Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; 150
Title: Florida citrus diseases
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Permanent Link: http://ufdc.ufl.edu/UF00005205/00001
 Material Information
Title: Florida citrus diseases
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: p. <13>-110 : ill. ; 23 cm.
Language: English
Creator: Stevens, H. E ( Harold Edwin ), b. 1880
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1918
 Subjects
Subject: Citrus -- Diseases and pests -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references and index.
Statement of Responsibility: by H.E. Stevens.
General Note: Cover title.
 Record Information
Bibliographic ID: UF00005205
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000922772
oclc - 18162293
notis - AEN3281

Full Text


August, 1918


UNIVERSITY OF FLORIDA
Agricultural Experiment Station





FLORIDA CITRUS DISEASES

By H. E. STEVENS


Fig. 6.-A sick citrus tree


Bulletins will be sent free upon application to Experiment Station,
GAINESVILLE, FLORIDA


Bulletin 150













CONTENTS
PAGE
INTRODUCTION, Acknowledgments ..................... .....-----------.. 15
GENERAL SUGGESTIONS ................-... ...............--------- 16
Grove Location -....... ----..............................------------- .. 16
General Care, disease control, insect control ................... -----............. .- 17
Spraying ................ --.. ............-------- ---------20
Fungicides-Bordeaux mixture, ammoniacal solution of copper
carbonate, lime-sulphur solutions .......-........ ............------- ...... 22
Fungicides and Insects .......-......-.......... ... ---------... 29
Pruning ......................................................------- .-------------...... 30
Antiseptics and Wound Coverings-Bichloride of mercury, crude
carbolic acid, carbolineum, lime and sulphur wash, bordeaux paste,
white lead paint, pine tar, coal tar....................-- ......-- 32
IMPORTANT DISEASES .... ........... ................. ................----------- 35
Withertip, appearance, Anthracnose, Tear Staining, Bloom Blight,
cause, control ..........-.........................------------- 35
Foot Rot, appearance, cause, control ............-...................----.....-- -... 43
Gummosis, appearance, Gummosis type, Psorosis type, cause, control 48
Blight, appearance, cause, control ......................... ... .....-- -------.. 54
Scaly Bark, appearance, cause, control-top working, heading back,
pruning, spraying ...................................-........-.................. 57
Citrus Canker, appearance, distinguished from other diseases, cause,
control ........----.......--------.............--------- 62
Dieback, appearance-gum pockets, bark excrescences, stained ter-
minal branches, ammoniated fruit, multiple buds; control-pre-
ventive methods, curative method ................................ 68
Melanose, appearance, cause, control .................. .. .............. 76
Citrus Scab, appearance, cause, control .......--.............- .................82
MINOR DISEASES ---- ------...........--.....-........---.. ------------ 87
Citrus Knot, appearance, cause, control .... ---.................-- ........... .... 87
Leaf Spots .................. ..--------------........... 90
Sooty Mold, control ...-........-.....-..-..... ------.....- 92
Septobasidium ............-....-........ ---- ----- ---- .. 93
Algae, appearance, control ... .............. .................... 94
Lichens, control .................. ...................-..-- 95
Frenching, appearance, control ....................... ..-........-. .. 97
Black Melanose, appearance ...............---... .. ....... ....-...... 98
Dodder ................. .................. ............ 100
Cassytha ................ ..........--...-.........- 101
Sunscald ............................................ ........102
Lightning Injury, appearance ...........-- ...-- ...-.. .......- ......103
Cold Injury -............- ...........-............106









FLORIDA CITRUS DISEASES
By H. E. STEVENS
Many requests have been received for a single publication
including all the common citrus diseases that occur in Florida.
Most of our well-known diseases have been given more or less
study in the past and the results have been published from time
to time, but this information is scattered thru a number of pub-
lications, some of which are not easily accessible to the citrus
grower. In the preparation of this bulletin an attempt has been
made to bring together the information of value and practical
use to the citrus grower relating to all the citrus diseases that
are found in the State.
While the publication is intended primarily for the considera-
tion of the fungus and bacterial diseases, a few other diseases
and injuries from various causes are also included where such
are common, unusual or likely to be confused with some other
disease. Technical expressions have been avoided as far as pos-
sible and the information is presented with a view to aid the
citrus grower in better identifying his diseases and to employ
efficiently the best methods for their control.
The important diseases are discussed more fully and illus-
trated to bring out their more prominent or impressive features.
Under "appearance," the nature of the injury caused is fully
described and illustrated, which should assist one to identify
the disease readily. Under "control," the best and latest ap-
proved methods of combating the disease are suggested.
A large part of the information contained in this bulletin is
the result of personal investigations and observations in the
grove; however, the writer has drawn upon all available sources
and has made free use of the publications from this Station,
other experiment stations and the publications of the United
States Department of Agriculture. A majority of the illustra-
tions are published for the first time. Others have been taken
from former bulletins and reports of this Station.

ACKNOWLEDGMENTS
In collecting the material for this bulletin the writer has had
valuable help from his assistants, Mr. J. Matz, who made
photographs for the original illustrations, and also from Mr.
Hayden M. McKay, assigned by the State Plant Board for field
work on foot rot and gummosis. Various employes of the State







Florida Agricultural Experiment Station


Plant Board have contributed specimens and field notes of value
concerning many of the diseases. Mr. F. M.'O'Byrne, State
Nursery Inspector, has given many helpful suggestions in his
criticism of a part of the manuscript.

GENERAL SUGGESTIONS

The successful control of plant diseases often depends on pre-
ventive or precautionary measures taken far in advance of the
appearance of the trouble. Before the field is plowed or the
seed are planted certain measures often can be taken to avoid
diseases. The same will apply in a way to the citrus grove where
often many precautionary measures can be included in the gen-
eral grove practice which will greatly reduce the chances for
disease invasion. Those subjects that may have some bearing
directly or indirectly upon the disease situation in the grove have
been briefly considered in the following pages.
GROVE LOCATION
The location of the grove may have considerable bearing on
the disease situation. Groves most favorably located will be
troubled more or less with certain diseases while those under
adverse conditions will be further handicapped by the effects of
outside factors that may only invite or stimulate greater dis-
ease development. The citrus tree is easily affected by outside
influences and usually responds readily to the conditions, with
which it is surrounded. These may be such as to promote a
uniform and normal development of the tree, and again they
may be such as to produce a stunted or weakened growth that is
soon attacked by diseases. It is not meant to give the impres-
sion that only weak or stunted trees are subject to attacks by
diseases for such is not generally true. There are certain dis-
eases that are capable of attacking the most vigorous and healthy
growth of the citrus tree. Still there are other diseases, and
some of a serious nature, that attack only weakened or injured
trees. They are unable apparently to affect the healthy growing
tissue but if a part becomes weakened or injured in some way
they may enter such tissue and complete its destruction. A
healthy, vigorous tree will have a certain amount of natural
resistance to many diseases and should it become diseased it
will c6me thru the attack in much better condition than one of
low vitality.
Soils poorly adapted to the growth of citrus trees, situations


16







Bulletin 150, Florida Citrus Diseases


favorable to excessive drouth or excessive moisture, exposure
to sudden changes in temperature or prevailing winds, and lack
of proper care are some of the factors that will affect the general
health and condition of the citrus tree. In selecting a site for
the grove these should be taken into consideration and some
thought given as to the probable effect they might have on the
grove in the future. In. groves that are established some of
these conditions may yet be modified to a decided advantage.
Frequently, irrigation, proper drainage, frost protection, wind
breaks, or better care can be introduced into groves where such
are necessary that will add much to the general improvement
of the grove condition.
The diseases of citrus that are caused by fungi or bacteria
are also influenced in their spread and development by moisture
and temperature. As a rule they require warm moist condi-
tions for their rapid development. Thus, groves located in low
shady situations where the trees are dense and crowded, will
afford very favorable conditions for the development and spread
of many such diseases. Frequently, by the removal of certain
trees or by pruning out the branches to let in the sunlight and
give better aeration, the disease situation can be greatly im-
proved.
GENERAL CARE
There is a wide difference in opinion regarding the proper
care of the citrus grove. In the cultural practices and the use
of fertilizers directly opposite methods are frequently employed
and both seem to give successful results. This is not strange
when we consider the different soil types, localities, and kinds
of citrus groves that come under cultivation. In regard to
tillage and the use of fertilizers, a grove in one locality may re-
quire a method of treatment entirely different from a grove in
some other, and the method of handling any grove must be deter-
mined largely by the local conditions by which it is surrounded.
Generally the citrus grower is usually well-informed as to the
cultivation and fertilizers best suited to his particular grove
and very little can be suggested as an improvement to his meth-
ods. It should be kept in mind, however, that the citrus grove
requires a certain amount of attention regularly and that a
sufficient amount of suitable plant food is necessary for the
normal growth and development of the tree. This should be sup-
plied at proper intervals and at a time when it can be fully







Florida Agricultural Experiment Station


utilized. The citrus tree of our standard varieties is a highly
specialized tree. It has been selected for its excellence in quality
of fruit and productiveness and thru this process of selection
and domestication it has lost much of its natural power to
resist outside influences. It has become more susceptible to
attacks of insects and diseases and it is easily affected by lack
of food, moisture, and sudden changes in temperature. In order
to produce its best results the tree is largely dependent upon the
aid of man for its food, care, and protection from external ene-
mies. A neglected or rundown grove is unprofitable and those
are the ones in which diseases and insect pests predominate.
The care of the grove is not limited then to a few cultural
operations each season or to the application of a certain amount
of fertilizer. Other factors of equal importance need be
taken into consideration, which may be the deciding factor in
producing and maturing a profitable crop. A grove may be
suitably located, well cultivated, judiciously fertilized and pro-
duce ample crops of fruit under such conditions; however, if
attacks of diseases and insect pests lower the grade of the fruit
or cause it to rot before it can be disposed of, little has been
accomplished for the time and money spent. There are many
such groves in existence where the grove practices are not well
balanced. As a rule, very little attention is given to the control
of diseases and insects until it is too late, or to the prevention
of other agencies that may have a far reaching effect on the
health and productive value of the grove.
The control of diseases and insect pests and protection against
drouth, cold and prevailing winds should be given more consid-
eration in the general care of the grove and provided for as any
other operation in connection with the production of citrus
fruits. This is especially true of disease control which is one
of the serious problems that the citrus grower must help to solve.
Diseases are not apt to become less numerous in the grove or to
disappear unless proper control measures are taken. On the
contrary, if they are allowed to follow their normal course, they
may be expected to become more abundant and destructive.
Many of the citrus diseases are so thoroly established in the
groves as to be considered permanent pests against which pre-
cautionary or control measures are necessary at certain periods
each season. The various citrus diseases are responsible each
year for heavy losses in fruit and trees, which may greatly






Bulletin 150, Florida Citrus Diseases


diminish the returns from a grove.. Such losses are largely pre-
ventable by the use of timely and effective control measures.
The importance of disease control should be fully realized
and given more study and thought by the citrus grower. It is
a necessary part of the annual grove practice and should be fully
considered as such and provided for in time.
BEGIN EARLY TO CONTROL DISEASES
Usually very little thought is given to a disease until it is
well established in the grove and its injuries are distinctly evi-
dent. Control measures attempted at this time are usually not
effective and may be only a waste of time. In the control of any
disease there is generally a period during which remedial or pre-
ventive measures can be successfully applied and at minimum
cost. Frequently a delay of a few days or weeks may render
such measures ineffective toward preventing injury or checking
the disease.
To handle properly the disease situation in any citrus grove
it is first necessary to understand something of the nature and
causes of diseases, the conditions under which they occur and
the methods most suited for their control. Not all diseases are
alike; neither can all be prevented or controlled by the same
method. Some diseases attack only the fruits and foliage, and
these are usually controlled by spraying with a fungicide. Others
attack the bark of the trunks, branches and roots of the tree and
connot be controlled by spraying. Such diseases are controlled
or eradicated by cutting away the diseased bark or pruning out
the affected branches. Spraying, pruning and cutting away of
diseased parts are the principal operations involved in the con-
trol of plant diseases and each will apply to a certain type or
group of diseases.
The citrus grower will not find it difficult to identify the more
common diseases that appear in his grove if he will study and
compare them. Each disease has certain peculiarities or char-
acteristics. By studying and applying the available information
regarding their nature and control a clear understanding of the
disease problem should result.
The prevention or control of diseases rests largely with the
grower and to him falls the task of putting control measures
into practical use. If this is done in a careless or indifferent
manner very little good will be accomplished. The effective-
ness of any control measure will depend upon a proper and intel-
ligent use of the information given.






Florida Agricultural Experiment Station


IMPORTANCE OF INSECT CONTROL
The control of insect pests is no less important than any other
grove operation and should be provided for each season. Aside
from the direct injury that results from insect attacks these
pests may aid materially in the distribution and development
of some of the serious diseases. Attacks of whiteflies and scale
insects may cause a large amount of dead wood or weakened
growth. The dead wood harbors certain fungi that cause trouble
and the weakened growth is more susceptible to the attacks, of
certain diseases. Thus the prevention or control of certain dis-
eases may be more or less dependent on an effective control of
insect pests.
Trees that suffer each season from extended periods of drouth
eventually become so weakened as to be an easy prey to diseases.
In groves located in exceptionally dry situations the conditions
may be remedied by a system of irrigation. Where irrigation
cannot be introduced into a grove it is often possible to conserve
the supply of moisture by frequent tillage, which will provide a
light, surface, dust mulch. Trees frequently may be carried
thru critical periods by this method.
Protection from cold and prevailing winds will be necessary
in groves that are likely to be exposed to such conditions and
some provision should be made to prevent serious injury from
these agencies.
Generally it will be found easier and less expensive to avoid
injury than it is to repair the damage after it has occurred. A
few precautions at the proper time may frequently save an end-
less amount of worry, time and expense. Citrus diseases should
be avoided rather than controlled, especially in starting with a
new grove and any condition or factor that is liable to prove
detrimental to the health of the tree should be altered without
delay.
SPRAYING
Spraying operations in the citrus grove are chiefly confined
to the control of insect pests; however, it is often necessary to
spray for the control of certain fungus diseases that attack the
foliage and fruits. A fungicide is used for this purpose and is
applied at frequent intervals to protect any exposed surfaces
thru the period during which the tissues may be attacked by
disease. However, spraying the citrus grove for the control of
fungus diseases has its limitations and it is not followed as a







Bulletin 150, Florida .Citrus, Diseases


general practice. While effective spraying schedules have been
developed for the control of insects and diseases in the peach and
apple orchard, these are not applicable to the citrus grove and as
yet' a satisfactory system of this nature has not been found for
the citrus tree.
The nature and growth habits of the citrus tree and the fact
that certain objections are found to the frequent use of our
standard fungicides in the grove have offered little encourage-
ment in the past to follow any general spraying program for the
control of citrus diseases.
Citrus trees are less adapted to treatment with our standard
fungicides than are deciduous fruit trees. The citrus tree is an
evergreen and retains its foliage the entire year. New growth
is put out at different seasons and frequently the tree is allowed
to carry its fruit the greater part of the year. Thus there is
no naturally dormant period when the leaves are entirely absent
that would permit the use of a strong cleansing fungicide on the
branches and twigs. Old infected leaves on the tree often carry
diseases for months, affording convenient sources for infecting
the new leaves that appear. The thick dense foliage of the citrus
tree also makes it difficult in any spraying operation to cover
thoroly the surfaces of leaves and branches, and frequently much
of the foliage or tree may be missed or unprotected. This is
often responsible for the poor results sometimes obtained in
using the fungicides and insecticides.
The greatest objection to the use of fungicides on the citrus
tree comes from the effect they have indirectly on the increase
of insect pests. When used in the proper strength fungicides
kill all fungi they come in contact with, hence the "friendly"
(entomogenous) -fungi are also killed, which allows the scale
and whitefly to increase rapidly. This requires extra spraying
with insecticides to control the insects, adding to the necessary
labor and expense of disease control.
In spite of these disadvantages a certain amount of spraying
will be necessary for proper disease control and the sooner the
citrus grower realizes it and plans to take care of this work in
a systematic manner the less trouble he will have with diseases.
The fruit and foliage diseases, as a rule, may be controlled or
held in check by spraying but the effectiveness of any system of
spraying will depend on several important conditions.
(1) A reliable fungicide must be used and in sufficient







Florida Agricultural Experiment Station


strength to kill the fungus spores. It should be properly prepared,
following strictly the directions for its preparation and use.
(2) The fungicide must be applied at the proper time to be
effective, which is usually before the disease is visible. A fungi-
cide merely forms a protective film on the surface of the leaf or
fruit to be protected and it must be applied before the spore has
lodged on the surface and has had opportunity to enter the
tissue. In many cases to spray after the disease is visible is
only a waste of time.
(3) The spray should be applied in the form of a fine mist.
This gives a more uniform distribution of the liquid, resulting
in a thin film covering the surface. If the spray is applied in a
coarse mist it collects in drops and runs off, resulting in a loss
of material and an incomplete covering of the surfaces. A good
spray pump should be provided, one that will give a pressure of
180 to 200 pounds. The sprayer should be kept in working order
and properly cleaned after use.
(4) The number and frequency of applications will vary ac-
cording to the disease and growth conditions of the tree. The
efficiency of a single application may not extend beyond 10 to
14 days, and where rapid growth occurs in a few days consid-
erable new growth surface may develop which will be unpro-
tected. The fungicide should be applied often enough to give
complete protection to all exposed surfaces and the spraying
should be continued thru the entire period during which the
tissue is liable to infection by the fungus. This may require
three or four different sprayings at intervals of ten days to two
weeks.
FUNGICIDES

