• TABLE OF CONTENTS
HIDE
 Front Cover
 Credits
 Table of Contents
 Summary
 How the whitefly injures trees
 Summary of life history
 Methods of control
 The fungus diseases
 Treatment with insecticides
 Winter treatment
 Spring, summer and fall sprayi...
 Spraying solutions
 Three species of whitefly
 Whitefly and freezing
 Quarantine
 Food plants
 Plants to be condemned
 Whitefly and increase of scale...
 When to spray for scales
 Resume of scientific results














Group Title: Bulletin - University of Florida Agricultural Experiment Station ; 103
Title: Whitefly control
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Permanent Link: http://ufdc.ufl.edu/UF00027694/00001
 Material Information
Title: Whitefly control
Series Title: Bulletin - University of Florida Agricultural Experiment Station ; 103
Physical Description: Book
Language: English
Creator: Berger, E. W.
Publisher: University of Florida Agricultural Experiment Station
Publication Date: 1910
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Table of Contents
    Front Cover
        Page 1
    Credits
        Page 2
    Table of Contents
        Page 3
    Summary
        Page 4
    How the whitefly injures trees
        Page 5
    Summary of life history
        Page 5
    Methods of control
        Page 6
    The fungus diseases
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
    Treatment with insecticides
        Page 14
        Page 15
        Page 16
    Winter treatment
        Page 17
        Page 18
    Spring, summer and fall spraying
        Page 19
        Page 20
    Spraying solutions
        Page 21
    Three species of whitefly
        Page 22
    Whitefly and freezing
        Page 22
    Quarantine
        Page 23
    Food plants
        Page 24
    Plants to be condemned
        Page 25
    Whitefly and increase of scales
        Page 26
    When to spray for scales
        Page 27
    Resume of scientific results
        Page 28
Full Text

SEPTEMBER, 1910


UNIVERSITY OF FLORIDA

Agricultural Experiment Station




WHITEFLY CONTROL

BY
E. W. BERGER, Ph.D.


Fig. I.-The cloudy-winged whitefly, Aleurodes nubifera.
Magnified 32 times.


The Station bulletins will be sent free upon application to the Experiment
Station, Gainesville.

E. O. PAINTER PRINTING CO., DeLand, Fla.


BULLETIN 103











BOARD OF CONTROL


P. K. YONGE, Chairman, Pensacola, Fla.
T. B. KING, Arcadia, Fla.
E. L. WARTMANN, Citra, Fla.
F. P. FLEMING, Jr., Jacksonville, Fla.
W. D. FINLAYSON, Old Town, Fla.





STATION STAFF

P. H. ROLFS, M.S., Director.
J. M. SCOTT, B.S., Animal Industrialist and Assistant Director.
A. W. BLAIR, A.M., Chemist.
E. W. BERGER, Ph.D., Entomologist.
H. S. FAWCETT, M.S., Plant Pathologist.
B. F. FLOYD, A.M., Plant Physiologist.
JOHN BELLING, B.Sc., Assistant Botanist ( and Editor).
S. E. COLLISON, M.S., Assistant Chemist.
A. P. SPENCER,* M.S., Assistant in Extension Work.
C. K. MCQUARRIE,* Assistant Superintendent Farmers' Institutes.
JOHN SCHNABEL, Assistant Horticulturist.
O. F. BURGER, A.B., Laboratory Assistant to Plant Pathologist.
MRS. E. W. BERGER, Librarian.
BERTHA EVES, Secretary.
K. H. GRAHAM, Auditor and Bookkeeper.
M. CREWS, Farm Foreman.
KATE BOULWARE,* Stenographer.


*Give all their time to extension work.



















CONTENTS

PAGE
How the Whitefly Injures Trees ................... ................. 5
Summary of Life History...................... ... ............... 5
Methods of Control...................... ... ..................... 6
The Fungus Diseases ...................... ......................... 6
T he R ed F ungus........... .. .............................
Experiments in Spreading Fungus ...............................
Introducing Red Fungus......................................... o
Other Fungi .............. ........... ........ ............. II
Pinning Leaves ................................................ 12
Artificial Culture of Fungus......................... ................ 12
Treatment with Insecticides................... ..... .. ............ 14
Experim ents in Spraying. .. ................................. .. 14
Fumigation .............................................. 17
W inter Treatment .................. ................. ............ I;
Localities Just Becoming Infested................................. 18
Badly Infested Localities... ................... .................... 18
Spring, Summer, and Fall Spraying. ................................... 19
Spring Treatment .................. .............................. 19
Summer Treatment ............. ......... .......................... 20
Fall Treatment ................... ........................... 20
Spraying Solutions .. .......................... .. ................ 21
Three Species of Whitefly.................. .............. .......... 22
Whitefly and Freezing........................... ................... 22
Quarantine .......... .............................................. 23
Food Plants ........... ............................................ 24
Plants to be Condemned.................. ........ .......................... 25
W hitefly and Increase of Scales.................... .............. ... 26
W hen to Spray for Scales....................................... 27




















SUMMARY


r. It is easy in Florida to start growths of the fungus parasites in
whitefly-infested trees at the proper time.
2. The proper time to spray fungus spores is when there are many
young larvae on the leaves and the weather is both moist and warm.
3. The fungi should be put on the trees as soon as favorable condi-
tions arise, in order that their growth may be helped by the summer rains.
4. If the fungi are applied late in the season, they will not increase
sufficiently to be of material advantage until the next year.
5. During a wet spring, favorable conditions for starting growths of
fungus may arise as early as April. Generally speaking, the period of
summer rains is the most certain time to start fungus.
6. In localities where there is not sufficient moisture, or when the
trees are out of condition, the fungi grow sparingly, and spraying with
insecticides or fumigation should be carried on to check the whitefly.
7. Spraying with insecticides should be done when there are few or
no adult whiteflies swarming about, and when all or most of the eggs
have hatched, which is about Io to 14 days after the last of a brood of
adults has disappeared.
8. In April or May, in October or November, and during winter, are
the times when the most effective spraying with insecticides may be done.
g. In summer the fungi should be applied, because during the period
of rains spraying with insecticides is difficult, but the fungi can then be
spread to the best advantage.









WHITEFLY CONTROL

BY

E. W. BERGER, PH.D.

It is important that the citrus grower whose trees are infested
or threatened with infestation by whitefly, should have at hand the
necessary information which will enable him to initiate and conduct
repressive measures to the best advantage. This bulletin is an
endeavor to bring together the essential facts of whitefly control
in a brief form. The whitefly may be controlled, though it is
almost impossible to eradicate it. To control this pest is to keep it
in check sufficiently for the trees to continue to bear clean fruit.

HOW THE WHITEFLY INJURES TREES

Badly infested citrus trees usually bear but a small amount of
truit, and what is borne is insipid and covered with sooty mold.
The direct injury done to the trees consists in the loss of the sap
which the insects suck out at the rate of more than 15 pounds per
month for each million of whitefly larvae. Indirectly the trees
are injured by the sooty mold which covers the leaves and fruit.
This sooty mold is a black fungus which develops in the honey-
dew, a sugary excretion ejected by all stages of the whitefly. This
mold is itself injurious to the trees, because by shutting off some
of the sunlight it interferes with the elaboration of food materials
in the leaves and also retards the ripening of the fruit. Tests with
iodine solution show that the parts of leaves covered with sooty
mold produce less starch than the parts not covered.

