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F123

Issued June 10, 1910.

Us; DEPARTMENT “OF AGRICULTURE:
BUREAU OF ENTOMOLOGY—CIRCULAR No. 123.

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

METHODS OF CONTROLLING TOBACCO
INSECTS,

Bie

A. C. MORGAN,
Agent and Expert.

40704—10——1 WASHINGTON : GOVERNMENT PRINTING OFFICE : 1910

2s

BUREAU OF ENTOMOLOG Y.

L. O. Howarp, Entomologist and Chief of Bureau.
C. L. Maruatt, Assistant Entomologist and Acting Chief in Absence of Chief.
R.S. Cuirton, Executive Assistant.
W. F. Tastet, Chief Clerk.

F. H. CHITTENDEN, in charge of truck crop and stored product 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 insect investigations.

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

E. F. Puiuies, in charge of bee culture.

D. M. Rocers, in charge of preventing spread of moths, field work.

Roiia P. Currie, in charge of editorial work.

MABEL Co.LcorpD, librarian.

SOUTHERN FIELD Crop INSECT INVESTIGATIONS.
W. D. HunrTER, in charge.

W. D. Pierce, R. A. CusHman, C. E. Hoop, E. 8. Tucker, Georce D. Smrru, W. A.
Tuomas, T. E. Hottoway, GEorGE W. Hoop, V. I. Sarro, Harry PInKus,
engaged in cotton boll weevil investigations.

F. C. BisHorr, J. D. Mircuett, H. P. Woop, R. A. CooLtry, W. V. Kine, engaged
in cattle tick life history investigations.

A.C. Morean, G. A. RUNNER, S. E. CRuMB, engaged in tobacco insect investigations.

D. L. Van Dine, engaged in sugar cane and rice insect investigations.

F. C. Pratt, engaged in cactus insect investigations.

WitmMon NEWELL, T. C. BARBER, engaged in Argentine ant investigations.

II

CIRCULAR No. 123. Issued June 10, 1910.

United States Department of Agriculture,

BUREAU OF ENTOMOLOGY.

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

METHODS OF CONTROLLING TOBACCO INSECTS.

By A. C. Morean,
Agent and Expert.

INTRODUCTION.

Investigation by the Bureau of Entomology of the United States
Department of Agriculture of insects affecting tobacco has been in
progress in the ‘‘dark tobacco” districts of Kentucky and Tennessee
since July, 1907.

In the work in Tennessee the Bureau of Entomology has had the
hearty cooperation of the Ten-
nessee agricultural experiment
station and of its director, Prof.
H. A. Morgan. During the sum-
mers of 1908 and 1909 Professor
Morgan assigned a student, Mr.
D. C. Parman, of the University
of Tennessee, as an assistant to
the Federal agent in charge of
the tobacco-insect investigations.
The writer wishes to express his
thanks to Professor Morgan for
the personal advice received from

him and for this valuable coopera- Fig. 1.—Agrotis ypsilon, one of the tobacco cut-
tion worms: a, Larva; b, head of same; c, adult.
: Natural size. (From Howard.)

In this investigation all in-
sects found affecting tobacco have been studied, but particular
attention has been given to the different species of cutworms, to
the tobacco flea-beetle (Epitrix parvula Fab.), and to the tobacco
hornworms (Phlegethontius sexta Joh. and P. quinquemaculata Haw.).
In this particular circular only the insects mentioned above are
considered. Although the investigation has not been completed,

1

2 METHODS OF CONTROLLING TOBACCO INSECTS.

it is thought that a description of remedies already in use, with
the addition of those discovered during the investigation, may be
of value to the growers.

It should be stated that the remedies herein treated will apply not
only to Kentucky and Tennessee, but should apply equally as well to
all tobacco-growing States which do not border on the Gulf.

