured out on the surface or where the material has
boiled over during the generation of the gas. The safest rule is to
avoid entirely the dragging of tents across sections of the grove
which have been recently fumigated. The residue or contents of the
jars after fumigating is very destructive to citrus trees if emptied
against the base of the trees. When emptied 3 feet or more from
the base of the trees there seems to be no danger whatever unless
roots are exposed, but to avoid all risk it is recommended that the
practice be adopted of burying the residue halfway between the rows,
as described under the subject of methods of procedure. Tents
should not be left during the day covering trees which are to be
fumigated at night, for the inside temperature is quite likely to be
raised to a point where the gas will cause excessive shedding of the
foliage.

EXPENSE OF FUMIGATION.

FOR EQUIPMENT.

The cost of the equipment, aside from the fumigating tents, is of
little importance. In procuring a set of tents one may either pur-
chase the material and arrange for the construction to be done by a
tentmaker according to directions, or the maker may provide the
material and furnish the tents according to specifications at regular
prices. It will be found advantageous to obtain quotations from sev-
eral tentmakers before placing an order. To give an idea of the
usual cost of fumigating tents in California, the following schedule
of prices recently quoted by a leading maker of fumigating tents in
that State is given:

Table XII. — Schedule of prices for sheet and bell fumigating tents.

Sheet tents, 8-ounce

Bell tents

6',-ounce

duck.

drill."

Diameter.

Price.

Dimensions.

Price.

Feet.

Feet.

17

$6.12

6 by 7

$2.66

24

12.24

8 by 9

4.55

30

18.90

6 bv 12

5.72

36

27.00

91 by 11

6.76

41

34.20

10.1, bv 14

9.10

43

41.40

12 by 15

13.00

45

43.74

48

47.70

52

59.40

55

65.70

64

86. K)

I OS! OF EQUIPMENT. 57

The cost of the sheet tents would be considerably reduced by the
use of one or two widths of 6^-ounce drill, sewed around the margin
as a skirt, as described under the subject of construction of fumigat-
ing tents. The difference between the cost of tent materials in Cali-
fornia and in eastern citrus-growing States, owing to the greater
distance of the former from the factories, should result in a reduction
i)i' from 2 to 5 per cent in the cost of an outfit ;it any point in the
( rulf States. In Florida theseason for rumigal ing against t he white fly
extends over from seven to ten weeks. During this time a fumigating
tent, used between thirty-five and fifty days on an average of eight
hours per day with forty-live4 minute4 exposures, would he used to
cover between 280 and 400 trees. A tent large enough to cover the
largest trees should ordinarily not cost over $110. It lias been
stated thai the tents used in the author's experiments in January
and February, 1007, have not deteriorated appreciably. With
proper care tents should last several seasons, whether untreated
or mildew-proofed. If such a tent as referred to above should he
used for only three seasons, and be used to cover only between 280
and 400 trees each season, the cost of the wear and tear of the tent
would amount to only from 9 to 12 cents per tree. Even taking into
consideration interest on the money invested, the cost per tree
would not exceed 15 cents. This is fully twice the cost of a tent
large enough to cover trees of average size.

In many cases it would not be advisable for an orange grower to
invest several hundred dollars in fumigating tents for his exclusive
use, although many with extensive groves would doubtless prefer
to do this. When possible individual ownership of an outfit is desir-
able. In some citrus fruit growing countries where fumigation is
practiced against scale insects several growers form a club and
-hare the cost of the fumigating outfit, which is left at the disposal
of each of the members in turn. Such a plan might be followed in
many eases in Florida. It is especially to be recommended where
several groves constitute a naturally isolated group, and cooperation
lias all the advantages of individual ownership of a single isolated
grove. A few citrus growers with a crop worth on an average $25,000
would not he put to unreasonable expense in the joint ownership of
an outfit costing SI, 200 or $1,500. The rapid growth of the idea of
orange growers' associations in Florida during the past few months
leads to the hope that a means is at hand for providing for systematic
campaigns against citrus pests. In some cases associations for this
purpose have already been organized. Fumigation by the contract
system, as it is now done to a large extent in California, may also
come into use in Florida. The plan which can he most strongly rec-
ommended is for the work to he done by the various counties. Each

58 FUMIGATION FOR THE CITRUS WHITE FLY.

county where the citrus-growing interests are of importance should
maintain an outfit of tents large enough for the needs of the orange
growers within its limits, and fumigation should be done at cost
under the direction of the county horticultural commission.

FOR CHEMICALS.

