ed

SB
818
C578
ENT

1Oselilitte Issued September 29, 1909.

United States Department of Agriculture,
-BUREAU OF ENTOMOLOGY,

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

PREPARATIONS FOR WINTER FUMIGATION FOR THE:
CITRUS WHITE FLY.

By A. W. Morritt and W. W. Yoruers.
INTRODUCTION.

As a result of investigations conducted by the Bureau of Ento-
mology during the past three years, fumigation for the citrus white
fly has been placed upon a practical basis, and the process has been
so simplified that any citrus grower can undertake the treatment of
his grove without depending upon experienced fumigators to con-
duct the operations. Under present conditions fumigation is the
most satisfactory and profitable method of controlling the white fly
in hundreds of infested groves in the Gulf coast citrus-growing regions,
and its usefulness will be extended to nearly all infested groves
when the practical recommendations in a forthcoming bulletin on
the white fly have been put into effect. The superior quality of
Florida citrus fruits when grown in groves free from injury from
insect pests and the awakening of progressive growers to the neces-
sity for organizations for combating insect pests and for marketing
the fruit point to the general adoption of the control measures to
be recommended in the publication referred to.

At the present time the authors would recommend fumigation for
the white fly under the following circumstances: In groves isolated
by a distance of at least 200 yards % from all other infested groves,
in citrus groves or in citrus-growing sections where the white fly has
recently appeared and is still of limited distribution, and in sections
where cooperation can be secured among growers in naturally isolated
groups. In many cases the owner of an extensive and valuable
grove which is isolated except for a small grove of a few acres from
other infested groves can well afford to loan his equipment, or, if
necessary, fumigate the neighboring grove entirely at his own expense,

a Experience so far has shown that as a rule in cases of isolation of much less extent
fumigation can be practiced without its being rendered unprofitable through the
migration of adults.

5937—Cir. 111—09 :

408390

2

rather than to permit the presence of such grove to interfere with
his results.

Full directions concerning equipment, chemicals, and methods of
procedure in fumigating for the citrus white fly have been published
in a bulletin of this Bureau.“ This bulletin is based upon results
obtained in January and February, 1907. Extensive field experi-
ments have been conducted during the last two seasons and the
additional results obtained will be embodied in a supplementary
report now in preparation by the authors of this circular. It is
hoped that before the beginning of the next fumigating season,
extending from December 1 to March 1, a publication in the Farmers’
Bulletin series of this Department will be available. This bulletin
will contain only such advice and directions as are of practical
importance in fumigation work against the white fly, omitting the
details of experiments published elsewhere as the necessary basis
for establishing practical conclusions. The present circular aims to
call attention to the desirability and in most cases necessity for
early preparations where fumigation work is planned for the coming
winter season; also to give full directions for such preparations.

EQUIPMENT.
TENTS.

- Orders for tents should be placed as soon as possible after it is
decided to fumigate a grove. Tent makers do not always have on
hand a sufficient quantity of desirable grades of canvas to fill large
orders. Delays in filling the order may necessitate shipment by
express, at a cost several times the expense of shipment by freight.
The first step is the determining of the sizes of tents required. It
is a more common mistake to underestimate the size of a tent required
than to overestimate it. Some allowance should be made for the
growth of trees, in consideration of the future use of the tents. If
the trees are nearly uniform in size, the largest trees should be selected
for measuring. A tape measure attached to a reel is used in meas-
uring trees to determine the size of tent required. Standing a few
feet from the outside branches of the tree to be measured, enough
of the tape is unreeled to extend over the top of the tree and about
half way to the ground on the other side, the free end of the tape is
held in one hand and the reel is thrown over the center of the tree
and unreels the tape by its own weight until it reaches the ground.
Two or three attempts may be necessary in order to have the tape
pass over the center of the tree. It should be borne in mind that the
weight of the tent will reduce the extreme height of the tree and that

«Bul. 76, Bur. Ent., U. S. Dept. Agr., Fumigation for the Citrus White Fly as
adapted to Florida conditions. By A. W. Morrill.
(Cir. 111]

3

it is therefore unnecessary for the tape to pass over the highest twigs.
For large trees 6 to 8 feet should be added to the number of feet over
the top of the tree, as shown by the measurement, and for small trees
4 to 6 feet should be added. In general, trees from 10 to 15 feet
high require tents between 32 and 44 feet in size*; trees from 16 to 20
feet high require tents 44 to 58 feet in size; trees 21 to 25 feet high
require tents 60 to 70 feet in size; and trees 25 to 30 feet high require
tents 70 to 76 feet in size.