CUTWORMS.

e

Tobacco is frequently very seriously injured by various species of
cutworms, of which two common species are illustrated in figures 1
and 2. Itis the
common experi-
ence of all farm-
ers that cut-
worms are the
most abundant
and injurious on
land that has
been left uncul-
tivated for some
time previous to
being planted to
a certain crop.
Where tobacco
follows clover
serious injury
from these pests
is likely to re-

Fig. 2.—A tobacco cutworm (Peridroma margaritosa): a, Moth; 6, normal
form of larva, side view; c, same, in curved position; d, dark form of larva, su l t. O n the
from above; €, egg, from side; f,egg masson twig. All naturalsize except ¢, other hand, if
which is greatly enlarged. (From Howard.) : 4

winter grain pre-

cedes tobacco very little injury is likely to occur. However, if tobacco
is to follow a clover sod it is a simple matter to rid the soil of these
“worms.” If it1s possible to do so, the sod should be plowed under in
the fall or winter and be kept free of vegetation by disking or harrowing.
Thus by keeping the field free of vegetation the cutworms will be
starved to death before the time forsetting the tobacco. When sod land
is plowed only a short time before setting the tobacco, a trap bait may
be used to rid the field of the worms. In Farmers’ Bulletin No. 120¢
Dr. L. O. Howard recommends thoroughly spraying a patch of weeds
or clover with Paris green, then cutting it and dropping it in little
bunches here and there throughout the field. Another trap bait that
meets with wide favor is also reeommended by Doctor Howard.? It

a Farmers’ Bulletin No. 120, United States Department of Agriculture, p. 23, 1900.
BO iioe: Cit:

——— = SCS Ul Ul Ue -

METHODS OF CONTROLLING TOBACCO INSECTS. 5)

consists of 1 pound of Paris green mixed with 50 to 75 pounds of bran,
sweetened with molasses and moistened with water to make a mash.
This should be dropped about the field three or four days before the
plants are set, or two or three teaspoonfuls should be dropped about
each hill after the plants are set. The cutworms are very fond of the
sweetened mash and will generally eat it in preference to the plants.
If seed beds should become infested with cutworms, the bran mash
may be drilled through the bed and the ravages of the worms will be
stopped. When trap baits are used great care should be exercised
in keeping all live stock and barnyard fowls out of the field until the
poisoned materials have been worked into the soil.

In the spring of 1908 the writer applied an arsenate of lead spray
(made at the rate of 1 pound of arsenate of lead in paste form to 12
gallons of water) to a plant bed that was seriously infested with cut-
worms, with the result that all the
cutworms were killed before they
had done any appreciable addi-
tional injury to the plants.

THE TOBACCO FLEA-BEETLE.

(Epitrix parvula Fab.)

The tobacco flea-beetle (H’pitrix
parvula Fab.) (fig. 3) is known
also by the common names of
‘‘tobacco flea’ and ‘“‘flea-beetle.”’
It may be found, from setting
time until frost in more or Fic. 3.—The tobacco flea-beetle ( Epitrix parvula):

ane 5 “ E a, Adult beetle; 6, larva, side view; c, head of
less injurious numbers in every larva; d, hind leg of same; e, anal segment of same;
tobacco neldam the United States. 722t2s ¢. 27, Enlarged about 15 times;.¢ de,

eae i more enlarged. (From Chittenden.)

The most injurious outbreak on
record occurred in the ‘‘dark tobacco” districts of Kentucky
and Tennessee in the spring of 1907. Nearly all plant beds,
except those tightly canvased, were devastated. Practically all the
first sowing was destroyed and in many cases the second and third
also. In consequence the acreage was reduced 15 to 20 per cent, and
owing to the fact that the crop as a whole was set much later than
usual an additional loss resulted. Late-set tobacco does not produce
the same number of pounds as the early-set tobacco, and because of
the lateness of harvesting and the near approach of cool weather this
tobacco frequently cures poorly and is graded lower than tobacco
that is harvested earlier in the season. The loss in Kentucky and
Tennessee in 1907 was not far from $2,000,000.

The tobacco flea-beetle passes the winter in the adult stage in piles
of dead leaves or dead grass in the woods, or in fence corners and

Ye NS
TERN

e

4 METHODS OF CONTROLLING TOBACCO INSECTS.

similar localities. The beetles begin to-emerge from hibernation in
Kentucky and Tennessee in March, generally about the time the young
tobacco plants are appearing in the plant beds. The young and
tender plants furnish a favorite food for the beetles, and unless the
beds are well protected by canvas considerable damage is sure to
result. The flea-beetle also seriously injures tobacco in the field.
The writer has observed fields where numbers of plants were killed
by its ravages. The young leaves were riddled with holes (fig. 4) and
new foliage was completely devoured as fast as it appeared.

