• TABLE OF CONTENTS
HIDE
 Title Page
 Table of Contents
 N.B.
 Introduction
 Injuries caused by whiteflies
 Life history of whitefly
 Natural enemies of whitefly
 Control of whitefly
 Food plants of whitefly
 Spread of whitefly
 Cloudy-winged whitefly
 Woolly whitefly
 Reference
 Press bulletins
 Bulletins and reports on hand for...














Group Title: Bulletin - University of Florida Agricultural Experiment Station ; 123
Title: Whitefly control, 1914
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027693/00001
 Material Information
Title: Whitefly control, 1914
Series Title: Bulletin - University of Florida Agricultural Experiment Station ; 123
Physical Description: Book
Language: English
Creator: Watson, J. R.
Publisher: University of Florida Agricultural Experiment Station
Publication Date: 1914
 Record Information
Bibliographic ID: UF00027693
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
    Title Page
        Page 1
    Table of Contents
        Page 2
    N.B.
        N.B.
    Introduction
        Page 3
    Injuries caused by whiteflies
        Page 3
        Page 4
        Page 5
    Life history of whitefly
        Page 6
    Natural enemies of whitefly
        Page 7
        Page 8
        Page 9
    Control of whitefly
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
    Food plants of whitefly
        Page 18
    Spread of whitefly
        Page 19
    Cloudy-winged whitefly
        Page 20
    Woolly whitefly
        Page 21
    Reference
        Page 22
    Press bulletins
        Page 23
    Bulletins and reports on hand for distribution
        Page 24
Full Text



September, 1914


UNIVERSITY OF FLORIDA



Agricultural Experiment Station





WHITEFLY CONTROL, 1914


BY


J. R. WATSON


Fig. I.-Purple Scale following Woolly Whitefly.

The Station Bulletins will be sent free upon application to the Experiment .-
Station, Gainesville, Fla.


THE E. O. PAINTER PRINTING CO., DE LAND, FLA.


Bulletin I23

















IMPORTANT FACTS

x. The drought has caused this year's fall brood of whiteflies to be the
largest that Florida has had for several years.
2. The red and brown fungi can be dried and kept over winter.
3. The ideal method of controlling the whitefly is to spread parasitic
fungus during the rainy season, and to spray with miscible oil
emulsion in spring and fall.
4. The planting of chinaberry and umbrella trees in citrus communities
should be prohibited by public sentiment and by law.
5. Owners of non-infested groves should adopt quarantine measures.




CONTENTS
Page
Introduction ----------------------------------------------- --- 3
Injuries caused by Whiteflies ----------------------------------------- 3
Purple Scales Follow Whitefly ------------------------------ 4
Life-History of Whitefly ----------------------------------------- 6
Natural Enemies of Whitefly ---------------------------------------- 7
Insects ---------------------------------------------- 7
Fungi ----------------------------------------- ------------ 7
Control of Whitefly ------------------------------------------ --- IO
'Spreading the Fungi ---------------------------------------- T
Contact Insecticides ---------------------------------------- 14
Program for Control ---------------------------------------- I6
Fumigation ---------------------------------------------- I8
Food-Plants of Whitefly ------------------------------------------ 8
Spread of Whitefly --------------------------------------------- 9
Cloudy-Winged Whitefly ------------------------------------- ---- 20
Woolly Whitefly ------------------------------------- ------ 21
References --------------------------------------- 22








N. B. For the formula on p. 14 of Bulletin
123, substitute the following:
W hale-oil soap...... ...... ......8 lbs. or 1 gallon
Paraffin oil, 24 or 28 Baume .. 2 gallons
W ater ............................... 1 gallon
This is Yothers' Formula No. 1, and is a better
one than the one given. Follow the directions as
given. J. R. WATSON,
Entomologist.











WHITEFLY CONTROL, 1914


BY J. R. WATSON


INTRODUCTION
There are indications that this year's fall brood of white-
flies will be the largest that Florida has had for several years. The
phenomenal drought of the spring reduced the amount of the
parasitic fungi in the groves to a point much below the normal
for that season of the year, and the relatively low humidity in many
parts of the State during the summer hindered the growth of the
fungi that were left. As a result, the whiteflies have been com-
paratively free from entomogenous fungi, and have increased great-
ly. To urge the growers to prepare for a vigorous fall campaign
against the pest, and to indicate the best methods, are the objects
of this bulletin.
There are in Florida four species of whiteflies that may infest
a citrus tree in sufficient numbers to demand measures for control.
They are: (I) the common citrus whitefly (Aleurodcs citri);
(2) the cloudy-winged whitefly (A. nubifcra); (3) the woolly
whitefly (A. howardi, Fig i), and (4) the waxy or bay whitefly
(Paralcyrodcs pcrscae). Of these, the woolly whitefly, a recent
importation from Cuba, has usually been held sufficiently in check
by a minute wasp-like parasite. The bay or waxy whitefly is a
native insect that is common in many groves, but is rarely suffic-
iently abundant to render remedial measures necessary. This bul-
letin is concerned mostly with the first two species.

INJURIES CAUSED BY WHITEFLIES
Whiteflies withdraw a great deal of sap, thus depriving the
trees of nourishment. From some careful experiments, E. W.
Berger calculated that at a temperature of about 70 degrees F. a
million whiteflies withdraw over fifteen pounds of sap in a month.
Further investigations by the writer have shown that at a tempera-
ture of between 40 and 50 degrees F. the amount was only about
oeip-tenth of this. On the other hand it may be much greater
3











WHITEFLY CONTROL, 1914


BY J. R. WATSON


INTRODUCTION
There are indications that this year's fall brood of white-
flies will be the largest that Florida has had for several years. The
phenomenal drought of the spring reduced the amount of the
parasitic fungi in the groves to a point much below the normal
for that season of the year, and the relatively low humidity in many
parts of the State during the summer hindered the growth of the
fungi that were left. As a result, the whiteflies have been com-
paratively free from entomogenous fungi, and have increased great-
ly. To urge the growers to prepare for a vigorous fall campaign
against the pest, and to indicate the best methods, are the objects
of this bulletin.
There are in Florida four species of whiteflies that may infest
a citrus tree in sufficient numbers to demand measures for control.
They are: (I) the common citrus whitefly (Aleurodcs citri);
(2) the cloudy-winged whitefly (A. nubifcra); (3) the woolly
whitefly (A. howardi, Fig i), and (4) the waxy or bay whitefly
(Paralcyrodcs pcrscae). Of these, the woolly whitefly, a recent
importation from Cuba, has usually been held sufficiently in check
by a minute wasp-like parasite. The bay or waxy whitefly is a
native insect that is common in many groves, but is rarely suffic-
iently abundant to render remedial measures necessary. This bul-
letin is concerned mostly with the first two species.