The principal item of expense in connection with fumigation is the
potassium cyanid. Fumigation was considered profitable in Cali-
fornia when this was sold in quantities for 65 cents per pound. At
present in lots of 100 pounds this can be procured for about 30 cents
per pound, while in ton lots the cost is from 20 to 23 cents per pound
in Florida. Sulphuric acid in iron drums containing about 1,500
pounds can be obtained for about 1J cents per pound. In carboys
containing about 200 pounds the cost is about 2 cents per pound.

FOR LABOR.

In California, labor is usually paid for by the hour. The fore-
man in charge of the outfit is generally paid about 40 cents per hour
and the remainder of the crew about 25 cents per hour. A crew of
seven men, which might be used to advantage with the method of
procedure herein recommended for use in fumigating for the white
fly, would cost SI 5.20 for a night's work of eight hours if wages were
paid at the above rates. These men could ordinarily handle from
10 to 15 tents of the largest sizes even' forty-five minutes and fumi-
gate 80 to 120 trees in eight or nine hours. If 80 trees were treated,
the cost for labor would be about 19 cents per tree. If smaller tents
were used and handled with changing poles, the same crew could
treat 200 trees in eight hours at a cost for labor averaging about 7\
cents per tree. If six men proved sufficient to do this work, the cost
for labor would be about 1 cent less per tree. In California contract-
ors charge from 4 to 1 2 cents per tree for covering trees which can be
covered without the use of the braced uprights or derricks. These
prices include from the contractor's standpoint: First, cost of labor;
second, cost of wear and tear on tents; third, a reasonable profit.
Contractor's prices stated above are exclusive of about 3 or 3\ cents
per pound usually allowed as payment for handling the cyanid, the
chemicals being furnished by the owner of the grove.

In estimating the expense for labor in fumigating a grove there
should be included, in addition to the labor in connection with cover-
ering the trees and generating the gas, an allowance for repairing
tents, hauling chemicals and water, and miscellaneous work. Tin's
ordinarily ranges from 1 to 4 cents per tree, according to size.

LOSSES PROM will II. ll.Y PREVENTED. 59

ECONOMY OF TREATMENT BY FUMIGATION.

LOSSES PREVEN III'.

bite Hy (figs. 8, 9) Is
grove, much benefit \\ ill

Fig. 8.— White fly (Aleyrodes citri) : a, Orange leaf, show-
ing infestation on under surface, natural size; b, egg;

c, same, with young insect emerging: <l. larval Insecl :
e, foot of same; /, larval antenna; g, scale like pupa;
h, pupa about to disclose adult insect : i, insecl escap-
ing from pupal shell; j, leg of newly emerged insect,
not yet straightened and hardened. All figures ex-
cept a greatly enlarged (rcengravcd from Rilej and
Howard).

Losses from tin irhih ////. When once tin

reduced to an inconsiderable quantity in

result from careful inspec-
tions and fumigations of sin-
gle trees, or groups of trees,
from time to time wherever
the insects are found to be
multiplying. This will greatly
delay the t ime when the mul-
tiplication o( the insects shall
have made a general treat-
ment again necessary. This
practice is followed in Califor-
nia in the control of various
scales. In wel 1-cared-for
groves, or where the county
horticultural commissioners
require it. scales are kept in
complete subjection by fumi-
gation and the appearance of
only a few live scales on a tree is considered a reason for fumigating
it and perhaps, also, surrounding trees as well, although these may
appear entirely free from the pest. The best results from fumiga-
tion are obtained when once the
various pests are brought under
control by continuing the prac-
tice as a preventive rather than
as a remedy. In other words,
when conditions for successful
fumigation for the white fly are
favorable or after they have
been made so/' fumigation can
be practiced with such success
that all damage from the white
fly will be obviated. When once
the practice has been adopted a
grov» er should not wait until the
foliage1 is blackened by the in-
sects before Fumigating the second time. It would be far more eco-
nomical to fumigate regularly once in two years, and prevent all
blackening of the foliage, than to fumigate once and wait until the fly

Pig. o.— White fly {Aleyrodes dtri): a, Winged male
insect . with enlarged view of terminal segments
;it /;.- r. dorsal view of winged female, with enlarge-
ments of ovipositor, bead, antenna, wing margin,
and leg al d, e,f, g, h,i. (Reduced from Riley and
BowardJ

a See discussion oi this subject, pp. 9-14.

60 FUMIGATION FOR THE CITRUS WHITE FLY.

had increased sufficiently to cause blackening of the foliage and

fruit before repeating the treatment.

The extent of the damage due to the white fly is difficult to estimate.
After supplementing his personal observation with direct information
and estimates on this point from more than 50 orange growers who
have had experience with the pest, the author would consider 50 per
cent a conservative estimate of the average annual loss in white-fly-
infested groves.

