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not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
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Copyright 2005, Board of Trustees, University
Bulletin 251 July, 1932
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
Wilmon Newell, Director
(In cooperation with Bureau of Entomology, U. S. D. A.)
CONTROL OF THE CELERY
LEAF-TIER IN FLORIDA
W. E. STONE, Associate Entomologist
B. L. BOYDEN, Associate Entomologist
C. B. WISECUP, Assistant Entomologist
E. C. TATMAN, Assistant Scientific Aid
Bureau of Entomology, United States Department of Agriculture.
Bulletins will be sent free upon application to the
AGRICULTURAL EXPERIMENT STATION
EXECUTIVE STAFF BOARD OF CONTROL
John J. Tigert, M.A., LL.D., President of the P. K. Yonge, Chairman, Pensacola
University A. H. Blanding, Bartow
Wilmon Newell, D.Sc., Director Raymer F. Maguire, Orlando
H. Harold Hume, M.S., Asst. Dir., Research Frank J. Wideman, West Palm Beach
Sam T. Fleming, A.M., Asst.Dir.,Administration Geo. H. Baldwin, Jacksonville
J. Francis Cooper, M.S.A., Editor J. T. Diamond, Secretary, Tallahassee
R. M. Fulghum, B.S.A., Assistant Editor
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Manager
K. H. Graham, Business Manager BRANCH STATIONS
Rachel McQuarrie, Accountant
NORTH FLORIDA STATION, QUINCY
MAIN STATION, GAINESVILLE L. Gratz, Ph.D., Plant Pathologist in Charge
MAN, LL R. Kincaid, M.S., Asst. Plant Pathologist
AGRONOMY W. A. Carver, Ph.D., Associate Agronomist
R. M. Crown, B.S.A., Assistant Agronomist
W. E. Stokes, M.S., Agronomist" Jesse Reeves, Farm Superintendent
W. A. Leukel, Ph.D., Agronomist
G. E. Ritchey, M.S.A., Associate* CITRUS STATION, LAKE ALFRED
Fred H. Hull, M.S., Associate
J. D. Warner, M.S., Associate John H. Jefferies, Superintendent
John P. Camp, M.S., Assistant Geo. D. Ruehle, Ph.D., Associate Plant Pathol-
ANIMAL HUSBANDRY W. A. Kuntz, A.M., Associate Plant Pathologist
A. L. Shealy, D.V.M., Animal Husbandman* B. R. Fudge, Ph.D., Associate Chemist
R. B. Becker, Ph.D., Specialist in Dairy Hus- W. L. Thompson, B.S., Assistant Entomologist
W. M. Neal, Ph.D., Associate in Animal Nutri- EVERGLADES STATION, BELLE GLADE
E. Thomas D.V.M., Assistant Veterinarian R. V. Allison, Ph.D., Soils Specialist in Charge
W. W. Henley, B.S.A., Assistant Animal Hus- R. N. Lobdell, M.S. Entomologist
W. W. bandmanley F. D. Stevens, B.S., Sugarcane Agronomist
P. T. Dix Arnold, B.S.A., Assistant in Dairy In- H. H Wedgeworth, M.S., Plant Pathologist
B. A. Bourne, M.S., Sugarcane Physiologist
vestigations J. R. Neller. Ph.D., Biochemist
CHEMISTRY A. Daane, Ph.D., Agronomist
R. W. Kidder, B.S., Asst. Animal Husbandman
R. W. Ruprecht, Ph.D., Chemist"* Ross E. Robertson, B.S., Assistant Chemist
R. M. Barnette, Ph.D., Chemist
C. E. Bell. Ph.D., Assistant SUB-TROPICAL STATION, HOMESTEAD
J. M. Coleman, B.S., Assistant
H. W. Winsor. B.S.A., Assistant H. S. Wolfe, Ph.D., Horticulturist in Charge
H. W. Jones, M.S., Assistant W. M. Fifield, M.S.. Assistant Horticulturist
Stacy O. Hawkins, M.A., Assistant Plant
ECONOMICS, AGRICULTURAL Pathologist
C. V. Noble, Ph.D., Agricultural Economist**
Bruce McKinley, A.B., B.S.A., Associate
M. A. Brooker, Ph.D., Associate I TATI
Zach Savage, M.S.A., Assistant FIELD STATIONS
ECONOMICS, HOME Leesburg
Ouida Davis Abbott, Ph.D., Specialist"* M. N. Walker, Ph.D., Plant Pathologist in
L. W. Gaddum, Ph.D., Biochemist Charge
C. F. Ahmann, Ph.D., Physiologist W. B. Shippy, Ph.D., Associate Plant Pathol-
ENTOMOLOGY K. W. Loucks, M. S., Asst. Plant Pathologist
J. R. Watson, A.M., Entomologist"* J. W. Wilson, Ph.D., Associate Entomologist
E. F. Grossman, M.A., Entomologist C. C. Goff, M.S., Assistant Entomologist
A. N. Tissot, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant Plant City