SUMMARY OF LIFE HISTORY

The young of the citrus whitefly (sometimes incorrectly called
eggs) are scale-like, and live on the under surfaces of the leaves.
They pass through five stages of development, increasing from
about one-eightieth of an inch to about one-eighteenth of an inch
in length. The sixth stage, or final one, is the adult winged white-
fly. The first four stages are spoken of as the first, second, third
and. fourth larval stages; and the fifth stage, the transformation
stage from which the winged whitefly emerges, is called the pupa.









WHITEFLY CONTROL

BY

E. W. BERGER, PH.D.

It is important that the citrus grower whose trees are infested
or threatened with infestation by whitefly, should have at hand the
necessary information which will enable him to initiate and conduct
repressive measures to the best advantage. This bulletin is an
endeavor to bring together the essential facts of whitefly control
in a brief form. The whitefly may be controlled, though it is
almost impossible to eradicate it. To control this pest is to keep it
in check sufficiently for the trees to continue to bear clean fruit.

HOW THE WHITEFLY INJURES TREES

Badly infested citrus trees usually bear but a small amount of
truit, and what is borne is insipid and covered with sooty mold.
The direct injury done to the trees consists in the loss of the sap
which the insects suck out at the rate of more than 15 pounds per
month for each million of whitefly larvae. Indirectly the trees
are injured by the sooty mold which covers the leaves and fruit.
This sooty mold is a black fungus which develops in the honey-
dew, a sugary excretion ejected by all stages of the whitefly. This
mold is itself injurious to the trees, because by shutting off some
of the sunlight it interferes with the elaboration of food materials
in the leaves and also retards the ripening of the fruit. Tests with
iodine solution show that the parts of leaves covered with sooty
mold produce less starch than the parts not covered.

SUMMARY OF LIFE HISTORY

The young of the citrus whitefly (sometimes incorrectly called
eggs) are scale-like, and live on the under surfaces of the leaves.
They pass through five stages of development, increasing from
about one-eightieth of an inch to about one-eighteenth of an inch
in length. The sixth stage, or final one, is the adult winged white-
fly. The first four stages are spoken of as the first, second, third
and. fourth larval stages; and the fifth stage, the transformation
stage from which the winged whitefly emerges, is called the pupa.





G FLORIDA AGRICULTURAL EXPERIMENT STATION

The best time to spread the whitefly-destroying fungi or to
spray with contact insecticides is when these insects are mostly
in the first three larval stages, or while they are still in the thin,
flat condition of the fourth stage. (For a detailed discussion, read
what is said under the heading of "Experiments in Spraying" on a
later page.) Those in the thickened condition of the fourth or
in the pupal stage, are less easily killed, requiring a stronger insec-
ticide. The eggs of the whitefly cannot be destroyed by ordinary
insecticides, and it is useless to spray the winged adults. The
whitefly begins its larval development about o1 days or two weeks
after the swarming periods in spring, summer, and fall. In other
words, the eggs hatch in 10 to 14 days, and there are three broods
of larvae. The spring brood of adults is definitely separated in time
from the summer brood, the intervening period being occupied by
-the spring brood of larvae, which may be expected in March, April
or May, according to season and locality. The summer brood and
the late summer to early fall brood are not so definitely separated
as the spring and summer broods of adults, because during the
warm summer weather the adults are emerging nearly all the time;
but large numbers of larvae are present during parts of July ana
August. The late summer to early fall brood is again separated
from the next spring brood by nearly the whole of the fall, the
whole of the winter, and sometimes a part of the spring.

METHODS OF CONTROL

There are three methods of control-the fungus diseases, spray-
ing with insecticides, and fumigation.

THE FUNGUS DISEASES

It is a well-established fact, but not a widely known one, that
insects are subject to diseases as well as other animals and man.
Among the principal agents responsible for the diseases of insects
are certain parasitic fungi, and the whitefly, fortunately for us,
is subject to attack by at least six of them. These are the red
fungus (Aschersonia aleyrodis) yellow fungus (Aschersonia fla-
vo-citrina), brown fungus (Aegerita webberi Fawcett), cinnamon
fungus (Verticillium heterocladum), white-fringe fungus (Micro-
cera sp.), and occasionally a species of Sporotrichum related to the
chinchbug fungus. These are all parasites of the larvae of whitefly,
except the last one, which has occasionally been found infesting
dead adult whiteflies, and presumably had caused their death.





G FLORIDA AGRICULTURAL EXPERIMENT STATION

The best time to spread the whitefly-destroying fungi or to
spray with contact insecticides is when these insects are mostly
in the first three larval stages, or while they are still in the thin,
flat condition of the fourth stage. (For a detailed discussion, read
what is said under the heading of "Experiments in Spraying" on a
later page.) Those in the thickened condition of the fourth or
in the pupal stage, are less easily killed, requiring a stronger insec-
ticide. The eggs of the whitefly cannot be destroyed by ordinary
insecticides, and it is useless to spray the winged adults. The
whitefly begins its larval development about o1 days or two weeks
after the swarming periods in spring, summer, and fall. In other
words, the eggs hatch in 10 to 14 days, and there are three broods
of larvae. The spring brood of adults is definitely separated in time
from the summer brood, the intervening period being occupied by
-the spring brood of larvae, which may be expected in March, April
or May, according to season and locality. The summer brood and
the late summer to early fall brood are not so definitely separated
as the spring and summer broods of adults, because during the
warm summer weather the adults are emerging nearly all the time;
but large numbers of larvae are present during parts of July ana
August. The late summer to early fall brood is again separated
from the next spring brood by nearly the whole of the fall, the
whole of the winter, and sometimes a part of the spring.

METHODS OF CONTROL

There are three methods of control-the fungus diseases, spray-
ing with insecticides, and fumigation.

THE FUNGUS DISEASES

It is a well-established fact, but not a widely known one, that
insects are subject to diseases as well as other animals and man.
Among the principal agents responsible for the diseases of insects
are certain parasitic fungi, and the whitefly, fortunately for us,
is subject to attack by at least six of them. These are the red
fungus (Aschersonia aleyrodis) yellow fungus (Aschersonia fla-
vo-citrina), brown fungus (Aegerita webberi Fawcett), cinnamon
fungus (Verticillium heterocladum), white-fringe fungus (Micro-
cera sp.), and occasionally a species of Sporotrichum related to the
chinchbug fungus. These are all parasites of the larvae of whitefly,
except the last one, which has occasionally been found infesting
dead adult whiteflies, and presumably had caused their death.






BULLETIN 103.


As it is not within the scope of this paper to fully discuss each
of these fungi, the red Aschersonia will alone be treated in some
detail as a typical fungus, while brief statements with regard to
the others will follow.