The consensus of opinion of the orange growers referred to is to
the effect that the reduction in the size of the crop alone amounts to
50 per cent or more, leaving out of consideration the loss through the
checking of the growth of trees, the retardation of ripening, the
expense of washing the fruit, and the impairment of its shipping
quality and flavor. In many cases the damage from the fly renders
citrus fruit growing unprofitable, although such losses are usually
unnecessary if proper care be given to cultivation and fertilization.
The beneficial effect of the fungous diseases of the white fly and the
economy of fumigation where the diseases are prevalent will be
discussed under another heading. The data at hand concerning the
cost of fumigation indicate that in most cases the expense would be
sustained by the increase in production if the losses of the white fly
were only 10 per cent, instead of the 50 or more as generally estimated.

Losses from scale insects. — In calculating the benefits derived from
fumigation, the effect of the treatment on other citrus pests is an
important consideration. Fortunately the high average of humidity
in the citrus-growing sections of the Gulf States results in the partial
control of scale-insect pests which would otherwise make direct
remedial measures necessary for profitable crops. The thoroughness
of this natural control varies greatly in different groves according to
local conditions. Fruit infested with the purple or the long scale is far
less valuable, as a rule, than is clean fruit. If such fruit is cleaned
before packing, the cost is usually from 10 to 15 cents per box. In
the markets scaly fruit in rare instances brings as much as fruit free
from scale, but ordinarily it brings from 25 to 75 cents less per box,
even after being cleaned by hand. If not cleaned it may fail to find
a market at any price. When handled by orange buyers and sold
upon the tree, even a small percentage of scaly fruit frequently
results in a considerable loss in selling value of the entire crop.

Direct information has been obtained from many orange growers
and shippers concerning the effect of scales upon the value of fruit.
The damage reported ranges from none at all to 26 per cent of the
total value of the crop. Ordinarily from 5 to 1 5 per cent of the crops
of oranges and grapefruit are sold as of an inferior grade owing to
infestation 1>\ the long and purple scales. One grower in Lee County
reported that last season (fruit shipped in December, 1906) he suffered
a loss of si ,500 on a crop of 1,000 boxes of oranges and 2,000 boxes of

LOSSES FROM SCALE INSECTS PREVENTED.

C)l

grapefruit. All of the grapefruit and 300 boxes of the oranges were

scraped by hand to remove the scale. 'Plus operation cost between s'-7.~>
and $300. The loss to the selling value of the oranges was about $225
and of the grapefruit about $1 ,000. Manj instances have come to the
writer's attention of Losses from scale amounting to 5 per cent of the total
value of the crop. In addition to direct losses of the kind noted above,
frequently more serious Losses are suffered as a result of the complete
destruction o( branches and weakening of the vitality of the trees by
the1 heavy incrustations of the scales upon the main branches or
trunks. The total damage from scales in Florida is usually too
small to make direct remedial measures profitable, but when this
damage can be to a Large extent obviated at the same time with that
of the white fly, the mat-
ter demands careful con-
sideration. It is the
writer's conviction that
in the cases of the ma-
jority of groves the de-
struction of the purple,
long, Florida red, and
other scale insects would
represent an increase
in profit which would
by itself offset the cost
of fumigation, leaving
as clear gain the ben-
efits derived from redu-
cing the numbers of the
white fly to a negligible
quantity.

The Florida n^\ scale
(Chrysomphalus ficus Ashm.) (fig. 10) is destroyed with a thorough-
ness near to absolute extermination by the same dosage which is
required for the white fly. This has been conclusively proved by the
experimental work conducted by the writer and Mr. W. W. Vothers
in January of the present year. Not infrequently in Florida the scale
insect referred to causes sufficient injury to make fumigation a very
profitable procedure against this insect alone, leaving out of consid-
eration the effect upon the other pests present.

The purple scale (Lepidosa plies beckii Newm.) (fig. 11) sometimes
called the "brown," '" oyster-shell/' or " hard " scale, is of greater eco-
nomic importance than the Florida red scale on account of its more
wide-spread distribution. The results in controlling this pest accom-
plished incidentally to work against I he white fly are most encouraging.
In the same grove where the effect of fumigation on the Florida red
scale was observed, the purple scale has been so abundant for years

Fig. 10.— Florida red scale (Chrysomphalus ficus): a, Leaves
covered with the male and female scales, natural size; /), newly
hatched insect with enlargements of ant enna and leg; <\d,e,f,
different stages in the development of the female insect . drawn
to the same scale; g, adult male scale, similarly enlarged.
(After Marlatt.)