INJURIES CAUSED BY WHITEFLIES
Whiteflies withdraw a great deal of sap, thus depriving the
trees of nourishment. From some careful experiments, E. W.
Berger calculated that at a temperature of about 70 degrees F. a
million whiteflies withdraw over fifteen pounds of sap in a month.
Further investigations by the writer have shown that at a tempera-
ture of between 40 and 50 degrees F. the amount was only about
oeip-tenth of this. On the other hand it may be much greater
3






Florida Agricultural Experiment Station


during the hot summer months. The loss of this sap is a serious
drain on the trees, stunting their growth and that of the fruit.
The fruits on badly infested trees are also fewer and inferior in
quality.
Whiteflies give off abundant honeydew, which is smeared over
the trees and furnishes food for the growth of the sooty mold, a
fungus which blackens the foliage and interferes with the pas-
sage of the sunlight necessary for the manufacture of food ma-
terial by the leaf. Leaves covered with sooty mold have been
proved to produce less starch than clean ones. The injury that
attracts most attention from the grower is the blackening of the
fruit. This makes necessary the added expense of washing, and
introduces a new liability of loss of fruit from scratches and in-
oculation with spores of the fungi that cause decay.

PURPLE SCALES FOLLOW WHITEFLY
A heavy infestation of whitefly is apt to be followed by
an increase of purple scale. This connection between purple scale
and whitefly has been noted for ni.ny years, and several explana-
tions, most of them unsatisfactory, have been attempted. The
writer has been studying this as a minor problem during the past
two years, and has worked out what he regards as the main cause.
The phenomenon is most marked in the case of the woolly whitefly,
a heavy infestation of wI ch has always been followed by a severe
infestation of purple scale. Here the explanation is evident enough.
The purple scales collh:ciL: i'-r the wool of the whitefly, because of
the behavior of the c:a\vnig your toward light. The writer in-
tends to publish elsewhere the clei .. of l.is studies along this line.
Here it will suffice to say that the crawlers avoid light of the in-
tensity usually met with in a citrus tree. This drives them under
things, such as the calyx of the fruit, where they are always rela-
tively abundant; or into the comparative shade formed by two
fruits in contact, or into the angle where the leaf-stalk joins the
stem. When colonies of woolly whitefly are present, ever if the
whiteflies themselves have been killed or have emerged, the per-
sistent wool forms a well shaded retreat. Here the young are par-
tially protected from some of their most inveterate enemies, such as
the twice-stabbed lady-beetle, and also from the spores of the para-
sitic fungi. The result is that they establish a flourishing colony of
scales, which forms a persistent breeding-ground from which crawl-
ers are constantly spreading out in all directions.






Bulletin 123


In the case of the common citrus whitefly, the sooty mold af-
fords somewhat similar conditions. Counts of the whitefly on large
numbers of leaves showed that, on the average, leaves that had
a heavy, somewhat loosely fitting coat of sooty mold had twice
as many purple scales as similar leaves taken from the same parts
of the trees, but comparatively free from sooty mold. This was not
true of a thin coat of fresh sooty mold. Such a coat fits too tight-
ly to the leaf to afford shade, and perhaps, too, it has been too re-
cently formed to allow time for the scales to collect and multiply.
Another factor that doubtless contributes to this increase of
scales is that a badly infested tree, being less vigorous and casting
less shade, will not furnish as good moisture conditions for the
growth of the parasitic fungi as will a healthy tree.


















Fig. 2.-Eggs of Common Whitefly Magnified. (From Bul. 97).

A heavy infestation of whitefly is not always followed by
abundance of scales. The weather and other factors enter in, and
affect the growth of the fungi which parasitize scale insects. Nor
is a heavy infestation of scales always dependent upon whitefly.
Other causes may produce the same result. But there is, no doubt,
a distinct tendency for the scale to increase in sooty trees.






Florida Agricultural Experiment Station


LIFE HISTORY OF WHITEFLY

In order to apply control measures intelligently it is necessary
to Vynderstand some points in the life-history of the insect. The
female lays a hundred or more eggs (Figs. 2 and 3) in the course of
her life of a week or ten days. Most of these hatch during summer
in ten or twelve days. The larvae issuing from these eggs crawl
about for a few hours until they find a suitable place to insert their
sucking beaks, after which they become stationary, and remain
stationary until they emerge as adults. They nearly always set-
tle on the under side of leaves. This is purely a result of their
desire to avoid too strong a light. If a leaf is turned over they will
settle just as readily on the upper side. For the same reason they
prefer the north side of trees. This is particularly marked on
small, and hence well-lighted trees. On such trees the writer has
counted ten times as many larvae on the north as on the south side.


















Fig. 3.-Eggs of Cloudy-Winged Whitefly Magnified. (From Bul. 97).

During its larval life, which averages a little over three weeks
in the hottest part of the year and from four to five in the coldest,
'the whitefly molts or casts its skin three times, becoming larger
each time. We speak of the three stages thus marked off as the
first, second, and third larval stage. After the third molt the in-
sect passes into the pupal stage. The insect is still stationary, and
closely resembles the third stage larva, especially in the early part






Bulletin 123


of its pupal life. So the pupal stage is often spoken of as the fourth
larval stage. The whitefly remains in this stage from two weeks
to ten months, as determined by the weather, and individual vari-
ability. (See U. S. Dept. of Agr. Bur. of Ent. Bul. 92). The
late summer brood spends the winter in this stage. From
the pupa the adult winged whitefly emerges, and the life cycle is
complete.
There are three main generations each year. In the latter
part of the summer these become much confused, but in the main
we can distinguish three broods or periods of maximum flight of
adults. The date of appearance of these broods will vary accord-
ing to latitude, weather, and other local conditions which are not
well understood. There may be a difference of a week or more in
two groves not a mile apart. The spring brood of adults is at its
maximum, taking the average of the whole State, in the latter part
of March; the next brood, in June; and the last and largest, in
the latter part of August and the early part of September.