The tobacco flea-beetle occurs upon many species of solanaceous
plants, as it has been found feeding upon tomato, potato, horse nettle,
ground cherry, and ‘‘jimson weed” (Datura stramonwm). It lays its
egos on or near the base of the stems of these plants and also upon
the stems of young tobacco plants. The principal injury to tobacco
is occasioned by the feeding of the adults upon the foliage, although

Fic. 4.—Leaf of young tobacco plant, showing work of the tobacco flea-beetle. (Original.)

the larve occasionally do considerable damage to the young plants
by feeding upon the roots and stems.®

PREVENTIVE MEASURES.

Properly canvased beds escaped uninjured in 1907. Only whole,
strong canvas should be used, with boards or straight logs for the
sides of the bed, banking up the earth 3 or 4 inches against the sides
so that no holes are left beneath the logs, and fastening the canvas
closely and securely to the sides. Beds canvased in this way will
not suffer from flea-beetle attack.

a The biology of this insect has been carefully worked out by Dr. F. H. Chittenden
in Bulletin No. 10, of this office, pp. 79-82, and in Bulletin No. 19, pp. 85-87.

METHODS OF CONTROLLING TOBACCO INSECTS, 5
REMEDIAL MEASURES.

Even though flea-beetles do gain access to the plant beds in great
numbers they can be controlled economically. Nearly all the severe
loss of 1907 could have been averted had the growers known the
proper remedy to apply. The writer has found the following insecti-
cide very efficient in killing the beetles and not at all injurious to
the plants:

Arsenate of lead (in paste form, or } pound powdered form) .pound. - i
NOPE Ss a aes ie eM i Ee et sie ce oe ea gallons.. 12 to 16

Mix the arsenate of lead thoroughly in a small quantity of water,
pour into the tank, and add sufficient water to make the desired
quantity; then apply to the bed with
a spray pump until every leaf is thor-
oughly dampened. Two very good
spray pumps are illustrated in figures 5
and 6. If a heavy rain falls soon after
the application is made it may be neces-
sary to make a second application; but
it must be remembered that arsenate
of lead will stick to the foliage much
longer than Paris green, and will not be
greatly dissipated by a light shower.
After the plants have grown consider-
ably it will be necessary to spray the
bed again if flea-beetles are still numer-
ous, for the new foliage will, of course,
not be protected by the first applica-
tion.

If flea-beetles are very numerous at
the time of setting tobacco, the plants
can be protected for several days by
dipping the tops, just before setting, in
the arsenate of lead spray recommended
for use upon the plant bed. If plants
are not dipped at setting time and if the
flea-beetles appear in the fields in inju-
rious numbers, apply the arsenate of
lead, in the strength recommended above, with a knapsack sprayer
(fig. 6). With this sprayer one man can spray from 5 to 6 acres of
young tobacco in a day at a cost of from 25 to 35 cents an acre for
arsenate of lead. :

Tobacco growers as a rule pay too little attention to protecting
their plant beds from insect attack. The result is that more of the

Fic. 5.—Compressed-air spray pump.

6 METHODS OF CONTROLLING TOBACCO INSECTS.

crop has to be set late than would be the case if the beds were pro-
tected. The grower should always be prepared to fight the flea-
beetle, for often prompt attention to insect attack upon the plant
bed will enable him to save his bed and thus be prepared to set all
his crop early.

An early-set crop of tobacco has two very important advantages
over a late-set crop. The first is the production of a better grade
and of more pounds to the acre, as mentioned above. The second
advantage is often more important than the first. An early-set crop
will frequently mature in time to be cut before the August ‘‘shower”
of tobacco worms is large enough to do it serious injury. This point
will be explained more fully in the fol-
lowing discussion of the tobacco horn-
worms.

THE TOBACCO HORNWORMS.

(Phlegethontius sexta Joh. and Phlegethontius
quinquemaculata Haw.)