62

FUMIGATION FOB THE CITRUS WHITE FLY.

that the owners' fruit-shipping records show annual losses from this
source amounting to between 15 and 20 cents per tree. Live scales
in all stages, particularly the egg and adult, were very abundant
before fumigating, but up to the 1st of June careful examinations of
thousands of leaves, twigs, and green fruits by Mr. Yothers and the
writer have not led to the finding of a single living specimen of this
>|>ecies in the section of the grove which was the most heavily
infested. At this season of the year there is usually no difficulty in
finding more or less abundant specimens of the spring brood of this
insect even where it was so scarce the previous season as to occasion
no appreciable damage to the crop.

COST OF FUMIGATION COMPARED WITH SPRAYING.

In Florida the average cost of spraying is between 2\ and 3 cents
per gallon of spray applied. When spraying is done with such effi-

Fig. 11.— Purple scale (Lepidosaphes beekii), showing different stages of female: o. Newly hatched larva:
b, same with first waxy secretion; c to/, different stages of growth: a. mature scale; //. same inverted,
showing eggs: i and ./'.half-grown and full-grown female insects removed from scale. All much enlarged
(after Marlatt).

ciency that blackening of the foliage and fruit by the sooty mold is pre-
vented, at least three applications per year, and usually four or more.
are necessary. The mechanical difficulties of spraying with as much
effectiveness as tins are so great as to make the results with ordinary
practices far inferior to those from fumigating. In fact the results
with sprays have with few exceptions been unsatisfactory in con-
trolling the white fly or preventing the blackening of the fruit and
foliage. In many cases this is largely a result of the character of the
labor which it is necessary to employ for such work. For the pur-
pose* of comparing spraying with fumigating in regard to cost, it may
be considered that three applications of sprays per year will control
the white fly in a satisfactory manner, although in actual practice
this is rarely accomplished unless drought or fungous diseases offer
material aid

FUMIGATION VERSUS SPRAYING. 68

The tented tree shown in PlateVI, figure 2, measured 12 feet over
the top from ground to ground and 59 feel in circumference.
According to the table given in the appendix a tree of this size
should be given 26 ounces of potassium cyanid. En covering a tree
of this size ordinary changing poles could be used instead of the up-
right shown in the illustration. The entire cost of fumigating the
tree for the white fly is estimated at 50 cents. This includes 36 cents
cost of potassium cyanid. 3 cents cost of acid. 6 cents cost of labor,
and 5 cents cost o'i wear and tear on t he tent . The tree shown at the
left o\' the tent in Plate VI, figure 2, measured I I feet over the top and
53 feet in circumference. According to the tables the tree requires 25 J
ounces o( potassium cyanid, the cost of fumigating therefore being
practically t ho same as for the first tree mentioned. Each of these
trees if sprayed would require six or seven gallons of liquid at each
application. Three applications in a year at the usual cost would be
from 45 to 63 cents as compared with 50 cents for fumigating. The
tree shown in Plate 1 measured, when tented. 33 feet over the top and
38 feet in circumference. A tree of this size requires 1 2 ounces of potas-
sium cyanid for effective fumigation. The total cost of one fumiga-
tion would be about 27 cents, including 16 cents as cost of potassium
cyanid. 6 cents as cost for labor, 1 cent as cost for acid, and 4 cent- for
wear and tear on the fumigating tent. A tree of this size would
require at least 3 gallons of spray at each application, and during the
year the cost for three applications would be from 22 to 27 cent-.

These data on the comparative cost of the two methods of control
show that the advantage of fumigation over spraying for the first year
is a matter of greater efficiency, except when more than three applica-
tions of spray are made, when fumigation is also less expensive.
Fumigation, however, in an isolated grove or under favorable condi-
tions as to location, when properly conducted would not require repeti-
tion for twoor more years. The best of spraying could not. unless aided
by abnormal climatic conditions, so reduce the white fly that the num-
ber of applications could be lessened the second year without interfer-
ing with the degree of success attainable by the practice. In two years
the cost of spraying the trees above referred to would double the cost
of one fumigation. In a series of five or more years spraying would
doubtless cost fully three times as much as would control by fumiga-
tion, the labor involved would be far greater, and the results far Less
satisfactory.

FUMIGATION VERSUS NATURAL CONTROL.

The present investigation of the white fly by the writer and his
associates covers all phases of t he subject . Due consideration is given

to all possible sources which give basis for the hope of effecting eco-
nomical control. The exposed con lition of the pest under considera-
tion, its vulnerability to attack by natural enemies, the high degree
of humidity in the citrus-growing region- of the Gulf State- which
49918 Bull. 76 08 5

04 FUMIGATION FOB THE CITRUS WHITE FLY.

favors the effectiveness of fungous and bacterial diseases, all give
basis for the hope that complete control by natural enemies will be
the eventual conclusion of the white-fly problem. A thoroughly
scientific and practical investigation, however, can not lead to Lasting
benefits if the conclusions represent merely desired results and are
unsupported by sufficient evidence and experience. While a great
deal has been learned concerning the fungous diseases of the white
fly, the present investigations of this Bureau have not thus far shown
that any method can be relied upon to materially assist nature in
controlling the pest to the point of preventing all or nearly all of its
injury. The dissemination of these diseases is readily accomplished
under certain favorable conditions, but how far artificial dissemina-
tion, at its best, with our present methods goes toward the successful
control of the white fly is still problematical.