THE RED FUNGUS

This important fungus, the red Aschersonia, has given satisfac-
tory results in localities where the summer rains were normal, or
where the trees were in good condition and the grove was in a
sufficiently moist state. In dry localities, or where the trees were
out of condition generally, the fungus could not always be depended
upon to check the whitefly or to bring the trees back into good
condition.
HELPING THE FUNGUS.-By diligent effort at spreading the
fungus, especially during periods of rain, some relief can be ob-
tained even under otherwise adverse conditions, if these be not
extreme. In the grove of Mr. W. E. Heathcote, of St. Petersburg,
Florida, into which this fungus had been introduced the previous
year, and in which it was not thriving especially well and was
giving only inadequate relief, a single spraying of the fungus spores
was made in August, 1908, into 6 trees, and the entomologist
counted, as a result, something like o1 times the amount of fungus
in these trees that was found in those on each side. Ten times as
much fungus, of course, implies ten tiines as many whitefly larvae
killed, and indicates that, in many instances, diligent application of
the fungus spores would give results more than repaying the time
and money spent. Introductions of fungus should be thoroughly
made, and if necessary repeated several times during the period of
summer rains. We must not expect the fungus to do all the work
unaided, but must help it to destroy the whitefly by spreading it
at the best time.

EXPERIMENTS IN SPREADING FUNGUS

In this connection the writer desires to refer to the results
produced by fungus in several groves into which it was intro-
duced artificially. The first of these is the R. S. Sheldon grove
at New Smyrna. The first introduction of the red fungus (red
Aschersonia) in this grove was made by spraying spores nindlr tl,-
writer's directions in October, 1906. A very small amount of fungus
developed that fall, but it spread well during the next summer and
no more was introduced before 1908. During the spring of the






8 FLORIDA AGRICULTURAL EXPERIMENT STATION

latter year some fungus was distributed by pinning leaves. On
August 22, 1908, the writer sprayed spores of the red fungus into
a few isolated trees near the Sheldon house. But little, if any,
fungus had developed in these trees previously and none had been
introduced. By September 13, 66 per cent. of the larvae counted
upon seven leaves, selected from some collected by Mr. Sheldon
from the trees sprayed August 22, were infected by the fungus
and dead. This happened in less than one month. The empty
pupa cases were counted as live larvae in making the calculations.
Following these excellent results, Mr. Sheldon continued to spread
fungus by spraying the spores during the rest of September.
Notes upon the grove were again taken on April 21, 1909, as
follows:

Grove has been practically cleaned of whitefly. There has been fungus
by the bushel, and other people have been collecting it for their use.
Fungus is now becoming much weathered and is peeling off, but there is
still plenty. Grove has a fine new growth and many trees have set a good
crop. Perhaps one-tenth as many adults on new growth as in other groves
in town where no fungus was applied. North third of grove has more
adult whiteflies because it is opposite a badly infested grove that was not
treated.

Considering the fact that this grove was not isolated but was
exposed to reinfestation, the results must be considered very satis-
factory. The whitefly was' brought under control in just about
two years. On the other hand, the writer now believes that the
same results might have been attained in less than one year if the
first spreading of fungus had been made during the period of sum-
mer rains. In fact, it appears that the work might have been
accomplished in something like a month if we had spread fungus
through the whole grove in August, 1908, as was done on the few
trees referred to above.
The first part of the work was an experiment designed to give
us accurate data as to the rapidity with which the fungus spreads
under those circumstances, and the control of the whitefly in the
grove as a whole was a secondary matter.
On July 9, 1910, Mr. Sheldon kindly furnished the following
data. The crop of fruit for 1909 was abundant, of good quality,
and clean. There were but few whiteflies in 1909 and very little
sooty mold. Whitefly considerable in 1910 but so far very little
sooty mold. Red fungus was spread in 1909, but so far none in
191o, because fungus is scarce. No other repressive measures have
been taken.





BULLETIN 103.


On December 22, 1909, the writer visited the 6-acre orange
and pomelo grove of Mrs. A. P. Gunther, at Pierson, and made the
following notes.
The larvae were in the flat condition of fourth stage and older. Perhaps
average of one alive per leaf. The first trees to become covered with
sooty mold were observed in summer of 1907. Considerable numbers of
larvae dead from unknown cause. Examination lasted one hour. Mr. E.
Gunther says fall brood of adults not nearly so large as spring brood. Very
good spread of red fungus (Aschersonia). Dozens to hundreds of pustules
per leaf. The fungus was first introduced by Mr. Frank Stirling, of DeLand,
early m the season; several introductions were made later. Trees look
very healthy, thrifty and good color. Good crop. last year. Tangerines
and pomelos bearing a small crop this year. Oranges about one-half crop;
some fruit covered with sooty mold and required washing.
The results in this grove appeared to be satisfactory in so far
as -the whitefly was concerned, and but little, if any, better results
could have been obtained by any other method under the same
conditions of exposure to reinfestation. This grove appears to be
an instance in which diligent spreading of the fungus, aided by
the "unknown cause" referred to in the notes, reduced the whitefly
to a condition of comparatively little importance in one season.
Other illustrations of the effectiveness of introducing and
spreading the fungi artificially under favorable conditions could
be' given. It is not the'writer's wish, however, to make the fungi
appear as a panacea for the whitefly, since their usefulness may be
greatly limited in dry localities and during periods of drought. It
appears desirable, however, to briefly report upon the fungus work
of Mr. Frank Stirling, of DeLand.
During 1908 Mr. Frank Stirling, of DeLand, began to spray
fungus spores on an extensive scale. That year he treated between
eight and nine thousand trees, in and near DeLand. During the
spring and summer of 1909, with one or two helpers, he sprayed
fungus spores into 127,500 trees. That is, he made 127,500 spray-
ings, many trees being sprayed several times. Some trees were
treated as frequently as five times. This spraying was mainly of
the red fungus, but some yellow and some brown fungi were also
used. The best results were had with the red fungus, but the
brown did well later in the season. The yellow fungus (Ascher-
sonia), Mr. Stirling says, is a "hustler" for the cloudy-winged
species of whitefly. Groves belonging to 58 owners were sprayed
at a contract price of 2 cents per tree. This spring and summer
(1910) Mr. Stirling is continuing to spray fungus spores. It will
thus be seen that the method of spreading fungus as directed by the
Experiment Station is receiving a most thorough test.





10 FLORIDA AGRICULTURAL EXPERIMENT STATION

The entomologist has had occasion to examine personally only
two of the groves treated by Mr. Stirling during 1909. These are
the Gunther grove at Pierson, referred to on a former page, and
the Temple groves at Winter Park. The results in Mr. Temple's
groves appear to be about equal to two good sprayings with insec-
ticides, but at less cost. Two sprayings in 1909, with fungus, one in
May and one in July, cost 4 cents per tree; to have sprayed with
insecticides would have cost 25 or 30 cents per tree. Mr. Stirling
is again treating Mr. Temple's trees this season. On April 21,
1910, Mr. Stirling said that in the Stetson groves at DeLand, some
of which were sprayed five times with fungus during the season
of 1909, the whitefly was held in check and kept from spreading;
and had not fungus been spread, one-third of the fruit would have
been covered with sooty mold.
KEEPING TREES THRIFTY.-It should be added here that proper
fertilizing and cultivation of the trees is important, since a thrifty
tree full of healthy foliage presents conditions favorable for the
growth of the parasitic fungi of the whitefly, and, of course, can
better withstand the attacks of insects. Irrigation would also fre-
quently benefit the trees and favor the fungus parasites of whitefly
and of scales.