In regard to the number of tents required, it is safe to estimate
that with one tent for each 100 trees the work of fumigation could
be completed in ten to four-
teen nights’ work. One crew
can handle from twenty to
twenty-five small tents, 45
feet in size and smaller, and ‘i
from eight to fifteen tents, 50 [Bie site ent i
feet insize and larger. Much |REQ@WwhiAh Gs Htviren tt tah tn
depends upon the trees being |r KIDS ; 3 4
so spaced as to obviate inter-
ference with the work of shift-
ing the tents.

Having decided upon the
number and sizes of tents
required, orders should be
placed as soon as_ possible.
Samples of 8-ounce army duck
should be obtained from tent
and awning makers who are
in a position to furnish the
tents. The selection of tent
material is a matter of great . :
importance. Samples of duck Fie. ac pee and a desirable type Ob ee: cot-

‘ z on duck for fumigating tents. (Original. )

can be classified roughly in

regard to tightness by the general texture and by the degree of
imperviousness to direct rays of light when held between the eye and
the sun, or any bright light. Neither of these methods is entirely
satisfactory, however, in selecting material for fumigating tents.
With a simple arrangement devised by the authors for testing the
tightness of material submitted to the laboratory at Orlando, Fla., for
examination, it has been found that samples of duck vary nearly 50
per cent in their comparative tightness.

Figure 1 illustrates two extreme samples of 8-ounce duck which
differ to the extent of 47 per cent in this respect. As a result of

ay
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,

ae

ayant

3 5

hd
by eet

a7The size of tents is expressed in terms of the distance between parallel sides of
the octagonal sheet of canvas of which the tent is composed.
(Cir. 111]

+

the examinations made so far, the authors strongly advise against
the use of drills of any kind. The appearance of these is much more
misleading than that of ducks, and it seems impossible to estimate
their comparative tightness except by tests with special apparatus.
Our experience up to the present time leads us to recommend closely
woven duck weighing 8 ounces per yard, when 284 or 29 inches wide,
or about 10 ounces per yard when the material is 36 inches wide.
The more expensive grades of cloth are not always the most nearly
gastight. In the case of two leading concerns which have supplied
large orders of tents for use in Florida, the medium grades of mate-
rial, as shown by the prices quoted, have been found to be superior
in gas-holding qualities to either the cheapest or the most expensive
of the three grades upon which prices were quoted.

The form of cover which is at present almost exclusively employed
is the flat octagon. Frequently those who have never seen a tent of
this kind fail to realize its simplicity. A square piece of canvas
would answer the purpose as well as the octagon, but to save material
and the handling of extra cloth the corners of the square are left off.
A perfectly circular cover would be more economical in respect to the
amount of cloth required, but the saving would not cover the extra
expense of construction in this form.

For specifications tentmakers may be referred to Bulletin 76 of
this bureau.¢ In general these specifications are simply that the
form is approximately octagonal, of any desired size, made of par-
allel strips of goods overlapped three-eighths or one-half inch,
double stitched, and all raw edges hemmed. In the case of tents
50 feet or more in size a reinforcement is desirable across the middle
section near each end, as described in the bulletin referred to. It is
desirable that allowances be made for shrinkage, otherwise a tent
after becoming wet and later drying may not be sufficiently large to
cover trees of the size for which it was intended. The following
published statement by the senior author is of importance in this
connection and is quoted in full:

Shrinkage of the goods after being thoroughly wet is an important consideration in
the economical construction of fumigating tents. In order that the tents approxi-
mate 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 allowance 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 shrink-
age 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} feet, while the tent would shrink less than 6 inches crosswise of the strips.
Such irregularities might be remedied by a skirt of 64-ounce drill, but it is simpler to

~

«For sale by the Superintendent of Documents, Government Printing Office,
Washington, D. ©. .Price, 15 cents.

b Bul. 76, Bur. Ent., U.S. Dept. Agr., pp. 17-18.

[Cir. 111]

5

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 differ-
ence is 6.6 per cent, and each per cent represents an actual difference of 6 inches. A
50-foot tent constructed in this manner would therefore measure before shrinkage
52} feet (49 feet 10} inches + 3 feet 4 inches) lengthwise of the strips through the
middle section, and 49 feet 104 inches crosswise of the strips. After shrinking, the
dimensions would be approximately 49 feet 44 inches in each direction.