P. W. Calhoun, Assistant, Cotton Insects A. N. Brooks, Ph.D., Plant Pathologist
R. E. Nolen, M.S.A., Asst. Plant Pathologist
A. F. Camp, Ph.D., Horticulturist** Cocoa
Harold Mowry, B.S.A., Horticulturist A. S. Rhoads, Ph.D., Plant Pathologist
M. R. Ensign, M.S., Associate
A. L. Stahl, Ph.D., Associate Hastings
G. H. Blackmon, M.S.A., Pecan Culturist A. H. Eddins, Ph.D., Asso. Plant Pathologist
C. B. Van Cleef, M.S.A., Greenhouse Foreman
PLANT PATHOLOGY West Palm Beach
W. B. Tisdale, Ph.D., Plant Pathologist* D. A. Sanders, D.V.M., Veterinarian
George F. Weber, Ph.D., Plant Pathologist Monticello
R. W. Voorhees, M.S., Assistant
Erdman West, M.S., Mycologist Fred W. Walker, Assistant Entomologist
"*In cooperation with U.S.D.A. Bradenton
"* Head of Department David G. Kelbert, Asst. Plant Pathologist
INTRODUCTION ................. ..... .... ............... .......... 5
TYPE OF DAMAGE .................................................. 5
METHODS USED TO AVOID LOSSES ................................. .. 5
Early H arvesting ............................................ 5
Crop Refuse Should Be Plowed Under .......................... 6
EFFECT OF WASHING THE CELERY .................. ............... 7
USUAL SPRAYING PRACTICES FOR CELERY PESTS ........................ 7
OBJECTIONS TO THE USE OF ARSENICALS. ............................... 7
THE GROWTH OF THE CELERY PLANTS AND SPRAY RESIDUES ............. 8
INSECTICIDE TESTS ....................... ....................... 10
DUSTING VERSUS SPRAYING ............. .......................... 11
CONTROL WITH PYRETHRUM DUST .................................... 12
Against the Moths ............................................ 12
Against the Eggs ........................ ..... ............ 14
Against the Larvae ................ .......................... 14
PROPER APPLICATION OF PYRETHRUM DUST ........................... 15
Dusting Machinery ........................................... 15
Arrangement of Duster Pipes ................................. 16
Dust Most Effective on Young Larvae .......................... 17
Effect of Wind, Temperature, and Moisture ..................... 18
COMPARATIVE EFFICIENCY OF UNDILUTED PYRETHRUM AND VARIOUS
MIXTURES ............ ...... .................. .............. 19
SUMMARY ........................................................ 23
CONTROL OF THE CELERY LEAF-TIER IN FLORIDA
W. E. STONE, Associate Entomologist, B. L. BOYDEN, Associate
Entomologist,1 C. B. WISECUP, Assistant Entomologist, and
E. C. TAgMAN, Assistant Scientific Aid, Bureau of Entomology,
United States Department of Agriculture.
The celery leaf-tier (Phlyctaenia rubigalis Guen.) is the major
celery insect pest in the Sanford district of Florida. When con-
ditions are favorable for its development, the pest is capable of
causing severe losses; however, the weather conditions which
usually prevail during the winter months limit its development
and it is only during seasons of high temperatures that the insect
causes serious damage to the celery crop. It is the caterpillar
of a moth.
TYPE OF DAMAGE
Injury by the celery leaf-tier is caused by the feeding of the
larvae, or "tiers," on the leaves and stalks of the plant. The
young larvae usually feed on the under side of the leaf, but as
they near maturity they may eat the entire leaf. When about
one-third grown, they begin to web or tie one or more leaves
loosely together. Often a larva will tie a part of one leaf to
another or to a different part of the same leaf, forming a fold
within which it feeds. The pest prefers to feed on the tender,
succulent growth just above the heart of the plant, and such
feeding results in injured leaves and stalks covered by webbing
and castings from the worm's body. (Fig. 1.)