INTRODUCING THE RED FUNGUS

In order to start a growth of the red Aschersonia, it is only
necessary to spray a mixture of the fungus spores in water on to the
whitefly larvae in the infested trees. The spores of the fungus are
produced in enormous numbers in the red elevations or pustules
covering the dead larvae. They vary considerably in size, and
13,6oo00,000 to as many as 52,000,000 could be arranged, one layer
thick, upon the surface of a square inch. About 40 pustules to a
pint of water have given good results. More can be used, or less,
if fungus is scarce. It is not necessary to allow the leaves with
fungus to soak longer than 5 or o1 minutes, but a longer time
does no harm, and the mixture of spores and water may even be
allowed to stand for 12 to 14 hours without injury. The mixture
of spores and water should be strained through coarse cheesecloth
or a fine wire sieve in order to remove all particles liable to clog
the pump. Mixtures of fungus spores and water should not be
allowed to stand in copper or brass pumps or vessels. It is best to
avoid copper and brass vessels altogether, since the copper may
injure the spores. Growths of fungus can generally be observed
with the unaided eye in about three weeks after spraying the spores.






BULLETIN 103.


The most successful introductions of the red Aschersonia have
been made during periods of rain and at a time when the whitefly
larvae were young. Thus one of the most luxuriant growths of
the Red Aschersonia that the writer succeeded in getting was at
DeLand during a period of rain in April, 1908, at which time also
the larvae of the spring brood were in the early stage of develop-
ment and very susceptible to infection by fungus. Generally
speaking, the period of summer rains is the most certain time to
spread fungus and to introduce it into new places. Seed fungus can
generally be obtained from whitefly-infested groves into which the
fungi have been previously introduced or in which they occur nat-
urally. Since the fungi do not spread during the winter, but are
nearly dormant, seed fungus is sometimes scarce during the spring
months, but some can generally be obtained. By midsummer a
crop of fungus will have matured upon the spring brood of whitefly
larvae so that fungus is then abundant. One should not attempt
to introduce fungus after the period of summer rains in over,
unless it is desired to spray the spores when seed fungus is most
plentiful, preparatory to having an early start when spring opens
The writer has, as an experiment, successfully introduced fungus
as late as October, November and December, and while but a
meager infection resulted, this spread rapidly during the following
spring and summer, as soon as sufficient moisture and warmth were
present. The data and complete details of experiments will not be
needed here since they were published in Bulletin 97, page 48; in
the Annual Report for 1907, page xxxii; in the Annual Report for
19o8, page liv; and in the Annual Report for 1909, page xl. On
a small place the mixture of spores and water may be applied by a
whisk broom when no pump is available.

OTHER FUNGI
The methods for introducing any of the other fungus para-
sites previously mentioned are in general the same as the method
just described for the red Aschersonia. Of these fungi the red and
the yellow Aschersonias can be introduced with the greatest cer-
tainty, and on the whole are generally the most efficient, excepting
the brown fungus when conditions for it are right.
One important point in regard to the yellow Aschersonia must
not be omitted. This fungus will thrive only upon the cloudy-
winged whitefly. This fact, which is fully discussed in Bulletin
97, page 52, and in the Annual Report for 1909, page xxxvi, is
important, since it would be useless to introduce the yellow fungus
on the white-winged species.






12 FLORIDA AGRICULTURAL EXPERIMENT STATION

PINNING LEAVES

Pinning leaves having whitefly larvae infected with a fungus
upon them has been extensively practiced in the past, but spore-
spraying has now almost entirely displaced this method; If leaves
are used, each leaf should be pinned with its fungus side down to
the lower surface of a leaf of the whitefly-infested tree, since the
fungus will be more readily distributed by natural agencies when
in its natural position.

ARTIFICIAL CULTURE OF FUNGUS

All the fungus parasites of the whitefly can be readily grown
artificially upon sterilized sweet potato and other media employed
for such purposes. This was proven over two years ago by the
Plant Pathologist, Prof. H. S. Fawcett, and the methods were
described in his paper on "Fungi Parasitic Upon Aleyrodes Citri,"
Special Studies No. I, University of the State of Florida, June,
1908. The brown fungus (Acgerita webberi, Fawcett) is the
only one which has so far failed to produce spores in artificial cul-
tures. Artificial cultures of this fungus can not at present be used
tor spraying, as can those of the other fungi.
The red fungus has been grown extensively in the writer's lab-
oratory on sterilized sweet potato, either in the form of plugs or
finely ground. The best results were obtained when the plugs or
ground sweet potatoes were placed in one-fourth pint and one-half
pint wide-mouthed bottles, which were carefully stoppered with
plugs of cotton batten. The potato was placed in the bottles which
were then stoppered with the cotton batten, and sterilized by steam.
Sterilizing destroys all the germ life in the bottle and on the
potato. This is necessary, for otherwise the development of bac-
teria and other fungi would choke 'ut the slow-growing red fungus.
The plug of cotton batten keeps out all undesirable germs, but
allows air to pass. The spores of the fungus are introduced into
the bottles either by spraying them in sterilized water with a small
atomizer, or by streaking them on with a sterilized platinum needle.
The work must be done in a properly prepared dust-proof room.
The last culture of red fungus consisted of about 50 bottles.
(See Figure 2.) Fungus grown as just described can be employed
for introducing into whitefly-infested groves as successfully as
that occurring naturally. This has been repeatedly proven in
infested trees near Gainesville and at other places. Since the
natural supply of red fungus has been generally sufficient, it is not





BULLETIN 103.


probable that it will become
necessary to grow it artifi-
,cially; but should it become
necessary to supply the artifi-
cially-grown fungus, this can
be done in ton lots or larger
with proper equipment.
While the spores of this
fungus germinate in 24 to 48
hours, fungus growth does not
become visible on sweet pota-
toes for about 7 days. This
time is about the same as upon
whitefly larvae. Some spores
are formed in 20 to 30 days;
and this again corresponds
with the development upon
whitefly larvae. Spore for-
mation appears to be completed
in about 30 to 60 days. The
fungus mass will then be of a
light brick-red; in fact, the ap-
pearance of this color may be
taken as evidence that spores
are forming. The 'fungus
should be used at that time,
but it will keep for a month,
and longer during winter and
early spring. This fungus
does not readily become weak-
ened, or lose its virulence, by
successive growths upon sweet
potato as a culture medium,
since successful growths of
Fig. 2.-Culture of Red Ascher- fungus have been started, upon
sonia on sweet potato, 17 days whitefly larvae from each of
old. Two-thirds natural size. the first five generations.
What has just been stated in regard to the red fungus holds
generally true for the yellow fungus, except that no extensive cul-
tures of this fungus upon sweet potato have been made.