The standard fungicides in common use for the control of
plant diseases are bordeaux mixture, ammoniacal solution of
copper carbonate, and the lime-sulphur solutions. All of these
are used to some extent in the citrus grove. Other materials are
sometimes used as fungicides, but usually they are employed in
special cases and have not been found as satisfactory for general
use as the standard solutions.
A fungicide is used merely as a preventive and must be ap-
plied before the fungus spores become distributed over the tissue
to be effective. It should contain a poisonous principle that
will kill the spores and at the same time not injure the tender
growth on which it is used. It is merely a protecting film or







Bulletin 150, Florida Citrus Diseases


covering that is applied to the surfaces of exposed growth, and
to give complete protection all surfaces must be thoroly cov-
ered and kept covered during the entire period in which it is
liable to infection by fungus spores. This requires that fungi-
cides be applied in the form of a fine mist and at frequent inter-
vals to rapid growing tissue to cover any new surfaces as a
result of increased growth. The preparation and use of fungi-
cides will require some little care and judgment as the efficiency
of any spraying solution will depend upon whether or not it has
been properly made, and the time and manner in which it is
applied.
The discouraging results often obtained from the use of fun-
gicides are more likely due to carelessness or improper methods
rather than to inefficiency of the fungicide or system advised.
It should be remembered that a fungicide is used for a partic-
ular purpose, under certain limited conditions. It is not a "cure
all" and should not be applied indiscriminately against any and
all diseases that appear in the grove. It has a special use and
if results are to be expected the fungicide must be used for the
purpose for which it was intended, in the proper proportions
and under the conditions stated. A better understanding of
the fungicides in general, their preparation, uses and limita-
tions will aid materially in obtaining satisfying results from
their use in the groves.
In the following pages, directions are given for the prepara-
tion of the more common fungicides. Under the diseases where
their use is advised the time and number of applications have
been suggested. It is hoped that this information will assist the
grower in using disease-control measures to the best possible
advantage.
BORDEAUX MIXTURE
Bordeaux mixture is the best known and most widely used of
the standard fungicides. It is made from copper sulphate (blue-
stone), fresh stone lime, and water in certain definite propor-
tions. The formula given for bordeaux mixture represents the
amounts of each of the different substances that go to make up
the mixture. The standard mixture is generally considered as
5-5-50 bordeaux, meaning that 5 pounds of fresh stone lime, 5
pounds of bluestone (copper sulphate) and 50 gallons of water
are contained in the mixture. Any desired formula can be made,
but the proportion of lime should equal or exceed that of the







Florida Agricultural Experiment Station


copper, otherwise the mixture is apt to be caustic. For spraying
against citrus diseases the 4-4-50 formula will probably give
satisfactory results and will effect some saving in the quantity
of copper sulphate. In certain cases the 3-3-50 mixture is ad-
visable.
The effectiveness of bordeaux mixture as a fungicide will de-
pend largely upon the materials used in its preparation and the
manner in which it is prepared: The bluestone should be of
good quality, and the lime the best obtainable. This should be
fresh stone lime and in no case should air-slaked lime be used.
The preparation of the mixture is of special importance since
upon this will depend the effectiveness of the solution. A worth-
less bordeaux may result from the best material if the solution
is prepared in a careless and indifferent manner. The amounts
specified for the required formula should be accurately weighed
and measured. Instructions should be followed explicitly in the
preparation of the mixture as there are definite reasons for
each statement given. The following procedure should be fol-
lowed to prepare 50 gallons or less of bordeaux mixture, of the
4-4-50 formula. Other formulas are prepared in exactly the
same way, the only difference being in the amounts of bluestone
and lime used.
First select two barrels or wooden vessels holding 25 gallons
or more. In one place 25 gallons of water (measured). Weigh
out 4 pounds of bluestone (copper sulphate), tie in a gunny sack
and suspend this just below the surface in the 25 gallons of
water. If finely powdered the bluestone will dissolve in a short
time, or it may be prepared and left over night.
Next weigh out 4 pounds of fresh stone lime, using nothing
but lumps. Place this in the other barrel or vessel and add
enough water to slake it properly. The lime should be stirred
occasionally to prevent burning. Note the amount of water used
in slaking the lime and after it is slaked add water to make up
to 25 gallons. If the bluestone has all dissolved the two dilute
solutions are now ready. Unmixed they may be kept as long as
desired if the required amount of water in each is maintained.
Any that is lost thru evaporation should be replaced as this
would affect the concentration of the solution. To make up the
full 50 gallons of bordeaux mixture the 25 gallons of water
containing the 4 pounds of bluestone and the 25 gallons con-
taining the 4 pounds of lime are poured together at the same
time into a third wooden vessel. The lime water should be







Bulletin 150, Florida Citrus Diseases


thoroly stirred first to form an even suspension. After the two
liquids are brought together they should be vigorously stirred for
a few minutes. A pale blue mixture should be obtained.
If only a few gallons of the mixture are required at one time,
the amount can be prepared from these dilute solutions by mix-
ing equal parts together as described above.
Bordeaux mixture will not keep long after it is prepared and
should be used the same day it is made. It is advisable to strain
the mixture thru cheese cloth before putting it in the sprayer
in order to remove any coarse particles that are liable to clog
the nozzles.
If a large amount of bordeaux mixture is desired or if it is
to be used frequently during the season, it is advisable to pre-
pare stock solutions of the lime and bluestone. For conver-
ience these can be prepared so that 1 pound of bluestone or
lime is contained in each gallon of water. Thus, 50 pounds of
bluestone are dissolved in as many gallons of water and 50
pounds of lime are slaked and water added to make 50 gallons.
Any formula may be prepared from these stock solutions.
If the 4-4-50 formula is desired, 4 gallons of the stock blue-
stone solution are added to 21 gallons of water. Four gallons
of stock solution of lime water are also taken and added to 21
gallons of water. The two dilute solutions thus obtained are
then poured together as previously described. The stock solu-
tions should be thoroly stirred before using and any loss of
water thru evaporation should be made up occasionally.
Never mix bordeaux in iron or galvanized iron vessels, as
iron precipitates the copper and ruins the efficiency of the mix-
ture.
It is not advisable to apply bordeaux mixture to fruits that
are mature or nearly mature, since it is likely to leave an ob-
jectionable stain that is difficult to remove.
AMMONIACAL SOLUTION OF COPPER CARBONATE
Ammoniacal solution of copper carbonate contains no sedi-
ment and on drying leaves no stain on the leaves or fruits. It is
preferable to bordeaux mixture for spraying fruits that are
mature or nearing maturity, due to the fact that it leaves no ob-
jectionable stain. It does not adhere so well as bordeaux mix-
ture and applications must be made often to afford the same
degree of protection.
The solution is prepared from copper carbonate, ammonia and
water in definite proportions. The ammonia used in making the







Florida Agricultural Experiment Station


solution should test 26 degrees Baume, and is commonly known
as strong ammonia. The copper carbonate comes in the form of
a fine light green powder. The formula most generally used in
the preparation of this solution is as follows:
Copper carbonate ............... .......................... ....- ..5 ounces
Ammonia ................ ....... .- .. .......... ...... ....... ..... ..... 3 pints
W ater ............... .... .......... .................. ...50 gallons

Weigh out 5 ounces of copper carbonate and make into a thin
paste with a small quantity of water. Three pints of strong
ammonia (26 degrees Baume) are then diluted with water to
make 2 gallons. A wooden or porcelain-lined vessel should be
used for this purpose. Add the paste of copper carbonate and
stir occasionally, allowing the solution to stand an hour or so.
A deep blue liquid will be obtained. After all the copper car-
bonate that will has dissolved, the solution should be carefully
poured off, avoiding any undissolved sediment in the bottom of
the vessel. This liquid is then added to 48 gallons of water and
the solution is ready for applying.
Occasional reports have been received of injury to the brass
parts of the spray pump by using ammoniacal solution of copper
carbonate.' In such cases the injury was the result of careless
ness in the preparation of the solution. The undissolved sedi-
ment was allowed to go into the spray tank and being forced
thru the pump under high pressure it cut out the valves and
brass parts, like so much sand. Where the solution is properly
prepared and properly diluted, it should have no injurious ef-
fects on the spray pump. Care should be taken, however, to pre-
vent any of the sediment from getting into the spray tank, and
the solution of copper carbonate in the ammonia water should
not be placed in the spray tank before the water necessary to
make fifty gallons is added.
Where a large amount of this solution is to be used during the
season it will be more convenient to make a stock solution on the
basis of 5 ounces of copper carbonate and 3 pints of strong am-
monia in 2 gallons of water. The desired formula is made from
this stock solution by adding 1 part to 24 parts of water.

LIME-SULPHUR SOLUTIONS
Lime-sulphur solutions have the properties of both a fungi-
cide and insecticide when used in certain strengths. Lime-sul-
phur is used in the citrus grove chiefly to control the rust mite







Bulletin 150, Florida Citrus Diseases


and red spider, in which the more dilute solutions are employed.
Concentrated solutions are obtainable from two sources and are
usually distinguished as commercial lime-sulphur and home-
made concentrated lime-sulphur.
COMMERCIAL LIME-SULPHUR
This is a concentrated product manufactured and marketed
by several different companies. It can be purchased in barrel
lots or in smaller amounts, such as five- or one-gallon cans.
These solutions usually test 32 degrees Baume, the basis on
which dilutions are made.
To be of fungicidal value these concentrated solutions should
be used in strengths of 1 part in 25 to 30 of water for solutions
testing 32 degrees Baume. As insecticides against the more pro-
tected scales they are used in strengths of 1 part in 10 to 12
of water, a concentration that is usually considered unsafe for
the citrus foliage. Injury to young citrus foliage often occurs
where the solution is used in dilutions of 1 to 30 and weaker.
As yet the lime-sulphurs have not proven entirely satisfactory
as a fungicide for the citrus tree and much more experimental
work is necessary to determine just how far they may be relied
upon in the control of fungus diseases.
The commercial lime-sulphur is more expensive than the home-
made product but it keeps better and eliminates the trouble of
making and storing the homemade solution. It is more conven-
ient to handle and is ready for use when diluted to the required
strength.
HOME-MADE CONCENTRATED LIME-SULPHUR SOLUTION
Where one has the time, labor and necessary equipment, a
concentrated lime-sulphur may be prepared at home at less cost
and it will give about as satisfactory results as the commercial
product. The following formula and method of preparation is
suggested:
50 pounds fresh stone lime (95% CaO)
100 pounds finely powdered sulphur (flowers or flour)
50 gallons of water
An iron kettle or feed cooker of sixty or seventy-five gallons
capacity and a sufficient number of barrels to store the finished
product should first be provided.
Weigh out the required amounts of lime and sulphur and sift
the latter to remove any lumps. Place 10 gallons of water in the
cooker and start the fire. Add the lime and when slaking has







28 Florida Agricultural Experiment Station

well started add the sifted sulphur. Add sufficient water to
make a thin paste, and mix thoroly. When the slaking has fin-
ished enough water should be added to bring the total up to 55
or 60 gallons. The solution should boil vigorously for fifty to
sixty minutes and it will require constant stirring during this
period. Do not let the total volume of the solution fall below
50 gallons and avoid either over or under cooking. It is im-
portant that the solution boil vigorously and constantly for at
least forty-five minutes. After the boiling has finished allow the
solution to cool and settle. It may be necessary to draw the fire
to prevent further boiling. When sufficiently cool the solution
should be strained to remove any coarse sediment. It can then
be diluted for use or stored in the concentrated form.
The finished product should be an amber colored liquid with
little or no sediment. It will keep fairly well if properly stored
to exclude the air, but no more than can be used during the
season should be made at one time. If closed barrels are used
they should be completely filled and the holes tightly closed.
When any of the solution is drawn from the barrel a covering of
oil should be poured over the remainder to exclude the air. Where
the solution is stored temporarily in open barrels, a covering of
oil may be poured on the surface to exclude the air. Paraffin or
engine oil. may be used for this purpose.
Before using, the density of such concentrated solutions should
be determined by a hydrometer which gives the density readings
in degrees Baume. This is necessary before any proper dilu-
tion can be made. Lime-sulphur hydrometers may be obtained
from some of the firms that handle lime-sulphur or spraying
materials. Homemade solutions vary greatly in Baume read-
ings and they may range from 20 to 30 degrees Baume. Quite
likely no two batches of the solution will give the same Baume
readings and they should not be used in the concentrated form
on the citrus foliage or fruits.
A Baume reading of 32 degrees is generally considered as a
standard on which the dilutions are based. Where the concen-
trated solutions show a lower or higher reading than 32 de-
grees any dilution can be made from these on the basis of 32
degrees.
Table 1 shows the corresponding numbers of dilutions of
lime-sulphur of different densities using 32 degrees Baume as a
standard. The first column represents concentrated solutions
of different densities from 20 to 33 degrees Baume. The top







Bulletin 150, Florida Citrus Diseases


of the column represents different dilutions that may be desired
from the various concentrates and the figures directly under
these represent the number of times the concentrate must be
diluted to give the required dilution using 32 degrees Baume as
a standard.
Thus if a concentrated solution shows a Baume reading of 29
degrees and it is desired to use this in the strength of 1 to 30,
on the basis of 32 degrees as a standard, in the column under
1 to 30 opposite 29 degrees will be found the number 26. This
indicates that 1 part of this concentrated solution should be
diluted to 26 parts in order to obtain a spraying solution of 1 to
30 or that 1 gallon of the concentrated solution is added to 25
gallons of water to give the desired solution.

TABLE 1.-Dilutions for Lime-Sulphur

Deg. Baume 1 to 25 1 to 30 1 to 35 1 to 40

20 14 17 20 23
21 15 18 21 24
22 16 19 22 25
23 16% 20 23 26
24 17 21 24 27
25 18 22 25 29
26 19 23 26 30
27 20 24 28 32
28 21 25 29 34
29 22 26 30 35
30 23 27 32 36
31 24 28 33 38
32 25 30 35 40
33 26 31 36 41

FUNGICIDES AND INSECTS
When any fungicide is used on the citrus tree, sooner or later
there will be a decided increase in insect pests, especially the
scale, unless precautions are taken to prevent it. There are cer-
tain fungus parasites known as friendly fungi that under nor-
mal conditions help materially in holding the scale and white-
fly in check. The fungicides kill these fungi as well as the dis-
ease parasites, which allows the insects to increase rapidly, in
the absence of a natural check. This is especially true in cases
where more or less scale are present on the trees when the fun-
gicide is applied.
After a tree has been thoroly sprayed with a fungicide, espe-
cially bordeaux mixture or the ammoniacal solution of copper







Florida Agricultural Experiment Station


carbonate, an increase of scale insects can be expected and the
necessary provisions should be made for their control in time.
Frequently such control measures are delayed until the scale
insects become numerous and quite evident. At this time it will
require more effort and expense to rid the trees of these pests,
when an application of some good contact insecticide applied at
the proper time might have prevented unnecessary trouble and
injury to the trees.
Scale insects are more easily killed in the young or crawler
stage and this is the most favorable time to attack them. There
are three main broods or crawler stages of the scale during the
year. The first appears thru March and early April; the second
thru June and July and the third thru September and October.
If a fungicide is -applied to the citrus tree at any time between
these periods or during the first part of any period, the crawlers
appearing afterward develop into mature scale insects. If no
control measures are employed the scale insects continue to in-
crease in number, since the friendly fungi that would normally
have kept them down has been killed by the fungicide.
Thus in using a fungicide on the citrus tree it should be fol-
lowed by some good contact insecticide within six weeks. In
some cases it may be of advantage, especially if crawlers are
present, to apply the insecticide within two or three weeks after
the fungicide spraying.
PRUNING
In the past pruning has not been followed as a regular prac-
tice in the citrus grove and it was seldom brought into use ex-
cept for the control of certain diseases. In the removal of dead
wood from the citrus tree many growers formerly relied entirely
on nature to do the pruning. The general opinion seems to pre-
vail that the citrus tree requires just as little pruning as pos-
sible. This may be true, and perhaps a healthy, normal citrus
tree does not require and is not adapted to the systematic prun-
ings followed in the peach, apple and pear orchards of the North.
However, the advent of diseases into the citrus grove has made
it necessary to do more or less pruning each season; the prac-
tice will have to be continued and should be provided for each
year.
Pruning is one of the methods employed for the control of
certain diseases, especially those that affect the branches and
limbs. In this case the parasite works within the bark or wood







Bulletin 150, Florida Citrus Diseases


and is not affected by a surface application of some fungicide.
To control such diseases, the affected part must be removed
and destroyed. Pruning, then, has its use in the citrus grove
for the control of active diseases and it should find a wider use
in the removal of dead wood and weakened growth from the
citrus tree. These invite certain fungus enemies that cause in-
jury to the foliage and fruits, and dead or weakened growth
certainly adds nothing to the productiveness of the tree. Aside
from the pruning that is necessary to eliminate certain special
diseases, the citrus tree should be pruned regularly each season
to keep it free from dead wood or weakened growth. Such
should not be allowed to accumulate for any length of time.
The most favorable time to prune is when the tree is in its
most nearly dormant state, which is usually thru December or
January. Where pruning cannot be done at this season of the
year, the next best period will be during June and July. It is
never advisable to prune when the tree is in an active growing
condition or putting out bloom, as more harm than good may
result.
In the removal of dead wood or weakened growth it is advis-
able to cut back an inch or so into live tissue. In all pruning
operations clean smooth cuts should be made, and no projecting
stubs left that may soon die or become diseased. Where large
cut surfaces are made they should be painted over with some
antiseptic or covering.
All dead wood and prunings from the tree should be destroyed
in some manner. Such rubbish may contain fungi and if al-
lowed to accumulate and rot under the trees may become a
source of reinfection. If there is a large accumulation of rub-
bish it can best be removed and burned, while smaller amounts
may be plowed in deep or burned in the grove.
There is some objection to the practice of burning the prun-
ings removed from the citrus tree owing to the loss of a certain
amount of humus. It is true that a certain amount of humus
may be lost in this way, but the future trouble and expense saved
by the burning may more than compensate for the small amount
of humus that might be saved. Where humus is required it will
probably be more satisfactory to provide it from some other
source.
Closely related to pruning is the treatment of diseases that
occur on the trunks and roots of the tree. In this case the dis-
eased bark or wood tissue is cut out carefully, removing -all







Florida Agricultural Experiment Station


parts that show any indication of disease. In cutting away
diseased patches of the bark, the edges of the wound should be
left smooth and the cut be made perpendicular to the surface
of the trunk. This method will expose the smallest amount of
living bark and allow the formation of new bark to proceed
more rapidly. All exposed wounds that result from such opera-
tions should be covered with some antiseptic or covering to pre-
vent re-infection or decay.
It is advisable to collect and burn all cuttings of diseased
tissue from such wounds especially if the disease is infectious.