Besides the damage to the crop from actual foliage destroyed,
the presence of the worms necessitates a closer stripping of the
plants at harvest time to remove the injured leaves. Then also
the accumulation of webbing and frass is objectionable and lowers
the market value of the product.
METHODS USED TO AVOID LOSSES
Early harvesting of celery has been practiced to some extent
to avoid injury by the pest. The moths invariably seek the most
mature celery on which to lay their eggs. Upon discovering an
1Transferred to Plant Quarantine and Control Administration Feb. 1, 1928.
6 Florida Agricultural Experiment Station
infestation in a crop that is almost mature, growers often prefer
the decreased yield resulting from early harvesting to the expense
incident to the control of the pest.
CROP REFUSE SHOULD BE PLOWED UNDER
Directly after harvest the crop refuse should be plowed under
to destroy the insects left in the field. Larvae and pupae which
are shaken off when the plants are being handled at harvest time
and those removed with the leaf stalks that are stripped off as
unfit for market remain in the field. As the stripped leaf stalks
remain succulent for some time, the larger larvae complete their
development, emerging later as moths to add to the infestation
Fig. 1.-Celery petioles showing characteristic injury by celery leaf-tier
of the remaining plantings. Counts made in a field having 50
worms per plant showed that as many as six larvae may be left
on the strippings from each plant. Pupae and larvae that are well
plowed under after harvest of the crop will cease to be a factor
in the infestation, for laboratory and cage experiments show that
only 33 percent of the moths emerged when the pupae were cov-
Bulletin 251, Control of the Celery Leaf-tier in Florida 7
ered by one-half inch of soil, and when covered by more than an
inch no moths emerged.1
EFFECT OF WASHING THE CELERY
Since 1923 there has been a steady increase in the use of wash-
ing equipment in the preparation of celery for the market. These
machines aid in the removal, not only of dirt and spray residues,
but also in some cases of a considerable number of celery leaf-tier
Results of tests with washers in which the celery stalks pass
through the machine on an endless chain, the water being sprayed
under pressure of about 15 pounds from above and below the
conveyor belt, showed that only a comparatively small number
of the worms were washed from the stalks. Where the water
was under a pressure of 55 pounds, about 70 percent of the worms
were removed. These tests demonstrate that, although washing
does not remove all the celery worms from the plants, it will
reduce the number that would otherwise remain on the market
USUAL SPRAYING PRACTICES FOR CELERY PESTS
The usual practice for the control of celery blight in the San-
ford district is to spray regularly every week or 10 days with a
bordeaux mixture 4-4-50 or stronger. A protective covering of
the fungicide is thus maintained upon exposed leaves. During
the early growth of the celery arsenicals are often added to the
bordeaux mixture for the control of celery and cabbage loopers
and the semitropical army worm. These insects feed, as a rule,
on the outer, exposed leaves, and can be controlled by the usual
applications of arsenicals. In the case of the celery leaf-tier,
however, the industry is confronted with an insect having en-
tirely different feeding habits; consequently different methods of
control are necessary to protect the crop.
OBJECTIONS TO THE USE OF ASENICALS
Applications of arsenicals in the ordinary manner are not
adapted to the control of the celery leaf-tier. This insect rarely
appears in injurious numbers until within a few weeks of harvest-
'Field observations by Dayton Stoner, of the U. S. Bureau of Entomology,
and R. L. Miller, formerly of the Florida State Plant Board, have confirmed
the results of these experiments.
8 Florida Agricultural Experiment Station
ing, and any arsenicals applied at this time will leave poisonous
residues on the celery.
Unpublished data of B. L. Boyden and J. O. Clark show that
arsenicals applied as a dust on celery leave a larger proportion of
residue on the plants than when a spray is used.
A series of laboratory experiments were made to determine
the actual value of arsenicals in the control of the celery leaf-
tier. The plants were thoroughly sprayed at the rate of 100
gallons of the mixture to the acre. Colorimetric prints of the
leaves showed an even distribution of the arsenical over both
upper and lower leaf surfaces, a condition not possible to obtain
in commercial sprayings. Tests were made with 2, 3, and 4
pounds of paris green to 100 gallons of water. The 4-pound
strength gave good control, but the other dosages were ineffective.