14 FLORIDA AGRICULTURAL EXPERIMENT STATION

TREATMENT WITH INSECTICIDES

In dry times, and in groves out of condition, the fungi may
not thrive sufficiently, and it may become necessary to spray with
insecticides, or to fumigate.
Spraying with insecticides has fallen more or less into disfavor,
Operations and experiments of the Florida Experiment Station
during the past year indicate clearly that effective spraying can be
done. The difficulties in the past have arisen from spraying being
done at the wrong time, or were clue to a lack of thoroughness, or
to reinfestation from surrounding groves. The difficulty of doing
the work so thoroughly that the under surfaces of all the
leaves become wet with the spraying solution can be overcome
in part by taking special care, and by spraying at a pressure of
Ioo pounds or over.
Spraying for whitefly can be carried on successfully during that
portion of any season when most of the insects are in the larval
or pupal stages. During the fall (beginning with October) and
the greater part of the winter we find the whitefly in the larval
stages, and later in winter in the pupal stages. During a part of
April or May, soon after the disappearance of the spring brood of
adults, there is another period of about a month when but few
adult whiteflies are present and the eggs have hatched. After May
until the end of September all stages of the whitefly, including the
adults, are generally present. During this period rains occur fre-
quently, while the adults fly away from the spray, and the eggs are
not generally destroyed by it. Spraying should then be done only
when necessary to save the trees.


EXPERIMENTS IN SPRAYING

In some orange trees (Mr. B. F. Hampton's grove near Gaines-
ville) which were sprayed on May 7, 1909, with "Golddust" at a
strength of I pound to 4 gallons of water, 91 per cent. of all larvae
of the first to the third stages were dead after o1 days. The per-
centage of fourth-stage larvae killed was only 30.
These are the results of counting the dead and live larvae on
o1 leaves, selected as representative of good spraying. On 36 leaves
an average of 92 per cent. of all stages were killed (An. Rept. 1909,






BULLETIN 103. 15

p. xliii). Allowance was made for natural mortality, the percentage
of which was computed upon leaves from unsprayed trees. The
following temperature conditions existed on the day the spraying
was made and during 6 days thereafter.


TABLE I

MAXIMUM AND MINIMUM TEMPERATURES FOR 7 DAYS

M.A, 1909 7th 8th 9th 10th 11th 12th 13th

Maximum ................... 88 82 86 88 87 82 83
Minimum .............. ..... ..... i 62 63 66 66 61 61 61


M ean of maxima .................................. .. 85 degrees F.
M ean of minima ............................. .. .. 63 degrees F.
General m ean ......................................... 74.5 degrees F.

The results obtained on some 25 Satsuma trees (also in Mr.
Hampton's grove), sprayed on June 2, 1909, with "Golddust" as
before, are as follows: 99.5 per cent. of the second and third
stages were killed, and 89 per cent. of the fourth stage and pupae.
The average of all stages killed was 91 per cent. Ten leaves rep-
resenting good spraying were selected nine days after spraying.
Natural mortality was allowed for and computed from un-
sprayed trees. The following temperature conditions existed on
the date of spraying and during 6 days thereafter.


TABLE II

MAXIMUM AND MINIMUM TEMPERATURES FOR 7 DAYS

JUNE, 1909 2nd 3rd 4th 5th 6th 7th 8th

Maximum...................... 99 88 82 90 90 90 88
Minimum ....................... 73 75 75 73 70 70 68

M ean of maxima ....................... ........... 89.6 degrees F.
M ean of minima .................................. 72 degrees F.
General mean ........................... ..........80.8 degrees F.






16 FLORIDA AGRICULTURAL EXPERIMENT STATION

The following table, published in the Annual Report for 1909,
was primarily arranged to show the effectiveness of the two soaps
indicated, but when compared with the two previous series of spray-
ings, this table becomes of greater interest, as is brought out in the
discussion following. The larvae were mainly in the flat fourth
stage of development, but no distinction of stages was made in
counting them. The table gives the result on ten leaves of spray-
ing two or three trees with each strength of soap. The leaves were
selected to represent good spraying. The sprayings were made
near Gainesville in Mr. James Cellon's trees, June 15 to 17, 1909.
and the leaves were collected 4 to 15 days later.


TABLE III

RESULTS OF SPRAYING WITH SOAPS


STRENGTH OF SOLUTION


KILLED BY WHALE- KILLED BY OCTAGON SOAP
OIL SOAP


1 lb. to 6 gals. water............. 91 per cent................96 per cent.......


1 lb. to 9 gals. water ..........
1 lb. to 12 gals. water........
1 lb. to 16 gals. water and


...88 per cent.. .. ......... 95 per cent .......

...77 per cent..... ........... 89 per cent .......


3 lbs. washing soda...... ...93 per cent,.................94 per cent .....

The following temperature conditions existed on the day of
spraying and during 6 days after.


TABLE IV


MAXIMUM AND MINIMUM TEMPERATURES FOR 7 DAYS


JUNE, 1909


Maximum .....................
Minimum .....................


15th 16th 17th


98 98 93
70 74 75


M ean of maxima ........................ .. ......... 94-3 degrees F.
M ean of m inima ......................... ............. 72 degrees F.
General mean .................... .................. 83.1 degrees F.


18th 19th


20th


88

69


89
72


21st


92
72


92
71


I I


I






BULLETIN 103.


In the above three series of spraying operations the figures in-
dicate that the June spraying was more effective than the May
spraying. Temperature, as well as stage of development, is appar-
ently a factor in successful spraying, since we would expect the
solutions to be more penetrating when several degrees warmer.
Thus only 91.3 per cent. of the stages I to 3, and 30 per cent. of
the fourth stage, were killed with "Golddust" with an initial tem-
perature of 88 degrees and a. mean for 7 days of 74.5 degrees;
while 99.5 per cent. of the stages 2 and 3, and 89 per cent. of the
fourth and fifth stages were killed when the initial temperature
was 99 degrees and the mean for 7 days, 80.8 degrees. The re-
sults of June 15 to 17 in Mr. Cellon's trees on fourth stage larvae
with the soap solutions were excellent, with an initial temperature
of 98 degrees and a mean of 83.1 degrees. These figures, in con-
junction with many general observations, indicate that we should
spray the young larvae in the first to the third stages, and the
thin flat condition of the fourth stage, rather than the older fourth
stage larvae and the pupae. They also indicate that spraying dur-
ing the hottest summer weather with the thermometer at about 99
degrees is more effective against all stages and especially against the
fourth stage and the pupae, than spraying in cooler weather.

FUMIGATION

Fumigation with hydrocyanic acid gas is recommended for
winter treatment, no eggs or adults being present. A bulletin on
the subject has been issued by the U. S. Department of Agriculture,
describing the work carried on by Dr. A. W. Morrill and his as-
sistants at Orlando. Those wishing to consult this publication
should address the Superintendent of Public Documents, Washing-
ton, D. C., enclosing 15 cents, and asking for Bulletin 76 of the
Bureau of Entomology.

WINTER TREATMENT

Winter is a favorable time to treat the whitefly, because this
insect is then in its larval stages, and there are no adults to fly
away, nor eggs that are difficult to kill.
There are two methods of winter treatment-fumigation, and
spraying. Where fumigation can be employed, it is to be pre-






18 FLORIDA AGRICULTURAL EXPERIMENT STATION

ferred. Those who have carried on extensive fumigation experi-
ments claim that it is less injurious to the trees than spraying
with insecticides. Quicker and better results can undoubtedly be
obtained with it, especially on the larger trees, where it is difficult
to wet all the leaves by spraying. For small and medium-sized
trees spraying can, however, be made nearly as effective.
The growers at Winter Haven have organized a protective
league, and assessed each grower one cent per year for each tree he
owned. In this locality the whitefly had just started in two or three
groves, and the results of spraying in winter have been so success-
ful that but few, if any, more whitefly larvae could be found
last fall than three years ago. These spraying operations appear
to be the most successful on record. The insecticide was (a
proprietary miscible oil. Another grower states that he has suc-
ceeded in keeping the whitefly confined to a few trees in one corner
of his grove for four or five years by thorough spraying with an-
other miscible oil.
For winter spraying the solutions must be used much stronger
than at other times, and whale-oil soap solution should not be used
weaker than I pound to 4 gallons of water.