ANTISEPTICS AND WOUND COVERINGS
In pruning operations and the treatment of diseases on the
trunks and roots of citrus trees, large cut surfaces are fre-
quently exposed. If these are not protected until a new bark
has started to form, fungi and bacteria may invade the tissue
and cause a decay or further spread of the diseased condition.
Cuts or wounds can be treated to better advantage if the sur-
faces are allowed to dry for a day or two before any covering is
applied.
There are a number of different preparations that may be
used as wound covering and antiseptics and the grower can se-
lect such that are the most easily obtained or prepared. The
following list includes those in more common use:
BICHLORIDE OF MERCURY
Bichloride of mercury used 1 part to 1000 of water is a strong
disinfectant and a very poisonous solution. It should be handled
with caution and should not be left where children or animals
can get to it. It can be purchased in tablet form from any drug
store and one tablet dissolved in a pint of water gives the proper
dilution. In case of highly infectious diseases it is advisable
to treat the wounds first with this solution before applying a
more permanent covering. It should be applied only to the
wounds.
CRUDE CARBOLIC ACID

Crude carbolic acid is a very good disinfectant that can usually
be obtained from any drug store. It comes in liquid form and
is poisonous. For the treatment of wounds it should be diluted
to half strength with water in which soap (whale oil or good
laundry soa) has been dissolved at the rate of one-pound to







Bulletin 150, Florida Citrus Diseases


the gallon. It does not form a very permanent covering and
should be used only in the treatment of wounds.
CARBOLINEUM
Carbolineum is a dark colored, rather thick liquid that is fre-
quently used for the treatment of wounds and as a wood pre-
servative. There are a number of preparations on the market
sold as carbolineum, some of which are too dangerous to use
on the citrus tree. Cases of serious injury to citrus have been
reported from the use of preparations purchased as carbolineum.
So far we have had no injurious effects from the use of a
preparation sold under the trade name of Carbolineum Aven-
arius and this has been tested out pretty thoroly on citrus dur-
ing the past few years. As a covering for wounds and for
painting the trunks of trees it has given very good satisfaction.
It may be used full strength on the trunks of trees of any age
without harm; however, it will give satisfactory results when
used at half strength and this will effect quite a little saving in
the cost of materials. It can be diluted very readily with water
in which soap has been dissolved. It has the properties of art
antiseptic and adheres well.
There are other preparations similar to carbolineum that
may be used with good results, however, the grower should be
cautious in the use of such unless he is certain of the effect that
will be produced. A very caustic solution can be applied in a
limited way to the wounds and cut places on the tree without
serious injury, but if the entire trunk of the tree is covered with
it the bark may be completely killed. It is wiser to avoid the
liberal use of any preparation that is not well known.

LIME AND SULPHUR WASH
Lime and sulphur wash is a thin paste made of equal parts
of powdered sulphur, air-slaked lime, and sufficient water to
make a thin paste that can be easily applied with a brush. It is
cheap, easily prepared and has given very good results as a cov-
ering for wounds and the entire trunks of trees. It has slight
antiseptic properties, but does not adhere so well as the carbo-
lineum, and applications may have to be repeated once or twice
during the season. This wash could be used to advantage as a
general treatment for the trunks of all trees inthe grove once
or twice during the season, painting them .from the ground up
a distance of three to four feet.







Florida Agricultural Experiment Station


BORDEAUX PASTE
Bordeaux paste has been used with apparent success against
certain citrus diseases in California for the treatment of wounds
Sand painting of trunks. One objection to its use in the Florida
citrus groves is that it seems to stimulate the freshly cut tissues
to excessive gumming. It has good antiseptic properties, but
does not adhere well. It is prepared as follows:
One pound of bluestone is dissolved in one half gallon of
water. Two pounds of fresh stone lime is slaked in one gallon
of water. After.the lime solution is cool, the two are poured
together and mixed thoroly. This should give a mixture about
the consistency of white wash, which is applied with a brush.
It should be used the same day it is prepared, as the mixture
does not keep well.

WHITE LEAD PAINT
White lead paint is merely applied to wounds or cut surfaces
as a protective covering to keep out moisture or agents of decay.
It adheres well and makes a rather. permanent covering. It
should be applied only to wounds and exposed cuts.

PINE TAR
Pine tar is used in the same way as white lead paint. It should
be applied only to exposed cut surfaces or as a covering for
wounds.
COAL TAR
Coal tar is sometimes used as a covering for wounds, or ex-
posed cuts. The coal tars vary and some are frequently found
that are caustic. They should not be used for painting the entire
trunks of trees.
Antiseptics are not cures for any diseased condition and it is
a waste of time to apply them to active diseased areas without
first cutting out all infected tissue. They are used to prevent re-
infection of exposed tissue and only kill.the fungus spores or
parts that are on the surfaces of the parts to which they are
applied. Any fungi or bacteria that are deep in the tissue are
not affected by a surface application, and they will continue
their destructive work even tho the surface of the infected part
has been liberally covered with some antiseptic.







Bulletin 150, Florida Citrus Diseases


IMPORTANT DISEASES

This group includes the more familiar and destructive citrus
diseases. The order of arrangement is based partly on the dis-
tribution, prevalence and economic importance of each disease
considered and partly on the relation it bears to its host. First
consideration is given to the diseases that affect the main part
of the tree such as the branches, roots and trunks. Following
are those that affect all parts of the tree and the last two deal
chiefly with diseases of the foliage and fruits.

WITHERTIP
Colletotrichum gloeosporioides Penz.

Withertip is a frequent source of trouble in the Florida citrus
groves. It is a disease of the twigs and branches, and severe
attacks may cause serious damage to the affected trees. All
citrus is more or less subject to withertip, but it seems to be
more severe in the lime and lemon varieties. However, the
disease is often destructye in bearing orange and grapefruit
groves thruout the State.
Withertip may occur on trees of any age from the young seed-
lings in the nursery row to bearing trees in the oldest groves. It
probably causes the greatest damage in bearing groves, where
valuable frees are often made unprofitable thru the loss of much
bearing wood or thru the weakened condition induced by the
disease. Severe and prolonged attacks on the same tree will
finally render it worthless if it is not killed. Trees that are
affected with withertip can not- make the normal growth re-
quirements and the crops of fruit they. produce are far from
satisfactory.
The disease is caused by a fungus that is widely distributed
over the State. This fungus also attacks other plants beside the
citrus group and it may be found to some extent in localities
where citrus has never been grown. Beside withertip the fun-
gus causes other types of injury to the citrus tree and fruits,
among which are anthracnose and tear staining of fruits, bloom
blight and shedding of newly set fruits-well known troubles
to the citrus grower.
The fungus rarely attacks vigorous growing tissues and with-
ertip. seldom occurs unless the trees are in a weakened or run-
down condition. Trees weakened from overbearing, drouth,
cold, lack of proper food and from insect attacks are very sus-







Florida Agricultural Experiment Station


ceptible to the disease, and it is in groves of this character that
withertip is most abundant and causes the greatest injury.

APPEARANCE
The term withertip is applied to the withering and dying back
of twigs and branches attacked by the fungus. Numerous small


Fig. 7.-Withertip: A typical case
dead terminal twigs, barren and discolored branches and the
yellowing and shedding of leaves, especially from the interior of
the tree, are typical symptoms of the disease. Affected trees
have a stunted or sickly appearance that is quite striking and in
severe cases there is usually much dead wood present and many
branches without foliage or nearly so. (Fig. 7.) Trees in this
condition are apt to drop much of their fruit. Withertip usually







Bulletin 150, Florida Citrus Diseases


starts on the outward twigs and works inward along the
branches to the main part of the tree. Tips of young twigs that
are attacked soon wither and lose their leaves. Larger branches
become sickly, turn yellowish and shed their leaves and finally
die, apparently from the poisonous effects of the fungus. The
disease may thus continue killing and defoliating even the larger
branches until a greater part of the tree is involved. Unless the
progress of the disease is checked the tree soon becomes worth-
less.
The disease is sometimes slow in progress and frequently af-
fected trees will have vigor enough to throw off or withstand
slight attacks. Slight attacks may cause little injury but in
severe attacks or advanced cases, especially if the tree is in a
weakened state, withertip may cause serious injury.
The numerous dead twigs, shedding of leaves and barren and
discolored branches are typical indications of withertip and
trees in this condition should be given immediate attention.
.The fungus causes two distinct types of injury to fruits that
are recognized as anthracnose and tear staining.

ANTHRACNOSE

Anthracnose is a spotting of fruits that often results in ser-
ibus 16sses. These spots vary in size and general appearance. A
common form 'is observed as a brown or dark colored spot or
patch on the surface of the fruit (fig. 8). Such spots may vary
from an inch or less in diameter to an area involving a fourth
of the fruit. A decay usually follows these spots and fruits
affected in this manner are practically worthless. Another com-
mon and more virulent form of spotting occurs at first as small
red specks or blotches on the surface of the fruits. These are
slightly sunken and appear as blotches at first but later they may
develop into larger sunken spots. This type of spotting often
gives trouble after the fruit is packed and shipped, as it seems
to develop rapidly while the fruit is in transit or storage. This
is especially true of fruits from trees that show the spotting
altho such fruits may be apparently free from spots when picked
and packed.
Anthracnose spotting develops on mature or nearly mature
fruits and its spread and development is greatly stimulated by
warm moist weather conditions. As soon as the disease appears
in the grove remedial measures are necessary.







Florida Agricultural Experiment Station


Fig. 8.-Withertip: Anthracnose spotting on grapeirumi


TEAR STAINING
Tear staining is not a serious injury altho it is quite common
and may mar the appearance of the fruits. It usually occurs as
reddish-brown streaks or bands on the surface of fruits extend-
ing from the stem-to the blossom end. These streaks are flush
with the surface and merely represent a stain on it. The interior
of the fruit is not affected. Tear staining may develop at any
time after the fruit is half mature until it is ready to pick.
Figure 9 shows an immature grapefruit that was collected in
early June and the streaks were evident at that time. The dead
twig above was killed by the fungus which continued its growth
in the dead part and later became the source for the development
of the tear staining effect produced on the fruit below.







Bulletin 150, Florida Citrus Diseases


Tear staining is more prominent on the ripened fruit as the
colored streaks stand out more in contrast.
BLOOM BLIGHT
Attacks of the fungus on the bloom may cause it to blight or
shed freely. The shedding of a great number of unopened flower
buds is a fairly reliable indication of the presence of this fungus,
especially if such show small red markings. These are the in-
juries induced by the
fungus and the buds or .--
blossoms may be partly ,
or entirely covered with, *
them. This trouble is --- .,
more likely to occur on
trees that show the ef- *
fects of withertip. If the
disease is not checked in
its attack on the bloom
it may continue and
under more favorable
weather conditions cause
a severe shedding of new-
ly set fruit later on.
CAUSE
Withertip and the ac-
companying in j u r i e s
previously described are
caused by the fungus
Colletotrichum gloeospo- '
rioides. It occurs abund-
antly in the citrus groves
and it is widely distrib-
uted over the State. The Fig. 9.-Withertip: Tear staining. Arrow
fungus is a weak para- points to dead twig-the source of the
trouble
site and seems to be able
to attack only weakened citrus growth. Vigorous thrifty
growth is usually not affected, or only slightly so.
On the twigs and branches or other tissue killed by the fun-
gus, fruiting bodies are produced abundantly. These are rep-
resented generally by dark colored pustules on the surface of the
dead part. Under moist conditions countless numbers of small
spores (seed) are exuded from these in pink colored masses. The







Florida Agricultural Experiment Station


spores are so small that they can be detected only with the aid
of a compound microscope. The spore masses are dissolved by
rain and dew and the spores are scattered over the foliage and
twigs of the tree. Being so small and light they are carried long
distances by the wind and no doubt the birds and insects aid in
their distribution. Under moist, warm conditions the spores
germinate and if they are in contact with a weakened leaf or
shoot the fungus enters and kills the tissue, causing the first
stage in the production of withertip. As the fungus continues
to grow in the infected shoot other tissue is killed until perhaps
a twig or larger branch is invaded. In the meantime spores are
being produced in the dead tissue and these may serve to infect
other parts of the tree. This process may be repeated over and
over as long as suitable moisture conditions prevail and fungus
spores and weakened growth are present at the same time.
The fungus is carried over from season to season in the dead
twigs and infected parts of the tree. There is always a suffi-
cient number of fungus spores present in any citrus grove to
cause trouble if the trees become weakened and sufficient mois-
ture for spore germination is present. The state or vitality of
the tree, however, is .usually the determining factor in the
development and progress of withertip.
CONTROL
Pruning seems to be the most effective method for controlling
withertip; however, certain precautions may be observed that
may greatly lessen the opportunity for this disease to develop.
Weakened citrus trees are almost certain to be more or less
affected by the disease and any weakened condition should be
avoided if possible. -Proper grove sanitation with a little extra
effort to keep up the vitality of the grove trees will go a long
way toward avoiding severe attacks of withertip. Trees that
are underfed, or severely infested with insect pests, fall an easy
prey to the withertip fungus. Trees weakened from drouth,
over bearing, or the effects of low temperatures are also rapidly
invaded by the fungus and may be severely injured in a brief
time. Any citrus tree in a depleted or neglected condition may
be expected to develop withertip if something is not done to
remedy such a condition.
Vigorous, thrifty citrus growth is seldom attacked by the fun-
gus and trees that are well cared for are little troubled with the
disease. By building up the vitality of weakened trees a very
large amount of withertip injury can be avoided, and frequently






Bulletin 150, Florida Citrus Diseases


an application of fertilizer that will stimulate the tree to vig.
orous growth will cause it to throw off or recover from slight
attacks of the disease. Some caution must be fsed here, how-
ever, in order not to cause active growth at a time when it might
be injured by low:temperatures.
If the disease has become well -established or attacks are
severe, pruning will be necessary to get rid of it. In such cases
drastic pruning
may ,be neces-
sary and con-
siderable bear-
ing wood may .
have to be sac-
rifled in order
to eliminate the
disease com- r
pletely. In prun-
ing it is import-
ant to remove
not only the dis-
eased branches
but all those
that show the
slightest indica-
tions of the dis-
ease. All dead
and diseased
branches or
weakened wood
should be re-
moved, cutting
back a foot or
more into heal-
thywood. Clean,
smooth cuts Fig. 10.-An instance of bad pruning. Arrow points
should be made to projecting stub left in pruning
and no projecting stubs (fig. 10) left for future trouble. Where
large cut surfaces result from the removal of large limbs these
should be painted over with carbolineum or white lead paint.
Sometimes only one side of a tree or only one limb will be af-
fected. The distance to which the disease has progressed can
frequently be detected by the presence of new shoots of a sickly







Florida Agricultural Experiment Station


yellow color. Since it is necessary to remove all affected growth,
it is far better to prune too much rather than too little. A tree
half pruned for withertip is in a worse condition than before
the pruning was made. After a drastic pruning of this nature
the trees should be given unusual care for a time. They should
be fertilized to bring about a vigorous growth in order to make
them more resistant to further attacks of the fungus. There are
two seasons of the year that pruning for withertip can be made
to the best advantage-during the winter season and during the
summer season. The winter pruning is preferable, since the
trees are more nearly dormant during that season. This prun-
iing should be made between the middle of December and the
middle of January. It is not advisable to delay the pruning be-
yond this date. Avoid any pruning while new growth is putting
out for it is quite certain to result in more injury than benefit.
The summer pruning should be made preferably in July. How-
ever this period may be extended from the middle of June to the
middle of August depending largely upon the condition of the
trees and their location. No citrus tree should be pruned at a
time when new growth is putting out vigorously as more injury
than benefit is likely to result.
Spraying in itself is not effective in controlling withertip.
However, a thoro application of bordeaux mixture 4-4-50, im-
mediately following the winter pruning may be advantageous as
it will serve as a cleansing spray. It would not be advisable fol-
lowing the summer pruning, as a general practice.
For the control of anthracnose, bloom blight and shedding
of young or newly set fruits, spraying operations with fungi-
cides will often be necessary. However, where thoro pruning
for withertip has beenmade these diseases should give the min-
imum amount of trouble.
Anthracnose may appear suddenly and spread rapidly over
the fruit if weather conditions are favorable. When the small
red blotches are evident on the fruits spraying should not be
delayed. Trees showing infected fruits should be thoroly
sprayed with the ammoniacal solution of copper carbonate, and
the sprayings may have to be repeated at intervals of a week or
ten days until the disease is checked.
For bloom blight, bordeaux mixture has given satisfactory
results where it is sprayed directly into the bloom. This may
cause some injury and loss of bloom but perhaps only a small
part of what might be lost if the fungus is allowed to continue