In the ‘‘dark tobacco” districts of
Kentucky and Tennessee the horn-
worms are the most injurious tobacco
insects, and they are important enemies
of this crop in every district in the
United States where it isgrown. There
are two species, the northern tobacco
worm (Phlegethontius quinquemaculata
Haw.) and the southern tobacco worm
_ (Phlegethontius sexta Joh.) (fig.7). The
northern tobacco worm is called also the ‘Spanish worm” in Tennessee
and Kentucky. This ‘‘worm,” or larva, is in general darker than the
southern tobacco worm, but the easiest way of distinguishing the
two species is by the white markings on the sides of the body. The
northern worm has 8 V-shaped markings on each side of the body,
each of which incloses a spiracle, or breathing pore. The southern
worm has 7 oblique lines on each side of the body, each of which
passes in front of a spiracle.

Fic. 6.—Knapsack spray pump.

DISTRIBUTION.

In general, as the common names indicate, the northern worm
is most numerous in the north and the southern worm is most
numerous in the south. The northern species is found as far south as
Florida, though it is rare, and the southern species has been collected
in Canada. At Washington, D. C., on the authority of Dr. F. H.
Chittenden, the northern species predominates, while in Tennessee

METHODS OF CONTROLLING TOBACCO INSECTS. (i

the southern species is much the most abundant. These two species
are so nearly alike in their work, life history, and seasonal history that
the remedial measures which apply to one will apply equally well to
the other. The life history and seasonal history notes given in this
article are from observations upon the southern species (Phlege-
thontius sexta Joh.).

LIFE HISTORY AND SEASONAL HISTORY.

This circular does not propose to describe in detail the hfe history
and seasonal history of the tobacco worms, but to give only such data

Cc

Fic. 7.—The Southern tobacco hornworm (Phlegethontius sexta): a, Adult; 6, larva; c, pupa. (From
Howard.)

as are necessary for the proper understanding of the reasons for
recommending certain methods of control. .

The tobacco moths begin to emerge from hibernation about June
1, and in a few days more they begin to deposit eggs. By reference
to Table I it will be seen that the eggs hatch in about 4 days, and that
the ‘‘worms,”’ or larvee, in from 19 to 20 days, pass through five stages
of growth. They then enter the soil to pupate (fig. 8). Those that
pupate not later than the last week of July will emerge in about three
weeks as adult moths of the second generation, and will commence

40704—Cir. 123—10 2

METHODS OF CONTROLLING TOBACCO INSECTS.

Those that pupate after the 10th of

August will usually hibernate, and will not emerge as adult moths
It is not until the third stage of growth—

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Fig. 8.—Hibernation of Southern tobacco hornworm: c, Pupa in hibernating

at the depth at which pupation usually takes place in the stiffer

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cell in soil

d from below; 0, pupal cell showing

S; a, cross section of pupal cell viewe

soil

( Original.)

thirds natural size.

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In the fourth (fig. 9) and fifth stages

af of tobacco in a single day.

are deposited

after the eggs

ays

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that is, about 10 to 1

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acco seriously.

one larva will ruin a small le

larvee injure tob

METHODS OF CONTROLLING TOBACCO INSECTS. 9

TABLE I.—Average length of different stages in life history of the southern tobacco
hornworm (Phlegethontius sexta).

| | |
Emer- | | Instars, or stages, in growth of larva.
gence |
|
}

of Incu- | | Total
moth | bation | | | larval pe

ee period.| wirst. ‘Second. Third. Fourth.) Fifth. Wes.
tion. | | | |
|

Days. | Days. | Days. | Days. | Days. | Days. | Days. | Days. | Days. | Days.
4 4 | 3 3 Sie ae te ONS, eG) Sine.) eas

The tobacco moths, as has already been stated, begin to emerge
from hibernation about June 1, or slightly earlier, and the emergence
continues until the middle of August or later. From Table I we see
that 48 days after the emergence of the moths from hibernation the
moths of the second generation will become adult, and that in 4 days
more they will begin to deposit eggs. These eggs will hatch in 4
days, and in 6 or 7 days more—that is, in about two months from the
emergence of the first moths from hibernation—the larve of the
second generation will pass into the third instar, the instar in which
they begin to injure tobacco seriously. For example, let us take 4
moths that have
emerged from hi-
bernation on the
following dates:
June 1, June 15,

July 1, and July :
Fia.9.—The Southern tobacco hornworm: Larva, fourth instar. Natural
oe eines second eto eee

generation of to-

bacco worms, the progeny of these moths, will begin to injure
tobacco seriously about August 1, August 15, September 1, and
September 15, respectively.