NATURAL ENEMIES OF WHITEFLY
It is important that the grower should be able to recognize
the natural enemies of the pests that infest his crops, so that he
may aid, or at least not hinder, their multiplication. The enemies
of whiteflies belong almost exclusively to one of two groups of
organisms, fungi and insects.

INSECTS
Insects are not of much account in the control of the common
citrus whitefly. The twice-stabbed lady-beetle, a valuable destroyer
o+ scale insects, destroys some of the crawling young of the white-
fly, and occasionally an older larva. The aphis-lions, the young of
the lace-wing flies, also destroy many crawlers; and a species of
trips eats some of the eggs.
FUNGI
On the other hand there are some parasitic fungi that do most
effective work. They grow mostly on the larvae, sending their
filaments in all directions through the body of their host, and ulti-
mately forming a dense cushion over the dead larva. When all of
the material of the larva that can be used is consumed, the fungus
produces spores, round or oval microscopic bodies, which are blown
about by air currents, or, being sticky, are carried about on the






Florida Agricultural Experiment Station


bodies of flying insects, and especially on the adult whiteflies them-
selves. None of them penetrate the tissue of the leaf; they derive
their food exclusively from the body of the larva.
BROWN FUNGUS.-The most efficient of these fungi is the
brown fungus (Aegerita webberi, Fig. 4). It is efficient because
it does not have to depend upon the dispersal of the spores to reach
other larvae on the leaf. Its microscopic thread-like branches. (hy-
phae) radiate from each dead larva far over the surface of the
leaf, and unless checked 'by cold or drought are sure to infect any
whitefly larvae present. Indeed these hyphae will often extend
down the stalk of the leaf, over the twig and up the stalks of other
leaves. The spores of this fungus are formed on branches of these
far-reaching hyphae which extend around the edge of the leaf to
the upper side. They may be seen as rust-brown patches on the
upper side of the leaves, although the individual spores are invisible


















Fig. 4.-Brown Fungus on Whitefly Larvae. (From Bul. 94).

to the unaided eye. In this position they are easily scattered by the
wind.
This fungus is particularly a late summer and autumn form.
It seldom appears before August, but will often continue to grow
well into November if the weather is sufficiently moist. It is more
difficult to get it started in a grove, particularly by the spore-
spraying method, than is the case with the red fungus, largely be-
cause the spores are scarcer. Pieces of hyphae broken from the






Bulletin 123


cushions on the underside of the leaves will start an infection, but
less readily than the spores.
RED FUNGUS (Aschersonia aleyrodis).-This fungus (Fig. 5)
is also an important enemy of the whitefly. It develops earlier in
the season than the brown fungus, and is more easily introduced
into a grove. It does not, however, kill all the larvae on a leaf as
does the brown fungus, and it usually does not flourish so vigorous-
ly in the fall. In this species the spores are formed on the dead
larvae, in pustules that burst open and set them free.
MICROCERA.-A third species of fungus that often does heavy
execution, particularly on the larvae of the cloudy-winged white-
fly, is Microcera (Fusarium), also named "the white-fringed fun-
gus." It derived its last name from the fact that, under particularly
favorable conditions of humidity and abundance of food, its hy-















Fig. 5.-Red Fungus on Whitefly Larvae. (From Bul. 67).

phae extend out from the margin of the dead larvae in the form
of a white fringe. But under grove conditions and on whitefly
larvae this fringe seldom forms. The filaments, being nearly col-
orless and scanty, are not conspicuous objects, as is the case with the
other fungi. The infected larva turns brown as it dies, and final-
ly fades to white, soon dropping off. On scale insects, particularly
the soft scales, Microcera is much more apt to form a fringe. It
is less virulent than either of the preceding fungi. It would seem
that many larvae resist infection by this fungus. At least when
leaves are dipped into water containing abundance of the spores
of this species, commonly only from ten to fifty per cent of the






1o Florida Agricultural Experiment Station

larvae die. Microcera is much less virulent on older larvae and
plpae than on younger stages. It is of quick growth, appearing in
from three to six days after introduction; whereas the other fungi
commonly require nearly a month before spores are formed. Be-
sides the larvae this fungus infects both adults and eggs. (Accord-
ing to H. S. Fawcett, it is probably Microcera that was found sev-
eral years ago on adults and identified as a Sporotrichum, the genus
to which the chinch-bug fungus belongs). Microcera grows most
rapidly during cooler weather than that required for the best
growth of the other fungi. It is apt to become abundant during a
rainy spell at any time during the winter. The most marked epi-
demics of this fungus among whiteflies have been observed in the
month of September.
CINNAMON FUNGUS.-In addition to these three most im-
portant fungi, there is another that occasionally does good execution
locally. This is the cinnamon fungus, which looks somewhat like
the brown fungus, but is lighter in color, and of a less compact ap-
pearance.
CONTROL OF WHITEFLY
There are two practical methods of controlling whitefly under
Florida grove conditions: (I) aiding in the spread of the para-
sitic fungi; and (2) spraying with contact insecticides. The ideal
method is to combine these two.

SPREADING THE FUNGI

When the whitefly first invades a grove, it is, of course, im-
pcrtant that the fungi should also be established there as soon as
possible. 'The fungi, however, exhibit a surprising ability to "find"
isolated groves infested with whitefly. The writer has visited groves
which were miles from other citrus, at which, within a year or two
after the appearance of the whitefly, the fungus also appeared with-
out any attempts having been made to introduce it. Nevertheless
the fungi should be introduced as soon as possible. The whitefly
usually does its worst within a year or two after it gets thoroughly
established in a grove. This is because the fungi have not as yet
established themselves thoroughly. Therefore it is important to
hasten their spread as much as possible.
But even after the first introduction, constant efforts should
be made to keep the fungi distributed over the grove during the
rainy season. The distribution, particularly at the beginning of the