Bulletin 150, Florida Citrus Diseases


unchecked. The 3-3-50 bordeaux mixture will be found most
satisfactory for this purpose. Where bloom blight is severe the
shedding of newly set fruit is very apt to follow and provision
should be made in time to prevent losses of this nature. One or
two thoro applications of bordeaux mixture 3-3-50, should aid
materially in preventing this trouble.
There are other agencies that may cause the bloom and fruit
to drop prematurely against which spraying will have no effect
and losses of this nature should not be confused with those
caused by the withertip fungus.
FOOT ROT
Phytophthroa terrestria Sherb.
Foot rot has been a destructive disease in the Florida citrus
groves for many years and it still causes considerable loss an-
nually in certain regions of the State. It is more common in the
old sweet seedling groves or in groves where rough lemon stock
is in use. The disease is widely distributed over the citrus belt.
but is usually confined to low,'moist shady situations. Stock of
the sweet orange and sweet seedling orange are very susceptible
to foot rot and it is also quite prevalent on the rough lemon and
grapefruit stocks. Sour stock is highly resistant to the disease
and is generally considered immune.
While foot rot has been known and recognized as a serious
disease for many years, its cause has been determined only
within the last two years. It is a fungus disease affecting the
crown and main roots of the citrus tree, causing a- decay of the
bark at or near the surface of the soil. The rot shows typical
symptoms that are readily distinguished from other citrus
troubles similar in nature. It frequently develops rapidly, kill-
ing large bearing trees in a single season. Again, trees may
show the effects of foot rot for several years before they are
finally killed by the disease. The kind and location of the dis-
eased tree has considerable bearing on the severity of the dis-
ease. While foot rot is a destructive disease, it yields rather
easily to control measures if such are applied in time.
APPEARANCE.
Foot rot begins in the bark of the crown or main roots of the
tree, usually at or just below the surface of the soil. A small
area of decayed bark is first noted, from which there is a slight
oozing of gum, generally in small drops. The decayed bark at
first has a water-soaked appearance and a watery gum is usually
found beneath. From such an area the disease may soon spread







Florida Agricultural Experiment Station


until the tree is girdled at the crown or all of the main roots are
affected. If this stage is reached the tree may as well be con-
sidered lost. In a great many cases trees are not discovered to be
affected with foot rot until the disease has advanced too far for
remedial measures. Since infection usually begins beneath the
soil (fig. 11) no indications of injury are evident until the dis-
ease has made considerable progress. It frequently happens
that a large part of the root system may be affected before there
are any visible indications of
trouble above ground. Trees in
such condition will begin to
show a yellowing of the leaves
as if affected by drouth. This
yellowing is usually pronounced
along the midribs of the leaves.
The disease often extends up-
ward along the trunks for a foot
or two above the surface of the
soil (fig. 12) and may extend
downward along the main roots
for an equal distance. This is
particularly true when one side
of the tree is attacked. In less
severe attacks irregular patches
are more commonly noted from
a few to several inches in ex-
tent, a portion of which may ex- .
tend upward from the surface ,. *,:
of the soil and the remaining
portion downward along the Fig. 11.-Foot rot: Infected root;
roots. From one to several diseased portion cut away
small spots may appear at the same time. They may increase
very little in size during the season and the progress of the dis-
ease will appear to be checked. As these areas become older
the affected bark tissue becomes dry and sinks below the level
of the healthy bark. When the disease becomes inactive for a
time the areas begin to heal at the edges and the dry, dead bark
cracks and pulls away from the living bark leaving a narrow
fissure outlining the diseased patch. At some later period the
disease may again spread from the edges of these areas that have
apparently healed and continue to spread until the greater part
of the crown and main roots is affected.







Bulletin 150, Florida Citrus Diseases


CAUSE
Various causes have been assigned to foot rot in the past. It
has been recognized as a serious disease in Europe for a num-
ber of years, especially on the lemon and sweet orange varieties.
It is an old and well-known
citrus disease in nearly all .
countries where the sweet
orange is grown. Early in-
vestigators have considered
the disease of parasitic ori-
gin, probably due to a fungus
or bacterium. However, no
specific organism was defi-;
nitely proved to be the pri-
mary cause of the disease.
Fusisporium limoni, a fungus
generally found associated
with the disease, has been ac- *.-
cepted by many as the proba- '
ble cause of foot rot. It was i: '
not demonstrated, however, "
that this fungus was capable
of producing the disease on -
healthy citrus trees.
Two years ago the writer
isolated from an active case .. '
of foot rot a fungus that ap-
peared very different in '_& &
growth characters from other "
fungi obtained from diseased
citrus trees. A little later i
this same fungus was isolated
from other cases of foot rot -. -.
in other localities. A rather L.---: -
extended survey was then Fig. 12.-Foot rot: Advanced stage,
made of the foot-rot groves extending some distance above
thruout the State, and- the ground on the trunk
fungus was repeatedly isolated from active cases of foot rot.
Pure cultures of the fungus were obtained from infected trees
in widely separated localities, covering the principal part of the
citrus belt. This fungus from cultures of known purity was in-
troduced into the bark of healthy citrus trees and in several







Florida Agricultural Experiment Station


cases diseased areas resulted that were typical of the foot-rot
areas developed under natural conditions. The fungus has been
identified as Phytophthora terrestria Sherb., which also causes a
rot of tomatoes described as buckeye rot.*
The more or less constant association of the fungus with
active cases of the disease in connection with the results obtained
by inoculations indicate that the type of foot rot common in
Florida is caused by Phytophthora terrestria. The fungus be-
longs to a group of fungi which contain some of our most de-
structive plant parasites. It may be properly considered a soil
fungus, since it can grow and continue in the soil for a long
period. In low, wet soils and in moist, shady situations the
fungus is most active and a rapid growth takes place. Spores
are produced during wet weather or where plenty of moisture
is available. Two types of spores are common, one of which is
a resting spore that is capable of carrying the fungus thru long
periods unfavorable to its growth.

CONTROL
The most effective method for avoiding foot rot is the use of
resistant stock for budding. Sour stock appears to be the most
resistant citrus to foot rot and on soil or in localities where such
can be used to advantage this is probably the surest way to
avoid trouble.
Where the disease has become established in a grove, other
methods for control will be necessary. The disease is more prev-
alent in the old sweet seedling groves or groves where lemon
stock is in use. It may also give trouble in the nursery, espe-
cially if sweet seedling or rough lemon trees are grown. While
grapefruit stock shows some resistance, the disease is frequently
found on grapefruit trees.
A tree attacked by foot rot should be given immediate atten-
tion and not neglected until the disease has firmly established
itself in the tree and has thoroly contaminated the surrounding
soil. It is well to remember that low, wet soils or moist, shady
situations favor a rapid growth and development of the fungus
and such conditions in the grove should be avoided or remedied
as far as possible. Any grove that is subject to foot rot should
be closely watched and as soon as the disease appears it should
be immediately gotten rid of. A small infection under favorable

*Buckeye Rot of Tomatoes. C. D. Sherbakoff. Phytopathology Vol. 7.
1917.






Bulletin 150, Florida Citrus Diseases


conditions may soon involve from one-half to two-thirds of the
crown and larger roots of the tree; thus it is important to locate
and remove these first small infections.
The early stages of the disease are not easily detected and in
groves where foot rot is known to exist, all the trees should be
examined frequently. From the time the growth starts in the
spring until late fall the disease may be active. Since the dis-
ease occurs chiefly on the crown and main roots it is necessary
first to clear away the top soil for three or four feet (fig. 11) to
expose any infections on the roots. All active diseased areas
should be cut out clean to healthy wood and some antiseptic be
applied to the wounds. All cuttings and diseased tissue removed
should be burned or destroyed to prevent further spread of the
fungus. For painting over the cut surfaces the following may
be used as antiseptics: Bichloride of mercury, 1 to 1000 solution;
aveiiarius carbolineum, either full or half strength; or, crude
carbolic acid, diluted one-half with water in which a little soap
has been dissolved. These should be applied directly to the cut
surfaces. It is a waste of time to apply any antiseptic or cover-
ing to the diseased areas before first cutting away the infected
bark or wood. The fungus has permeated this. diseased tissue
a:.nd the application of any substance to the surface of the bark
will not penetrate sufficiently to kill the fungus.
Where all the diseased areas have been treated the trunk and
exposed roots may also be painted with a wash made of equal
parts of air-slaked lime and powdered sulphur mixed with suffi-
cient water to form a thin paste that can be easily applied with
a brush. The entire trunk should be painted for three or four
feet above the surface of the soil. This wash is somewhat anti-
septic in itself and may aid materially in preventing future at-
tacks for a time.
It is also advisable after treating an infected tree to leave the
crown and main roots exposed for several weeks, if there is no
danger of injury from cold. This will allow the soil to dry out
and become aerated, which will materially reduce the fungus
present. Stirring the soil frequently during dry periods around
the base of trees subject to foot rot may be advantageous in pre-
venting attacks. Spores and parts of the fungus are abundant
in the soil around infected trees, and much of this may be elim-
inated by the stirring process. This can best be done during
dry, hot weather.







Florida Agricultural Experiment Station


Trees that have been treated for foot rot should be inspected
for a time for new outbreaks which should be attended to as
soon as they appear.
Removing the soil to expose the crown or main roots is often
a laborious and tedious operation, especially where large seedling
trees are involved. It should be done as carefully as possible
and with tools that will not scar or injure the root system. Where
water is available the soil can be quickly and easily washed out
from around the crown and main roots if a sufficient pressure is
obtainable.
GUMMOSIS
Gummosis occurs in many of the citrus groves thruout the
State. It has been known in Florida for a number of years but
only in recent years has it attracted much attention. It is ap-
parently becoming more prevalent each season and is rather
generally distributed over the citrus belt, However, the disease
is less abundant in groves in the southern part of the State.
Gummosis is a disease of the bark, and the injuries appear
chiefly on the trunks and larger branches of bearing trees. It
is rarely found on young trees that have not yet come into
bearing. Small twigs and branches are seldom attacked and no
symptoms of the disease are recognized on the foliage and fruits.
Attacks of the disease are frequently more pronounced on
the grapefruit and sweet orange varieties; however, any tree
may become affected with gummosis. In some localities the dis-
ease appears to be more prevalent on the grapefruit while in
others the oranges are more severely affected. Severe cases of
the disease are often observed on the satsuma, tangerine and
lemon.
The cause of gummosis common in Florida is still unknown.
It develops and spreads rather slowly but severe and continued
attacks will ultimately cause serious damage if not the loss of
the tree. The disease may be kept well in check by proper rem-
edial measures.
APPEARANCE
Gumming of citrus trees is not uncommon in any citrus grove,
and it may result from several different causes. Attacks of cer-
tain fungi will stimulate the tree to gum, and when certain
chemicals are introduced into healthy citrus bark, gumming has
been induced. The presence of gum in itself is not significant of
any particular disease. A certain amount of gumming usually







Bulletin 150, Florida Citrus Diseases


accompanies foot rot and occasionally there is a slight amount
of gum formation associated with scaly bark and withertip.
Small drops of gum are often found oozing from minute cracks
in twigs, from cuts, wounds or other injuries in the tree which
may result from the invasion of one or several species of fungi
commonly found in the citrus grove. The citrus tree shows a
tendency to gum readily and any foreign object or substance
entering the bark tissue may in-
duce the formation of a certain I, e -
amount of gum.
Aside from the foregoing ,
forms of gumming we recognize
a typical disease of citrus trees as
gummosis. Gumming is one of V
the characteristic symptoms of
the disease; however, taken 't
alone, it is not a reliable test for '
gummosis.
Gummosis occurs mainly on -
the trunks and larger branches
of the tree. (Fig. 13.) It is easily
recognized by the scaly, ulcerated
areas formed in the bark with
which are associated more or less
gum flow. The diseased areas re-
sult from the killing of the bark '
tissue in certain localized spots. '
The dead tissue becomes perme-
ated with gum and hardens. As
new growth forms beneath, the '
dead bark is pushed up, breaking- ,-' i
into strips or flakes. These -. -'i
eventually fall away leaving a -'
brownish, resinous scar with a .
pitted or irregular surface, and Fig. 13.-Gummosis: Citrus tree
the wound apparently remains badly attacked
healed for a time. Later the area
again becomes active at one or two points on the edge and the
splitting up and scaling off of the bark proceeds as before. A
copious flow of gum may be associated with the affected areas
or in some cases it may be reduced to small drops oozing from
minute cracks in the bark. The oozing of gum indicates anii







Florida Agricultural Experiment Station


active stage of the disease and as the progress of the disease is
arrested and the areas begin to heal the gum flow ceases. In cer-
tain stages little or no gum may be found associated with the
areas.
There are apparently two types or phases of gummosis that
are frequently observed in the grove. Both are similar in gen-
eral character, but appear quite distinct on closer examination.
One will be referred to as Psorosis which was described by Web-
ber and Swingle several years ago, and it was probably the pre-
dominant type at that time. The other type may be designated
gummosis and this seems to be the more prevalent and widely
distributed
type today.
GUMMOSIS I

The gum- '
mosis type ',
is usually .... ''
characteriz- i '
ed by ap- .
hearing ai n
definite aro
spots on the
trunk and f :
the larger
branches. It m
is never
found on
twigs. A
small spot Fig. 14.-Gummosis: A small spot. An early stage, show-
first appears ing the beginning cracks in the bark, as indicated by
in which the arrow
bark is killed down to the wood, or irregular patches of tissue
several inches in extent may mark the beginning of the disease.
(Fig. 14.) At first the diseased bark appears water-soaked and
there is usually a .opious flow of gum. This dead bark is later
impregnated with gum, becomes hardened, cracks, and the sur-
face scales up in large flakes or strips, as new tissue is formed
beneath. (Fig. 15.)
After a time the disease may appear checked, gum flow ceases
and the affected area apparently heals. The dead surface bark
finally scales off, leaving a brownish,, roughened, scar. Usually







Bulletin 150, Florida Citrus Diseases


the disease again becomes active, breaking out anew at the edge
of the old area (fig. 16). Spots from one-half inch to six or
eight inches in diameter may be ob-
served and frequently several dis-
eased areas coalesce which may
girdle the affected limb or trunk. In
the gummosis type the distinct band
or zone is not evident as in the case
of psorosis.
Psonosis TYPE .
The psorosis type appears to be
the same disease known as scaly












advanced stage, showing the
bark breaking up into flakes

bark in California. It must not
be confused, however, with the
Scaly bark of citrus in Florida, as
the two diseases are entirely dif-
ferent.
The psorosis type may be
t found on the trunks, larger
branches and even the smaller
twigs. (Fig. 17.) It usually gir-
dles the affected part (fig. 18)
Fig. 16.-Gummosis: Diseased forming a zone or band from a
area healing at the center but
spreading from the ter but few inches to two or three feet
in width. The surface of the dis-
eased area scales up in small thin flakes and the gum flow is not
so copious, being usually reduced to scattered drops at either







Florida Agricultural Experiment Station


end of the affected zone. The progress of the, disease is up and
down the affected limb or branch. There appears to be a contin-
ued recurrence and apparent healing of the disease within the af-
fected area. The new bark formed within the affected area is
much thickened, rough and brownish and gives the affected part
an enlarged and ulcerated appearance.
Psorosis;is less common than the gummosis type, but appar-




















"' -,'~-', ` :'i '"" ":"






Fig. 17.-Gummosis: Psorosis type of gumming. An ad-
vanced case
ently more severe. It is more commonly observed on the limbs
and branches. However, trunks frequently show severe attacks.
CAUSE
The cause of gummosis is as yet undetermined. It resembles
in many respects a disease of parasitic origin, however, the
parasitic nature of the disease has not yet been established.
Several species of fungi have been found associated with active







Bulletin 150, Florida Citrus Diseases


gummosis areas and these have been isolated and studied. Some
have been introduced into healthy citrus bark, but, in all cases
negative results have been obtained. A slight gumming has been
induced in a number.of these inoculations, but the wounds soon
healed with a slight killing of the tissue and without forming the
typical ulcerated areas characteristic of the disease. Attempts
have also been made to transfer the disease to healthy citrus bark
by inoculating the same with diseased bark from active diseased
areas. The results of these inoculations have not shown conclu-
sively that the disease is infectious in nature, and it is question-




















Fig. 18.-Gummosis: A limb girdled by the psorosis type of gumming
able whether any fungus or bacterial species is directly respon-
sible for the first stage or beginning of gummosis. No doubt, in
the later stages of the disease, after the cracks are formed and en-
larged, certain fungi enter and assist in killing the bark tissue.
They are probably largely responsible for the slow and gradual
spread of the affected areas which may develop to an extent that
would ultimately cause the death of the tree or affected limb.
Slight attacks of the disease, especially the gummosis type, may
do little injury, as small spots one or two inches in diameter fre-
quently heal without attention. Larger areas, however, may
gradually develop into a more serious state and should not be
neglected.