Although inate of both the first and second generations are
depositing eggs during late July and in August, we will show later
that by far the greater percentage of them has just emerged from
hibernation, and belongs, therefore, to the first generation. This
fact has a very important bearing upon the recommendation of fall
plowing.

Tobacco worms begin to enter the soil to pass the winter (i. e.,
hibernate) about the middle of August, and continue doing so until
frost. Usually they penetrate the soil to a depth of from 3 to 6
inches. Several observations upon ‘‘second bottom” soils of the
Cumberland River have shown the average depth to be 4 inches; that
is, to nearly the greatest depth to which the land was plowed in pre-

Nore.—For the purposes of this article the date of oviposition 1 may be considered as
taking place at any time from June 1 toJ uly 15, for there will not be a second genera-
tion from eggs deposited after the latter date.

iB

10 METHODS OF CONTROLLING TOBACCO INSECTS.

paring it for the tobacco crop. After the larve, or ‘‘worms,” have
reached this depth they twist and turn many times, finally forming
by this action oval cells, in which in a few days they transform to the
hibernating form, or pupe (fig. 8). The cells protect the pupe much
better from changes in the weather conditions than if the soil were
lying in close contact to them. The insects remain as pupe in the
cells during the winter and, as has been stated, begin to emerge about
the Ist of the following June as adult moths ready to deposit eggs
upon tobacco.

EMERGENCE OF THE SOUTHERN TOBACCO HORNWORM FROM HIBERNATION.

Careful records of the emergence from hibernation of the moths of
the southern tobacco worm (Phlegethontius sexta) were kept during
the seasons of 1908 and 1909 with very interesting results. In 1908
the emergence began about the last of May and continued until
August 13. In 1909 the emergence began June 1 and continued
until August 22, a period of 83 days. The records of 1908 were from
an emergence of 58 moths. The records of 1909 were taken from an
emergence of 1,667 moths, and are, therefore, of more value than the
records of 1908. The most interesting part of the data is the fact
that in both years a large percentage of the moths issued after mid-
summer. Table II shows the most important data obtained from
the emergence records.

TaBLE I1.—Record of emergence of tobacco moths from hibernation.

| Emergence | Emergence
Period of emergence. | during || Period of emergence. during
| period. || | period.
| |
1908.a | Per cent. | 1909.5 | Per cent.
LIAS IL WO dwwhy Ws sesos ks soesssdbeeesuse | aye Ah dinars iio) ADIN Tee se cess a mea sno Sue DTI
Mtr livall GabOPANT SUS Glo amines eee oe | Gos0 0) edlyallGstOeATICUST 22 see eee Wed
Juilyr AI io Um Bikege oe ses as osseeesanee S2u led tli 29 CORACU CTS E O2ee ae eee aie anes 50
July 21 to August 13..... RRR i Be es Re | 63.8 || July 29 to August 22..._......-..-..... 59
|
a Emergence began about June 1. b Emergence began June 1.

From Table II it will be seen that there was a large wave of
emergence in 1908 in the 11 days from July 21 to July 31, inclusive,
and that 52 per cent of the total emergence took place during that
period. The record further shows that after July 15, 5 per cent of
the total emergence took place. In 1909 the results were very
similar. The large wave of emergence took place during the 11 days
from July 29 to August 9, inclusive, and 77.3 per cent of the emer-
gence occurred after July 15.

REMEDIAL MEASURES.

It has been the belief that the larger percentage of the tobacco
worms that appear in late July and in August and September are of
the second generation. This is not true, for nearly all the worms

METHODS OF CONTROLLING TOBACCO INSECTS. 1a

that appear before the middle of July are killed by hand worming,
and we have already shown by means of the life-history records that
it will be two months from the emergence of the hibernating genera-
tion before the “‘worms,” or larvee, of the second generation will be
large enough to injure tobacco seriously.