Lead arsenate was used in mixtures of 3, 6, and 10 pounds to 100
gallons of water. Only the 10-pound strength showed any meas-
ure of effectiveness. Calcium arsenate was tested at the rates of
4, 5, and 8 pounds to 100 gallons of water, with no apparent effect
on the celery leaf-tier. These experiments show that excessive
dosages of lead arsenate and paris green are required to effect
control of the celery leaf-tier under laboratory conditions, and
that calcium arsenate is ineffective even when used in large
These tests, combined with results of field experiments and the
experience of the growers, show that arsenicals are of little value
against the celery leaf-tier; consequently the use of these poisons
is not recommended.
THE GROWTH OF THE CELERY PLANT AND SPRAY
In connection with the problem of spray and dust residues,
records were kept on the growth of several representative plants
of both the winter and spring crops of celery. As the celery plant
develops the young leaf stalks displace the old ones, which grad-
ually die and fall off. During growth each leaf stalk was tagged
and its record was tabulated.
Figure 2 shows the development of a celery plant during the
winter season from the time it was set in the field until it was
ready for market. It will be noted that 15 leaf stalks dropped
from the plant during growth and 10 others were stripped off in
the field at harvest, leaving 15 leaf stalks to be crated for market.
Bulletin 251, Control of the Celery Leaf-tier in Florida 9
L J mo. 2Ld mo. 3r mo. 4 mo. 5 mo.
rpd in growth
Fig. 2.-Diagrammatic representation of the growth of a celery plant
during the winter season.
The development of the plant through each month of the season
is illustrated by the photographs at the bottom of Fig. 2.
Figure 3 shows in a like manner the development of a celery
plant during the spring season. Although the plants represented
in Fig. 2 took almost five months to mature, and those in Fig. 3
only 3 1/3 months, practically the same number of leaf stalks
were marketed in each case.
In both the winter and spring crops only that part of the plant
which developed during the last five weeks of growth was mar-
keted. As the leaves could not be tagged until they had devel-
oped from the bud about a week, such leaves were really formed
about six weeks before harvest. In Fig. 3 the oldest leaf that
was retained after stripping was between five and six weeks old
when the plant was cut for market.
From the growth records shown in Figures 2 and 3 it will be
seen that all residue from sprays applied before the last six weeks'
period will be removed in the field in connection with harvest;
so arsenicals can be applied with safety previous to this time.
10 Florida Agricultural Experiment Station
Le ri mo. 2 1 mo. 3Lmo. h mo.
-+- = --
Fig. 3.-Diagrammatic representation of the growth of a celery plant
during the spring season.
This practice will control the semitropical army worm and loopers,
but will not control the celery leaf-tier.
Since the celery leaf-tier normally feeds above the heart within
the canopy of the celery plant, an ideal insecticide for its control
must be harmless to the consumer and also noninjurious to the
tender celery heart. In the search for such an insecticide a con-
siderable number of stomach and contact poisons, both dusts and
sprays, were used, some of which proved poisonous to the celery
leaf-tier larvae but also caused severe foliage injury. Nicotine,
in both dust and spray form, an extract of derris, and derris
powder were all ineffective. The most satisfactory insecticide
tested was pyrethrum dust.
As early as 1896 Quaintance2 recommended the use of pyre-
thrum, as either dust or spray, against celery insects. Pyrethrum
dust was thus utilized rather generally by the growers through-
2Quaintance, A. L.: Insect enemies of truck and garden crops. Fla. Expt.
Sta. Bul. 34, 327 p. 1896.
Bulletin 251, Control of the Celery Leaf-tier in Florida 11
out the Sanford district for control of the celery leaf-tier, but
with varying degrees of success. On account of this lack of
uniform control a study was made of the factors which might
have a bearing on the effectiveness of pyrethrum.
DUSTING VERSUS SPRAYING
The nature of the growth of the celery plant determines the
method of application of an insecticide against the celery leaf-tier.
The principal varieties of celery grown in Florida are the Golden
Self-Blanching and several strains of Special, all of which are
noted for their habit of compact growth, as illustrated in Fig. 4.
Fig. 4.-Photograph of a celery plant, showing area in which majority of
leaf-tier eggs are deposited and illustrating density of growth which
necessitates the use of a dust. The letters A, B, C, D and E refer to
parts of the plant from which the leaves correspondingly lettered in
Fig. 5 were taken.
The method of planting tends to accentuate this compactness, as
the plants are spaced three to four inches in the rows, which are
28 or 30 inches apart. Under these conditions the outer canopy
of leaves forms an almost impenetrable cover, protecting the inner
heart leaves from applications of spray.