Florida Agricultural Experiment Station


CONTROL
Trees affected with gummosis should not be neglected with the
hope that they will eventually recover. Small areas may soon
heal with little or no apparent effect to the tree. Larger areas
or more active cases may continue to spread to such an extent
as to threaten the vitality of the tree. In treating gummosis
all dead and diseased bark should be removed down to healthy
wood. Some antiseptic may then be applied to the wound to
prevent reinfection of the exposed tissue. Avenarius carbolin-
eum, pine tar, or white lead paint may be used as a covering for
the wounds.
In groves where the disease is troublesome the trunks of all
trees, both healthy and diseased, should be painted with an anti-
septic wash one or two times a year until the disease has disap-
peared. For this purpose a thin paste or wash made of equal
parts of air-slaked lime and powdered sulphur mixed with water
may be used to advantage. It should be applied to the trunks
of the trees with a brush, extending from the surface of the soil
up two or three feet. This preparation is cheap and may be
easily obtained by any grower.
Commercial lime-sulphur or homemade concentrated lime-sul-
phur may be substituted in place of the lime and sulphur paste.
These should be used in a dilution of 1 part in 10 to 15 of water
for solution testing about 32 degrees Baume.
The psorosis type is more difficult to handle and has thus far
proved incurable. Badly infected trees should be removed and
destroyed or the affected parts removed, where possible to do so.
If an affected tree is producing enough fruit to warrant keeping
it the diseased parts may be kept covered with some antiseptic
to prevent any possible spread. Lime and sulphur wash or bor-
deaux paste may be used for this purpose.
BLIGHT
Blight has been a much dreaded disease by the Florida citrus
grower. So far it has proved incurable and an infected tree ul-
timately means a lost tree. Little is known of the occurrence
and distribution of blight outside of Florida. However, it has
been reported as occurring in Cuba*. The disease is sometimes
known as wilt or leaf curl and it apparently affects all citrus
plants of commercial importance grown in the State. Trees on
light hammock soil appear to blight more readily, but no locality
*Fawcett, H. S., Cal. Agr. Exp. Sta. Bul. 262, p. 185, 1915.







Bulletin 150, Florida Citrus Diseases


in the State has been found entirely exempt from the disease.
In the past, blight has caused serious damage to some of the best
citrus groves, and the disease was found widely distributed thru
many of the best citrus producing localities. In certain locali-
ties from 1 to 10 percent of the trees blighted annually.
The disease has undoubtedly become less prevalent, for fif-
teen or twenty years ago it was reported as causing a loss to the
citrus growers in Florida of from one hundred to two hundred
thousand dollars annually. Blight is much less in evidence today
altho it may yet be found in certain localities. Within the last
five years the writer has observed blight in but two localities,
and only a few affected trees were noted in each case. No doubt
this marked decrease in blighted trees has been brought about
by the prompt elimination of all affected trees and perhaps to
some extent by the more intensive methods of grove practices
that are in general use today.
APPEARANCE
Blight attacks only trees that have attained considerable size
and have begun to bear fruit. It may occur suddenly on trees
that seemed perfectly healthy before. A wilting of the foliage
as if the tree were suffering from drouth is the first indication
of the disease. The wilting may at first be slight and be notice-
able only on dry hot days. It soon becomes more pronounced and
during the rainy season the wilting may be very evident, even
where rains are of daily occurrence.
Blight usually makes its first appearance in early spring from
February to April. 'As this is usually a dry season of the year
the disease may at first be easily confused with a wilting of the
trees such as might result under prolonged drouth conditions.
Cases of blight may also appear in midsummer under excessive
moisture conditions, indicating that the development of the dis-
ease is little influenced by the presence or absence of moisture.
After the wilting becomes severe the foliage begins to drop and
in a few weeks or months the affected branches shed a greater
part of their leaves.
- The disease may first appear in a single branch, or the whole
top of the tree may be affected. In either case the entire tree
is finally involved. When blight appears in the spring the af-
fected tree may not die at once, and may appear to revive during
the rainy season. The trunk and branches put out numerous
water sprouts which grow vigorously for a time but later become







Florida Agricultural Experiment Station


sickly and gradually die back. (Fig. 19.) Blighted branches
may retain some of their leaves for a year or more after the at-
tack, but such leaves are usually small and a dingy green color.
A blighted branch or blighted tree 'will show a tendency to
bloom profusely at the regular blooming period following an
attack of the disease. This bloom may continue for ten days to
two weeks after the normal blooming period and will be found
to consist of small flowers that fail to set fruit. Very little fruit
is produced by a tree after it is attacked by blight and such fruit
is usually undersized.
Ordinarily, trees af-
fected by blight contin-
ue to decline until they
die or are 'removed
from the grove. In ex-
ceptional cases a dis-
eased tree may linger'
for ten years or more, :." "
making a slow, sickly .
growth and producing -.r
a small amount of fruit.
No case of permanent b
recovery from an at-
tack of blight is known;
however, the behavior
of diseased trees is fre-
quently deceptive in
putting out new growth
which grows vigorously ,
for a time. In severe
attacks of the disease -
the tree may die so sud-
Fig. 19.-Blight: Citrus tree badly affected
denly that the leaves
do not fall, but simply wither and turn brown on the twigs.

CAUSE
The cause of blight is still unknown .regardless of the extended
studies that have been made of the disease. It, is probably para-
sitic and shows certain features that would suggest it to be con-
tagious. It closely resembles peach yellows, a dreaded disease
of the peach that has long baffled investigators, and the cause
of which is yet unknown.







Bulletin 150, Florida Citrus Diseases


Blight attacks trees in groups and appears to spread from
diseased to healthy trees. Where a blighted tree appears in a
grove and it is allowed to remain for any length of time, a year
or two later adjacent trees will usually show blight on the
branches nearest the diseased tree. It is also noted that if a
single branch becomes affected the disease finally spreads over
the entire tree. This would indicate the contagious nature of
the disease.
CONTROL
There is no known method of saving a tree that is affected
with blight., The serious and destructive nature of the disease,
the uncertainty as to its cause, and its apparently infectious
nature permits of only one safe course to follow in dealing with
citrus blight. As soon as a known case of the disease is discov-
ered the affected tree should be immediately destroyed. To
avoid any possible spread of the disease the tree should be dug
up and burned on the spot.
Various methods have been tried to restore blighted trees to
health again but all have proved unsuccessful and it is an unwise
practice to temporize or experiment with a disease of this char-
acter.
SCALY BARK
Cladosporium herbarum, var. citricolum Fawcett
Scaly bark occurs chiefly on the sweet orange and its present
distribution is limited to a few of the citrus growing sections
of the State. It is more abundant in the Pinellas Peninsula
where the disease has caused serious damage in some of the
older groves. Scattering cases have been found in the central
part of the State and in a few localities along the East Coast.
In those localities where it has not yet appeared every effort
should be made to prevent its introduction.
Scaly bark is caused by a fungus which attacks the bark, fruit,
and, occasionally, the leaves. More recently it has been found in
old neglected nurseries on rough lemon stock and it has also
been found on the sour orange. Occasionally a few scaly bark
spots may be observed on grapefruit trees; however, the grape-
fruit and tangerine are considered highly resistant to the disease.
Scaly bark can be controlled but severe cases will require time
and probably considerable expense. With its present distribu-
tion within the State it is more a matter of prevention with the







Florida Agricultural Experiment Station


possibility of complete eradication in those districts in which it
has appeared.
APPEARANCE
Scaly bark is found on the trunks and branches of the tree. It
it a bark disease and the early stages are quite distinct and char-
acteristic. In more advanced stages it may sometimes be con-
fused with gummosis which it resembles in certain respects. A
distinctive character of the disease is represented by the typical
spots formed in the bark of the younger twigs and branches.








44,












Fig. 20.-Scaly bark: Spots on orange twigs. A, Begin-
ning of spots; B, more advanced spotting; C, scabby
stage
These appear as round or oval shaped spots, one-fourth to one-
half an inch or more in diameter, raised above the surface with
well marked edges, and rusty in color. (Fig. 20.) In their be-
ginning stages the young spots appear as greenish-yellow
blotches on the surface of the green bark, somewhat watery or
oily in appearance. As the spots grow older the surfaces be-
come glazed, brittle, and usually break into cracks. A zonated
effect is often noted in the more advanced stages. Eventually
the surfaces break into small flakes. The spots may be isolated
and distinct or in severe cases several may come together form-






Bulletin 150, Florida Citrus Diseases


ing large patches of rusty or reddish-brown scabby bark. On
the larger limbs and trunks of trees where the disease is of long
standing, the surface of the bark will be rough and shaggy.
(Fig. 21.) The spots in this case are not distinct and the entire
surface of the affected part will be covered with thin flakes or
scales. This stage of the disease resembles gummosis in many
respects. Frequently an affected trunk or limb will be entirely
girdled by rough shaggy bark.
Scaly bark rarely appears on twigs less than six months old
and the spots are more com-
monly observed in the bark
of growth from nine to eigh-
teen months old. Bark or
wood much older than this is
subject to attack as is shown '*v1 t
by the effect on the trunks '.:6
and limbs of old bearing. '
trees. The disease is slow to
develop and the greatest num- .. .
ber of infections seem to ap-
pear from about June first to
December first.
Spots on the leaves are of
rare occurrence and of little -F. '-'l, S
importance. They appear as
brown blotches showing thru i j:
on both sides of the leaf. The -
edges are usually marked by ~.,S- L,._ i
a pale yellow color and some- Fig. 21.-Scaly bark: Old or advanced
times a white area is ob- stage on orange limb
served at the center.
The effect on the fruit is quite typical and this phase of the
injury is referred to as nail-head rust. The injury is usually
confined to the rind, producing an unsightly and unsalable fruit.
Affected fruits may show from a few to many brown sunken
spots some of which are apt to be in the form of sunken rings
(fig. 22). These spots are at first yellowish to reddish-brown
on the green fruits but finally become dark and sunken. In the
ringed spots the rings first become sunken with a raised portion
at the center. Later the center may sink and the whole area
inside the ring becomes dark. Spots on the fruit are usually
round and vary in breadth from one-fifth to one-half an inch.







Florida Agricultural Experiment Station


They begin to appear on the green fruit about July or August
and may continue to appear until the fruit ripens. They are
more apparent as the fruit begins to color.
CAUSE


Both scaly bark and nail-head rust are caused
Cladosporium herbarum, var.
citricolum*. The primary in-
fections seem to result from at-
tacks of this fungus but the
withertip fungus also appears
to aid in the development of the
later stages of the disease. The
scaly-bark fungus propagates in
the infected spots, forming
spores that aid in the further
distribution of the disease.
When these spores lodge .on
healthy tissue they germinate


under suitable conditions
and penetrate the bark or
rind tissue forming a spot
that marks the beginning
of the disease. Later the
withertip fungus ent e r s
and helps to complete the
destruction of the affected
tissue. The scaly-bark fun-
gus is slow in developing
injuries and it does not
seem to attack twig growth
which is less than four
months old. In the case of
fruits, however, infection
probably occurs on tissue


by the fungus


..z
....- .....* .

^ ^'. 7 .




Fig. 22.-Scaly bark: Injury to fruits.
Nail-head rust


somewhat younger than four. months.
CONTROL
Experiments have demonstrated that scaly bark can be con-
trolled and the losses from nail-head rust may be greatly dimin-
ished even in districts where the disease is severe.-, Prevention,
*.Fawcett, H. S., Fla. Agr. Expt. Sta. Bul. 106.


r.
.c.
~t







Bulletin 150, Florida Citrus Diseases


however, is the most important factor to observe in those sec-
tions where scaly bark is still unknown.
Several lines of treatment may be followed in the control of
scaly bark. However, the nature of the disease and its slow
development will delay the effect of any method used. The
method of control to be used will vary according to the severity
of the disease and the attitude of the grower toward his grove.
Top working may be practiced in which the grove is worked over
to some resistant variety of. citrus, or heading back may be re-
sorted to until the bodies of the trees are entirely freed from the
disease. These are the more drastic measures recommended
and will apply to cases of severe infection. In slight attacks of
the disease pruning or spraying may be used to advantage.

TOP. WORKING
The grapefruit, tangerine and mandarin have proven highly
resistant to scaly bark and these varieties may be used for top
working over badly infected groves. Where this method is pre-
ferred it can be carried out without serious loss by top working
alternate trees in the row or alternate rows. The work should
be done in December or January when the trees are most nearly
dormant.
The larger limbs may be sawed off and the top grafted or the
trunk sawed off at the ground and crown'grafts put in. Where
the diseased trunk and branches are allowed to remain they
should be treated either with bordeaux mixture 5-5-50 four or
five times during the season or with an application of Avenarius
carbolineum diluted to one-half with water in which 1 pound of
soap has been dissolved. In using the bordeaux mixture it
should be thoroly applied to the trunk and branches just after
the top has been removed. This application should be followed
by three or four others during the season at intervals of about
two months apart. If the carbolineum is used a thoro applica-
tion should be given to all parts of the tree after the top has
been removed. One application during the year will probably be
sufficient.

HEADING BACK
If it is undesirable to bud to other varieties, .diseased: trees
may be simply headed back and the remaining trunk and
branches 'cleaned of the disease. The tops should be cut out dur-
ing the dormant period, December or January, leaving only the
4







Florida Agricultural Experiment Station


trunk and stubs of larger branches. All foliage and small limbs
should be removed. Bordeaux mixture or Avenarius carbolin-
eum should be applied as recommended under Top Working.
PRUNING
In less severe cases pruning may give satisfactory results in
keeping the disease in check. All dead wood and diseased
branches should be removed. Where large cut surfaces are ex-
posed some antiseptic or covering should be applied. Diseased
trunks in this case may be scraped and given an application of
Avenarius carbolineum.
SPRAYING
Spraying has been effective in reducing the disease on
branches and also in preventing loss in fruit from nail-head
rust. Spraying may give only temporary relief yet it can be
used to advantage in protecting the fruits. From the results of
certain experiments it would seem that four thoro sprayings
with bordeaux mixture made during the season gives sufficient
protection to the fruit to prevent any great injury from nail-
head rust. The first application should be made in the dormant
period, December or January. This spraying should be thoro,
care being taken to cover the interior of the tree ratlHer than
the foliage, since the diseased spots are located on the twigs,
branches and trunks of the tree. A second spraying is neces-
sary just before the bloom opens. A third after the fruit has
set and a fourth in the latter part of July or early August.
Bordeaux mixture of 5-5-50 formula should be used and it
must be kept in mind that scale insects will undoubtedly increase
following such a treatment.
CITRUS CANKER
Pseudomonas citri, Hasse
Citrus canker is the worst disease of citrus that has ever been
introduced into Florida and had it become generally distributed
over the State it would undoubtedly have caused disastrous
results to the citrus industry. Fortunately, the serious nature of
the disease was early recognized and sufficient sentiment was
created to undertake its complete eradication. Thru the effec-
tive campaign carried out by the State Plant Board this is about
to be accomplished and the citrus growers will probably be
troubled very little with citrus canker in the future. If it is







Bulletin 150, Florida Citrus Diseases


once eradicated our quarantine laws should be sufficient to pre-
vent its reintroduction. However, the disease should not be lost
sight of as an isolated case may appear in some remote district
at some future date and become a menace to the surrounding
country. One case of citrus canker in any citrus district will
afford a dangerous source for spreading infection and such a
grove will remain a danger center for a year or more after the
infected tree is destroyed. For this reason the citrus grower
should be familiar with the general appearance of the disease
and report at once any suspicious cases that may come to his
observation.
Citrus canker attacks all varieties of citrus trees of commer-
cial importance in Florida, except the kumquat. Any part of
the tree above ground may become infected. Grapefruit is ap-
parently most severely attacked, the infections occurring on
leaves, twigs, branches and fruits, and occasionally in the bark
of exposed roots. Citrus trifoliata is probably next in suscep-
tibility and then follow some of the varieties of sweet orange.
According to Dr. E. W. Berger, whose statement is based on field
observations, the different varieties of citrus are susceptible to
the disease about in the order named: pomelo (grapefruit),
citrus trifoliata, Key lime, navel orange, satsuma, tangerine,
mandarin, King orange and lemon. The writer has observed
infections on all parts of citrus trifoliata above ground, except
on the fruits. The disease has been observed on leaves, twigs
and fruits of the navel and some other varieties of sweet orange.
Scanty infections have been found on the leaves and twigs of the
satsuma, tangerine and lime. The rough lemon seems to be quite
susceptible. Almost any of the varieties of citrus may be se-
verely attacked by canker, if all the conditions are favorable
for the development of the disease. Inoculations made on sweet
orange, citrus trifoliata, rough lemon and grapefruit trees indi-
cate that these varieties show about the same degree of suscep-
tibility to infection, where growth and moisture conditions are
the same. The young growth is more readily attacked by can-
ker, but tissue of any age may become infected. Canker has
been observed to develop in the bark of grapefruit branches that
were two or three years old.

APPEARANCE ,
The distinguishing feature of citrus canker as observed in the
field is the characteristic spotting produced on the fruit and







Florida Agricultural Experiment Station


foliage. As usually seen, the infection appears as small, light
brown spots, from less than one-sixteenth to one-quarter of an
inch in diameter. The spots are usually round and may occur
singly, or several may run together, forming an irregular area.
This last condition usually occurs on fruits. The spots are
raised above the surrounding healthy tissue, and are composed


S. Fig.; 23-Cittus canker spots on. leaves and stem

of a spongy mass of dead cells, covered by a thin white or gray-
'ish membrane.: The membrane finally ruptures and turns out-
ward forming a lacerated or ragged .margin around the spot.
On the leaves, infections first appear as small, watery dots,
with raised convex surfaces. (Fig. 23,) These dots are usually
of a .darker green than the surrounding tissue. Sometimes,
v6wever,, th surface of the spots is' broken- as soon as they ap-
pear. Spots may appear on either surface of the leaf, but they do







Bulletin 150, Florida Citrus Diseases 65

not at first penetrate thru the leaf tissue. They gradually increase
in size, change to a light brown and become visible on both sides
of the leaf. In the older spots one or both surfaces may be bulged
or raised, and
such spots are
commonly sur-
rounded by a
narrow, yellow-
ish band or
zone. In the
more advanced
stages the sur-
face of the spots ...
becomes white .
or grayish, and -.,..
finally ruptures, ..
exposing a light .
brown spongy '" -
central mas s.
Old spots soon '
become over- P ,'-
grown by sap-' ",': .'
rophytic fungi, Fig. 24.-Citrus canker spots on grapefruit
and may appear
pink or black on account of these fungus growths.
On the fruits the spots are very similar to those formed on
the leaves. (Fig. 24.) They project, and retain a circular out-
line. They .do not penetrate far into the rind. They may be
scattered over the surface, or several may occur
.. together forming an irregular mass. Gum-

S '.... "......'...