On account of the variation in the shrinkage of different brands of
duck it is necessary to test the crosswise and lengthwise shrinkage in
the sample selected. This may be done by marking, with a lead
pencil, lines 1 foot or more in length, both crosswise and length-
wise of the strip of goods. The sample should be shrunken twice,
each time wetting by submerging in water for two or three hours
and drying in the sun. The amount of the shrinkage can then be
determined by measuring the pencil lines just referred to.

The marking of the tents with graduated stripes, which is a part
of the process ie determining dosage requirements originated by the
senior author,? requires less hes an hour for each tent. The neces-
sary preparations for this, therefore, consist in procuring suitable
paint and arranging for a patch of open field where the tents may be
spread flat to become saturated with rain or dew, thus producing the
desired shrinkage. The importance of the tents being thoroughly
shrunken before the measuring for the graduations is obvious.

Directions for “‘ mildew-proofing”’ the tents will be given in publi-
cations now in preparation and it is not necessary to include them
in this connection. Tents should be thoroughly dried in the sun
before being folded for storage, and in preparing them for field use
they should not be exposed to rains or dews any more than is neces-
sary to shrink as advised above.

POLES AND DERRICKS.

In the Gulf States, seasoned cypress is probably the best material
available for the manufacture of poles and derricks used in shifting
tents. These serve practically the same purpose, the former being
used in handling tents up to 50 feet in size and the latter in handling
tents 50.feet in size and larger. The poles have no other attach-
ment than a rope, while the derricks each consist of a pole with a
crosspiece and braces at the base and eye-bolt attachment for pulley
and tackle at the small end. These poles and derricks can be pre-
pared for use in a short time, but it is very important that the poles
be cut and peeled long enough before they are needed for use to
permit them to become well seasoned. Poles should be carefully
selected in order to have them as straight and free from knots as
possible. While only two poles or two derricks are needed for use
at one time, an extra supply of both should always be in readiness,

aLoc. , pp. 32-33.
[Cir. 111]

6

so that in case of breakage the work can be continued with
little interruption. The length of the shifting poles should be
about 2 feet more than the height of the average trees, and the small
end should be about 14 inches in diameter. The poles for derricks
should be about 3 or 4 feet more in length than the height of the
average tree, and when ready for use should be between 3 and 4
inches in diameter at the base and between 2 and 3 inches in diam-
eter at the top. The method of attaching the crosspieces and braces
is described and illustrated in Bulletin 76 of this Bureau. If ordinary
three-eighths or one-half inch bolts are at hand, a pair of derricks can
be prepared for use in less than half an hour, and this need not there-
fore be considered a necessary part of the early perparations for
fumigation. Cypress poles should be seasoned in a barn or packing
house, or if out of doors they should be in the shade. Straight poles,
while being seasoned, should be so supported as to prevent bending
or warping. If, after cutting, a pole is found to be crooked, it may
perhaps be made practically straight by the proper arrangement of
the supports when seasoning.

GENERATORS OR CROCKS.

In generating the gas earthenware crocks are used. In general,
trees 5 to 8 feet high will require crocks of 14 gallons capacity; trees
9 to 12 feet high, crocks of 2 gallons capacity; trees 13 to 16 feet high,
crocks of 4 gallons capacity; trees 17 to 20 feet high, crocks of 4 or 5
gallons capacity; and trees 21 to 30 feet high, crocks of 5 or 6 gallons
capacity. For trees up to about 18 feet in height one crock will be
needed for each tent, but for larger trees two crocks should be used,
dividing the dosage into two equal parts. Crocks with straight sides
can be used with more cyanid for each gallon of capacity than crocks
which narrow at the top, and it is to the former style rather than to
the latter that the preceding statements refer.

The foregoing directions should enable anyone preparing to fumi-
gate to determine the actual number and sizes which will be needed.
It is always advisable to have several extra crocks at hand, so that
delays will be avoided in case of breakage.

Crocks of more than 2 gallons capacity can not be readily obtained
as a rule and frequently even the smaller sizes can not be obtained
of local dealers in sufficient numbers to equip a large outfit. It is
important, therefore, that orders for crocks be placed as soon as
possible when preparing to fumigate. As the tops or covers are not
needed, dealers should take this into consideration in quoting prices.
When not purchased of local dealers and no allowance is made in the
price on account of the covers of the crocks, instructions should be
given not to include the covers in the shipment, in order to avoid
unnecessary freight or express charges.

[Cir. 111]

Convenient handles for the crocks can be made of a large size® of
wire. If properly arranged the ends of the handle will be held in

position on opposite sides of the crock, otherwise they may cause
considerable annoyance.