Bullein 123


rainy season, is often very uneven among the different trees of a
grove, and even in different parts of the same tree. This arises,
from the circumstance that the fungi (at least the red and brown
fungi) ordinarily make little or no growth during the winter and
spring. Thus if there should be a protracted dry spell, as was the
case during the spring of this year, the fungi may die out almost
entirely. The old spores of the previous year lose their vitality,
or are washed out of the trees by the occasional showers. As a
result, at the beginning of the rainy season, usually some time in
June, there is often little fungus in the grove, so that the restock-
ing of the trees is slow, and the rainy season may be over before
the fungus gets a good start. Giving a little aid at this time in the
fcrm of artificial dissemination of the spores will usually result in
a much more satisfactory development of the fungus.
SOURCES OF FUNGus.-Usually the grower can find, at the
beginning of the rainy season, in some favored situation, either in
his own or in some neighboring grove, sufficient fungus for rein-
troduction. Often, however, this is not the case; and the fungus
must be secured from a distance, unless it has been artificially pre-
served during the winter. The Experiment Station, although often
appealed to, has no funds available for the collection and distribu-
tion of fungus. Usually, however, the department of Entomology
is in touch with growers from whom the fungus may be obtained.
Several men make it their business to supply growers with fungus,
and even to spray it into the trees if desired. Those that now have
a supply on hand are Mr. Hammond, of New Smyrna; Mr. F. P.
Henderson, of Gainesville, and Mr. S. L. Story, of Eustis.
PRESERVING THE FUNGUS.-The habit of depending upon the
likelihood of being able to find some fungus somewhere when needed
in the early summer is a risky one, as has been shown this year. It
is far safer to preserve a supply, carrying it over from the preceding
autumn.
Perhaps the safest way, if one has the facilities, is to place
leaves with fungus cushions in cold storage in the autumn. For
this purpose, leaves with plenty of fungus should be collected, and if
possible to obtain them, those with spores of the brown fungus.
These leaves are spread out to dry for a day or two in a current of
air, but out of the direct sunlight. When the leaves are fairly dry,
but the fungus still bright, they are put in tin cans with tight covers
and placed in a refrigerating plant, where they are kept as near 32
degrees F. as possible.






Florida Agricultural Experiment Station


But refrigerating plants or ice factories are out of the reach of
most growers. Under such circumstances one may resort to the
method of drying the fungus material. This dried material has
failed to germinate in the hands of some careful investigators; but
the writer has succeeded during the past two winters, and others
have reported success. The leaves were collected as before, but
allowed to dry thoroughly, being spread out in the air in a dry place
for weeks. They were then piled loosely in a large box which was
covered loosely to prevent much dust from getting in. When ready
to use, the material was soaked in water for an hour or two, and
then applied like fresh material.
GROWING RED FUNGUS.-If one has but little fungus he can
increase the amount by raising it on artificial media, starting his
culture six to eight weeks before the fungus will be needed. For
this purpose large sweet potatoes are cut into strips a half-inch
square in cross section, and three or four inches long. These are
washed in running water for an hour or more, and then placed in
wide-mouthed half-pint or pint bottles. A half inch of water is
placed in the bottom of each bottle, which is then stoppered with a
plug of cotton. It is now ready to be sterilized. For this purpose
the best instrument is a steam autoclave such as those used by bac-
teriologists, but an ordinary oven can be made to answer. The
bottles are placed in this, and gradually heated until the water boils
for at least ten minutes. This is repeated the next day, and again
the third day. The bottles and the contents should now be sterile;
that is, all bacteria and their spores should be dead. It is well to
allow them to stand for a few days to see if they are really sterile,
that is, that no growth takes place in them and that the potatoes
retain their appearance and odor. The cotton plug is now removed
from each of the bottles in turn, and some spores of the red fungus
introduced, after which the plug is quickly replaced. This plug
keeps out the bacteria (which would quickly destroy the fungus
because they grow more rapidly), while it also admits air into the
bottle. The spores are introduced either dry or in water. The
water must be sterilized by boiling on three consecutive days, as
were the bottles. When the water is cooled from the last boiling,
carefully pick out some spores from a clean pustule, place them in
thr sterilized water in a sterilized atomizer and spray
into each of the bottles. In the dry method, sterilize
a hat-pin by placing it in a flame until it is red.
As soon as it is reasonably cool, carefully stick it into a clean, fresh






Bulletin 123


pustule and draw it over one of the slices of potato. Repeat the
process with the other slices in the bottle. Some of the spores of the
fungus will be sure to stick to the needle and be rubbed off on the
potato. All of this must be carried on in a room as free as possible
from dust and currents of air. In about seven days, growth will be
visible on the potato; and in twenty or thirty days the red spores
will begin to appear. In from ten to thirty additional days the fun-
gus will be ready to use, and the contents of the bottle can be mixed
with water and filtered through a piece of cheesecloth and then
sprayed into the trees.
TIME TO APPLY FUNGUs.-The fungi can usually be success-
fully introduced only during a period of moist weather and when
there are plenty of young larvae on the leaves. Although good
catches have been obtained during a rainy spell in April, it is not
generally until the summer rains commence, usually some time in
June, that success in introduction can be expected. At this time also
young larvae are beginning to appear on the leaves, and they will
increase in numbers until the latter part of July. The brown fungus
is most apt to make a good catch later, in August or early Septem-
ber. Although the bulk of the whiteflies are in the form of adults
or pupae at this time, the broods have become so mixed that there
are still plenty of young larvae on the leaves. However, when
spraying fungi, as many of those parasitic upon whitefly as are ob-
tainable should be included, as well as those parasitic on scale in-
sects. Of the latter, the red-headed scale fungus, the white, or
gray-headed, and the black, are most important enemies of the purple
scale.
APPLYING THE FUNGUS.-E. W. Berger has found that the
spores and pieces of fungus could be washed off into water, which,
after being filtered through cheesecloth, could be sprayed on to the
trees and produce a "catch." This is the best method for an ex-
tensive grove when one has plenty of fungus.
In the case of a few trees or little fungus, an excellent method is
to place the leaves in a dishpan or similar receptacle, and cover with
water. Branches of the trees are then dipped in this, or the wet
leaves can be rubbed over the under surface of the leaves on the
trees. This seems to be a surer method of introducing the brown
fungus than the spore-spraying way. An atomizer has been used
successfully in small groves. The original method of introducing
the fungus was to place in the trees small potted trees which carried
the parasitic fungi. Later it was found that the same results could






14 Florida Agricultural Experiment Station

be achieved by pinning on to the leaves of the tree leaves with
the parasitic fungi. This is a handy method, and is still valuable
if only a few citrus trees are to be treated.