Fig. 25.-Citrus canker on young citrus twig
ming is sometimes associated with the spots formed on the
fruits. Canker apparently does not cause a rot of the fruits
directly but opens the way for other fungi to enter and cause
infected fruits to rot.







Florida Agricultural Experiment Station


The spots on young twigs are like those on the leaves and
fruit. (Fig. 25.) On the older twigs they are more prominent,
and more or less irregular in shape. This is especially true of
old spots. They show the same spongy tissue as is found in the
spots on the leaves, but assume a cankerous appearance and the
surface membrane completely disappears. (Fig. 26.) These
spots or cankers are formed in the outer layers of the bark
tissue, and do not penetrate into or kill the wood. The spots
once formed in the bark are persistent and are not readily
sloughed off. They may remain for a long time, and form cen-
ters from which infections may readily spread.

CANKER DISTINGUISHED FROM OTHER DISEASES
Other citrus diseases with which canker may be confused are
scab, scaly bark, and, possibly, anthracnose. It can, however,
be readily distinguished from any of these by noting the follow-
ing points:
1. It differs from scab in the typically round spots produced,
the size of the spots, and the fact that the spots penetrate thru
the leaf tissue. It does not distort the leaves. There are no
wart-like projections. Canker occurs on older wood; scab does
not.
2. Canker differs from scaly bark in the size of the spots,
which are much smaller and more circular than those of scaly
bark, and the spongy nature of the spots; scaly-bark spots are
hard and glazed. Canker is common on grapefruit; scaly bark
is not. Canker forms spots on leaves; scaly bark rarely does.
3. Canker differs materially from anthracnose in the size
of the spots, which are much smaller than those of anthracnose.
Canker spots are raised; anthracnose spots are sunken. Canker
has spots of a spongy character; those of anthracnose are hard.
Canker occurs on young shoots and older twigs; anthracnose
does not.
CAUSE

Citrus canker is a bacterial disease. It is caused by Pseudo-
monas citri, a short rod shaped, motile organism that can be
seen only with a compound 'microscope. These bacteria are
foundin countless. numbers in the canker spots and they are
exuded.in masses whenever the spots become moistened by rain
or, dew. Drops. of water contaminated with bacteria spread the
disease and when the organisms come in contact with citrus







Bulletin 150, Florida Citrus Diseases


tissue, especially the. tender foliage, twigs and fruit, new canker
spots are rapidly formed. In the older bark on the branches and


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Florida Agricultural Experiment Station


trunks of trees the bacteria probably gain entrance thru small
wounds or cracks.
The disease may be spread some distance by the wind and
beating rains, or any agent coming in contact with the moistened
foliage of an infected tree is apt to spread the disease to other
trees. The bacteria are known to live and multiply in moist soil
and they are capable of surviving in the soil for many months
and still retain their virulent nature. Soil infected with the
canker bacteria has no doubt been an important source in
spreading the disease in many cases.

CONTROL
The prompt and complete destruction of all canker infected
trees is the only practical method that has yet been found for
checking the disease in Florida. Any canker or cases of sus-
pected canker should be promptly reported to the State Plant
Board, Gainesville, who will attend to the eradication of the
disease.
DIEBACK*
Dieback is a common disease of citrus trees that is widely
distributed over the State. It may appear on any citrus variety
planted on any type of soil and perhaps there are few groves in
the State that have not had more or less dieback during some
period of their history.
The disease is important on account of its relation to the
organic matter in the soil and any attempt to feed trees or build
up the soil with large amounts of organic matter is apt to result
in the development of dieback.
Injury from attacks of the disease will vary greatly in any
community and in individual cases may appear relatively small.
However, prolonged attacks on the trees produce a weakened
condition and ultimate injury that cannot be easily estimated. It
may limit the growth of the tree, the production of fruit, and
the character of the fruit produced so when taken as a whole the
total injury in the State each year may amount to many thous-
ands of dollars.
The cause of the disease is unknown, yet it seems to be neither
infectious nor contagious. It is probably brought about by cer-
tain substances that are taken from the soil by the tree and
which stimulate the tissue to abnormal growth or development,
*Compiled from the work of B. F. Floyd, Bul. 140 Fla. Expt. Sta. For
detailed report of the disease see this bulletin.






Bulletin 150, Florida Citrus Diseases


resulting in the production of the different characters recog-
nized as symptoms of the disease.
Dieback may be prevented and controlled in those groves
where it is troublesome.
APPEARANCE
The effects of dieback may be observed on the twigs, branches,
leaves and fruit. There are five characteristic symptoms that
will usually distinguish the disease from other citrus diseases,
namely: Gum pockets, stained terminal branches, ammoniated
fruits, bark ex-
crescences and
multiple buds.
In addition to
these, trees af-
fected with die-
back show other
characters that
will help in rec-
ognizing the dis-
ease. (Fig. 27.)
Usually, affected
trees or those on
the verge of die-
back if growing
under favorable .
conditions of "
moisture and "
food, will show -
foliage of an ex-
ceptionally deep ,.-..
green color. The
leaves are often
large and t h e Fig. 27.-Dieback: Orange tree severely affected
tree in general may have a promising appearance. In more
severe cases abnormally thickened, coarse leaves of very large
size are observed. Where trees make a rapid, rank growth,
long, immature, angular, branches of a distorted shape are fre-
quently produced. These are generally bent into an S-shape
(fig. 28) and are frequently associated with affected trees or
appear just preceding an attack. Dead terminal twigs and
branches may also be associated with dieback, but this is a more
common character of withertip.






Florida Agricultural Experiment Station


Dieback is a .disease of the growing tissue which results in a
certain amount of gum formation. Old mature tissue is not af-
fected and it is less likely to occur on slowly or normally grow-






'V ..









Fig. 28.-Dieback: Distorted S-shaped growth of terminal branches
ing trees. Rank or rapidly growing trees are more likely to be-
come affected.
GUM POCKETS
These are common symptoms of the
disease, and they form only on the
young, succulent terminal branches and
before they have fully matured. These
appear as blister-like swellings on the
surface of twigs, usually near the point
where the leaf is attached. (Fig. 29.) 4
If the surface of a blister is cut away /
the interior will be found to contain a
clear or amber-colored gum of a liquid
consistency. As the affected stem grows
old and new wood is formed the gum
pockets disappear. They never result
in the death of. the branch.
BARK EXCRESCENCES
These develop in the bark of nearly
mature or mature terminal twigs. In
severe cases however, they may form in Fig. 29.-Dieback: Gum
the bark or larger branches or on the pocket, indicated by ar-
row







Bulletin 150, Florida Citrus Diseases


trunks. They are rather striking and distinct from other in-
juries to citrus twigs. These excrescences appear as eruptions
on the surface of the affected twigs from longitudinal cracks in
the bark. (Fig. 30.) The gummous tissue apparently swells
and protrudes thru the ruptured bark, form-
ing narrow raised reddish-brown masses.
SThese eruptions may be numerous and
thickly stud the surface of the affected part.
/ STAINED TERMINAL BRANCHES
S A staining of the terminal branches is a
common symptom of dieback that occurs
while the branches are young and somewhat
succulent. The surface of the bark is
stained a glossy brownish color, and the
areas are only slightly raised if at all. The
staining is sometimes observed on the peti-
oles and base of the leaf blades attached to
: i the affected twig. (Fig. 31.)
AMMONIATED FRUIT
A similar staining is noted on fruits in
S connection with dieback injury. The stains
r or marks occur on the fruit in the form of
spots or irregular areas (fig. 32), glossy and
brownish in color. These stains may occur
S on any part of the fruit and at any time
after it is a month old until nearly full size.
The surface of the discolored areas frequent-
ly becomes cracked in a criss-cross manner
like that of dried mud. Splitting of stained
fruits is also quite common and splitting and
dropping may occur extensively during mid-
summer when the fruit begins to take on
size.
Fig. 30.- Dieback:
Bark excrescences MULTIPLE BUDS
Multiple buds often form as a result of dieback attacks. From
a few to a number of buds may form in the axil of a leaf where
two would occur normally.. (Fig. 33.)
CONTROL
In general, two methods are in use in Florida for the control
of dieback, namely, preventive and curative.







Florida Agricultural Experiment Station


PREVENTIVE METHOD
In this method an attempt is made to correct the soil condi-
tions under which the disease has developed and to provide the
tree with the proper facilities for making normal growth. Since
the disease is an abnormal
growth development b r o ug h t
about by some unusual condition
of the soil, this must first be cor- '
rected and modified before the i
disease will disappear. Soil and-
seasonal conditions change and
it sometimes happens that the-
conditions under which the dis-
ease is developing becomes cor- .'
rected without any effort on the
part of the grower and the af- .
fected trees grow out of the dis-
eased condition.
It requires time for the disease
to develop and it will require
some little time before the effects
of any method of treatment are .
evident. Symptoms that have de-
veloped cannot be removed by
treatment, but a further develop-
ment of the disease on the suc-
ceeding growth .may be pre-
vented.
The practices commonly used
in the grove to prevent dieback
are, starving the trees for am-
monia and stopping or reducing
cultivation to a minimum. The
effectiveness of these ipethods
will depend largely upon the soil
conditions. Where it is clearly Fig. 31.-Dieback: Stained ter-
evident that the disease is due to minal branch
over feeding with organic ammoniates, starvation will be help-
ful. The entire omission of ammonia from the fertilizer is a
dangerous practice and it should not be omitted from more than
one application. In succeeding applications a low percentage of
ammonia should be used and this practice should not be contin-







Bulletin 150, Florida Citrus Diseases


ued beyond two or three applications, after which the normal
amount of ammonia should be used. The ammonia in the ferti-
lizers used for this purpose or where the disease occurs on soils
well supplied with humus and moisture should be derived en-
tirely from mineral sources.
Where the disease occurs on dry sandy soils of the high pine
and spruce pine lands and has not been brought on by over feed-
ing the use of stable manure in limited amounts has proved


Fig. 32.-Dieback: Ammoniated fruit
helpful in curing the disease in a number of cases. Ordinarily
stable manure will induce dieback on many soils.
-CULTIVATION AND COVER CROPS
The stopping of cultivation is a helpful practice where the dis-
ease appears under certain conditions. In cultivated groves af-
fected with dieback the system should.be modified to avoid any
plowing as much as possible. Any grass, weeds or legumes pres-
ent' should be removed or left to rot on the ground with-
out turning under. If it is necessary to break the sod in order
to use the acme harrow, -the cut-away harrow should .be ,used in
preference to a plow;. ,,







Florida Agricultural Experiment Station


Clean cultivation is not advisable as such a practice greatly
reduces the humus content of the soil, and the excessive stirring
of the soil appears to be favorable to the development of die-
back.
The repeated growth of corn or other crops in the grove that
require deep cultivation may bring on a dieback condition, and
should be avoided. An occasional
Growth of such crops may not be harm-
ful, but care should be taken to use a
fertilizer for the crop that is adapted to
Sthe tree.
Since the disease occurs on trees
Growing under such different condi-
Stions, methods of prevention in one
case will not apply to all others and
the treatment of the disease in any lo-
cality will depend much on the local
conditions. In all cases the diseased
trees should be pruned to remove dead
and weakened wood, and badly diseased
I' or stunted trees may well be replaced by
new ones.

LACK OF DRAINAGE
Sometimes the disease is induced by
i excessive moisture in the soil. This may
be present only at certain periods of
the year but the conditions should be
avoided or remedied. In low soils where
drainage cannot be provided, it is some-
S times helpful to raise and mound the
Fig. 33.-Dieback: Multiple trees. Frequently, ditching or breaking
buds of the hard pan will provide the neces-
sary drainage where the water collects in pockets. After drain-
ing, the land should be put in good tilth and lime applied to the
soil if needed. If the land is heavy and well supplied with or-
ganic matter, only mineral fertilizers should be used. Cultiva-
tion should be reduced as much as possible and any cover crop
may be removed for hay or used as a mulch.
If the wet lands are sandy and lacking in humus and a cover
crop does not grow well, a light scattering of stable manure







Bulletin 150, Florida Citrus Diseases


(one or two tons per acre) worked into the soil may be helpful.
The application should not be repeated for a year or more.
Where possible, the trees should be mulched and normal cultiva-
tion be given the middles. The average amount of ammonia
should be used in the fertilizer, which should be applied in reg-
ular applications and not in large amounts.
EXCESSIVE CULTIVATION
Where dieback is brought on by the excessive cultivation of
pineland, flatwods or interior hammock, the cultivation should
be reduced as much as possible. The grove should not be plowed
for a year or more and the cut-away harrow may be used to
break the sod. The use of the acme harrow is only necessary
to conserve the soil moisture. Cover crops can be cut and
worked into the soil with the cut-away harrow. Mineral ferti-
lizers with a low ammonia content should be used for one or
two applications if the grove has been well fed previously.
Frequent stirring of the soil in groves located on the shell
lands or lands where coquina rock occurs near the surface may
be favorable to dieback. When the disease appears on .such
soils cultivation should not be practiced. The tree should be
mulched and the cover crop left on the ground.
IRREGULAR MOISTURE CONDITIONS
Irregular moisture conditions may lead to the development of
dieback in either the high or low soils. The disease is more
likely to develop in well fed trees under such conditions. In such
groves extreme dryness of the soil is to be avoided as much as
possible by cultivation, mulching or irrigation. Care should be
used in the amount of fertilizer applied, following a long period
of drouth. If the previous application was not well washed into
the soil only a light application should be made of a formula
somewhat low in ammonia. If heavy rains follow and the trees
later show the need of ammonia the application can be supple-
mented by an application of a readily available source of am-
monia.
SPRUCE PINELAND
The disease is common on the loose dry soils of this type of
land, owing to the deficiency in humus and dryness of such soils.
Soils of this character should be built up and the cultivation
should be shallow and made only where it is necessary to con-
serve the moisture. The space around them may be heavily
mulched and plowing should be avoided as much as possible.







Florida Agricultural Experiment Station


Cover crops, preferably some legume, may be grown and worked
into the soil and the fertilizers applied should be largely from
mineral sources.
CURATIVE METHOD
Bluestone or copper sulphate is used in various ways as a cure
for dieback and under certain conditions some of these methods
have given favorable results, but they are not known to be ef-
fective under all conditions. One method in use is to apply the
bluestone directly to the soil in the same manner as a fertilizer.
The crystals are spread on the surface around the diseased trees
and worked into the soil. There is some difference of opinion in
regard to the amount of bluestone to be applied to the trees but
both light and heavy applications have been suggested. The
Experiment Station found that two pounds per tree applied to
severely affected trees twenty years old, was effective in pre-
venting dieback, while an application of one pound per tree was
much less effective. The trees were located on high pineland
and the application was made in April. Larger applications may
be used under certain conditions but in the more moist soils
bluestone should be used with caution. A number of cases of
injury to citrus from bluestone have been reported.
Bordeaux mixture sprayed upon the foliage and fruit of af-
fected trees has been found to be an effective preventive for
dieback. To be most effective it should be applied just prior to
the flush of growth that may be affected with the disease, hence
the sprayings should be made in late winter, late spring or late
summer. A 3-3-40 bordeaux mixture will be of sufficient strength
for this purpose.
Small crystals of bluestone are frequently inserted beneath
the bark to cure dieback and the results obtained from this
method are more or less conflicting. When used in this man-
ner it causes more or less direct injury to the bark and the
method cannot be recommended as a safe practice.

MELANOSE
Phomopsis citri, Fawcett
This is chiefly a disease of the foliage, young twigs and fruits.
It is widely distributed over the State and is probably the most
common citrus disease .in the Florida groves.: Melanose is re-
sponsible for a large percentage of the unsightly fruit grown
each season and the.annual loss from this disease is increasing
from-year to year. In certain groves the disease is much more







Bulletin 150, Florida Citrus Diseases .77

severe than in others, e pecially those located in low or moist,
shady situations. An exc ptionally wet season during the spring
and early summer usual y favors a severe development of the
disease.
Melanose is caused b a fungus which is found abundantly
in the dead wood in cit us trees, thus the disease may. be ex-
pected to be most sever in groves where the trees contain a
large amount of dead t igs and branches.


Fig. 34.-Melanose: Typical injury to citrus leaves, stem and fruit

The fungus affects only young, succulent, growing tissue but
only when a sufficient amount of moisture is present. Hence
the disease is apt to occur only when new growth, moist condi-
tions and spores of the fungus are present at the same time. A
leaf or a twig may be affected with melanose from the time it
appears until six or eight weeks later, while fruits are liable to
attack for a period of several months. From the time the bloom
drops until four or five months later a fruit may be injured by
melanose when spores of the fungus come in contact with the
surface that has been wet with rain. or dew.







Florida Agricultural Experiment Station


The control of melanose will depend largely on keeping the
trees free from dead wood. This will require careful and sys-
tematic pruning and attention to all other agencies that are
likely to cause dead or weakened wood in the citrus tree.