Manatee County is the only large orange-growing district where the
fungous diseases have proved of much assistance. Data obtained
from many orange growers and personal observation by the writer
and other entomologists connected with the Bureau of Ento-
mology indicate that the fungi, without artifieal aid, reduce the
injury from the white fly about one-third. Undoubtedly without the
aid of these fungous friends the damage in Manatee County would
average more than 50 per cent. With this as a minimum estimate.
the average damage in Manatee County, allowing a benefit of one-
third from the fungi, amounts to 34 per cent. One year in three, it is
the experience of the growers in this county, the fungi have so
thoroughly cleaned up the pest that the fruit is clean and requires no
washing. The following year the insects are in the ascendency and
the fruit and foliage become blackened with sooty mold to as great
an extent as, can be observed anywhere in the State. This is due to the
fact that the fungi have diminished the white flies the previous year to a
point where they cease to flourish. Late in the second year, however,
with the fly abundant . the fungous enemies develop rapidly. The third
year the effect of the blackening of the foliage is apparent in a greatly
reduced crop, while during this year the fly is again reduced to a negligi-
ble quantity, permitting a good crop of fruit t<> set and remain clean
from sooty mold during the following season. The above is the usual
course followed in individual groves. Considering the county as a
whole in 1906, fully three-fourths of the groves were so free from sooty
mold as to require no washing of the fruit. It was generally con-
sidered that this condition had never before been equaled since the
white fly first obtained a foothold in this county. In one case, how-
ever, it was claimed by one of the leading orange growers that an
isolated grove had become practically clean through some unknown
agency, the prevailing fungous diseases not being present in sufficient
abundance1 to accomplish any noticeable result. Nevertheless, the
fungous enemies referred to were undoubtedly of prime importance

FUMIGATION VERSUS NATURAL CONTROL. 65

in producing the high degree of freedom from white-fly damage at-
tained in L906. Other conditions may have had minor influence.
As a natural consequence of the lack of abundant food for the fungous

parasites in 190b, the situation in 1907 showed a complete reversal,
with more than three-fourths of the groves thoroughly blackened by
Booty mold. It is not uncommon to find that individual groves vary
considerably from the average condition of the groves in the county
as a whole.

In the close vicinity of Fort Myers, in Lee County, the fungi have
reduced the numbers of the white fly to a greater extent than observed
at any Other place. The result of this is to cause a considerable
variation from the usual succession of predominance of host and
parasite, but in the course of a ten-year period the benefits from the
fungous diseases under natural conditions will evidently be little if
any greater than in Manatee County. In the town of Fort Myers the
condition^ are not comparable with those in large commercial groves.
In one such grove, however, located on the south side of the Caloosa-
hatchie River, nearly opposite Fort Myers, the fungous diseases have
proved more than ordinarily beneficial during the past two years.
Then1 is strong evidence even here that the white fly will regain its
usual abundance in the course of the present season unless artificial
methods of control are resorted to or experiments result in the dis-
covery of a more satisfactory method than is now known of artifi-
cially encouraging the growth and spread of the fungous enemies.

The writer's observations lead to the conclusion that in 99 per cent
of the groves in those localities where the fungous diseases are most
effective, for every dollar expended for well-conducted fumigation the
profits from the groves will be increased not less than $4, or at the
rate of 250 per cent on the investment. If the expense of fumi-
gation were doubled the adoption of this practice would still be
profitable, at least until such time as the natural enemies at hand can
be made more successful or new ones discovered to accomplish
effective control.

The spores and mycelium of the fungi are not affected by fumiga-
tion, as far as lias been determined thus far. In experiments in the
artificial dissemination of the brown and red fungous parasites the
results obtained were as satisfactory when the material was collected
from fumigated trees as when collected from those not fumigated.
Ordinarily this point is of lit tie importance, since successful fumigation
would always result in practically absolutely checking the further multi-
plication of the parasites through the destruction of the host insects.
The further multiplication of the fungous parasites following fumi-
gation is therefore an indication of ineffectiveness of the treatment
or of the increase in the numbers of the pest through migration from
untreated groves.

APPENDIX.
TABLE OF DOSAGE FOR THE CITRUS WHITE FLY.