LOCALITIES JUST BECOMING INFESTED

Winter treatment should not be omitted in any locality in which
the whitefly is just coming in and is confined to a limited area.
Under such circumstances there is too much at stake to permit of
delay. Co-operation should be started in the form of a protective
league as just illustrated. All the groves in such a locality are
threatened, and no grower can afford to omit paying his share
towards keeping the pest confined within its present limits as long
as possible. It pays better to help fight the pest in another man's
grove than to have it in one's own. Work should not be postponed
with the thought that something can still be done in the summer,
since by so doing the whitefly is given another chance to spread
during its swarming period in April or May. Fumigate, if possi-
ble; if not, then spray thoroughly.

BADLY INFESTED LOCALITIES

Where a locality is completely and heavily infested, the trees
should be treated in winter in order to give them a better chance





BULLETIN 103.


to set fruit in spring. If co-operation can be effected, it is possible
to do the work so thoroughly that no further treatment will be
necessary until the next fall or winter. If co-operation for an en-
tire locality is impracticable, it may be feasible to effect co-
operation on the part of the owners of localized groups of groves.
Where no co-operation whatever is possible, each grower should
nevertheless treat his own trees. In this instance spraying should
be the method of winter treatment. It would be inadvisable to go
to the expense of fumigation where the grove is not isolated and
reinfestation is certain, but spraying should be done. Later in
April or May, when the grove has become reinfested from the
groves of indifferent neighbors, it should be sprayed again. There
is a time in April or May when the whitefly larvae are young and
easily destroyed by whale-oil soap (I pound with 6 to 9 gallons
of water) or by any other good insecticide diluted sufficiently to be
harmless to the leaves or young fruit. This period comes about
two weeks after the spring brood of adults has disappeared from
the wing. After that, during the period of summer rains, if con-
ditions are at all favorable for fungus growth (plenty of mois-
ture, and good condition of trees) the fungus diseases of the white-
fly should be introduced. Finally, if necessary, the trees should
be sprayed again in October or November; in which case treat-
ment during the following winter will not be necessary. (See
also under the following heading).

SPRING, SUMMER AND FALL SPRAYING

SPRING TREATMENT

Spring treatment should begin about two weeks after the winged
whiteflies have disappeared. There are then only young larvae
present. This period may occur during April or May, or some-
times earlier, depending upon the season and the locality. In lo-
calities where the spring rains are abundant and the general mois-
ture conditions throughout the season generally suitable, the fungi,
preferably the red Aschersonia, may be introduced as previously
directed. Where the conditions for the fungi are not suitable, or
where it is desired to depend altogether upon spraying, the spring
period indicated is a most suitable one during which to spray. The
advantages of spraying at this time may be summed up as follows:






20 FLORIDA AGRICULTURAL EXPERIMENT STATION

(I) The whiteflies are in the young larval stages and are easily
killed; (2) they are mainly on the new growth and more easi-
ly sprayed; (3) the larvae are destroyed before sapping the
strength of the new growth, and before much sooty mold has
developed; (4) rain is not likely to interfere with the spraying.

SUMMER TREATMENT

Spraying may also be carried on during the summer after the
second brood of adult whiteflies has passed its period of greatest
numbers, some time in July. During this time the whitefly de-
velops more or less irregularly, there being all stages present in
considerable numbers at nearly all times, and rain is generally
abundant. For these reasons spraying at this time of the year is
not generally advised, excepting when the trees are suffering great-
ly. The fungi can generally be introduced to good advantage at
this time, and they should be applied freely whenever the whitefly
is present in sufficient numbers, and conditions are favorable for
fungus growth.

FALL TREATMENT

Fall is an important time to spray for the whitefly, and treat-
ment may begin in October or November, or soon after the adult
whiteflies of the late summer brood have disappeared, and after
the last layings of eggs have hatched. The Knight grove at Bay
View, and F. M. Campbell's grove at Anona were sprayed in the
early part of November 1908 with a spraying mixture whose prin.-
cipal ingredient was whale-oil soap (about i pound to io gallons
of water), and about 90 per cent. of the larvae were killed. For
the late fall spraying, whale-oil soap should not be used weaker
than I pound to 4 or 6 gallons of water, but I pound to 6 or 9
gallons may be used earlier.
It is not necessary to spray two or three times during fall or
winter, as some think. By doing thorough work 95 per cent. of the
larvae are destroyed, and the remaining 5 per cent. will not in-
crease until spring. In other words, spraying should be done so
thoroughly that it will be unnecessary to repeat it for that brood.
The advantages of fall spraying may be summed up as follows:
(1) The young larvae are abundant and easily killed; (2) they






BULLETIN 103.


are killed before they wax fat at the expense of the trees; (3) the
trees remain clean for nearly five months; (4) there are few rains
to interfere with spraying.


SPRAYING SOLUTIONS

Since spraying to kill the young whitefly larvae must be done
in spring, summer, or fall, when either tender leaves or fruit are
on the trees, it is evident that a spraying solution must be used
that will not injure the foliage or the fruit. Almost any good con-
tact insecticide can be employed, provided it is sufficiently diluted.
The experiments reported on a previous page show that soap
solutions of I pound of soap to 6 gallons of water, destroyed all
larvae in the first three stages, and most of those in the fourth
and pupal stages. Thorough work resulted in destroying between
90 and 96 per cent. of all the larvae. Soap solutions of I pound of
soap to 9 gallons of water destroyed about 90 per cent. Good's
potash whale-oil soap No. 3 was used, and also Octagon soap. It
is probable that any kind of soap will be effective against these
young larvae. In winter and late fall the soap solutions should
be used stronger, about I pound to 4 gallons of water, but a weaker
solution used in spring, summer, or early fall, will generally kill
as many of the insects as the stronger solution in winter.
Experiments reported on a previous page show that "Golddust"
based on young larvae at the rate of I pound to 4 gallons of water
killed 90 to 95 per cent. Preliminary chemical examination showed
that it consisted of about 25 per cent, of soap, 62 per cent, of wash-
ing soda, and about 13 per cent. of water. When we mixed one
pound of whale-oil soap with three pounds of washing soda and
based one pound of this mixture to 4 gallons of water we got about
the same results as we did by using one pound of "Golddust" to 4
gallons of water. One pound of whale-oil soap alone to 9 gallons
of water gave about the same result as the whale-oil soap and soda
mixture. The cost in each case was a little less than half a cent per
gallon. Whale-oil soap is therefore decidedly a cheaper material
to use for spraying than "Golddust." A mixture as good as
"Golddust" can be made at about one-half the cost by using I
pound of whale-oil soap and 3 pounds of washing soda to 16 gallons
of water.