APPEARANCE
The type of injury caused by melanose should not be easily
confused with that of other citrus diseases. It is a disease of
the leaves, twigs and fruits and only attacks tissue that is tender
and succulent. However, on the older leaves and mature fruits
these injuries
stand out more
prominently.
Melanose may be
easily recognized ..I* ,
by the typical
markings produc-
ed on the surface :
of the affected '
parts. These are. '
the same in gen- .
eral appearance ,
whether they oc-
cur on leaves,
twigs or fruit.
(Fig. 34.) The
injury is more
commonly ob-
served in the
form of small, Fig. 35.--Melanose: Grapefruit streaked by the
disease
circular, h a r d,
brown spots or specks with smooth glazed surfaces which are
raised above the healthy tissue. These spots result thru the
killing of a few layers of surface cells by spores of the fungus.
The dead cells become hardened and they are gradually pushed
up as growth of the tissue continues below. Often spots run
together forming irregular masses, circles, streaks or bands.
Fruits are frequently marked with streaks resembling the tear-
staining effect produced by the withertip fungus. (Fig. 35.)
Sometimes the entire surface of the fruit is affected, producing
a russet appearance. (Fig. 36.)
Melanose may occur on any citrus tree as no variety of com-







Bulletin 150, Florida Citrus Diseases


mercial importance has yet been found to be immune. Rapidly
growing or the more succulent citrus tissue will usually show
the spotting more prominently, which is particularly true of
the grapefruit. However, the grapefruit appears to be no more
susceptible to the disease than any other citrus tree. Under
favorable conditions any citrus tree may be severely affected by
melanose.
Melanose injury does not result in a total loss of the affected


Fig. 36.-Melanose: Type of severe injury
mature fruits. The injuries are confined to the surface and the
interior is not affected. It causes no decay and there is no ap-
parent effect on the quality of a fruit affected by the disease,
but it greatly mars the appearance of fruits, making them lower
in grade and less easily disposed of.
Severe attacks of melanose may cause a considerable shed-
ding of newly-set fruits, and young shoots that are badly affected







Florida Agricultural Experiment Station


frequently drop their leaves and die. While the effect on the
foliage is usually considered of minor importance, there is no
doubt but that severe and continued attacks of the disease will
greatly lower the vitality of the tree.

CAUSE
Melanose is caused by the fungus Phomopsis citri, which is
widely distributed in the citrus groves thruout the State. 'It
lives and propagates chiefly in the dead twigs and branches of
the citrus tree, and in the bark of such, fruiting bodies and
spores of the fungus are produced in great numbers. The spores
serve the purpose of seed in propagating the fungus and they
are also responsible for melanose injury to fruits and foliage.
When dead citrus bark containing the fruiting bodies becomes
moistened, the spores are exuded in minute strings or thread-
like tendrils that are washed down on the foliage and fruits dur-
ing rainy periods. If the spores then come in contact with
young succulent leaves or fruits and sufficient moisture is pres-
ent for germination, melanose injury results. Thru germina-
tion the spores affect a certain area of surface cells, which are
killed and later become hardened and brown in color.
SAs the leaf or fruit tissue continues to grow, this mass of dead
cells is elevated, resulting in the typical melanose spot. No
growth of the fungus and no fruiting bodies are produced in
these melanose injuries and the disease does not spread from
leaves or fruits affected with melanose to healthy ones. The
source of melanose injury is the fungus spores formed in the
dead citrus twigs. The spores are so minute that they can only
be detected with a compound microscope, and they are easily
blown about by the wind or carried by other agents for great
distances. Those that lodge on dead wood germinate and grow
in the dead bark, forming fruiting bodies and other spores. This
may be repeated several times thru the season, with the result
that the dead wood soon becomes well filled with fruiting bodies
and spores of the fungus.
This same fungus causes stem-end rot of citrus fruits. In this
case the mature fruits or those that are nearing maturity are
attacked by the fungus and a decay soon follows, resulting in a
total loss of the fruit. Apparently only those fruits that have
been weakened in some way develop stem-end rot. Scale insects
-that collect around or beneath the calyx, weaken the fruit at
.the stem endand .the fungus penetrates the tissue at this point.







Bulletin 150, Florida Citrus Diseases


The fungus continues to grow within the fruit, breaking down
the interior and causing a rapid decay. On the rotted fruits that
are allowed to dry and mummify on the ground beneath the tree,
the fungus frequently produces fruiting bodies and spores. These
fruiting bodies exude spores that become mixed with the soil and
may later be carried back into the tree by the wind. Stem-end
rot frequently causes serious losses in individual groves, yet it
is more or less sporadic in occurrence. By keeping down the
scale insects, one of the conditions for the development of this
rot may be largely avoided.

CONTROL
It will be no easy task to control melanose and persistent and
systematic efforts will be necessary to reduce the injury in
groves where the disease is well established. There is little
encouragement for relying upon the use of fungicides alone to
control the. disease owing to the extended period during which
the fruit is susceptible to attack. A large number of spraying
operations would be required each season to protect the fruit
thoroly and the source of the trouble would still be present.
Thoro and systematic pruning seems to offer the most prac-
tical method of control and has the added advantage of removing
the source and cause of the trouble. Dead twigs and branches
in the citrus tree harbor the fungus and as long as they remain
in the trees melanose injury may be expected. Where this dead
wood is removed from the trees and destroyed, and such trees
are afterward kept free from dead wood, little trouble should be
experienced from melanose injury.
It is not possible by the most careful pruning to prevent
melanose entirely, but by pruning regularly each season, remov-
ing all visible dead wood and sickly or weakened branches, the
amount of fungus can be reduced to a minimum, which will
materially decrease the injury from melanose.
Pruning alone is not sufficient to keep down the dead wood,
and other agencies that are liable to cause weakened growth or
dead wood should be looked after. By keeping down the scale
insects and whitefly and keeping the tree supplied with the
necessary food material at the proper time a very large amount
of dead wood may be prevented.
Pruning for melanose may be done at two seasons of the
year-in the winter and in the summer. The winter pruning
is preferable and should be made when the trees are in their







Florida Agricultural Experiment Station


most nearly dormant state-during December and January. It
is not advisable to prune in the spring while the trees are putting
out new growth or bloom. Immediately following the winter
pruning and before the new growth starts, a thoro application
of bordeaux mixture 4-4-50 formula is advisable. This will
serve as a clean-up spray and take care of any spores that may
have lodged on the surfaces of leaves and branches.
Where it is not convenient to prune in the winter season,
the grower may do his pruning in the summer thru the latter
part of June and in July, at a time when vigorous growth is not
putting out. The bordeaux spraying should be omitted at this
season.
In taking out the dead wood and weakened growth it is advis-
able to cut back into the healthy wood an inch or two. Clean,
smooth cuts should be made and no projecting stubs left to be-
come infected later. Where large 'cut surfaces are exposed
these should be covered with some antiseptic.
All prunings and rubbish should be removed from under the
trees and either burned or buried to destroy the fungus. It is
also a good practice to remove and destroy all dropped fruits
that collect under the trees.

CITRUS SCAB
Cladosporium citri, Massee
Citrus scab is widely distributed over the State and the disease
may be found on several citrus varieties. It is a disease of the
leaves, young twigs and fruit which often causes serious damage
to the grapefruit in many sections of Florida. The sour orange,
lemon, rough lemon and grapefruit are severely attacked by scab
and the disease may frequently cause injury to the satsuma, lime
and tangerine. Occasional cases of scab have been found on
members of the sweet orange group within the last few years,
but the sweet oranges are generally considered very resistant to
the disease.
Citrus scab is caused by a fungus parasite that forms a char-
acteristic injury on the affected part. It resembles melanose in
certain respects in that it attacks only the young and succulent
growth when such is in a wet or moistened condition. It is
primarily a fruit and foliage disease and the greatest losses from
scab result from the injury to grapefruit. It frequently happens
in severe attacks of the disease that from fifty to ninety percent
of the fruit in an infected grove will be injured by the disease.







Bulletin 150, Florida Citrus Diseases


Scab is a disease for important consideration, especially in re-
gard to its present effect on grapefruit and the effect it may have
on the citrus industry in the future. Not long ago grapefruit was
reported as virtually immune to scab, while now it is severely
affected in many localities and the disease in general is becom-
ing more severe on this host each year. The fungus appears to
be capable of adapting itself to new members of the citrus group,
and a few re-
ported attacks of
scab on the sweet
orange may indi-
cate that it is
only a matter of
time until scab
will be as severe
on the sweet or- i l i
ange as it is on
t h e grapefruit.
In this connec- -.
tion, the import-
ance of controll-
ing or eliminat-
ing scab from in-
fected trees in
the vicinity of
sweet orange
groves cannot be
over estimated.
The disease
may be kept un-
der fair control
by taking proper
precautions and
it may be entire-
it may be eliminated Fig. 37.-Citrus scab on leaves and twig
ly eliminated
from infected groves by the use of more drastic measures.

APPEARANCE
The disease is evident on the leaves, young twigs and fruits,
appearing on the surfaces of such as circular to irregular ele-
vated scabby masses and wart-like projections. The earliest
infections appear on either surface of the leaves just unfolding







Florida Agricultural Experiment Station


as minute light brown points. Later these enlarge and the spots
become depressed on one side and raised on the other. (Fig. 37.)
Spots may be small and scattering or several may run together,
forming irregular patches. As the spots grow older they change
from light brown to pinkish or dark brown. Frequently the
leaves are crinkled or distorted by the disease and in severe at-
tacks shoots are frequently killed or shed their leaves.
Fruits attacked when young often become misshapen and in
severe attacks warty projections extend from the surface. (Fig.
38.) A severe shedding of newly-set fruit may result. On
mature fruits the disease is more commonly observed as small
irregular scabby spots or caked masses, light brown to purplish
in color, covering the -. ..
greater portion of the :'
surface. (Fig. 39.) These
infections are superficial
and do not affect the in-"
terior of the fruit. How- .
ever, as in the case of
melanose, an unsightly ..
or cull fruit is the result.
CAUSE
The disease is caused" ''
by Cladosporium citri, a
minute fungus that -:i______
fruits on the surface of
the spots or s c y- Fig. 38.-Citrus scab on young fruit
the spots or scabby- "
masses. Under moist conditions spores are produced and when
these come in contact'with moistened young growth new infec-
tions occur. Only very young and tender tissue is attacked by
the fungus and a liberal supply of moisture is necessary before
infection can take place. Leaves and shoots may become affected
from the time the growth puts out until perhaps three or four
weeks later, and fruits are probably subject to infection for a
month or six weeks after the bloom drops. If dry weather pre-
vails during this period no scab will develop, even tho the old
foliage on the tree is badly infected with scab. If cool wet
weather prevails at the time the new growth is putting out or
about the time the fruit has set, the disease is apt to be severe
on such growth in groves where scab has become established.
The fungus is carried over from one period of new growth to







Bulletin 150, Florida Citrus Diseases


another in the spots and scabby masses on the old mature leaves.
It is also probable that spores or parts of the fungus that lodge
on the surface of the branches or foliage may retain their
vitality for several months and then be capable of infecting
young growth when more favorable conditions appear.
CONTROL
The comparatively short period during which the foliage and


Fig. 39.-Citrus scab on grapefruit. Severely affected
fruits are subject to infection makes it possible to protect the
fruit fairly well by spraying. Bordeaux mixture or ammoniacal
solution of copper carbonate will give the best results. The first
spraying should be made just before the new growth puts out,
using the 3-3-50 bordeaux mixture. The old foliage and the
branches on the interior of the tree should be thoroly covered
with the solution to kill any of the scab spores that may have
lodged there. A second spraying should follow about the middle







Florida Agricultural Experiment Station


of the blooming period, and a third after the fruit has set. The
bordeaux mixture 3-3-50 formula or the ammoniacal solution of
copper carbonate may be used. Where such spraying is prac-
ticed a close watch should be kept on the scale insects and when
they are found to be increasing a good contact insecticide may
be used.
Scab may be eliminated from badly diseased groves by the
use of more drastic measures provided the grower is willing to
sacrifice one crop of fruit. Perhaps this method should be used
only in extreme cases where the disease is well established and is
serious year after year. This consists in pruning off the foliage
and all outer twigs of the past year's growth. Every particle of
such growth should be removed, taken from the grove and
burned. Such a pruning should be made in the winter season,
either December or January. Immediately after the trees are
pruned the trunks and remaining branches should be thoroly
sprayed with bordeaux mixture, 5-5-50 formula, before any new
growth starts. Trees that have been given such treatment
should be stimulated to put out a vigorous growth in the spring
to prevent attacks from withertip, and they should be kept free
from scale insects.
In recent years scab has become more troublesome in young
grapefruit groves that have not come into bearing and those
that have been planted but a short time. In such cases where
the infections are scattering it is advisable to go thru the groves
and cut out all infected foliage and twigs. These should be
burned or destroyed. The trees may be sprayed thoroly three
or four times with bordeaux mixture ,3-3-50. The first spraying
should be made a week or ten days previous to any new growth
and the other sprayings should follow at intervals of two weeks
apart.
Where young trees are severely affected and this condition
is general over the grove, it is advisable to defoliate them com-
pletely during the dormant period, in December or January.
Immediately after defoliation they should be sprayed with bor-
deaux mixture. A second spraying should follow when the new
growth begins to appear, and a third about two or three weeks
later, using the 3-3-50 bordeaux.
Drops or culls affected with scab should not be allowed to re-
main in the grove under the trees or collect in piles around pack-
ing houses. They should be buried or disposed of at once.
All sour orange or lemon sprouts in the grove should be cut







Bulletin 150, Florida Citrus Diseases


out and destroyed, as they are usually badly affected with scab
year after year and form a constant source of danger.

MINOR DISEASES

This group includes a number of minor diseases and injuries
due to various causes. Some are often mistaken for serious
troubles or frequently confused with the more common diseases.
A few are parasitic in nature and under favorable condition may
cause more or less injury. Others are of little or no importance
in regard to the damage they cause.
To avoid confusion and assist the grower in identifying these
troubles the following are described and illustrated.

CITRUS KNOT*
Sphaeropris tumefaciens, Hedges
Citrus knot has been reported from Jamaica where it has
caused much trouble to the limes. One authentic case on the
lime in Florida seems to have been reported a few years ago, and
in recent years on several occasions knots or galls on citrus
have been received from a few localities in the State, resembling
in outward appearance the disease described as citrus knot. It
is a fungus disease and so far has been reported as occurring
naturally on the lime and orange. Its distribution in Florida
is unknown, but must be rather limited owing to the few cases
reported. It has never become common enough in any particular
locality to attract much attention and a disease so striking in
appearance would not be readily overlooked.
As to what effect the disease might have on the citrus trees
of Florida should it become established here, is a matter of con-
jecture. However, it is unwise to experiment with new diseases,
and a description of citrus knot is included that the grower may
recognize it and take the necessary steps to deal with it effec-
tively.
APPEARANCE
The disease may occur on trees of any age, attacking the old
growth as readily as the young. The knots vary in size from
three-eighths of an inch to two or three inches in diameter.
(Fig. 40.) They are usually round but in the early stages before
surrounding the affected stem they may be somewhat flattened.
*Hedges, F., and Tenney, L. S., Bul. 247, Bur. Plant Ind., U. S. D. A.







Florida Agricultural 'Experiment Station


The first indication of infection is a slight swelling of the
branch, which ultimately develops into
a well formed knot. In the early stages
of growth the surface of the knot is k '.
light colored and rather smooth. With
age the surface becomes darker and
more or less fissured and an old knot
from which the bark has disappeared
may be almost black, rough and deeply
furrowed. Frequently, in rapid growth,
knots of large size develop with the '
bark intact and the surface smooth and
light in color.
A striking character of the lime
knot is the growth of a number of
shoots from the knot, forming typical
"witches' brooms." Sometimes only one
or two shoots will grow from a knot
and again there are cases in which a
great number appear. These shoots
may grow rapidly for a time and also
develop knots, but usually they die after -
a period of a few months. When a knot
appears on a twig or branch it usually
forms a girdle which eventually results
in the death of all the part beyond the
knot. Trees that are badly infected
with the disease may show a large num-
ber of dead parts beyond the encircling
knots, and what is left of the tree may
be greatly weakened and of no value.
As the disease continues, other knots ,
form on the main branches and trunk, '
often extending down to the soil, and
the death of the entire tree soon results.

CAUSE
The disease is caused by the fungus Fig. 40.-Citrus knot: Old
parasite Sphaeropsis tumefaciens. It knots on twig. (Speci-
men supplied by the
penetrates and grows within the af- State Plant Board)
fected tissue which it stimulates to the
formation of the typical galls or knots. In these the vegetative







SBulletin 150, Florida. Citrus Diseases


part of the fungus can usually be found, abundantly. Living
.parts of the fungus may also be detected in the tissue of appar-
ently healthy twigs several inches beyond the knots. .
Fruiting bodies and spores of the fungus develop on the knots
and sometimes in the bark of the dead twigs beyond the knots.
They may be found more readily in the early stages of the de-
velopment of the disease or in knots one or two years old that
have made only small development. The spores spread the dis-
ease from infected to healthy trees. After the fungus has
gained entrance into the bark or tissue of a branch or twig, it
may continue to spread by vegetative growth thru the bark and
woody tissue.
CONTROL

All citrus trees affected with citrus knot, or knots or galls in
any way resembling the disease, should be immediately removed
and destroyed. Where infected trees have been cut off at the
ground the new shoots that come up often show knots so it is
advisable to remove all infected trees, root and branch, and not
plant a new tree in the same location for several months after-
ward.
In Jamaica where the disease is often troublesome, it has been
kept under control by pruning out all affected parts of the
tree. This method is fairly successful where attacks are slight
and confined mainly to the smaller twigs and branches. Such
measures for Florida would hardly seem advisable with the
present status of the disease in this State. Very few cases have
been reported up to the present time and perhaps the majority
of these were merely suspected cases.
Thus with the limited occurrence of the disease and the un-
certainty as to how difficult its control might be should it be-
come firmly established here, it would seem a wiser plan to
destroy any case of citrus knot or suspected cases as soon as
they are discovered and not to attempt any method of control.
There are other knots and galls sometimes formed on the
citrus tree that seem to be different from citrus knot. Their
causes and nature are little understood at present and they have
usually been considered as unimportant. However, it is proba-
bly a safer policy to look upon all galls and knots that appear
;on the citrus tree with suspicion and get rid of the affected tree
as soon as possible.