Although the celery leaf-tier moths deposit their eggs almost
anywhere on the plants, it has been found that the majority are
12 Florida Agricultural Experiment Station
laid within the area surrounded by the outer canopy of leaves, as
shown by the dotted line in Fig. 4. On 75 celery plants taken
from the field during one season 2,422 eggs were deposited, 68
percent of which were in this part of the plants. The larvae
also prefer the more tender leaves of the inner area and tend to
concentrate there. Practically all the damage is thus done in the
marketable part of the plant.
Sprays, even under high pressure, do not penetrate the outer
canopy of leaves and reach the point where they are needed.
Figure 5 shows sulphide prints of leaves of both dusted and
sprayed celery plants made by the method devised by Hamilton
and Smith.3 The parts of the plants from which leaves were taken
are shown by the letters A, B, C, D and E in Fig. 4. The upper
surface of each leaf is shown above the letters and the corre-
sponding lower surfaces beneath. It will be noted that the spray
was distributed only on the outer canopy of leaves (Fig. 5 above,
A and B), and adhered mainly to the upper surfaces, leaving the
area subject to celery leaf-tier damage unprotected. On the other
hand, the dust penetrated to the heart of the plant, collecting
particularly in this area. (Fig. 5 below, C, D, and E.) These
results indicate that the nature of the plant growth requires that,
to be effective against the celery leaf-tier, an insecticide should
be applied as a dust.
CONTROL WITH PYRETHRUM DUST
AGAINST THE MOTHS
Growers will often dust when they see the greatest number of
celery leaf-tier moths. Invariably they report a good kill, and
the small number of moths remaining in the field after a dusting
seems to confirm their contention.
A field having 135 moths per 300-foot row was dusted with
pyrethrum. As soon as the dust settled in the plants, the moths,
annoyed by the dust, began to rise and drift with the wind from
the test area to adjacent fields at the rate of three per second.
No dead moths were found the next day. A check on the adjoin-
ing fields showed an increase of 10 moths per row while the dusted
field showed only 10 moths per row remaining. However, nine
days after dusting the treated field became infested with moths
3Hamilton, C. C., and C. M. Smith: A colorimetric method for showing
the distribution and quantity of lead arsenate upon sprayed and dusted
surfaces. Jour. Econ. Ent. 18:502. 1925.
Bulletin 251, Control of the Celery Leaf-tier in Florida 13
A B C D E
Fig. 5.--Above, pictorial presentation of penetration of spray on celery
plants; below, pictorial presentation of penetration of dust on celery
plants. The letters A, B, C, D and E in the upper picture show, by
reference to Fig. 4, the parts of the plant from which the leaves were
14 Florida Agricultural Experiment Station
and a second treatment was required to prevent severe damage
by the celery leaf-tier. Dusting for moths of the celery leaf-tier
therefore is of doubtful value, for few moths are killed and others
are driven to neighboring fields where they may intensify a mild
infestation in younger celery.
When tree swallows, which destroy large numbers of moths,
are present, dusting for moths is of some value, as the pyrethrum
disturbs the moths and allows the swallows which swoop over
the dusted field an opportunity to capture them.
Laboratory tests show that pyrethrum dust actually kills the
moths when they are dusted in a confined space. In this case,
however, the dust is applied directly to the moths, under condi-
tions unobtainable in the open field.
AGAINST THE EGGS
The belief that pyrethrum dust kills the eggs of the pest has
been advanced by some celery growers. In an effort to find out
what effect, if any, pyrethrum had on the eggs of the celery leaf-
tier, pyrethrum in varying quantities was placed on fresh celery
leaf-tier eggs on leaves in the laboratory and allowed to remain
for the period of incubation. Less than 20 percent of the eggs
treated in this way failed to hatch. Untreated eggs used as checks
all hatched. These eggs receive a heavier and more even appli-
cation of dust than would be possible in the field. In the case of
plants brought from a field dusted heavily with pyrethrum only
6 percent of the eggs failed to hatch.
AGAINST THE LARVAE
Pyrethrum is more effective against the larva of the celery
leaf-tier than against any other stage of the insect's development.
A very small quantity of the dust adhering to the skin of a tier
will induce excitability, followed in a few minutes by partial
paralysis and finally by death. Both laboratory experiments and
field observations show that all larvae receiving a very small
quantity of pyrethrum dust are killed. The minimum lethal dose
of pyrethrum has not yet been determined, as it varies with the
size of the larvae. However, it appears that a minute quantity
of fresh pyrethrum dust scattered over the body of the larva is
all that is required.