The statement has been frequently made to the writer, and personal
observation has convinced him of its truth, that no difficulty is experi-
enced in keeping tobacco free of worms by hand worming until the
middle of July or later. Therefore, if tobacco is not injured by
worms until after the middle of July, the conclusion is that until that
date very few large tobacco worms have escaped hand worming and
that the second generation from those that have escaped will be a
very small one. By far the greater portion of tobacco worms that appear
wn late July and in August are the offspring of moths that have emerged
from hibernation; for the second generation of worms, the offspring
from those worms that mature after July 15 will not be of sufficient
size to injure tobacco seriously until about September 15. If tobacco
has been set early the crop will be ready for the barn by this date
and will, therefore, escape the second generation of worms.

FALL AND WINTER PLOWING.

Numerous experiments in 1907, 1908, and 1909 have demonstrated
that as a rule only about one-fourth of the tobacco worms that hiber-
nate are able to survive the winter and become adult. A part of the
mortality is due to parasites, but a greater part of it is due to the
unfavorable weather. The hibernating period is, therefore, a very
critical period in the seasonal history of the tobacco worm, and many
of those that do survive this period must be greatly weakened.
Hence, any artificial disturbance of natural conditions will produce
an additional mortality. As has been stated, the hibernation period
is passed in the pupal stage in an oval cell (fig. 8), about 4 inches below
the surface of the soil.

The most simple method of disturbing the pupz during hibernation

is to disk or plow the land. Both methods were tried. It was found
that the disk would reach only from 5 to 10 per cent of the cells, and
that therefore little benefit could be derived from that treatment.
The experiments in plowing the land killed more than half the pupex
that would otherwise have passed the winter successfully. The ground
should be plowed to the same depth as it was in preparing it for
tobacco, for many of the tobacco worms will go down to the hard
soil to form the hibernating cell, that is, to the greatest depth to
which the soil has been broken. Plowing will throw the pupe and
the cells up to or near to the surface, will break the cells in nearly all
cases, and will place the pupe in close contact with the earth, in

12 METHODS OF CONTROLLING TOBACCO INSECTS.

which condition they are most susceptible to changes in temperature
and to other climatological changes.

A week or ten days should elapse between the time of cutting the
tobacco and the plowing of the land, in order to give all larve that
are in the soil time to change to the more helpless pupal stage. Plow-
ing should be done as soon thereafter as possible, so that the pupe
will be exposed as long as possible to unfavorable conditions.

It is the practice in many localities of Kentucky and Tennessee to
disk the land that has been in tobacco in preparation for the wheat
that is usually sowed after the tobacco crop has been harvested. In
some localities it is thought that disking tobacco land is a better
preparation than plowing, for the reason that plowing loosens up
the soil too deeply and that the wheat will freeze out more easily.
Undoubtedly this may be true for some soils, that is, soils that con-
tain little clay and do not, therefore, run together very compactly.
There is, however, a large proportion of clayey soils in the Tennessee
and Kentucky tobacco regions in which wheat should not freeze out
easily. In fact, many farmers always plow their tobacco land in
preparing it for wheat because they believe they obtain a better
yield. Whether it is wise or not to plow tobacco land for wheat is a
question that each farmer must decide for himself. But it is certain
that plowing will cause the death of more than half the pupz, while
disking will kill very few. Upon the looser soils it would, perhaps,
be better to change the rotation and to sow some crop other than
wheat after tobacco.

COMBATING TOBACCO HORNWORMS UPON GROWING TOBACCO.

If tobacco is planted early the hand worming, necessary to kill all
worms that appear before the large emergence wave in late July
(Table II), can be made incidental to other processes in the growing
of tobacco, and will require very little additional time and labor.
Usually, in addition to the cultivation with farm implements, tobacco
will receive the following attention: Two hoeings, hilling, priming,
and topping, and much of the early tobacco will besuckered. During
these necessary operations it is very easy to discover and to kill the
few tobacco worms that have appeared, but when the large wave of
emergence appears, hand worming will be found very costly, and in
some localities impossible because of the scarcity of labor.

When tobacco worms are numerous it will require an outlay of at
least $8 to $10 an acre to hand-pick the worms, and frequently the
outlay will exceed $10 an acre.