CONTACT INSECTICIDES

These must be resorted to in case of a severe infestation dur-
ing the dry season. The most efficient and widely used of these
are the miscible oils, emulsions of paraffin oils with soap. W. W.
Others, of the U. S. Dept. of Agr., Bureau of Entomology, sta-
tioned at Orlando, has worked out perhaps the most satisfactory
ones. The following extracts are taken from his Circular 168.

OTHERS' FORMULA.
W ater (boiling) ........................ ....... ..... gallons 5
Distillate, 28 degrees Baume ...................... ..... .. gallons 5
W hale-oil soap .................................. ..... .pounds 1/2
For the oil one may use "Diamond Paraffine Oil" to be obtained
fiom the Standard Oil Company, or "Red Insecticide Oil" of the
Gulf Refining Company.
In preparing the stock mixture the soap should be put into a receptacle of
about 5 gallons' capacity, and the oil should then be added very slowly while
the mixture is being vigorously stirred. It is important that the oil be added in
small quantities at first, and also that the stirring be sufficient to keep the
oil and soap in the form of an emulsion after each addition of oil. Thus at first
about a pint of oil should be added to the soap, and the mixture stirred until
no free oil appears. As the amount of oil is increased, it should always be
stirred or mixed thoroughly before the next addition is made. After the re-
quired amount of oil has been added, and after free oil has ceased to appear
on top of the soap, the water is slowly poured in, about a quart at a time.
To determine whether the mixture will form a perfect emulsion, add a little
of it to soft water, and if no oil floats, the mixture is perfect and may be
used for spraying. The presence of floating oil indicates an imperfect mixture,
and results from adding the oil too suddenly, or from insufficient stirring.
This condition may be remedied by the addition of more soap, which is pre-
ferable to throwing away the entire mixture.
For spraying orange trees, use I gallon, of the stock mixture prepared
as just described to 50 gallons of water; or use the entire amount to make
200 gallons of spray material. This dilution contains approximately I per cent.
of oil, which is the maximum strength required for whiteflies and the purple
scale. For three-fourths of I per cent. of oil, add I gallon of the stock mixture
to 66 gallons of water; and to obtain one-half of I per cent., add I gallon of the
stock mixture to loo gallons of water.
Many alterations may be made in the foregoing formula. The quantity of
soap will depend largely upon the time consumed in adding the oil, and the
amount of stirring accompanying this process. The amount of soap is lessened
if the stirring is uniform, and if ample time is taken in the preparation. Petro-
leum fuel oil, or "crude oil," and distillate, or gas oil, may be used instead
of the paraffin oil, but in these cases a mixture of about twice the strength will
be needed to kill the insects. The amount of water is unimportant, since the
emulsion should be perfect if either I or 4 quarts be added. The only thing
to be remembered is that the diluted spray should contain .the required percent-
age of oil.






Bulletin 123


There are several proprietary insecticides widely sold and used
in Florida which are similar to the above in composition. These
are ready to use, except for mixing with water. The grower should,
however avoid those that contain carbolic acid, sulphuric acid, or
other chemicals that are apt to damage fruit or leaves. Others'
formula is also sold already mixed by one or more firms which
handle insecticides. Whale-oil soap, one pound to from four to six
gallons of water, is fairly good and handy for the small grower
who may not have the oils. The strength will depend upon the
weather and the water. Use it stronger in the winter and with hard
water. It is perhaps better, if one uses hard water, to first "break"
or soften it with washing soda. To soften hard water add a measured
quantity of soda (say one-half ounce) to a measured quantity (say a
gallon) of the water to be softened. A dirty-looking sediment will
appear in the water. Filter this water through a fairly closely
woven cloth, or allow it to settle, and then pour off the clear liquid
and add more soda. If no more sediment appears, you have added
enough, perhaps too much, soda; if more sediment does form, you
did not add enough soda. In the latter case, add another half
ounce per gallon and then filter and test as before. Repeat this
process until the filtered water no longer forms a sediment, and
you will have found out how much soda you must add to each
gallon of your spray solution.

To secure satisfactory results, the application should be thorough and with
sufficient force to break up the liquid into a fine mist. The kind of pump
to be used should be governed by the size of the grove and other conditions.
A barrel pump will serve every purpose if the trees are low and only a small
amount of spraying is required. For larger operations, a gasoline-power out-
fit will give better satisfaction. For Florida such an outfit should be light in
weight, with 6-inch tires and an engine of not less than two and one-half horse-
power. To keep the machinery free from sand, the engine should be pro-
vided with canvas curtains. To obtain satisfactory results, it is necessary to
have the proper equipment for applying the insecticide. Much of the prejudice
against spraying for the control of whiteflies arises from the inefficient results
due to improper equipment.
Since the insects congregate on the under side of the leaves, the spray
should always be directed upward. To accomplish this, one should use a
straight nozzle attached to an elbow which makes an angle of approximately 45
degrees, or, better still, an angle nozzle which will not get entangled in the
foliage and branches. A nozzle which emits the spray in the form of a cone
having an angle of about 90 degrees has been found to be very efficient, where-
as a flat or solid stream will not give satisfactory results.

WHEN TO SPRAY.-The younger the larvae, the more easily
they are killed. Then too, by killing them in their early stages the
glower saves to the trees the sap required to bring the larvae to a
larger size, and reduces the amount of honeydew formed. On the






Florida Agricultural Experiment Station


other hand, the eggs are not killed by the spray. It would there-
fore be unwise to spray when any large proportion of the whiteflies
are in the egg stage; or, what amounts to the same thing, when
there are many adults about. The best time then is as soon as pos-
sible after most of the eggs have hatched. Turning to our life-
history sketch we find that there are three more or less distinct
broods, with their maximum abundance of adults in March, early
June, and late August or early September; and that it takes two
weeks for the eggs to hatch. On the average the spring brood will
have about disappeared by April 15. Waiting two weeks for the last
eggs to hatch will bring the most favorable time to spray to the
very last of April. The date of emergence varies as already indi-
cated, so that the proper time to spray will also vary. It is impos-
sible to give the exact date, which will vary with the latitude, sea-
son and grove. The above is but an average for the State. The
best plan is to frequently examine the leaves with a good lens,
particularly the new and tender growth, and when nearly all of the
eggs have hatched, then spray. But, as many growers are not pro-
vided with a sufficiently strong lens, or sufficient familiarity with the
eggs to be able to determine the right time by direct observation, the
next best plan is to watch the flight of the adults and note the time
when it about ceases. Wait two weeks longer and then spray.
This spring spraying is usually important.
In July there comes a similar favorable period in the life-his-
tory, but there are some factors less favorable to spraying at this
time. It is apt to be rainy, and hence spraying is difficult. At
this time, too, the fungi should be flourishing, making insecticides
less necessary, especially as the brood should be small if the spring
spraying was thorough and the grove is not too close to neglected
groves.
In late August and early September there comes the last brood
of the season. The broods have now become badly mixed, and it is
well into September before the adults are gone. This will bring
another favorable time to spray some time in October, the exact
date to be determined as for the spring brood.