Bulletin 251, Control of the Celery Leaf-tier in Florida 15
PROPER APPLICATION OF PYRETHRUM DUST
Many attempts were made by the growers to secure control in
the field by applying pyrethrum dust with some form of hand
duster. Invariably a poor kill of the celery leaf-tier resulted;
consequently, it was claimed that control could not be secured by
the use of pyrethrum. Careful tests showed that the method of
application was at fault and not the pyrethrum. With the hand
dusters it was impossible to place the dust under the outer
canopy of leaves.
In the Sanford district the horse or mule drawn traction duster
of the four-row type is used. Figure 6 shows this type of duster
with the discharge pipes arranged to show the different methods
used in the application of dusts. These dusters all apply varying
quantities of pyrethrum, but the older models are limited to a
maximum of about 25 pounds per acre. When tested against one
another, or observed under similar conditions, there appears to
be very little choice between various makes of machines. The
chief difficulty with these machines has been that the flow of
dust is not continuous and an uneven distribution of dust results.
Fig. 6.-Traction duster with different arrangement of pipes in use in the
Sanford district, and plow attachment used in experimental work in an
effort to secure better penetration of dust. A, discharge pipe too high
above plants; B, nozzle arrangement of this type is of no value; C, proper
adjustment, outlet well down in plant row; D, special "plow" attachment
for opening canopy of leaves.
16 Florida Agricultural Experiment Station
The new models mix the dust with the air in the fan chamber and
have a force feed from the-hopper which gives a continuous flow
of dust so that better control can be expected.
ARRANGEMENT OF DUSTER PIPES
Under optimum conditions-i. e., little wind, dry plants, and
high temperature-many growers were securing a kill not ex-
ceeding 10 or 15 percent of the larvae present, while others were
getting very good control. It appeared, therefore, that the de-
ciding factors must be the method and the time of application of
the dust in relation to the stage of larval development.
In Fig. 6 are shown various arrangements of the discharge
pipes for applying the dust, all attached to the same duster. A
shows the usual method of application, with the opening of the
pipe entirely above the celery plant. With this arrangement very
little of the dust is forced through the outer canopy of leaves,
and even a slight breeze dissipates the dust before it can settle
into the plants. B shows the method used in the application of
fungicides for disease control. The difficulty of securing pene-
tration through the overhanging leaves is evident. C illustrates
the method of application found to give the best control under
all conditions. The outlet of the duster pipe has been placed as
low as possible in the celery plant, so that the dust is discharged
within the canopy of leaves, rebounding and drifting throughout
the plant. D illustrates a "plow" arrangement designed to open
the plants in front of the lowered pipe shown in C. This arrange-
ment gave only a slight increase in control, which did not com-
pensate for the time required to keep the "plow" properly ad-
A kill of from 10 to 25 percent is all that can be expected when
the pipe opening is above normal celery plants. The maximum
kill was only about 65 percent and was obtained when the plants
had rather short stalks with an open canopy due to abnormal
growth during the warm spring weather. Likewise the kill se-
cured by using two nozzles, one on each side of the row, was poor.
A 30 percent kill with the old-model dusters arranged in this
manner is considered high.
Figure 7 shows all four discharge pipes arranged in the proper
manner to give the best control. Despite the compact growth of
the celery plants, the lowered pipes are drawn through the leaves
with a negligible amount of injury to the plant. Dust applied in
Bulletin 251, Control of the Celery Leaf-tier in Florida 17
this way covers the heart leaves, as shown by the sulphide prints
in Fig. 5.
No rule for the setting of the pipes can be given, owing to dif-
ferences in the growth of celery. They must be placed deep
enough to deposit dust on the heart of the celery plant without
actually coming into contact with it. If no dust is found on the
heart of the plant after dusting, a poor kill is likely to result.
Fig. 7.-Proper arrangement of dusting pipes to secure maximum control
of the celery leaf-tier.
The method of planting celery in the Sanford district is so exact
that when the pipes are set at a certain depth and spaced for the
rows an entire field can be covered with only minor adjustments.