Use of Paris green.—After the appearance of the July and August
‘‘shower of worms” an application of Paris green with a dust gun
(fig. 10) will be found to be the most economical means of combat.
In Tennessee and Kentucky Paris green is generally applied without

METHODS OF CONTROLLING TOBACCO INSECTS. JES

a carrier, but the writer prefers to mix it with twice its weight of
finely powdered air-slaked lime, for when the application is made
without a carrier the cloud of dust from the nozzle of the dust gun
is so thin that it is impossible to determine whether the application is
being made evenly. On the other hand, if the Paris green is mixed
with about twice its weight of lime, the cloud of dust from the nozzle
will always show whether the gun is working properly, and a clogging
of the tubes can be discerned instantly. Apply the dust early in the
morning when the dew is upon the plants and when there in no breeze.

Fic. 10.—Applying Paris green to tobacco with a dust gun. (Original.)

Use a dust gun that has a strong fan power, and apply to only one
row ata time. Great care should be taken to make the application
even and thorough. No definite date can be given for making the
first application. The time will depend upon the appearance of the
young tobacco worms, and it may be the last week in July or not
until about the middle of August. In 1908 and 1909 some of the
early planted tobacco at Clarksville, Tenn., did not require poisoning,
and in 1909 some of it required almost no worming. The first appli-

14 METHODS OF CONTROLLING TOBACCO INSECTS.

cation should be made within three or four days after the eggs begin
to hatch. A thorough application of from three-fourths of a pound
to 1 pound to the acre should be sufficient to kill the young larve.
Do not wait until the worms become half grown before making the
application, for in addition to being very much harder to kill than
the young ones, they will do considerable damage to the leaves before
they are killed. In dry weather a thorough application will remain
effective for a week or ten days, but if there is a rain the application
should be repeated immediately. The number of applications and
the dosage will be influenced by weather conditions—whether wet
or dry—by the numbers of young worms that appear, and by the
earliness or lateness of the crop. By watching the effect of an applica-
tion it can be easily determined whether it is losing its effectiveness
and whether another application is necessary. The presence of a few
large worms does not necessarily mean that the poison is ineffective.
Some worms will escape the most careful applications, and these
should be hand picked. The strength of the later applications upon
tobacco that is nearly grown may be increased to 1, 14, or even 2
pounds to the acre.

Caution.—Do not apply Paris green until two or three days have
elapsed after suckering, for if a light rain should wash the Paris
ereen into the fresh wounds made by breaking out the sucker, the
caustic effect of the free arsenic may cause the leaves to drop off;
also, do not apply a heavy dose of Paris green to tobacco when it is
beginning to ‘‘grain,” for the leaves are then more susceptible to
‘‘Paris green burn”’ than they are a few days previous to ‘‘graining.”’

Spraying tobacco versus dusting.—In this circular we have recom-
mended dusting tobacco instead of spraying for two reasons: First,
the labor of spraying is very much greater than that required to
apply the dust. When tobacco is nearly full grown, that is, has
begun to lap in the row, it will require from 120 to 150 gallons of
water to spray an acre. Therefore, to apply the spray to 1 acre a
5-gallon knapsack sprayer must be refilled from 24 to 30 times.
Second, the Paris green is not kept in suspension very easily in a
knapsack sprayer and the last of the spray from the tank is likely to
contain more than its proportion of the Paris green and thus cause
injury to the plant. Furthermore, if great care is not used in apply-
ing the spray, a part of the plant is very likely to be drenched and
the Paris green will be collected along the midribs and in the axils
of the leaves in sufficient quantity to cause serious injury. It is not
denied that a more even and thorough application can be made in
spray form, but with negro labor, and with most white labor, we do
not believe it will be made as satisfactorily as in the dust form.

Arsenic left wpon tobacco.—There is fear among growers that if
arsenicals are used a sufficient amount of arsenic may be left

METHODS OF CONTROLLING TOBACCO INSECTS. 15

upon the cured tobacco to injure the user. This fear is groundless.
Prof: H. Garman,® state entomologist of Kentucky, reports the
results of several experiments to determine the amount of arsenic
left upon treated tobacco. Paris green was used at the rate of
1 pound to 160 gallons of water. The experimental row that received
the greatest amount of Paris green received 8 sprayings with a total

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Fig. 11.—Applying Paris green to tobacco with a knapsack spray pump. (Original.)