PROGRAM FOR CONTROL

Many growers depend entirely upon the parasitic fungi
for the control of whitefly. But, except for groves
particularly favorably located, as those in low hammocks,
we do not advise it. If our rainy season lasted throughout the






Bulletin 123


year, we would need to use no insecticides. But during the drier,
cooler season, the whitefly fungi are at a standstill, or they may
almost entirely die out. There are three broods of whiteflies, and
thle careful grower who wishes his trees and fruit to be of the very
first class should combat each brood; especially if, as is too often
the case, he is surrounded by more or less neglected groves from
which his grove is reinfested at each flight. The summer brood
usually, and the fall brood sometimes, can be satisfactorily con-
trolled by the fungi; but the spring, and often the fall brood, should
be attended to by insecticides. We advise, therefore, that for the
average grove in the average year, the owner should plan to spray
thoroughly with one of the miscible oils in the spring and fall, and
that during the summer he should spare no pains to spread the
fungi. This is not intended for a hard and fast program. If there
are not enough larvae on the trees to do important damage, it would
be a waste of good money to spray, unless the scale insects need at-
tention. (Attention should perhaps here be called to the fact that
these same miscible oils are the very best insecticides known for
the control of scale insects). On the other hand should July be
dry, or the fungi inactive for any other reason, and whitefly abund-
ant, the owner should not hesitate to spray with insecticides. We
do not, however, advise the application of these oils to trees more
than two or three times a year. Experiments showed that three
heavy applications, made in June, July and August, stunted the
fruit and retarded its ripening.
For the grower who is surrounded by groves in which the
whitefly is not controlled, there is another reason for the abundant
use of fungi. These will spread to a considerable extent into the
surrounding neglected groves and thus reduce the numbers of white-
flies that are constantly flying into his grove. This is also true, al-
though to a less extent, of the chinaberry and other host plants, in-
cluding the wild ones. An important and comforting fact in rela-
tion to the use of the oils in connection with the fungi, is the
fact that these oils are not fungicides and will not kill out the spores
of the friendly fungi.
Unfortunately the same cannot be said concerning sulphur and
lime. This solution is one of the very best means of controlling the
russet mite and also the six-spotted and purple mites. It also acts
as a stimulant to the fruit, apparently making it larger and earlier
in maturing. It is a very valuable spraying solution. When ap-
plied in the spring when there is most need for it, it does little






Florida Agricultural Experiment Station


harm except to necessitate the reintroduction of the fungi. But its
use during the summer is incompatible with the use of the friendly
fungi, either those parasitic upon whitefly or upon scale insects.
Whether the grower shall give up his friendly fungi or the summer
use of lime and sulphur, is a question which must be decided by the
relative importance of the rust mite and the parasitic fungi. Doubt-
less this will vary under different situations and care.

FUMIGATION
This is the most thorough method of ridding a tree of insect
pests, and is much used in California, though not popular among
the growers of Florida. This is because it can be employed here
for only a short time in winter, and because it is expensive, and does
not produce lasting results unless every grove and other host plant
in the community is fumigated at the same time. A fumigated
grove is quickly reinfested from unfumigated surrounding ones, if
such exist. Nevertheless, where a grove or community of groves is
isolated from other groves and other host plants, it is a very good
method. In operation a tent is spread over the tree, and under it
hydrocyanic-acid gas is generated. This should not be attempted
except under expert supervision.
This method is used to rid nursery stock of scale insects. For
this purpose the stock to be fumigated is placed in a tight box. In
an earthenware vessel water is placed to the amount of three fluid
ounces for each 150 cubic feet of space to be fumigated. Into the
water is poured one fluid ounce of concentrated sulphuric acid; and
then one ounce of potassium cyanide (or three-fourths of an ounce
of sodium cyanide) in a paper bag is dropped into the liquid, and the
jbox quickly closed and left for twenty-four hours. Both the potas-
sium cyanide and its gas are extremely poisonous, and must be
handled with great caution, but can be safely used in the hands of
a careful person.

FOOD PLANTS OF WHITEFLY.

The common citrus whitefly has been observed to mature on the
following plants, arranged approximately in order of preference:







Bulletin 123


Preferred (in order as named).
Chinaberry and umbrella tree.
Citrus, all varieties and species.
Tangerines.
Satsumas.
Round oranges.
Trifoliata.
Kumquats.
Lemons.
Limes.
Grapefruit.
Cape jessamine (Gardenia).
Privet.
Prickly ash.
Japanese and native persimmons.


Less Severely Infested.
Cherry laurel.
Coffee
Pomegrarate.
Smnilaa sp.
Wi'd olive (Osianuthus anmericanus).
Green ash.
Japonica (Camellia japonica).
Jessamine (Jasninum sp.).
English ivy.
Water oak.
Trumpet flower (Tecoma radicans).
Ficus sp.
Scrub palmetto.
Honeysuckle.
Blackberry.
Oleander.
Viburnum nudum.
Button bush (Cephalanthus occident-
alis)
Boston ivy.
Mexican orange (Choisya ternaa).
Osage orange (3Iachrla anrantiaca).
Portugal Cherry (Cerasus sp.).
Tree-of-Heaven (Ailanthus).


The wild and useless plants in the above list, particularly those
near the head, should be destroyed when growing near groves. Of
these the China and umbrella trees are particularly important. The
planting of these trees in citrus communities should be prohibited
by public sentiment and by law. It has been estimated that a good-
sized chinaberry tree will produce on the average between 25,000,-
ooo and 50,000,000 whiteflies each season. From these trees the
adults of the late summer brood fly out to infest citrus trees when
the maturing leaves of the chinaberry are no longer attractive.