The table of dosage herein given is based upon the author's experi-
ments conducted in January and February, 1907. The mathe-
matical calculations are tabulated and explained in the body of this
bulletin. The most important object of fumigation experiments
against the white fly has been the development of methods for the
practical utilization of the fumigation process in Florida and the
gaining of a knowledge concerning the dosage requirements. The
former subject has already been disposed of through the methods
herein described. The investigations concerning the latter subject
have resulted in placing fumigation for the white fly on a basis
whereby the process may be used against this insect with greater
economy, thoroughness, and certainty of results than at present it
can be used against any other species. Incidentally it should be
remarked that the dosage requirements for the white fly are greater
than for the Florida red scale and perhaps greater also than for
the purple scale. It is beyond the scope of these investigations to
determine the possibility of reducing the dosage below the white fly
standard without interfering with its efficiency against these other
pests. It is sufficient to know in most cases that the white fly dosage
is equal to the actual requirements for the pests of secondary impor-
tance. The dosage table here presented does not necessarily repre-
sent the exact amounts for greatest utility in the case of the different
sizes of trees. The extensive tests of the dosage table during the
past winter, when, as has been stated, nearly 4.000 trees were fumi-
gated under the direction of the agents of the Bureau of Entomology,
show the doses recommended to be very close1 to the aecessary
amounts with tents of equal tightness with those used in the original
experiments. The dosage should never be decreased when effective
work against the white fly is desired, hut under certain conditions it
may be increased from 10 to 25 per cent with advantage.

If there i> a slight breeze of sufficient strength to make the advisa-
bility of fumigating questionable, an increase in dosage of 10 per
cent or more may allow the work to proceed without interfering with
the efficiency; hut with ordinary tents of 8-ounce duck such increases
do not offset the effects of strong or gusty breezes, which sway the

66

DOSAGE TABLE. 67

sides of the tent. II' the onl) available tents arc of inferior quality and
fall short of being a> aearly gas-t ight as t he best of material, increases
in dosage may be advisable. When it is desired to Fumigate with a
thoroughness approaching extermination, an increase may be made
of From K) to 25 per cent. Such a course is frequently advisable to
check the Further spread of the fly in newly infested localities or in
newly infested groves. In the Fumigation ^\' yery small trees, 20 feet
over or less, there seem to he certain Factors sometimes interfering
with efficiency which have not so Far been thoroughly investigated.
It is possible that in the4 using oi' crocks of 2 or .') gallons capacity For
doses less than 5 ounces the mixture of acid and water Fails to gen-
erate sufficient heat to cause quick chemical action, the heat absorbed
by the jar being the disturbing factor. This may be partly obviated
by using powder or very small lumps of potassium cyanid when the
Ai»v is 5 ounces or less, but it seems advisable also to increase the
amount by one-half or three-fourths above the recommended dose.
If the size i^( the crock and consequent undue loss of heat is the prin-
cipal disturbing factor, future experience may show that it is desirable
to have on hand for use in fumigating very small trees a supply of
half-gallon crocks or 1 -quart stone chinaware pitchers.

In the table the amount in each case represents the next half ounce
above the dosage which the detailed estimate calls for, whenever this
dosage was more than one-tenth ounce above the even ounce or half
ounce. For example, when the detailed calculation calls for 19.2
ounces the number in the working table is 19t ounces, and when For
19.7 ounces the number is 20 ounces. In using the table in the field,
when the reading on the graduated tent shows the approximate dis-
tance over the top to be an odd number of feet, the next even num-
ber above should be selected. In the same way, when the exact cir-
cumference is not shown at the top of the table, the next highest
number should be selected.

To illustrate the method of using the table of dosage, the Following
examples show the measurements and dosage called for in the case
of five trees of various sizes:

Measurements of, and dosa<j< f<>r each of jive ir<,s of various sizes.

Distance

Circumfer-

Amount <.l"

over tented

ence "i

cyanid
called lor.

t ree.

tented 1 ree

Feet.

/■• •

Ouii'

28

15

10

i^

CD

34

:,i

68

47

80

71

61

72

80

89

At all times it should be borne in mind that it is advisable to use
one-half or even 1 ounce more than called For by the table rat her than

the smaller amount.

68

FUMIGATION FOR THE CITRUS WHITE FLY.

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NDEX

Page
Ash, prickly. (See Xanthoxylum clava-herculis.)

Atmospheric humidity as affecting fumigation L2 I I

Banana shrub. Sec Magnolia fuscatum.)

Bay, sweet. 'Sec Magnolia virginiana.)

Bos tents or covers for fumigating small trees in grove 54

Cactus, prickly pear. (See Opuntia sp.)