of 44 pounds to the acre. The last spraying was made August 22,
and the tobacco was cut September 4. Analysis of this tobacco
showed 0.651 grain arsenious oxide to the pound. In the several
experiments performed by Professor Garman only one experiment
gave more than one grain of arsenious oxide to the pound of dried
tobacco, and the tobacco in this experiment was sprayed the day it

2 Bul. 63, Ky. Agr. Exp. Sta., pp. 69-74.

16 METHODS OF CONTROLLING TOBACCO INSECTS.

was cut. Professor Garman concludes that very little danger may
be apprehended from the arsenic left upon tobacco. In 1909 the
writer made several experiments to determine the amount of arsenic
left upon tobacco. To make the test severe, arsenate of lead was
used because this arsenical adheres to tobacco much longer than
does Paris green. August 13 the experimental plat received a spray-
ing at the rate of 5 pounds to the acre, and on August 18 a second
spraying at the rate of 4 pounds to the acre. Arsenate of lead in
dust form was used, hence the two dosages, amounting to 9 pounds,
were almost exactly equivalent in the amount of combined arsenic
to Professor Garman’s dosage of 44 pounds of Paris green. The
tobacco was cut September 8. The analysis, made by the Miscel-
laneous Division of the Bureau of Chemistry, showed an average of
0.347 grain arsenious oxide per pound. Heavier dosages of powdered
arsenate of lead left only 0.501 and 0.531 grain arsenious oxide per
pound. A fatal dose of arsenic for an adult is about two-thirds of a
erain, and this, of course, has to be taken into the stomach. Since
tobacco is not taken into the stomach, and since so little arsenic
will be taken into the mouth at any one time, it is not believed that
there is the slightest danger in using tobacco that has been poisoned
with either Paris green or arsenate of lead; in fact, the writer is per-
sonally acquainted with tobacco growers who have been applying
Paris green to their tobacco for from six to eight years and who have
been chewing and smoking the cured tobacco without injurious

effects.
POISONING THE TOBACCO MOTHS.

The custom of poisoning ‘‘ jimson”’ blooms with arsenide of
cobalt (flystone) to kill the tobacco moths when they feed has long
been recommended and has been practiced in nearly every tobacco
region, but unfortunately the custom has fallen into disuse. This
method of combating tobacco moths should be revived, for the kill-
ing of one female moth at “‘ jimson”’ blooms will be equivalent to the
killing of several hundred worms later.

The following is the formula for this poison:

Arsemide oiscobalt (dlystone) =. 5-245 22s eee eee ee ounce ss4.a
Waters ss 2222026 sett aoe se Sle Rete ae meee eee ee joie al

Sweeten, just before using, with molasses or honey. Place a few

drops in each bloom late in the afternoon.

SUMMARY.
CUTWORMS.

1. Plow sod land in the fall in preparing it for tobacco and keep
down all vegetation during the winter and spring. This will
starve the cutworms.

10.

11

METHODS OF CONTROLLING TOBACCO INSECTS. Zi

. If sod land has not been treated as reeommended above, use the

poisoned bait four or five days before setting tobacco, or drop
the bait about each hill directly after setting tobacco.

FLEA-BEETLES.

. Canvas seed beds tightly with strong whole canvas and thus

prevent entry of the beetles.

. Spray infested beds with arsenate of lead at the rate of 1 pound

paste form (or 4 pound powdered form) to 12 gallons of water.

. If flea-beetles are very numerous at setting time dip the tops of

the plants in the arsenate of lead recommended in No. 4.

. If flea-beetles continue to injure plants after setting, spray with

arsenate of lead at the strength given above.

TOBACCO HORNWORMS.

. Nearly all the destructive late July and August ‘‘shower’’ of

worms Is the direct offspring of tobacco moths that have issued
from hibernation during late July and early August.

. Over 60 per cent of the hibernating generation of moths emerge

from hibernation late in July and in August.

. Fall plowing of land that was in tobacco during the year will

destroy more than half of the hibernating generation and will
thereby reduce proportionately the number of tobacco worms
that will appear the next year late in July and in August.
Poison worms upon tobacco plants by dusting with Paris green.
Poison tobacco moths by placing a few drops of arsenide of
cobalt (flystone) solution in “jimson”’ blooms.

Approved:

JAMES WILSON,
Secretary of Agriculture.

Wasuineton, D. C., April 18, 1910.

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