SPREAD OF WHITEFLY

There are still considerable sections of the southern part of the
S:ate that have not been invaded by either species of whitefly, and
some others where the cloudy-winged species only is found. It is
very important to these communities that the pest should be kept
out, and to this end a study of its method of dispersal is important.
For every year the whitefly is kept out of a grove there is a saving
of at least 50 cents per tree.
The spread of A. citri from grove to grove has been largely
by the flight of the adults. It has been well established that they
can by this means reach a grove more than a mile from their birth-
place.






20 Florida Agricultural Experiment Station

Formerly nursery stock was a common and important means
of spreading the insect, perhaps the usual method of infesting new
communities. The thorough system of nursery inspection now in
operation, with rigid insistence upon complete defoliation of all cit-
rus trees shipped out, has reduced this danger to a minimum. There
is still some danger from the illegal movement of nursery stock and
the transfer of gift trees. In this connection one must bear in mind
the other host plants mentioned above. The careless shipping of any
of these can spread the pest. The danger from any particular one
is in direct proportion to its position in the list and the frequency
of its transportation.
But the adults often catch rides on trains, automobiles and other
passing vehicles. To reduce the danger from trains, it is particularly
important to have no chinaberry trees or other host plants about
stations and right of way, and to watch closely all other plants in
such situations and stamp out the first infestation. Watch particu-
larly the trees about the house and barn if these be located in a grove,
as it is there that the -first infestation usually appears.
Although the whitefly has been spread chiefly by the adults and
the larvae on nursery stock, there is danger of the crawlers or leaves
with pupae being carried from grove to grove on picking baskets
or other utensils.

CLOUDY-WINGED WHITEFLY
(Aleurodes nubifera Berger)
This species was discovered by E. W. Berger in 1908. It had
long existed in the State, but had not been distinguished from the
clear-winged species. In Florida it has been found only on citrus,
and is not now generally found in the northern part of the State.
This is probably due to the "big freeze" of 1894-95 which killed all
the citrus trees in this section to the ground. The clear-winged
species survived the catastrophy on other host plants.
The adults of this species can be distinguished from those of
the other species by a rather indefinite darker shading on each fore
wing, whence the name "cloudy." The eggs are nearly black, and
covered with a fine net-work, as seen under a lens. The color of the
eggs and the presence of the yellow fungus are the most ready
means of detecting the presence of this whitefly. There are differ-
ences in the larvae, but a good lens is necessary to detect them.
In most places in the State the cloudy-winged whitefly occurs






Bulletin 123


nixed with the other species. Under such circumstances it is of
secondary importance. A. ci',ri seems to be able to largely crowd
it out. Its generations are from two to eight weeks behind those
of A. citri. There is an additional fungus parasitizing it, the yellow
fungus, which is closely related to the red fungus, differing chiefly
in its color and inability to grow on A. citri. Also the cloudy-
winged whitefly is much more susceptible to infection by Microcera
than is A. citri. The adults have even a more marked preference for
the new growth on trees than those of the clear-winged species.
Otherwise A. nubifcra closely resembles A. citri.
CONTROL.-This is identical with that of A. citri except for the
following points. The yellow fungus can be added to the water
used in spraying, and the use of Microcera (Fusarium) is more im-
portant than for A. citri. When this species is mixed with the clear-
winged whitefly, the time for spraying with insecticides will be the
same as if the colony were pure citri, as this is by far the more im-
portant whitefly in mixed colonies. But when the cloudy-wing
alone occurs in a grove, the time for the spring spraying will be
delayed about two weeks, and that for the fall six to eight weeks.
The same rule applies for determining the exact date as in the case
of A. citri. The great preference of A. nubifera for new growth
leads it to collect on the water-sprouts. These can be cut out of a
tree after most of the eggs are laid, thus often getting rid of a ma-
jority of the insects.

WOOLLY WHITEFLY
(Alcurodes howardi Quaint.)
This insect has been known to be in Florida since 1908. Al-
though it is too early to make any sure predictions, it does not seem
likely that the woolly whitefly will ever become the serious pest that
the other two species are. It has, however, shown itself capable of
inflicting very severe damage for a few months. Much depends
upon the prevalence of a minute wasp-like parasite which lays eggs
within the larvae. The young hatching out in these larvae kill the
whitefly.
It can be controlled by the same oils which are used for
A. ci'ri, but only when the larvae are young. The proper periods
for spraying will fall approximately on the last of March, the middle
of June, the first of September, and late November. (This species
is the subject of a bulletin which will soon appear).







22 Florida Agricultural Experiment Station


REFERENCES

The following list gives some of the most important papers on
the citrus whitefly. Bulletins marked with an asterisk (*) are out
of print; but they may be seen in many public libraries, or in the
library of the Florida Agricultural Experiment Station.

I. *HUBBARD, H. G.-Insects Affecting the Orange. U. S. Dept. of Agr.,
Div. of Ent. 1885.
2. *MORGAN, H. A.-The Orange and Other Citrus Fruits. La. Agr. Exp.
Sta., Special Bul. 1893.
3. *WEBBER, H. J.-Sooty Mold of the Orange. U. S. Dept. of Agr., Div. of
Veg. Physiol. and Path., Bul. 13. 1897.
4. *GoSSARD, H. A.-Whitefly. Fla. Agr. Exp. Sta. Bul. 67. 1903.
5. *BERGER, E. W.-Whitefly Conditions in 1906. Fla. Agr. Exp. Sta., Bul.
88. 1907.
6. BERGER, E. W.-Reportof Entomologist. Report Fla. Agr. Exp. Sta.
for 1907. 1908.
7. *ROLFS, P. H. and FAWCETT, H. S.-Fungus Diseases of Scale Insects and
Whitefly. Fla. Agr. Exp. Sta. Bul. 94. 1908.
8. MORRILL, A. W.-Fumigation for the Citrus Whitefly. U. S. Dept. of Agr.,
Bur. of Ent., Bul. 76. 1908.
9. FAWCETT, H. S.-Fungi Parasitic upon Aleyrodes Citri. Univ. of Fla.
1908.
10. BERGER, E. W.-Report of Entomologist. Report of Fla. Agr. Exp. Sta.
for 1908. 1909.
II. *BERGER, E. W.-Whitefly Studies in 1908. Fla. Agr. Exp. Sta., Bul. 97.
1909.
12. BERGER, E. W.-Report of Entomologist. Report of Fla. Agr. Exp. Sta.
for 1909. 191o.
13. *FAWCETT, H. S.-An Important Entomogenous Fungus. Mycologia, Vol.
2, No. 4. 1910.
14. BERGER, E. W.-Whitefly Control. Fla. Agr. Exp. Sta., Bul. 103. 191o.
15. BERGER, E. W.-Report of Entomologist. Fla. Agr. Exp. Sta. Report
for 191o. 1911.
16. BERGER, E. W.-Report of Entomologist. Fla. Agr. Exp. Sta. Report for
1911. 1912.
17. WATSON, J. R.-Report of Entomologist. Fla. Agr. Exp. Sta. Report for
1912. 1913.
18. YOTHERS, W. W.-Spraying for Whiteflies in Florida. U. S. Dept. of
Agr., Bur. of Ent., Circ. 68. 1913.
19. ROLFS, P. H.-Fungus Diseases of Scale Insects and Whitefly. Fla.
Agr. Exp. Sta., Bul. 119. 1913.
20. WATSON, J. R.-Report of Entomologist. Fla. Agr. Exp. Sta. Report for
1913. 1914.