DUST MOST EFFECTIVE ON YOUNG LARVAE
A factor equally as important as the adjustment of the dusting
machine is the stage of development of the larvae. Many times
a celery leaf-tier outbreak is not noticed until the larvae are half
grown or larger and have protected themselves by webbing the
leaves together. When this is the case a kill sufficient to control
is not obtained even when pyrethrum is applied under proper
conditions, with the pipes deep in the plants. A kill of 65 percent
of the larvae, when dusting is delayed until they are two-thirds
grown, is obtained only under the most favorable dusting con-
18 Florida Agricultural Experiment Station
EFFECT OF WIND, TEMPERATURE, AND MOISTURE
During past seasons many tons of pyrethrum dust were applied
while medium or fairly high winds were blowing. Pyrethrum
dust is a very light substance that will drift with any breeze, dis-
sipating itself above the plants without coming into contact with
the insects. The properties that make it so well adapted to dust-
ing demand a quiet day for proper application. When fields are
dusted on windy days, the kills are never more than 65 percent
and usually are much smaller.
A common practice when dusting during windy weather is to
drag cloth trailers behind the duster, as shown in Fig. 8. This
Fig. 8.-Traction duster with trailer attachment which, experiments prove,
is of no value in confining dust to the celery plants.
apron is supposed to hold the dust over the plants long enough to
allow it to penetrate. An experiment, conducted during a 13-mile
wind, showed that dusting without the apron gave control as good
as, if not better than, was obtained with its use, although both
methods gave poorer control than was obtained on a calm day.
It is well known among growers that, other things being equal,
the best control is secured when pyrethrum is applied on a warm
day. The effect of temperature upon the reaction of pyrethrum
is not understood, but it is known that temperature directly affects
the activity of the celery leaf-tier larvae. This activity on a
Bulletin 251, Control of the Celery Leaf-tier in Florida 19
warm day undoubtedly increases the likelihood of a larva's com-
ing in contact with the dust.
During a series of windy days many growers, realizing the
waste involved in dusting during the day, when the wind is high,
dust at night or early in the morning. This practice is recom-
mended if done at a time when there is little dew or other mois-
ture on the celery. Plants from fields dusted while damp showed
caked areas of dust just below the nozzle openings, indicating
poor distribution. Since under such conditions the dust adheres
to the wet leaves and does not circulate through the leaf stalks
of the plant, a large proportion of the larvae escape contact with
COMPARATIVE EFFICIENCY OF UNDILUTED PYRE-
THRUM AND VARIOUS MIXTURES
Only closed-flower pyrethrum of the best grade obtainable has
been used in the Sanford area, and it has thus far been applied
full strength at the rate of 40 to 50 pounds per acre in two appli-
cations about 30 minutes apart. Good control has not been accom-
plished by one application of pyrethrum, because it is seldom
possible for the dust to penetrate between the webbed leaves in
sufficient quantities to effect a satisfactory kill. The larvae are,
however, irritated sufficiently by the first dusting to cause them
to move about in the plants, and they will thus receive a lethal
dose from the second application.
As the price of pyrethrum increased from 30 cents per pound
in 1927 to 50 cents per pound in 1929, it became imperative that
the cost of control be reduced. Experiments during the season
of 1928-29 were made with Japanese pyrethrum flower dust,
which is much cheaper than closed-flower dust, as it consists of
both open and closed flowers ground together. Mixtures of this
dust with hydrated lime and sulphur dust were tested experi-
mentally. Lime was used because of its good dusting qualities
and low price, sulphur because of its value in controlling the red
Early-season experiments under unfavorable conditions showed
that a 50 percent mixture promised as good control as did the
undiluted pyrethrum, when both were applied in the same quan-
tity. Under as near ideal conditions as possible, a series of tests
were made which definitely showed the value of these mixtures
in controlling the celery leaf-tier. A fairly heavily infested field
20 Florida Agricultural Experiment Station
of celery was chosen and careful counts were made as a check
the day before the dusts were applied. Approximately 20 per-
cent of the larvae present were well over half grown, while the
remaining 80 percent ranged from newly hatched to nearly half
grown larvae. The discharge pipes of the duster were kept as
deep in the celery as possible. The results of these experiments,
given in Table I, show a kill with 50 percent mixtures equal to that
from the undiluted pyrethrum. Double application of the pyre-
thrum-lime dust gave a kill of 91 percent, the best secured. The
diluted dust was used at a rate of approximately 50 pounds per
acre, in two applications of 25 pounds each, at intervals of 30
minutes. The second best kill, 88.4 percent, was obtained from
the pyrethrum alone applied at the rate of approximately 40
pounds to the acre in two applications, as used in the other test.
When pyrethrum mixtures are used, it is recommended that the
lime or sulphur be mixed with the pyrethrum immediately before
application, as it is not known how long the pyrethrum will retain
its effectiveness when mixed with these materials. It is essential
Fig. 9.-Section of an infested celery row 10 days after being dusted with
a pyrethrum-sulphur mixture.