Cape jessamine. 'Sec Gardenia jasminoides.

Chemicals for fumigation, cost 58

handling, and protection from moisture 25

proportion of water and acid 25 27

purity required 25

Cherry lam-el. See Primus laurocerasus.)

Chinaberry. 'See Melia azedarach and M. a. u/mbraculiformis.)

( Jirysomphalw ficus, losses prevented by fumigation 61

Citrus, f 1 plants of white fly in

insects, history of fumigation 7-8

trifoUata, food plant of white fly 10

white fly. (See White fly.)

Concerted action favoring fumigation !)

( londit ions favoring or necessary to good results in fumigation 9-14

< Jontrol, natural, of white fly, versus fumigation 63 65

>f fumigation compared with spraying 62 63

( hlbic contents of tented tree, methods of computation in fumigation 39 40

Cyanid of potash. (See Potassium cyanid.)
Derricks. (See Upright-. I

Dews as affecting fumigation 12-14

Diagram of grove as guide in fumigation 23 24. 38

Dimensions of tented tree, methods of computation 39 10

Dio8pyro8 haki, food plant of white fly 1<>

virginiana, food plant of white fly L0

Dosage requirements in fumigation against white fly 10 50

table for rumigat ion against white fly 66 68

Economy of treatment by fumigation 59 63

Equipment for fumigation 1 1 24 56 58

Expense of fumigation 56 -"^

Ficus. Set Pig

alti8sima, food plant of white fly 10

Pig, reported food plant of white fly io

Food plants Of white fly 10

Food plants, other than citrus, of white fly, absence or elimination favoring

control by fumigation !>-10

Fumigating tents. {Set Tents.

69

70 FUMIGATION FOE THE CITRUS WHITE FLY.

V&ge.

Fumigation against citrus insects, history 7-8

white fly, absence or elimination of food plants other than

citrus favorable 9-10

appearance of dead larvae and pupa? 50-51

chemicals, cost 58

handling, and protection from mois-
ture 25

proportion of water and acid 25-27

purity required 25

concerted action favorable 9

conditions favorable or necessary to good results.. 9-14

cost compared with spraying 02-03

density of gas at various heights above ground. . 51

dosage requirements with bell or hoop tent 49-50

sheet tent 40-49

economy of treatment 59-63

effect on trees and fruit 51-54

equipment 14-24

expense 50

history 7-8

isolation of grove favorable 9

losses prevented thereby 59-00

measuring trees 30-35

meteorological elements favorable 11-13

method of generating gas. 35-30

handling bell tents 29

sheet tents 27-29

methods of computing cubic contents of tented

tree 39-40

dimensions of tented trees 39-40

miscellaneous experiments and observations 50-54

requirements 22 24

nursery stock for shipment 54-55

poles for handling tents 20-21

precautions 55-50

procedure: 27 ' \S

proportion of water and acid 25 27

season of year favorable , 10-11

table of dosage 66-68

tents, care L9 20

construction 15-19

mildew-proofing, oiling, and painting 19-20

shrinkage 17-18

st vies 14-15

time required 38-39

trees, regularity of setting favorable 14

size favorable 14

small, in the grove 54

nursery 54

uprights for handling tents 21

versus natural control 03-05

work routine : '30-3S

Fungous diseases in control of white flv 04-05

INDIA. 71

Page

Gardt nia jasminoides, f « >« »» 1 plant of white fly id

density at various heights above the ground 5]

method of generating

Grapefruit as affected by fumigation M

trees as affected by fumigation 52

( frove, diagram, as guide in fumigation 23 24,38

Humidity as affecting fumigation L2— 14

Hydrocyanic-acid gas. (Set Fumigation.)

Icerya purchasi, control by fumigation 7

Isolation of grove favoring fumigation 9

Jessamine cape. (See Gardenia jasminoides.)

"Jingler1 ' 18

Labor for fumigation, cost 58

Laurel, cherry. (See Prunus laurocerasus.)

Lepidosaphea bechii, losses prevented by fumigation 61-62

Light as affecting fumigation against white fly 11

lAgustrum Bpp., feed plants of white fly 10

Lilac, food plant of white fly 10

- from scale insects prevented by fumigation 60-62

white fly prevented by fumigation 59-60

Magnolia fuscatum, feed plant of white fly 10

virginiana, food plant of white fly 10

Measurements of trees, necessity in fumigation 30-31

Melia azedarach and M. a. umbraculiformis, food plants of white fly 10

Meteorological elements favoring fumigation 11-13

Moisture. {See Humidity.)