22 FLORIDA AGRICULTURAL EXPERIMENT STATION

THREE SPECIES OF WHITEFLY

About two years ago it was discovered that there are two
distinct species of whitefly that seriously infest citrus trees in
Florida. The second species, Aleurodes nubifera, is spoken of as
the cloudy-winged species, and the other, Aleurodes citri, as the
white-winged species. Previous to 1908 it was supposed that only
one species infested the trees, namely, the white-winged species.
The cloudy-winged species (see Fig. i) is so called because there
is a delicate cloud-like or smoky area toward the ends of the wings.
It should not be understood, however, that this cloudy-winged
species is a recent comer. On the contrary, examination by A.
L. Quaintance of whitefly material preserved in the Bureau of
Entomology, Washington, D. C., has shown that this species ex-
isted in Florida prior to 1895. According to some drawings made
in Louisiana in 1893 by Prof. Morgan, the cloudy-winged species
existed there at that time. The white-winged species began to be
studied back in the 70's, and was first described in 1893. So far
as records show it appears that both species were probably in-
troduced about the same time. The present distribution of the
cloudy-winged is quite as extensive eene as that of the white-winged one.
Sometimes both species can be found in the same locality and on the
same tree. The white-winged one is the more destructive, and
where both occur together the cloudy-winged species is relatively
insignificant; although when alone this latter species frequently
causes severe infestation.
A third species has recently gained entrance to the State, the
so-called woolly whitefly, Aleurodes howardii. This species has
been known to infest citrus trees in Cuba and other West Indian
islands for some time, but has only recently become established in
Florida about Tampa and Ybor City. Dr. E. A. Back of the
Bureau of Entomology, Washington, D. C., stationed at Orlando.
has written a brief account of the occurrence of this species in
Florida, in the Florida Fruit and Produce News for November 26,
1909, p. 5; and in Bulletin 64, part viii, Bureau of Entomology,
Washington, D. C.

WHITEFLY AND FREEZING

The benefits to the grower of any freezing sufficient to de-
foliate citrus trees may be considered about the equivalent of a






22 FLORIDA AGRICULTURAL EXPERIMENT STATION

THREE SPECIES OF WHITEFLY

About two years ago it was discovered that there are two
distinct species of whitefly that seriously infest citrus trees in
Florida. The second species, Aleurodes nubifera, is spoken of as
the cloudy-winged species, and the other, Aleurodes citri, as the
white-winged species. Previous to 1908 it was supposed that only
one species infested the trees, namely, the white-winged species.
The cloudy-winged species (see Fig. i) is so called because there
is a delicate cloud-like or smoky area toward the ends of the wings.
It should not be understood, however, that this cloudy-winged
species is a recent comer. On the contrary, examination by A.
L. Quaintance of whitefly material preserved in the Bureau of
Entomology, Washington, D. C., has shown that this species ex-
isted in Florida prior to 1895. According to some drawings made
in Louisiana in 1893 by Prof. Morgan, the cloudy-winged species
existed there at that time. The white-winged species began to be
studied back in the 70's, and was first described in 1893. So far
as records show it appears that both species were probably in-
troduced about the same time. The present distribution of the
cloudy-winged is quite as extensive eene as that of the white-winged one.
Sometimes both species can be found in the same locality and on the
same tree. The white-winged one is the more destructive, and
where both occur together the cloudy-winged species is relatively
insignificant; although when alone this latter species frequently
causes severe infestation.
A third species has recently gained entrance to the State, the
so-called woolly whitefly, Aleurodes howardii. This species has
been known to infest citrus trees in Cuba and other West Indian
islands for some time, but has only recently become established in
Florida about Tampa and Ybor City. Dr. E. A. Back of the
Bureau of Entomology, Washington, D. C., stationed at Orlando.
has written a brief account of the occurrence of this species in
Florida, in the Florida Fruit and Produce News for November 26,
1909, p. 5; and in Bulletin 64, part viii, Bureau of Entomology,
Washington, D. C.

WHITEFLY AND FREEZING

The benefits to the grower of any freezing sufficient to de-
foliate citrus trees may be considered about the equivalent of a






BULLETIN 103.


fumigation or extra good spraying so far as the effects upon white-
fly are concerned. The great majority of the whitefly larvae die
on leaves killed by cold; but a few may survive, especially on any
leaves that are drifted into some moist place where they do not
dry out completely. In November and January 1907-8, the writer
collected fallen leaves at DeLand with live fourth-stage larvae and
pupae upon them, some of which matured after being taken to the
Experiment Station at Gainesville (see Bulletin 97, p. 62). The
degrees of cold that have hitherto occurred in Florida have not ex-
terminated the whitefly except in one or possibly in two places. At
Crescent City the freeze of I894-5 did exterminate the cloudy-
winged species, probably the only one present there at that time.
But as all citrus trees were frozen to the ground, and as this species
appears to live on citrus only, it is easy to understand how the ex-
termination took place. Freezing destroyes directly but few, if any,
of the larvae on leaves that remain uninjured.


QUARANTINE

The whitefly can be kept out of non-infested groves for a con-
siderable length of time. With but a little attention, growers
can save for themselves thousands of dollars. This should be
an incentive to every resident of Florida, whether a grove-owner
or not, to help in checking the whitefly and keeping it from spread-
ing. Something can be accomplished by closing private gates
against vehicles coming from infested districts, since the winged
whiteflies are frequently carried on persons and vehicles for long
distances. Nursery stock and ornamentals when brought to one's
premises should be defoliated if there is the least possibility of
any whitefly being present. The whitefly is undoubtedly more
frequently carried long distances on nursery stock than by any
other means. As a special precaution, nursery stock may be fumi-
gated after defoliating. To what extent whitefly may be carried
on pickers' implements is an open question, but it is easy to con-
ceive of adults or young larvae being carried in that way. Certain
growers in non-infested localities have very wisely excluded the
implements which have been used in infested localities. Such
implements can be made safe, however, by a thorough spraying
with soap solutions or other contact insecticide, care being taken to
saturate all crevices with the solution. Picking bags and the outer





24 FLORIDA AGRICULTURAL EXPERIMENT STATION

garments of pickers may be fumigated in air-tight containers with
carbon bisulphide, at the rate of I to 3 ounces for a space the size
of a barrel, leaving them in fumigation over night. Hydrocyanic
acid gas may also be used. Gasoline used in an air-tight container
will also do the work.

FOOD PLANTS

The cloudy-winged species (Aleurodes nubifera) has not yet
been found alive on any plants except species of citrus. Mr. A.
L Quaintance, however, reports A. nubifera on some gardenia
leaves collected at Crescent City, Florida, in 1895, by H. G. Hub-
bard, and preserved in the Bureau of Entomology, Washington, D.
C. (see Bulletin No. 12, part IX., Technical Series, Bureau
of Entomology, U. S. D. A.). The following is a revised list of
food plants of the white-winged species (Aleurodes citri). With
regard to those marked by an asterisk, it has not yet been determin-
ed whether A. nubifera or A. citri, or both, infest them. The
writer is of the opinion that all were probably infested with A. citri.

Class I.-FOOD PLANTS PREFERRED BY A. CITRI.

Native species:
Prickly Ash (Fagara Clava-Herculis (L.) Small).
Wild Persimmon (Diospyros Virginiana) L.)
Wild Olive (Osmanthus Americana (L.) B. & H.).
Green Ash (Fraxinus lanceolata, Borck).