Bullein 123 23

PRESS BULLETINS.
*GOSSARD, H. A.-The Whitefly. Fla. Agr. Exp. Sta. Press Bul. 4. 190l.
*SELLARDS, E .H--Whitefly Conditions in North Florida. Fla. Agr. Exp. Sta.
Press Bul. 56. 1905.
BERGER, E. W.-Whitefly. Fla. Agr. Exp. Sta. Press Bul. 62. 1907.
*FAWCFTT. H. S.-Cinnamon Fungus of Whitefly. Fla. Agr. Exp. Sta. Press
Bul. 76. 1907.
*BERGCR, E. W.-Soraying with Fungus Spores. Fla. Agr. Exp. Sta. Press
Bul. So. 1908.
*BERGER, E. W.-Tl troducing the Friendly Fungi. Fla. Agr. Exp. Sta. Press
Bul. 82. 1908.
*BERGER. E. W.--Whitefly in Chinaberry Trees. Fla. Agr. Exp. Sta. Press
Bul. ToS. 1909.
*BERGER, E. W.-Whitefly in April. Fla. Agr. Exp. Sta. Press Bul. 115.
1909.
*BERGER. E. W.-When to Spray for Whitefly. Fla. Agr. Exp. Sta. Press
Bul. 124. 1909.
*BERGFR. E. W.-Winter Treatment of Whitefly. Fla. Agr. Exp. Sta. Press
Bul. 143. 1910.
*BERGER. E. W.-Scales and Whitefly. Fla. Agr. Exp. Sta. Press Bul. 145.
1910.
*BERGER. E. W.-Summer Spraying for Whitefly. Fla. Agr. Exp. Sta. Press
Bul. 151. 191o.
*BERGER. E. W.-The Citrus Whitefly in the Fall. Fla. Agr. Exp. Sta. Press
Bul. 156. 190o.
*BERGER. E. W.-Whitefly Fungus in Cold Storage. Fla. Agr. Exp. Sta.
Press Bul. 162. 1911.
WATSON, J. R.-The Cuban or Woolly Whitefly. Fla. Agr. Exp. Sta. Press
Bul. 212. 1913.
WATSON, J. R.-Preserving Fungus Parasites of Whitefly. Fla. Agr. Exp.
Sta. Press Bul. 217. 1913.







Florida Agricultural Experiment Station


BULLETINS AND REPORTS ON HAND FOR DISTRIBUTION

at the
AGRICULTURAL EXPERIMENT STATION, Gainesville, Florida.

(These Bulletins and Reports are sent free on request.)

BULLETINS
19. Tobacco -------------------------------------- J. P. DePass. 1892
26. Big-Head --------------------------------------A. W. Bitting. 1894
28. Liver Fluke ---------------------------------A. W. Bitting. 1894
30. Culture of Tobacco ---------------------------F. B. Moodie. 1895
37. Pineapples at Myers ---------------0. Clute and W. A. Marsh. 1896
38. Tobacco in Florida ---------------------------F. B. Moodie. 1897
42. Strawberry Insects ------------------------A. L. Quaintance. 1897
55. Feeding With Florida Feed Stuffs ----------H. E. Stockbridge. 19oo
103. Whitefly Control --------------------------------E. W. Berger. 19ro
104. Pineapple Culture-Vll -------A. W. Blair and R. N. Wilson. 191o
o15. Japanese Cane for Forage -----------------------J. M. Scott. 1911
io6. Sca!y Bark or Nail-Head Rust of Citrus ------H. S. Fawcett. 1911
107. Stem-End Rot of Citrus Fruits ---------------H. S. Fawcett. 1911
io8. Diseases of Citrus Fruits-----------------------------
P. H. Rolfs, H. S. Fawcett, and B. F. Floyd. 1911
1o9. Citrus Scab ----------------------------------H. S. Fawcett. 1912
IIo. Native and Grade Cattle-Breeding --------------J. M. Scott. 1912
inl. Melanose and Stem-End Rot----B. F. Floyd and H. E. Stevens. 1912
113. Pig-Feeding ----------------------------------J. M. Scott. 1913
114. Milk Production-II ---------------------------J. M. Scott. 1913
115. Sugar and Acid in Oranges and Grapefruit----S. E. Col!ison. 1913
r16. Lettuce Drop -----------------------------------0. F. Burger. 1913
117. Tomato Diseases -------------------------------P. H. Rolfs. 1973
118. Sugar-Cane and Syrup Making ---------------A. P. Spencer. 1913
120. Irish Potatoes in Florida ----------------------A. P. Spencer. 1914
121. Cucumber Rot ----------------------------------0. F. Burger. 1914
122. Citrus Canker ----------------------------------H. E. Stevens. 1914

ANNUAL REPORTS
Report for 1896 Report for 1907-8
Report for 1897-98 Report for 19o9-io
Report for 1901-2 Report for 19I10-1
Report for 1902-3 Report for 1911-12
Report for 1903-4 Report for 1912-13
Report for 1905-6




University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs