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Whitefly control

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Whitefly control
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Bulletin - University of Florida Agricultural Experiment Station ; 103
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Berger, E. W.
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University of Florida Agricultural Experiment Station
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English

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University of Florida
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SEPTEMBER, 191o


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. 0. PAINTER PRINTING CO., DeLand, Fla.


BULLETIN 13











BOARD OFCONTROL


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.
0. 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 W whitefly Injures Trees . . 5 Sum m ary of Life H istory . . 5 Methods of Control 6
T he F ungus D iseases . 6
T he R ed F ungus . .
Experiments in Spreading Fungi-is .
Introducing Red Fungus . I0 O th er F ungi . II P inning L eaves . 12 A rtificial Culture of Fungus . 12 Treatm ent with Insecticides . 14
Experim ents in Spraying . 14 F um igation . 17 W inter T reatm ent . I;
Localities just Becoming Infested . 18 Badly Infested Localities . is Spring, Summer, and Fall Spraying . 19
Spring T reatm ent . 19 Sum m er T reatm ent . 20 F all T reatm ent . 20 Spraying Solutions . 21 Three Species of W whitefly . 22 W whitefly and Freezing . 22 Q uarantine . 23 F ood P lants . 24 Plants to be Condem ned . 25 W whitefly 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 conditions 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 10 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.
9. In summer the fungi should be applied, because during the period of rains spraying with insecticides is difficult, but the fungi can then bL 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 wvill 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 xvhitefly may be controlled, though it is almost impossible to eradicate it. To control this pest is to keep it i n check sufficiently for the trees to continue to bear clean fruit.

HOW THE XVHITEFLY INJURES TREES

Badly infested citrus trees usually bear but a small amount of fruit, 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 nionth 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 honeydew, 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 livc 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 whitefly. 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.





6 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 insecticide. 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 Io days or two weeks after the swarming periods in spring, summer, and fall. In other words, the eggs hatch in 1o 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 ano 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, spraying 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 (Ascherso jia aleyrodis) yellow fungus (Aschersonia flavo-citrina), brown fungus (Aegerita webberi Fawcett), cinnamon fungus (Verticillium heterocladum), white-fringe fungus (Microcera 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 (lead 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 satisfactory 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 obtained even under otherwise adverse conditions, if these be not extreme. In the grove of Mr. WV. 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 wvas giving only inadequate relief, a single spraying of the fungus spores was made in August, 19o8, into 6 trees, and the entomologist counted, as a result, something like io 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 tuines 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, hut 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 introduced 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 viler tb,(writer's directions in October, 1906. A very small amount of fungils developed that fall, but it spread well during the next summer and no more was introduced before 19oS. 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 trout the trees sprayed August 2,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, 19a9, 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 satisfactory. 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 summer 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, 19o8, as was done on the few trees referred to above.
The first part of the work was an experiment designed to give uts 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 i910, because fungus is scarce. No other repressive measures have been taken.





BULLETIN 10J.


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 in thc 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 whit ' fly 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 unknownn 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 19o8 i\Ir. 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 i909, with one or two, helpers, he sprayed fungus spores into 127,500 trees. That is, he made 127,500 sprayings, 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 latcr in the season. The yellow fungus (Asch, rsonia), 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 (i910) 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 insecticides, 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 frequently 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 13,600,000 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 io 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 arid 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 development 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 naturally. 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 fungis as late as October, November and December, and while bult a meager infection resulted, this spread rapidly during the followinIg spring and summer, as soon as sufficient moisture and warmnth 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 iqoS, page liv; and in the Annual Report for 1909, page xl. On a small place the mixture of -pores 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 parasites 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 certainty, 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 cloudywinged 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 .irlfectecl with a fungus upon them has been extensively practiced in he past, but sporespraying 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 mn 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 (zlcgerita -zebberi, Fawvcett) is the only one which has so far failed to produce spores in artificial cultures. 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 laboratory 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 bactcria 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 artificiallv; but should it become necessary to supply the artificially-g-rown 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 potatoes 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 formation appears to be completed in about 30 to 6o days. The 3 fungus mass will then be of a

pearance of this color may be take as evidence that spores are forming. The 'fungus should be used at that time, but it will keep for a month, 2 and longer during winter and Early spring. This fungus i~does not readily become weakened, 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 cultures of this fungus upon sweet potato have been made.






J4 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 praying can be done. The difficulties in the past have arisen from spraying being done at the wrong time, or were chue 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 wvet with. the spraying solution can be overcome in part by taking special care, anid 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 frequently, while the adults fly away from the sl5ray, 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 Gainesville) 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 io days. The percentage of fourth-stage larvae killed was only 30.
These are the results of counting the dead and live larvae on 10 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 DAYS

M\AY, 1909 7th 8th 9th 10th 11th 12th 13th

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


Mean of miaxima. 85 degrees F.
Mean of minima. . 63 degrees F.
General mean . 74.5 degrees F.

The results obtained on some 25 Sats-uma 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 unsprayed trees. The following temperature conditions existed on the date of spraying and during 6 days thereafter.


TABLE 11

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

Mean of maxima . 89.6 degrees F.
Mean of minima . 72 degrees F.
General mean .go.8 degree.- F.










































3 lbs. washing soda . . 93 per cent . I . 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


M axim um . . M inim um . .


16 FLORIDA AGRICULTURAL EXPERIJUENT STATION

The following table, published ill the Annual Report for igog, was primarily arranged to show the effectiveness of the two soaps indicated, but when coinparcd with the two previous series of sprayings, 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 spraying 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 Ill

RESULTS OF SPRAYING WITH SOAPS


KILLED BY WHALE- KILLED BY OCTAGON SOAP
OIL SOAP


STRENGTH OF SOLUTION


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


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


. 88 per cent. . 95 per cent . . 77 per cent . . 89 per cent .


20th 88 69


21st 92 72


89 72


92 71


M ean of maxima . 94.3 degrees F. M ean of m inima . 72 degrees F. General m ean . 83.1 degrees F.


15th 16th 17th 98 98 93 70 74 75


18th 19th






BULLETIN 103.


In the above three series of spraying operations the figures indlicate that the June spraying was more effective than the May spraying. Temperature, as well as stage of development, is apparently 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 "Goiddust" with an initial temnperature of 88 degrees and a mean for 7 days Of 74.5 degrees; while 99. 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, 8o.8 degrees. The resuits 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 conjunction 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 during the hottest summl-er weather with the theiniometer at about 99 degrees is more effective against all stages and especially against the fourth stage and the pupae, than spraying in cooler weather.

FUiMIGATION

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 assistants at Orlando. Those wishing to consult this publication should address the Superintendent of Public Documents, Washington, 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

feared. Those who have carried on extensive fumigation experiments 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 onecent 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 successful 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 succeeded in keeping the whitefly confined to a few trees in one corner of his grove for four or five years by thorough spraying with another 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 possible; 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 entire locality is impracticable, it may be feasible to effect cooperation 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 AMay, when the grove has become reinfested from the grroves 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 twxo weeks after the spring brood of adults has disappeared from the wing. After that, during the period of summer rains, if conditions are at all favorable for fungus growth (plenty of mnoisture, and good condition of trees) the fungus diseases of the whitefly should be introduced. Finally, if necessary, the trees should be sprayed again in October or November; in which case treatment 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 sometimes earlier, depending upon the season and the locality. In localities where the spring rains are abundant and the general moisture conditions throughout the season generally suitable, the f ungi, 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 easily 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 develops 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 treatment 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 19o8 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 increase 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 ive nionths;- (4) there are few rains to interfere w ith spraying.


SPRAYING SOLUTIONS

Since spraying to kill the young whitefly larvae must be donec in spring, summer, or fall, when either tender leaves or fruit are on the trees, it is evident that a spraying solution must be usedt that will not injure the foliage or the fruit. Almost any good contact 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 larva ae. Soap solutions of i pound of soap to 9 gallons of water destroyed about 90 per cent. Good's potash wkhale-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" Lised 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 2' per cent, of soap, 62 per cent, of washing soda, and about 13 per cent, of water. When we mixed one pound of whale-oil soap with three pounds of washing soda and ased one pound of this mixtu-re to 4 gallons of water we got about the same results as we did by -using one pound of "Goiddust" 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 nubif era, is spoken of as the cloudy-winged species, and the other, Aleurodes citri, as the white-winged species. Previous to 19o8 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 corner. On the contrary, examination by A. L. Quaintance of whitefly rhaterial preserved in the Bureau of Entomology, Washington, D. C., has shown that this species existed 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 introduced about the same time. The present distribution of the cloudy-winged is quite as extensive 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. F. 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 defoliate citrus trees may be considered about the equivalent of a






BULLETIN 103.


fumigation or extra good spraying so far as the effects upon whitefly 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 exterminated the whitefly except in one or possibly in two places. At Crescent City the freeze of I894-, did exterminate the cloudywinged 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 extermination took place. Freezing destroves directly hut few, if any, of the larvae on leaves that remain uninsured.


QUARANTINE

The whitefly can be kept out of non-infested groves for a considerable 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 spreading. 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 fumigated after defoliating. To what extent whitefly may be carried on pickers' implements is an open question, but it is easy to conceive 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 bisuilphide, 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. Hubbard, and preserved in the JBureau 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 determined 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 (Fraxrinus 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 PREFERRED BY A. CITRI.

Native Species:
Cherry Laurel or Mock orange (Laurocerasus Caroliniana (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 inegacarpa (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 aimless 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 xvhiteflies. 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 abnorm-ally 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 alw ays accomnpaniied 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 exhausting the sap of the trees. The lack of sufficient moisture weakened the trees. It also checked the development of the furtgaus 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 v igor of the trees. These leaves would also have supplied m-ore moisture to the air, and their shade would have kept the interior of the trees moister. Thii 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 whitefly 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 infested 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 spraying for scales in spring, summer, or fall.
i. Spray v,-hen many young scales can be seen with a lens to be crawling about, or to have just attached themselves. Tlles,, young scales appear either as oval moving specks or as round whitish 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 tkose just set, together with the young whitefly larvae, without injuring the trees.
3. Avoid insecticides that are recommended as useful for fungus diseases, because they also destroy the fungus diseases of the scales and whitefi ,. 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 surnmer 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, and are not destroyed in -reat 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.
io. Proof that spraying with insecticides is most effective in hottest weather, against younger larvae.
i i. A second species of whitefly.
12. Some new food plants of whitefly.




Full Text

PAGE 1

BULLETIN ro3 SEPTEMBER, 19ro UNIVERSITY OF FLORIDA Agricultural _ Experiment Station WHITEFLY CONTROL BY E. w. BERGER , Ph.D. Fig. r.-The cloudy-winged whitefly, Alrnrodes nubifera. Magnified 32 times. The Station bull etins will b e sen t free upon application to the Experiment Stati o n , Gainesville. E. 0. P A INTER PRINTING CO . , DeLand, Fla.

PAGE 2

BOARD OF CONTROL P. K. YONGE, Chairman, Pensacola, Fla. T. B. KING, Arcadia, Fla. E. L. W ARTMANN, 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. M cQu ARRIE, * Assistant Superintendent Farmers' Institutes. JOHN SCHNABEL, Assistant Horticulturist. 0. 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 e xtension work.

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CONTENTS How the Whitefly Injures Tr ees . .... . ........ .. .. . .. . . ... . . . .. . . . .... . . Summary of Life History .. .. . ....... . . ... ... ... . . . . ... . . . ... . . . . . . ... . Methods of Control. ...... ..... . . . .... . ............................. .. . The Fungus Diseases ....... .. . . ....... . . ...... . ......... ... ... . ...... . . The R e d Fungus .......... . .... . ... .. . .... . . ... .. ...... . ..... . ... . . . Exp e rim e nts in Spreading F ungus ... .. ..... ... . .. .... . .. . . . .. ... ... . Introducing R ed Fungus ..... .... ... . ..... . ........................ . Other Fungi ... . . ........ ... . ...... .. ....... . . ........ . ........... . Pinnin g Leaves .................... .. ............. . . ......... . .... . Artificial Cultur e of Fungu s ..... .. . ......... . ...... . ............... . Treatment with Ins ecti cides .. .. . . .... . ..... .. . . . .... . ........ . ..... . ... . Exp er im e nts in Spraying ............ . .. .. . . .... ... ...... .. ........ . . Fumigation ... . . ....... . . . . . .. ... .. .. .. .. . . .... . ......... . .... .... . \II/inter Treatment ... ... ..... . ......................... . .. . . . . . ... .. . . . Localiti e s Just Becoming Infested .. . . ... ...... . . .. .. . . .......... . . . . Badly Infested Localities ................ . ... .. . .. ....... .. ......... . Spring, Summer, and Fall Spr aying . .... .. . . . . . . . . . . . .. . . . . . ..... . . . ... . . Sprin g Treatment .... . .. . .... ........ . . . . .. .. ... . .... ... . . .. .. ... . . Summer Treatm en t .... . ....................... . ................... . Fall Treatment ................. ... . . ... . .. .. ...... . . . ............ . Spra y ing Solutions .... . . .... . .. ....... .. ..... .. . . . . ......... .. . .. ... . . . Three Species of Whitefly ... ...... .... . . . ....... ...... ..... .. . . ....... . \Vhitefly and Fre ez ing ........ ... ....... .. .... . .... .. ...... ..... ...... . . Quarantine ....... . . .. ..... . ........ .. .. . . ..... ... .. . ................. . F o od Plants ................. . ... ... ... .. ... ... ... . . . .... . . .. ... . . ... . . Pl a nts to be Condem ned . ..... . .. ... . ............... . ... ...... ... ... . ... . Whitefly and Increas e of Scales .......... . ..... . .... .. ................. . When to Spray for Scales .... ...... . .... . ..... . ... .......... . .......... . PAGE 5 s 6 6 i 7 IO II 12 12 q 14 17 1; 18 18 19 19 20 20 2 1 22 22 23 24 25 26

PAGE 4

SUMMARY I. It is easy in Florida to start growths of the fuR.gus 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, arc 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.

PAGE 5

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 1~ecessary 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 p.:st is to keep it in check sufficiently for the trees to continue to bear clean fruit. HOW THE vVHITEFLY INJURES TREES Badly infested citrus trees usually bear but a small amount of ruit, 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 I 5 pounds per month for each million of whitefly larvae. Indirectly the trees are injured by the sooty mold which covers the leaves ~nd 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 s tarch 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 firs't 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.

PAGE 6

G FLORIDA AGRICULTURAL EXPERIMENT ST AT ION 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 id 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 1~thods 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 a:t least six of them. These are the red fungus ( Aschersonia aleyrodis) yellow fungus ( Aschersonia fiavo-citrina), brown fungus ( Aegerita webberi Fawcett), cinnamon fungus (Verticilliun i 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 t1ead adult whi:teflies, and presumably had caused their death.

PAGE 7

BULLETIN 103. 7 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 otherwis e adverse conditions, if these be not extreme. In the grove of Mr. 'vV. 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 IO 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 times as many whitefly larvae killed, and indicates that, in m a ny 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 :it 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 spra y ing s por e ~ 1111rlp1 th ; writer's directions in October, 1906. A very small amount of fongn s developed that fall, but it spread well during the next snrnmer anrl no more was introduced before 1908. During the spring of the

PAGE 8

B 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 agiain taken on April 21, 1909, as follows: Grove h a s been ' practic a lly 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 ne , w growth and many trees have set a good crop. Perhaps one-tenth as many adults on ne , w growth as in other groves in town where no fung,us was applied' . North 11:hird of grove has more adult white/lies because it is oppo s ~te a badly infested grove that , was not treated. Considering the fact that this grove was not isolated but was exposed to reinfestafion, 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 ci,complished in something like a month if we had spread -fungus through the whole grove in August, 1908, as was done on the few trees ref erred 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 r909 and very little sooty mold. Whitefly considerable in 19m but so far very little sooty mold. Red fungus was spread in 1909, but so far none in 1910, because fungus is scarce. No other repressive measures have . been taken.

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BULLETIN . 103. 9 On December 22, 1909, the writer visited the 6-acre orange 2.nd pomelo grove of Mrs. A. P. Gunther, at Pierson, and made the following notes . The larvae were in the flat condition oi fourth stage and older. Perhai;,s average of one alive per leaf. The first trees to become covered with sooty mold were observed in summ e r 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 sprea d of red fungus (Aschersonia). Dozens to hundreds of pustules per leaf. The fungus was first introduced by Mr. Frank Stirling, of DeLand, early m tht s e ason; se\'eral introducti o ns were rnade later. Tr ees look very healthy, thrifty and good , color. Good crop . last year. Tangerines and pomelos bearing a small crop thi s year. Oranges a bout 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 whit~fly 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 ( Asc!-1 1 ~r sonia), Mr. Stirling says, is a "hustler" for the cloudy-winged species of whitefly. Groves belonging to 58 owners were sprayed al a contract price of 2 cents per tree. This sp,ing and summer ( 1910) Mr. Stirling is continuing to spray fungus sp8res. It will thus be seen that the method of spreading fungus as directed by the Experiment Station is receiving a most thorough test.

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IO FLORIDA AGRICULTURAL EXPERIMENT STATION The entomologist has had occasion to examine personally only !wo 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 W , inter Park. The r , esults 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 ag.i.in 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 th e season of 1909, the whitefly was held in check and kept from spreading; and had not fungus been spread, one-1:hird 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 pres,ents condi,tions 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 quentl y benefit the trees and favor the fungus parasites of whitefly and of scales. I N TROD UCING 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 wate r on to the whitefly larvae in the infested trees. The spores of the fungus are produced in enormous numb e rs in the red elevations or pustules covering the dead larvae. They vary considerably in size, and 13,600,000 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 fungu s is scarce. It is n o t necessary to allow the leaves with fungus t o soak longer than 5 o r 10 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 s hould 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.

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BULLETIN 103. 11 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 iarvae so that fungus is then abundant. One should not attempt to introduce fungus after the period of summer rains in over. unless it is desirea 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 a:= late as October, November and December, and while b11t 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 1908, page !iv; 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.

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12 FLORIDA AGRIC U LT U RAL EXPERIMENT STATION PINNING LEAVES Pinning leaves having whitefly larvae ~nfected wi 1 th a fungus upon them has been extensively practiced in :he past, but spore spraying has now almost entirely displaced this method , If leaves are used, each leaf should be pinned with its fungm, side down to the lower surface of a leaf of the whitefly-infested tret. 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 citscribed in his paper on "Fungi Parasitic Upon Aleyrodes Citri," Special Studies No. I, U niversiity of the State of Florida, June, 1908. The brown fungus ( Acgerita 7.uebbcri, 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 for spra y ing , as can those of the other fungi. The red fungus has been grnwn extensively in the writer's lab oratory on sterilized sweet potato, either in the form of plugs or finely ground. The best resnlts were obtained when the plugs or ground sw<:et 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 ,vere 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 .::tit the slow-growing red fungus. The plug of cotton ba:rten 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 clm;t-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 reel fungus has been generally sufficient, it is not

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BULLETIN 103. 13_ Fig. 2 . -Cu l ture of R e d Ascher sonia on sweet potato, 17 day s old. Two-third s n at ural s i ze. probable that it will become necessar y to grow it artifi , cially; but shou ld it become necessary to s uppl y the artifi cia ll y grown fungus, this can be clone in ton l ots or larger with proper equipment. While the spores of thi s fungus germinate in 24 to 48 hours, fungus growth does not become visible on sweet pota toes for about 7 clays. This time i s about the same as upon whitefly larvae . Some spores are for m ed in 20 to 30 clays; -and this agam corresponds with the devetopment upon whitefly larvae. Spore for mation appears to be completed in about 30 to 60 days. The fungus mass will then be of a li ght brick-red; in fact , the ap pearance of this color may be taken as evidence -that spores are forming. The 'fungus s hould be used at that time, but it will keep for a month, and longer during winter and early spr ing. This fungus does not readil y become weak ened, or lose it s virulence, by successive growths upon sweet potato as a cu ltur e medium, since successfu l growths of fuugus have been started . upon hitefly larvae from each of 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 tu res of this fungus upon sweet potato have been made.

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J4 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 cl ea rly that effective :-spraying can be done. The difficulties in the past have arisen from spraying being done at the wrong time, or were cine 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 l eav es become wet with . t he s praying solution can be overcome in part by taking special .'. are , and by spraying at a pressure of 100 pounds or over. Spraying for whit efly 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 r pound to 4 gallons of water, 91 per cent. of all larvae of the first to the third stages were dead after IO days. The per centage of fourth-stage larvae killed was only 36. These are the results of counting the dead and live lar vae on IO leaves, selected as representative of good spraying. On 36 leaves an average of 92 per cent. of all stages were killed (An. Rept. 1909,

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BULLETIN 103. 15 p. xliii). Allowance was made for natural mortality, the percentage of which was comp ut ed upon l eaves from unsprayed trees. The following temp e rature conditions exis ted on the day the spraying was made and during 6 days thereafter. TABLE I MAXIMUi\[ AND MI NIMU )I T E:\I PER ATU RES FOR 7 DA YS l'vI..-. Y. 1909 ~---I 7th j 8th i 9t h ' Wth 11th / 1 :!th I 13th -_ _ __ ____ _ _ __ ! _ _ __ __ . __ Maximum ...... , . . . ..... . _ _ ... _. \ 88 I 8:! 813 88 Si 82 83 Minimum i 6:.? i 133 06 60 61 61 6 1 ........ .... ..... __ ..... , I Mean of maxim a .... ...... ...... . _ ... ................ _85 degr ees F. M e an of minim a ... . . . ...... .. .. .. .. . . ..... .. .. ....... . 63 degrees F. Genera l mean . ... _ .. . . .... ... _ . . ... ___ . .. ... . ....... -74 5 degre es F. The results ob tained on some 25 Sa tsuma trees ( also in Mr. Hampton's grove), spra yed on June 2, 1909, with "Golddust" as before, are as follows: 99.5 per cent . of the second and third stages were killed, and g9 per cent. of the fourth stage and pupae. The average of a ll stages killed was 91 per cent . Ten leaves rep resenting good spraying were se l ected nine days after spraying. Natural mortality wa s a llow ed for and computed from un sprayed trees. The following temperature conditions existed on the date of spraying and during 6 clays thereafter. TABLE II MAXIMUM AN D MINIMUM TEMPER ATU RES FOR 7 DAYS I ~l_~t~ I } UNE, 1909 2nd 3rd 6th ' 7t h 8th --Maximum ....................... 99 88 82 90 90 90 88 M in imum ............. . .... . ..... 73 75 75 73 70 70 68 Mean of maxim a ...... _ ... _ .. . .... . . _ .... ... . . . ... . .. _8g_6 degrees F. Mean of minima .... ........ . . ...... .. . ... _ . ......... 72 degrees F. Gen e ral mean ....... . ..... . . . .......... . . ... .... .... 80.8 degree:; F.

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16 FLORIDA AGRIC U LT U R A L E X PE RI M ENT ST A TION Th e following table , published in the Annual Report for 1909 , was primarily arranged to s how the effectivenes s of th e two s oaps indic ate d , but when compared with the two previous s erie s of spra in gs, t hi s table becomes of gr e ater interest, as is brought out in the discus s ion following. The larvae were mainly in the flat fourth stage of development, but no distinction of stages was made in countin g them. The table giv e s the result on ten leaves of spray ing two or three trees with each s trength of soap. Th e leaves were sele c t e d to represent good s pra y ing . The sprayings wer e made near Ga ine sv ille in Mr. J a m es Ce llon 's trees, June 15 to 17 , 1 9 0 9 . and th e l e av es were collect e <;l 4 t o 15 days later. T AB LE III RESULTS OF S P R AY ING WITH SOAPS S T RENGT H O ; SOLUTION KI L L E D uv \NH AL E O! L S oAP KILLED BY O C T AGO N SOA P 1 l b . t o 6 g al s . w ater . .. . ... ... .. . 9 1 p e r ce nt . . .. .. . . ..... .. . . 96 p e r ce nt. .... . . l lb . t o 9 gak w ater ......... . . .. 88 p e r ce nt . . ... . ...... . ... 95 p e r cent . .. . . . . 1 lb . t o 1 2 g als . w ater . ..... ... .. 77 p e r ce nt . .......... .. . .. 89 p e r ce nt .. .... . 1 lb. t o 1 6 ga l s . water and 3 lb s. wa s hing sod a . ... . . . . . 93 p e r c e nt .. ............... 9 4 per ce nt .. .. .. . -----------------~ --The following temper a tur e c o nditions existed on the day of s pra y ing and during 6 days aft e r . TA B LE I V MA XI MUM AN D MINIMUM TEMP E RATURES FOR 7 DAYS JUNE, 1909 15th 1 6 th 1 7 th 18th 19th 20th 2 1st ----,__ Maximum . . ...... . ... . .... . . .. .. 9 8 98 93 89 9 2 88 9 2 Minimum .. . . ........... . .. .. .. .. 70 74 7,5 72 71 69 7 2 M ea n o f maxima . ... . .... . . .. . . . . .. .. .. . ... ..... . . .... 94 . 3 d egre e , 'F ' . M e a n o f minima .. .. . .. . .. . . . . . . . . . .... .... . . ..... . . . . 72 d eg r ees F . Ge n e r a l me an ... . . . . ... . . . . . . ... . .. .. . . .. ..... . ... . . . . 83.1 de g r ee s F .

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BULLETIN 103. 17 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 pen etratin g 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 th(: 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 r7 in Mr. Cellon's trees on fourth stage larva e with the soap solutions were excellent, with an initial temperature of 98 degree s a nd a mean of 83. I degrees. These figures, in con junction with many general obseffations, indicate that ,ve shoul d spray the young larvae in the first to the third stages, and th e thin flat condition of the fourth stage, rather than the older fourth stage larvae and the pupa e . They also indicate that sp raying dur ing the hott est sum mer weather with the thermometer at about 99 degrees is more effective against all stages and especially against th e 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 th e work carried on b y Dr. A. vV. 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 I 5 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

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18 FLORIDA AGRICULTURAL EXPERIMENT STATION erred. 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 rhe 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 r 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

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BULLETIN 103 . 19 to set frmt m spring. If co ope ration 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 localit y is impracticable, it ma y be feasible to effect co operation on the part of t he ow ners of localized groups of groves. Where no co-operation wh ateve r is possible, each grower should nevertheless treat his own trees. In this instance spraying should be the method of winter tr eatme nt. It would be inadvisable to go to the expense of fumigation where the grove is not isolated ancl reinfestation is certain, but spraying should be done. Later in April or 1lay , when the grove has become reinfested from the groves of indiff e rent neighbors , it should be sprayed again. There is a time in Ap ril or May when the whitefly larvae are yo ung and ea s ily destro yed by whale-oil soap ( r 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 co mes about t,,vo weeks after the spring brood of adults has disappeared from the wing . Afte r that , during the period of summer rain s, if con ditions are at all favorable for fungu s growth (plenty of mois ture, and good condition of trees) the fungus diseases of the white fly should be introduced . Finally, if n ecess ary, 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. 'vVhere 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 :

PAGE 20

20 FLORIDA AGRICULTURAL EXPER IMENT STATION ( r) The whiteflies are in the young larval stages and are easily killed; ( 2) they are mainly on the new growth and more easi l y sprayed; (3) the larvae are destroyed before sappi ng the strength of the new growth, and before much sooty mold has developed; (4) rain is not likely to interfere with the spraying. SUMM ER 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 spray ing at this time of the year is not ge n erally 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 whitetly, and treat ment may begin in Octob er or November, or soon after the adult whiteflies of the late summ er brood have disappeared, and after the la s t 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 principal 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 s oap should not be used weaker than I pound to 4 or 6 gallons of water, but I pound to 6 or 9 gal lons 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 unneces sary to repeat it for that brood. The advantages of fall spraying may be summed up as follows: (I) The young larvae are abundant and easily killed; ( 2) they

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BULLETIN 103. 21 are kilied before they ,vax fat at the expense of the trees; (3) th e tr ee s remain cl e an for nearly five month s; (4) there are few rains to interfere with spraying. SPRAYING SOL U TIONS Since spraying to kill the young whitefly larvae must be done in spring , summer, or fall , when either tender leav e s or fruit are on the trees , it is evident that a spraying solution mt1 s t 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 pota s h 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 larva e. In winter and late fall the soap solutions should be used stron g e r, about I pound to 4 gallons of water, but a weaker solution u se d 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" t1sed 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 consi s ted 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 11sed one pound of this mixtur e to 4 gallons of water we got about th e s ame result s as we did by using on e pound of "Golddust" to 4 gallons of wat e r. One pound of whal e -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 1 pound of whale-oil soap and 3 pounds of washing soda to 16 gallons of water.

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22 FLORIDA AGRICULTURAL EXPERIMENT STATION THREE SPEOIES 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 nubif era, is spoken of as the cloudy-winged species, and the other, Aleurod es 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. 1) 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, \i\Tashington, 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 7o'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 distribut i on of the cloud y -winged is quite as extensive as that of the white-winged one. Sonietimes 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, Aleitrodes 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

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BULLETIN 103. 23 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 No ve mber and January r9oi-8, the writer collected fallen leaves at DeLand with live fourth-stage larvae and pupae upon them, some of wiiich 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 1894-5 did exterminate the cloudy win ge d spe _ cies, 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 r e main 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 winge
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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. nitbifera on some gardenia leaves collected at Crescent City, Florida, in r895, by H. G. Hub bard, and preserved in the J3ureau of Entomology, Washington, D. C. (see Bulletin No. r2, 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.-Foon PLANTS PREFERRED BY A. CITRI. Native species : Prickly Ash ( F agara Clam-fl erculis ( L.) Small). Wild Persimmon (Diospyros Virginiana) L.) Wild Olive (Osmanthus Arnericana (L.) B. & H.). Green Ash ( Fraxinus lanceolata , Borek). Introduced Sp ecies : Citrus ( all varieties). China berry (Melia Azedarach L.). Umbrella ( lvl elia Azedarach umbraculifera Sarg.). Cape Jasmine (Gardenia jasminoides Ellis). Privets ( Ligustrum spp.). Japan Persimmon (Diospyros Kaki L. .). Class II.-Foon PLANTS SOMETIMES INFESTED BUT NOT PREFER RED BY A. (ITRI. Native Species: Cherry Laurel or ' Mock orange ( Laurocerasus Caro liniana (Mill.) Roem.1.

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BULLETIN 103. Viburnum nudum L. Buttonbush (Cephalanthus occidentalis L.). ,Smilax (Smilax sp.). *Blackberry ( Rubus sp.). *Water Oak (Quercus nigra L.) 25 *Scrub Palmetto ( Sabal megacarpa ( Chapm.) Small). Introduced Species: Coffee (Coffea Arabica L.). Pomegranate ( Punica Granatum L.). Allamanda ( Allamanda neriifolia Hook.). *Honeysuckle ( Lonicera J aponica H alliana). * 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 J aponica (Camellia J aponica 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

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26 FLORIDA AGRICULTURAL E X PERIMENT 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 dtrus 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 i ncreased 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 s ap of the tree s . The lack of sufficient moisture weakened t he trees. It also checked the development of the fon 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 mor e food to the t ree s . (Leaves are not only the lungs of the tree, but also the organs in which food is elaborated.) This food would have b e en used in part to feed the scales and whitefly, and in part to maintain th e 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. Thi, would have result e d in a thrifty growth of the almost universally present fungus diseases of scales. I t ha s been noticed that scale fungi and whitefly fungi often thrive remarkably well even in dry localities in vigorously g rowing 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.

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BULLETIN 103. 27 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 ~r are not thriving. In this case spraying with some contact insecticide, or fumigation, should be employed to give immed.iate 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 onl y the most severely infested trees. \Vhen 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. 1. Spray when many young scales can be seen with a lens to be crawling about, or to have just attached themselves. The s ,: 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 tkose 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, an ~ l 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 th e old scales, are not easily destroyed by sprays. The old scales are protected by their waxy covering, arid are not destroyed in grea t 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.

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28 FLORIDA AGRICULTURAL EXPERIMENT STATION RESUME OF SCIENTIFIC RESULTS 1. 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 vess e l when the mixture is allowed to stand in it. 4Proof 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 fungu s attack. 9. Use of soap solutions for spraying whitefly. IO . Proof that spraying with insecticides i s most effective in hottest weather, against younger larvae. 1 r. A second species of whitefly. 12. Some new food plants of whitefly.