MISCELLANEOUS REQUIREMENTS.

Of the numerous articles of minor importance which sometimes
are not easily obtained and should therefore be arranged for as early
as possible are rubber gloves and glass graduates. Two or three
pairs of rubber gloves ren be Sbtamed for a large outfit. One
pair is needed for the one who measures the acid and generates the
gas, and one pair should be available for use by the helper who
empties the contents of the crocks after fumigating. The third pair
should be on hand in case one of the pairs in use is lost or destroyed
by any means. Rubber gloves can be purchased of or ordered
through electrical supply houses or electric-light companies. Black
rubber gloves with cloth lining are preferable to the red rubber
gloves without lining which are sometimes used. The latter are not
easily removed from the hands, especially after they become wet on
the inside, and are on this account very troublesome. One should
avoid gloves which are so thick that a wet glass graduate can not be
easily handled when wearing them.

A glass graduate of 16 ounces capacity is needed for each outfit,
and if not obtainable of local dealers one or two extra ones should
be always on hand. They can be purchased through local druggists
or directly of wholesale drug houses. It is important that the num-
bers on the graduate be plain and easily readable.

Torches are preferable to lanterns, and if possible three or four
of the former should be obtained.

Balances, stoneware pitchers, dippers, water buckets, ropes, pul-
leys, and other articles can usually be obtained of local merchants.

CHEMICALS.

The chemicals required in fumigation with hydrocyanic-acid gas
are potassium cyanid (KCN) and sulphuric acid (H,SQ,)

POTASSIUM CYANID.

The cyanid ordinarily used in fumigating citrus trees is put up in
200-pound cases and costs between 21 and 23 cents a pound in ton
lots. It should be guaranteed to be 98 to 99 per cent pure. In
calculating the amount of cyanid required, a tree should be selected
which represents as nearly as can be estimated the average size of the
trees in the grove. The distance over the top can be obtained by
the tape measure in the same manner as described in connection with
estimating the sizes of tents required. In addition to this measure-
ment ae circumference of the tree should be qensuned with the

aNo. 9 has been ieee ne ee authors for this purpose.

[Cir. 111]

8°

tape line. This can be done by attaching the free end of the tape to
a twig and passing around the tree, hanging the tape on the outer
twigs as it is unreeled. If the grove consists of two sizes of trees, as,
for example, large seedling and medium-sized budded trees, an aver-
age specimen of both kinds should be measured. The amount of
cyanid required for these average specimens can be determined from
the dosage table given herein. The following examples illustrate the
method of using the table after the distance over and the circum-
ference of the tree have been obtained:

}
| Amount of |
Example | Distance Circumfer- | potassium
No. | over tree. enceoftree. cyanid
| required. |
Feet. Feet. | Ounces. |
1 24 40 | 9 |
2 38 55 26
3 52 72 58
4 66 | 79 96

The amount of cyanid in ounces having been obtained for the aver-
age tree in the grove, this amount is multiplied by the total number of
trees to be treated and divided by 16 to reduce to pounds. It is advis-
able to obtain from 5 to 10 per cent more cyanid than the amount esti-
mated, in order to avoid delays in case of underestimation. The
cyanid, being put up in air-tight tin cases inclosed in stout wooden
boxes, may be stored for months without deterioration. Excess
cyanid can usually be disposed of without difficulty.

SULPHURIC ACID.

Sulphuric acid can be purchased in iron drums containing about
1,500 pounds at about 1;;cents a pound. One drum of acid is required
for about 4 cases of cyanid. The acid should be guaranteed 66°
Baumé or 93 percent pure. It is advisable to have a sample tested
with an acid hydrometer, an inexpensive instrument which can be
obtained through any druggist. . Acid should not be stored for more
than two or three weeks in the drum. Unless it is to be used at once
the entire contents should be emptied into carboys, the mouths of
which should be closed with wooden plugs, strips of burlap, and plaster
of Paris. Empty carboys can be purchased for $1.50 or $1.75 each,
and 9 are required to contain the contents of an acid drum. Only
carboys in good condition should be used, since the container is made
of thin glass and breaks easily if the bottom of the wooden case becomes
weakened and fails to support the contents. Great care should be
used in handling the acid. Probably the quickest and safest way of
emptying acid from the large drum into carboys is a method which
has been used on several occasions by the authors. The drum is
mounted on two heavy planks resting on the ground and is arranged

so that it can be rolled forward and backward easily. At one end of
(Cir. 111]

9

the planks a pit about 3 feet deep is dug. This should be large enough
for two men to stand in and place the empty carboy in position and
lift it out when filled. A large-mouthed funnel made of sheet lead is
placed in the mouth of the carboy. A piece of cast-iron piping about
6 or 8 inches long and properly threaded is a convenience, but not a
requirement. This, if available, is screwed into the opening in the
drum, which is arranged so that the acid will pour into the funnel lead-
ing to the carboy. A piece of heavy plank or other suitable lumber
should be strongly spiked across the ends of the two plank supports of
the drum to prevent its being rolled too far forward. Whenever there
is a suitable platform available, or timber is available for making
a rough one, the trouble of digging the pit can be obviated. It is not

28-36| 33-40 | 32-39
x ;
Badr
miei | a eee
10%
= Sie ee
10% oe if 20%
ye 54 38-50/37-51 |36-40
=

A FFAG J le

Fig. 2.—Diagram of regularly set grove in process of fumigation with an outfit of four tents: X, X, trees
missing. (From Morrill.)

advisable to empty drums from railroad stations or packing-house plat-
forms, as more or less acid is ustially spilled. No one should stand
near the carboy when the acid is being poured, and care should be taken
to prevent any spattering of the acid from reaching the face. When
handling acid it is always well to have water at hand for use in case
of accident. With proper care sulphuric acid can be handled without
danger of any kind.

DIAGRAMS OF GROVES, AND DOSAGE TABLES.

While it is not always necessary that diagrams of groves be made,
it is always advisable as a matter of record and to prevent errors.

Figures 2 and 3 illustrate methods of making diagrams when trees
[Cir. 111]

10

are set in the square and in the alternate system, respectively. The
figures in the squares represent the records of the trees fumigated,
the two upper figures separated by a dash representing the dimen-
sions of the tented tree and the lower figure the amount of cyanid
given.” These records are made at the time each tree is fumigated.

In presenting the dosage table recommended in Bulletin 76 it was
stated that the amounts of cyanid could be increased from 10 to 25
per cent with advantage under certain conditions. At the present
time the authors advise for general use a table (fig. 4) representing

-. 43-62
33-47 on RE
2 eg
42-50 47-60} 23
eae reat Lt |
aie iet
es

23

At Bee Cc DES Fs .1Gar nn
S.
Fig. 3.—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. (From
Morrill.)

an increase of 25 per cent over the minimum requirements previously
given in tabular form. This seems desirable, owing to the wide
variations in the weave of various tenting materials and to the fre-
quency with which slight winds might interfere with the results.

MISCELLANEOUS SUGGESTIONS.

With the gradual extension of the process of fumigation in the
control of the white fly in Florida and other citrus-growing sections
of the Gulf coast, the value of a citrus grove will be considerably

“The amount is according to the dosage table given in Bulletin 76 of this Bureau,
page 68.
(Cir. 111]

11

affected by the difficulties in fumigation presented by excessive
height of trees, closeness of planting, unevenness of ground, and other
conditions. The systematic treatment of groves to overcome these
difficulties, so that the trees may be easily fumigated, will not only
be of value in this respect, but will constitute a good cultural practice.
Trees planted too closely for fumigation to be practicable are too
close for best results in productiveness. Limiting the height of trees
by pruning not only lessens the expense of fumigation, but reduces
the expense of picking the fruit without reducing the quantity.

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76 98 [lo2[107,2[Ni7 121 ]125 139176.

Fic. 4.—Dosage schedule for use in fumigating for the citrus white fly. (Original. )

In preparing for the fumigation of a grove, if the branches inter-
lock to any extent, either pruning of branches or transplanting of
alternate trees or rows of trees is advisable. Deadwood on the outer
parts of the trees should be thoroughly removed in all cases to avoid
the tearing of tents. Watershoots should be thoroughly removed
at the same time, since about 1 per cent of the white fly pupz present
during the winter months survive fumigation and the resistance of
the insects on watershoot leaves is much greater than elsewhere on

the trees.
[Cir. 111}

LIBRARIES

: wi HMMM

If possible, the cultivating and fertilizing of groves = a uaa
should follow fumigation. It is much more difficult to handle the
fumigating tents on newly cultivated ground, and the dust arising
in the shifting of the tents is sometimes a matter of considerable dis-
comfort to the men engaged in the work.

Approved:
W. M. Hays,
Acting Secretary of Agriculture.

Wasuineton, D. ©., August 10, 1909.
[Cir. 111]

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