Introduced Species:
Citrus (all varieties).
Chinaberry (Melia Azedarach L.).
Umbrella (Melia Azedarach umbraculifera Sarg.).
Cape Jasmine (Gardenia jasminoides Ellis).
Privets (Ligustrum spp.).
Japan Persimmon (Diospyros Kaki L. f.).
Class II.-FooD PLANTS SOMETIMES INFESTED BUT NOT PREFER-
RED BY A. CITRI.

Native Species:
Cherry Laurel or Mock orange (Laurocerasus Caro-
liniana (Mill.) Roem.).






BULLETIN 103.


Viburnum nudum L.
Buttonbush (Cephalanthus occidentalis L.).
Smilax (Smilax sp.).
*Blackberry (Rubus sp.).
*Water Oak (Quercus nigra L.)
*Scrub Palmetto (Sabal megacarpa (Chapm.) Small).

Introduced Species:
Coffee (Coffea Arabica L.).
Pomegranate (Punica Granatum L.).
Allamanda (Allamanda neriifolia Hook.).
*Honeysuckle (Lonicera Japonica Halliana).
*Ficus altissima.
*Ficus sp. (from Costa Rica).
Oleander (Nerium Oleander L.).
Cultivated pear (Pyrus sp.).
Lilac (Syringa sp.).
Banana Shrub (Michelia fuscata Blume).
Camellia, or Japonica (Camellia Japonica L.).

PLANTS TO BE CONDEMNED

The cape jasmine, chinaberry, umbrella trees, prickly ash,
privets, wild olive, trifoliate orange (Citrus trifoliata), and all
useless and abandoned citrus should be condemned and destroyed
in all citrus-growing communities. Destruction of these plants will
retard the restocking of citrus groves with whitefly after repressive
measures have been carried out, and greatly check the spread of the
whitefly in localities only partly infested or just becoming infested.
While it is safest to destroy all these plants, it is the chinaberry
and umbrella trees that are the most dangerous. It has been found
by counts and calculations that a large infested umbrella tree may
set free tens of millions of adult whiteflies during late summer and
early fall, so that a dozen umbrella trees may be counted upon to
liberate hundreds of millions of these insects each year to re-stock
a treated grove.
These hundreds of millions swarm about apparently in an aim-
less manner, but have been observed to migrate a mile beyond their
place of origin, indicating clearly how these trees are instrumental
in spreading the whitefly to the outlying citrus groves. The other






26 FLORIDA AGRICULTURAL EXPERIMENT STATION

deciduous trees of the condemned list stand in the same relation
to the whitefly as the chinaberry and umbrella trees, but being
smaller they harbor fewer whiteflies. The late summer and fall
migration of the whitefly from the umbrella and other deciduous
trees is due to the fact that no new foliage is produced at that
time. The whitefly prefers to deposit its eggs upon new and tender
foliage, and when this is absent, it instinctively leaves the trees.
apparently in search of evergreen trees such as citrus, cape jasmine,
and others, on which to deposit its eggs.

WHITEFLY AND INCREASE OF SCALES

Scale insects have in some instances increased abnormally in
citrus trees that were infested with whitefly. It has been thought
that this increase of scales had been somehow brought about by the
latter insect. That the whitefly cannot be the principal cause is
indicated by the fact that increase of scales has not always been
preceded by whitefly, and that whitefly infestation is not always
accompanied by increased numbers of scales. The worst cases
of infestation by scales, causing partial or complete defoliation and
much loss of small twigs, were in localities suffering from lack
of rain. It appears that this lack of moisture is the primary factor,
and that the whitefly made a bad condition worse by further ex-
hausting the sap of the trees. The lack of sufficient moisture
weakened the trees. It also checked the development of the fun-
gus diseases which normally keep the scales under control. Had
the trees been supplied with sufficient moisture they would have
been able to put on a fairly good growth. The new leaves would
have supplied more food to the trees. (Leaves are not only the
lungs of the tree, but also the organs in which food is elaborated.)
This food would have been used in part to feed the scales and
whitefly, and in part to maintain the vigor of the trees. These
leaves would also have supplied more moisture to the air, and their
shade would have kept the interior of the trees moister. This
would have resulted in a thrifty growth of the almost universally
present fungus diseases of scales. It has been noticed that scale
fungi and whitefly fungi often thrive remarkably well even in
dry localities in vigorously growing trees. It therefore follows
that the better the condition in which the grove is kept, the less
likely is it to suffer from the depredations of insects.






BULLETIN 103.


When there is a great increase of scales, whether or not white-
fly is also present, it is evident that the fungus diseases of these
insects are absent or are not thriving. In this case spraying with
some contact insecticide, or fumigation, should be employed to give
immediate relief.

WHEN TO SPRAY FOR SCALES

In the spring, summer, and fall, it is not possible to use strong
spraying mixtures, so that it may be necessary to spray the in-
fested trees several times at intervals of some weeks. It will not
always be necessary to spray the whole grove, but only the most
severely infested trees. When whitefly is present the spray
should, of course, be applied to these as well as to the scales.
The following precautions should be kept in mind when spray-
ing for scales in spring, summer, or fall.
I. Spray when many young scales can be seen with a lens to
be crawling about, or to have just attached themselves. T!hes,,
young scales appear either as oval moving specks or as round whit-
ish dots. They are easily destroyed by a weak spraying solution
which will not injure the fruit or foliage in any stage of growth.
2. Any contact insecticide may be employed, such as soap
solutions, emulsions of oils, or good proprietary insecticides. Soap
solutions of I pound of soap and 6 to 9 gallons of water will
destroy the crawling scales and those just set, together with the
young whitefly larvae, without injuring the trees.
3. Avoid insecticides that are recommended as useful for fun-
gus diseases, because they also destroy the fungus diseases of the
scales and whitefly. Whale-oil soap causes little or no injury to
these fungi, and the same is true of some of the best proprietary
insecticides.
4. During the period of summer rains the fungus diseases of
the scales and whitefly should be distributed to those trees in which
they do not occur in sufficient quantity.
5. The eggs of the scale insects, being sheltered beneath the
old scales, are not easily destroyed by sprays. The old scales are
protected by their waxy covering, ard are not destroyed in great
numbers by spraying solutions, unless of extra strength. Hence,
repeated spraying in warm weather when the young are hatching,
may be made more effective than winter spraying.






28 FLORIDA AGRICULTURAL EXPERIMENT STATION

RESUME OF SCIENTIFIC RESULTS

I. Less starch produced by trees affected with sooty mold.
2. Definite advantages gained by spraying fungus over natural
spread.
3. The vitality of spores is probably injured by a brass vessel
when the mixture is allowed to stand in it.
4. Proof that the fungi grow best in hot wet weather.
5. Yellow fungus thrives only on A. nubifera.
6. Cultures of fungi used for spraying with success.
7. Cultures of fifth generation retain their virulence.
8. Pupae apparently more or less immune to fungus attack.
9. Use of soap solutions for spraying whitefly.
o1. Proof that spraying with insecticides is most effective in
hottest weather, against younger larvae.
ii. A second species of whitefly.
12. Some new food plants of whitefly.




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