TABLE I.-EFFECT OF PYRETHRUM DUSTS UPON MORTALITY OF THE CELERY LEAF-TIER IN EXPERIMENTS
CONDUCTED DURING THE SEASON OF 1928-29.
Quantity Larvae counted alive Kill 24 hours after
Plot Applica- Quantity of pyr- per plant 24 hours dusting c.
No. Dust applied tions of dust ethrum after dusting Z"
per acre per arce ----- ----
Small Large Total Small Large Total
Number Pounds Pounds Number Number Number Percent Percent Percent
1 Pyrethrum................................ 1 19 19 6.6 5.4 12.0 83.3 47.5 76.0
2 do .............................. 2 38 38 2.1 3.6 5.7 94.7 65.0 88.6
3 do ................. .............. 3 57 57 2.6 3.9 6.5 93.4 62.1 87.0
4 Pyrethrum 50, Lime 50 .................... 1 27 13.5 7.2 3.6 10.8 81.8 65.0 78.4
5 do ....... ................ 2 54 27 2.0 2.4 4.4 94.9 76.7 91.2
6 Pyrethrum 50, Sulphur 50................... 1 23 11.5 11.0 4.5 15.5 72.2 56.3 69.0 t
7 do ............... .............. 2 46 23 7.6 4.7 12.3 80.8 54.3 75.4 >
8 Pyrethrum 50, Sulphur 25, Lime 25........... 1 29 14.5 6.8 3.8 10.6 73.3 56.8 69.0
9 do .............................. 2 58 29 4.0 2.8 6.8 84.3 68.1 80.2
Counts on plots Nos. 1 to 7 preceding dusting......................... 39.7 10.3 50.0
Counts on plots Nos 8 and 9 preceding dusting....................... 25.5 8.8 34.3
--- --- ------- -------------
22 Florida Agricultural Experiment Station
that the pyrethrum be thoroughly mixed with the carrier. Any
ordinary dust mixer, such as one of the common barrel type, is
satisfactory. The mixing should not be left to irresponsible help.
Freshly-ground pyrethrum should be secured whenever possible,
as in a humid climate the dust tends to cake and harden.
A comparison of the percentages of small and large larvae
killed shows an average of 22 percent increase in kill among the
small larvae for the four dusts tested, indicating the value of
dusting when the larvae are very small. A severe infestation
can be predicted when a large number of moths are flushed out
of the celery in the course of normal cultural operations. Soon
after most of the moths have disappeared it is time to look for
leaf-tier damage. If, upon opening the leaves of the canopy, it
is found that the tender foliage above the heart is being skeleton-
ized by the young larvae, dusting cannot be delayed many days if
good control is to be obtained.
Figure 9 shows celery plants taken from the sulphur-pyre-
thrum plot 10 days after receiving two applications of dust.
Though only a 75 percent kill was secured on this plot, the plants
Fig. 10.-Section of celery row in check plot, showing destruction by the
celery leaf-tier 10 days after adjacent plots were dusted with pyrethrum.
See Fig. 9.
Bulletin 251, Control of the Celery Leaf-tier in Florida 23
were not damaged by the leaf-tier. An adjacent undusted plot
photographed at the same time is shown in Fig. 10. The celery
in this check plot was completely destroyed by the feeding of the
larvae. This shows the amount of damage accomplished by a
large number of larvae in the short period required for their
The increased kill due to the second application for each of the
four dusts used was found to average 11 percent, or five larvae
per plant. Where celery growth is retarded by warm weather or
other unfavorable conditions, this number is sufficient to cause
considerable damage in the period before harvest.
Celery leaf-tier damage results in a smaller yield of celery, due
to heavy stripping, and in a product that is of lower market value.
Proper cultural and harvesting practices are useful in aiding
in the control of this insect.
Arsenicals are of little value in controlling the celery leaf-tier,
and in addition their use may result in a dangerous arsenical
residue in the harvested product.
Fresh pyrethrum dust, either alone or mixed with lime or
sulphur, applied to dry plants on a calm day with a traction
duster, is effective against the larvae of the celery leaf-tier.
Pyrethrum dust must reach the heart of the celery plant in
order to be effective against the celery leaf-tier.
The treatments should be directed against the immature larvae
as they are more susceptible to the action of the pyrethrum than
the nearly mature forms.