Mold. Booty, resulting from white-fly attack - 64

Nerium oleander, food plant of white fly 10

Nursery stock for shipment, fumigation against white fly 54-55

trees, fumigation against white fly 54

Oak. water. (See Quercus nigra.)
Oleander. (See Nerium oleander.)

Opuntia sp., use of juice for painting fumigating tents 19

Orange fruit as affected by fumigation 53-54

trees as affected by fumigation .• 51-53

Palmetto, scrub. (See Sabal megacarpa.)

Pear, food plant of white fly 10

Persimmon. Japan. (See Diospyros haki. I

wild. (See Diospyros virginiana.)

Poles for handling fumigating tents 20-21

Potassium eyanid for fumigation, cost 58

handling, and protection from moisture 25

purity required 25

Prickly ash. (See Xanthoxylum clava-herculis.)

pear cactus. (See Opuntia sp.)
Privets. (See Ligustrum Bpp.)

Pruning trees as aid in fumigation 14

Prunua caroliniana, food plant of white fly 10

laurocerasus, food plant of white fly — " 10

Pyrus sp. Set Pear. !

Quercus nigra, reported food plant of white fly 10

Sabal megacarpa, food plant of white fly 10

7Z FUMIGATION FOR THE CITRUS WHITE FLY.

Page.

Scale, black, control by fumigation 7

"brown." See Lepidosaphes beckii.)
c<»tt<»ny cushion. See Icerya purch
Florida red. (See Chrysomphalus fonts.)
•• hard." (See Lepidosaphes becJ:ii. I

insects, losses prevented by fumigation 60-02

"oyster-shell." (See Lepidosaphes bechii. i
purple. (See also Lepidosaphes beckii. >

control by fumigation 7

red, contr< >1 1 >y fumigation 7

Season of year favoring fumigation 10-11

Shedding of foliage in fumigation 52-53

Shrinkage of tents 17-18,32

Spraying, cost compared with fumigation 62- 63

Sulphuric acid for fumigation, cost 58

handling, and protection from moisture 25

purity required 25

Sweet bay. (See Magnolia virginiana.)
Syringa sp. (See Lilac.)

Table of dosage for fumigation 66-68

Tangerine fruit as affected by fumigation 54

trees as affected by fumigation 52

Tannin, use in mildew-proofing fumigating tents 19-20

Tents, bell, construction 15

dosage requirements 49-50

method of handling 29

box, construction 15

dosage requirements 54

care 19-20

construction 15-19

cost 56-57

hoop. (See Tents, bell.)

marking for estimating dosage 31-35

mildew-proofing, oiling, and painting 19-20

sheet, dosage requirements 40-49

method of handling 27-29

shrinkage 1 7-18, 32

styles 14-15

Time required in fumigation of grove 38-39

Tray, commissary, for fumigation 22

Trees as affected by fumigation 51-54

measurements in fumigation 30-35

regularity of setting favorable for fumigation 14

size when tented, methods of computation 39-40

sizes most favorable for fumigation 14

small, in grove, fumigation against white fly 54

nursery, fumigation against white fly 54

Uprights for handling fumigating tents 20-21

Viburnum nudum, food plant of white fly 10

White fly, appearance of larva? and pupae when destroyed by fumigation 50-51

citrus. (See While fly.

control by fumigation, history 7-8

food plants 10

[NDEX. 78

White fly fumigation, absence <>r elimination of food plants other than citrus

favorable 9 10

appearance of dead larvae and pupae •'»(» 51

chemicals, cost 58

handling, and protection from moisture 25

proportion of water and acid 25 27

purity required 25

concerted action favorable 9

conditions favorable or necessary to good results 9 M

density of gas at various heights abcv e ground 51

dosage requirements wii b bell or hoop tenl l!i 50

sheel tenl 10 19

economy of iroatmcnt .Vi 63

effect on trees and fruit 5] 5 I

equipment It 24

expense 51

isolation of grove favorable 9

losses prevented thereby 59 60

measuring trees 30-35

meteorological elements favorable II L3

method of generating the gas 35- 36

handling bell tents 29

sheet tents 27-29

methods of computing cubic contents of tented tree... 39-40

dimensions of tented tree 39-40

miscellaneous experiments and observations 50 54

requirements 22-24

nursery stock for shipment 54-55

poles for handling tents 20-21

precautions 55 :>< i

procedure 27-38

season of year favorable 10-1 1

table of dosage 66-68

tents, care 19-20

construction 15-19

mildew-proofing, oiling, and painting 19-20

shrinkage 17-18

styles 14-15

trees, regularity of setting favorable 14

size favorable 14

small, in grove 54

nursery 54

uprights for handling tents 21

versus natural control 63 65

work routine 36-38

Wind as affecting fumigation 12

Xanthoxylum clava-herculis, food plant of white fly 10

i