Florida Agricultural Experiment Station


Specimens and information concerning the appearance of
knots or galls on the citrus tree will be greatly appreciated by the
Experiment Station.

LEAF SPOTS
Various leaf spots other than those caused by the common and
familiar diseases are often observed on the citrus tree. These
are of little importance as
far as their injurious ef- --..
fects are concerned. They '-
may frequently attract in-
terest as being something .
new or unusual and they -
are often mistaken for
some of the more serious. i '
diseases. In most cases the .
causes of such spots are un- "
known or merely suspected. .
A few are quite character- .. -.
istic and have been collected *
in limited numbers from ;
different localities in the "
State. Some of the more. ,- ..
common types are here de-
scribed and illustrated.
Figure 41 shows a hard
glazed spot that is often
noted on citrus leaves. This
is a small, round, brown
spot usually on the upper
surface but sometimes it
penetrates the leaf tissue
showing thru on both sides. Fig. 41.-Leaf spot: Hard glazed spot
These spots vary from one- on citrus leaf
eighth to three-eighths of an inch in diameter, and from a few
to a number may appear on a single leaf. The surfaces are hard,
smooth, and appear glazed. Often a small puncture-like depres-
sion is noted at the centers and a pale narrow margin outlines
the spots in most cases.
The cause is not definitely known, but from observations in
the field they are suspected as resulting from the punctures made
by the pumpkin bug.







Bulletin 150, Florida Citrus Diseases


Figure 42 shows a spot somewhat similar to the foregoing tho
much larger and less frequently observed. These spots are
brown, slightly thickened and show
on both sides of the leaf. They vary
from three-eighths to a quarter of
an inch or more in diameter and they ,
are bordered by a broad brownish- *,
colored band. The surfaces are smooth,
hard and glazed with a round sunken
pit at the centers. Surfaces some-
times appear zonated. The cause is "
unknown.
Figure 43 shows a dark colored -
spot that is probably of fungus ori-
gin. It has been classed temporar- ,
ily as a Cercospora spot as this fun-








-.. Fig. 42-Leaf spot: Large
brown spot on citrus leaf
gus is constantly found associat-
S ed with spots of this character.
.":"- i. ^ The spots are round to oval in
S .-'. shape, dark brown to black, and
S show on both sides of the leaf.
Frequently the upper surfaces
S are smooth and covered with a
,silvery membrane. Older spots
may show a dark, fuzzy, indis-
tinct, surface growth.
This spotting is not abundant
and it is commonly associated
With frenched leaves.
Fig. 43.-Leaf spot: Cercospora Figure 44 shows a spot that
(?) spot on citrus leaf .
might be readily mistaken for cit-
rus canker. It is of rare occurrence and the cause is unknown.
The spots are generally round and more prominent on the under







Florida Agricultural Experiment Station


surface of the leaf. They are raised, light brown in color, and
somewhat hard and compact.. They do not show the spongy
interior, which is characteristic of citrus canker spots. On the
upper surface of the leaves the surfaces of the spots appear flat
or slightly sunken, brown in color, and are frequently covered
with a thin white membrane.


Fig. 44.-Leaf spot: An unusual spotting of citrus leaves

SOOTY MOLD


Sooty mold is too well known to need description. It is a
black fungus growth, forming a thin paper-like membrane over
the surfaces of leaves and fruits. The fungus does not attack the
citrus tissue but merely grows on the surfaces of affected parts
in the honeydew secreted by the whiteflies and other insects.
Where the whiteflies are numerous, sooty mold develops abund-
antly and may cause considerable injury of an indirect nature







Bulletin 150, Florida Citrus Diseases


to trees and fruits. Trees that are covered with the fungus
usually make slow growth and the blooming and fruiting is gen-
erally retarded. Fruits that are covered with the fungus are
retarded in ripening and usually color unevenly. Many green
and small fruits result.
CONTROL -
If the whiteflies are kept under com-
plete control there will be little trou- I
ble from attacks of sooty mold. Trees
are easily cleaned of the fungus if
thoroly sprayed with a good contact
insecticide. It is not necessary or ad-
visable to use a fungicide against the
sooty-mold fungus. '
SEPTOBASIDIUM
Septobasidium pedicillatum (Schev) Pat.
Septobasidium is a fungus growth
that is occasionally observed on citrus
twigs. It is frequently found on the
plum and pear and occurs on many
other trees. It causes little if any
direct injury to the citrus tree.
On citrus twigs, and sometimes ex-
tending along the petiole and base of
the leaf, the fungus appears as a soft
leathery-like covering, light brown to
gray in color. The growth completely
surrounds the affected twig and may
occur as a raised band one or two
inches wide. (Fig. 45.) The surface
is smooth and compact or membrane- i_
like, while beneath this the mass is soft Fig. 45.- Septobasidium on
and spongy. The growth is entirely living grapefruit twig
on the surface and does not appear to
penetrate the bark tissue.
The occurrence of the fungus is so rare and the injury so
insignificant as to hardly warrant any control measures. It
may be gotten rid of, however, by pruning out all affected twigs
and branches.
6







Florida Agricultural Experiment Station


ALGAE
Citrus trees are sometimes attacked by algae. However, the
injury caused by these parasites is usually considered of minor
importance. Under certain conditions they may cause severe
injury to the citrus tree. Such injuries appear in the form of
a spotting of leaves and of attacks on the bark of twigs and
branches. In Cuba* an alga is reported as causing a spotting
of citrus leaves, and in the Isle of Pinest a species is reported as
frequently affecting the bark of the lemon and lime trees.
Specimens of algae have been received from localities in
SFlorida within the last three years on
both citrus leaves and bark. The at-
tack on the citrus bark seemed to be
4 more serious in nature and was re-
ported as causing material injury to
large grapefruit trees. This species
has been identified as Cephaleuros vir-
S.' \ escens..
-: Algae are low forms of plant life
V'Q'i closely akin to fungi. In general they
'inhabit the water but a few have be-
come parasites on some of the higher
plants. A common example of algal
*.-. growth occurs in the green scum that
S... forms on the surface of pools or ponds.
These, however, are not of the para-
sitic type.
APPEARANCE
Fig. 46.-Alga spots on The diseased condition caused by
citrus leaf algae can usually be easily distinguish-
ed from other troubles. Attacks on the bark appear as irregular
patches an inch or more in extent. The affected bark is slightly
raised and the surface is studded with short reddish-brown,
stubby, hair-like structures. The reddish-brown color may
soon disappear and the surface of older areas will become
greenish-gray and velvety in appearance. The affected twig
may be girdled, in which case the bark will appear swollen

*Fawcett, H. S. Cal. Bulletin. 262.
tEarle, F. S., and Rodgers, J. M. Ann. Rept. San Pedro Pathological
Laboratory, Isle of Pines, W. I. 1915.
JIdentification by Miss Charles, Assistant Mycologist, Bureau Plant Ind.,
U. S. D. A.







Bulletin 150, Florida Citrus Diseases


and the twig enlarged at this point. The parasite affects ap-
parently only a few surface layers of bark cells.
On the leaves, small, round, definite spots (fig. 46) are pro-
duced. These may vary from an eighth to one-fourth of an
inch in diameter and appear on either surface of the leaf. The
spots are raised and do not penetrate thru the leaf tissue. In
general they are brownish in color but in the early stages the
surfaces may be covered with short, stubby, reddish-brown, hair-
like structures, the fruiting bodies of the parasite. As the spots
become older they may show a greenish cast and the hair-like
structures eventually disappear.
CONTROL
In groves where conditions are damp and warm the disease
may cause considerable trouble if it once becomes firmly estab-
lished in the grove. All affected twigs should be pruned out
as soon as the disease is discovered and the affected tree should
be thoroly sprayed with some fungicide. Bordeaux mixture
4-4-50 should be effective.
The treatment could be ap-
plied perhaps to the best ad-
vantage during the dry sea-
son of the year. All prun-
ings should be collected and
burned.
Attacks on leaves may
cause little damage but if
the disease becomes very
abundant on the foliage it
can be checked by one or two
thoro applications of some
fungicide.

LICHENS

Lichens frequently occur
on the trunks, branches and
leaves of the citrus tree and Fig. 47.-Lichens on the trunk and
they are sometimes mista- branches of a citrus tree
ken for injurious pests. In general, the lichen is considered
harmless and those that are found on the citrus tree do little
damage other than give it an unsightly or unkept appearance.







Florida Agricultural Experiment Station


Lichens are low forms of plant life that are common in humid
localities. They are an association of fungus and alga living
together, and obtain their food material chiefly from the air. It
is not uncommon to find them thriving on fence posts, rocks
and other inanimate objects, as well as on the trunks and
branches of many different trees. They are apt to be more













^-- ..- ', _^---^

Fig. 48.-Lichens on citrus leaf
numerous in citrus groves located in damp, shady situations and
are frequently conspicuous in old neglected and run down groves.
A very common form is a grayish-green paper-like growth
that occurs on the bark of citrus trees (fig. 47). This growth
may cover a spot an inch or more in diameter or it may present
an irregular patch several inches in extent. The edges are
usually free, lobed and curl upward. Another type appears in
the form of a round pinkish-white spot adhering closely to the
bark. Still other forms appear as small black dots on a white,
indefinitely outlined background. One form, of interest, fre-
quently appears as a cluster of short white ridges that might
easily be taken for scale insects.
Occurrence on the leaves is less common., One of the type.)
noted is shown in figure 48.

CONTROL

The trees may be rid of lichens by spraying the trunks and
branches with some fungicide. One thoro application of bor-
deaux mixture will usually accomplish it. If only a few trees
are involved the trunks and larger branches may be cleaned with
a strong solution of lime-sulphur. Commercial lime-sulphur







Bulletin 150, Florida Citrus Diseases


diluted 1 to 15 will give satisfactory results and has the added
advantage of killing any scale present. This should be applied
with a brush and care taken not to get any of the solution on the
tender growth or foliage.
Any of the fungicides are effective against lichens.
The removal of lichens will hardly pay for the expense and
trouble of the operation, unless an improved appearance of the
tree is the aim.

FRENCHING
Frenching is of common occurrence in citrus groves and may
appear as an independent trouble altho it is frequently associated
with diseases such as withertip or dieback. It is not a distin-
guishing symptom or character of either, however. The cause
of frenching is not fully understood and it may develop under
varying conditions. In California, where the disease is known
as mottle leaf, several factors have been given as probable causes
of the trouble. Among these, poor drainage, irregular moisture
supply, an excess of lime, magnesium or organic matter, a de-
ficiency of lime, iron or organic matter, and attacks of nematodes
have been considered as causes for the development of mottle
leaf. More recent studies of the disease in that state indicate
a close relationship between the occurrence of the disease and a
low humus content of the soil.
Similar factors may be largely responsible for frenching as it
occurs in Florida. It is apparently brought on by some disturb-
ing factor in the soil and this may vary widely in different local-
ities and under different conditions. Apparently, ground lime-
stone added to to certain soils will bring on a condition of french-
ing,* and the occurrence of the disease is frequently attributed
also to poor drainage.
The amount of injury caused by frenching is variable. In
some cases a few twigs or branches of a tree will be affected
and the remainder of the tree will remain normal. This dis-
eased condition may persist for a time and eventually disap-
pear. Frequently trees are more seriously affected and a greater
part of the foliage may be frenched. Trees in this condition are
greatly weakened and are easily attacked by withertip. The
disease is rarely found generally distributed over the grove.
Trees .in certain spots may be affected or an occasional limb
*Floyd, B. F. Fla. Agrl. Expt. Sta. Bul. 137.







Florida Agricultural Experiment Station


or branch here and there thru the grove will show the disease.

APPEARANCE
Frenching only appears in the leaves. It may be readily
detected by the peculiar markings on and the size of the af-
fected leaves. (Fig. 49.) Frenched leaves usually show yellow
or pale areas on either side of the mid-rib between the main
veins. Such leaves are usually undersized, stiff, and more or less
pointed. The affected branches or twigs have a stiff, bushy ap-
pearance due to the dwarfed leaf and twig development.
CONTROL

method of con-
trol can be sug-
gested for french- y i
ing. Since it may
be brought on by ,
several different Y ;
factors, the first -
step is to deter- *
mine the proba-
ble disturbing .
factor and re-
move or correct '
it as far as possi-
ble. Often trees
slightly affected
with frenching Fig. 49.-Frenching of citrus leaves
will eventually
grow out of it without any assistance. If the condition is severe
and persistent, however, remedial measures will be necessary.

BLACK MELANOSE
Black melanose or greasy spot are terms applied to a charac-
teristic spotting of citrus leaves that is of common occurrence in
many citrus groves in the State. It appears to be more preva-
lent in southern Florida, and is also found abundant in the citrus
groves of Cuba and the Isle of Pines. The cause is not known
and the disease is not considered serious in nature, altho it ap-
pears to become more abundant each season. The spotting has
been observed only on leaves and it does not seem to develop







Bulletin 150, Florida Citrus Diseases


until the leaf tissue has well matured. While severe spotting
may cause more or less injury to the affected leaf tissue, black
melanose has never been considered serious enough to warrant
remedial measures.

APPEARANCE

The spotting is typical and may occur on either surface of


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Fig. 50.-Black melanose or greasy spot on citrus leaves

the leaf. It is probably more common on grapefruit leaves but
it may be found on the orange and other citrus varieties.
The spots (fig. 50) have a dark, slightly raised appearance
and may be more or less circular in outline or appear as a blotch.
Spots are thickened and usually show on both sides of the leaf,
tho more prominently on one side than the other. Where the
spots are prominent on the upper surface of the leaf the under
surface of the spot will be less bulged and will present a greasy-


t






Florida Agricultural Experiment Station


like stain, lighter in color than the upper surface. The spots
vary in size from an eighth to one-fourth of an inch in diameter,
and may appear few in numbers and well scattered, or the sur-
face may be thickly studded with them. Frequently, several
spots will grow together forming an irregular, black, greasy-
like mass on the surface of the leaf. The greasy appearance of
an affected leaf is a striking character. No fungus or bacterial
growth has yet been detected in connection with these spots,
either by microscopic or cultural studies.
The disease bears no relation to true melanose and should
probably be called "Greasy Spot" to avoid confusion. It does
not appear to be infectious or contagious and there is no evi-
dence by which it can be suspected of parasitic origin.

DODDER
Cuscuta sp.
Dodder is one of the parasitic flowering plants that occur on
several different hosts. It is frequently observed in Florida
where it is most commonly found on the wild plants, and
has not been considered a troublesome pest. In the North it
is often troublesome and destructive in clover and alfalfa fields.
Recently, dodder has been observed on the grapefruit in
Florida. Specimens collected from one locality were received
thru the State Plant Board. While the injury in this particular
case was reported as slight, it is of interest to know that the
citrus tree is a possible host for the parasite which may become
a troublesome pest if once established in a grove. Under fav-
orable conditions, especially where small trees are concerned,
dodder may cause considerable damage for it has the habit of
spreading rapidly-when once introduced.
The dodder appears as a small, yellowish vine-like plant
twined around the affected twigs, adhering tightly to the bark.
(Fig. 51.) Root-like processes from this vine penetrate the bark
at intervals and take up food material from the tree. A luxur-
ient growth of the parasite may soon develop in the form of yel-
lowish thread-like tendrils covering the greater part of the tree.
Yellowish bud-like clusters of flowers are generally produced in
abundance.
Attacks of dodder may rapidly sap the vitality of the tree,
causing a weakened or stunted growth and may eventually cause
the death of the tree. Affected trees should be attended to at
once. All vine-like parts of the parasite should be removed and






Bulletin 150, Florida Citrus Diseases


destroyed and the affected twigs and branches should be pruned
off and burned. After all traces of the parasite have been re-
moved the tree should be inspected frequently to see that no
more dodder appears.


-rJ


J



4j


Fig. 51.-Dodder on grapefruit twigs
Any dodder on wild plants in the vicinity of the grove should
be completely destroyed. This may be done by cutting down
the affected growth, covering it with kerosene and burning over
the affected area. The heat will destroy the seed of the para-
site that may be on the surface of the soil.
CASSYTHA
Another vine-like growth that sometimes appears on the cit-
rus tree is a species of Cassytha which is frequently mistaken
for dodder. The following note describing this plant and its
effect on the citrus tree was supplied by Director P. H. Rolfs:
"This plant grows through a considerable portion of the
tropics and is abundant on the lower East Coast of Florida.
It may occur almost anywhere in the region south of Melbourne,
and more sparingly even to the northward. Its first appear-







Florida Agricultural Experiment Station


ance is so much like that of dodder that it may readily be mis-
taken for it. Its habit of growth however is strikingly different
in that it is a perennial and the small tendril-like branches are
usually of a light green. The flowering parts of the plant are
inconspicuous and may be readily overlooked unless one searches
for them. The vine has no leaves.
"It is frequently seen in the piney woods, especially the spruce
pineland, growing over the underbrush. It is a much more vig-
orous grower than the dodder and makes a looser, more open
appearance when the tree is attacked. The seed germinate in
the soil and from this the young plant makes its way into the
tree. After it has become fully established in the tree the por-
tion attached to the soil may rot off or become disconnected.
As it is a parasite it grows on the vitality of the tree. In long
neglected cases it may entwine the entire head of the tree, badly
stunting it. The only remedy is to remove as much of the
vine as can be readily taken off. It is not a serious pest and
requires no more attention than would be the case with ordinary
vines."
SUNSCALD

Sunscald or sunburn (fig. 52) is frequently noted on citrus
leaves. It is more common on the under surface of leaves that










S. ..


4-
,


Fig. 52.-Sunscald: Different types of the injury on citrus leaves






Bulletin 150, Florida Citrus Diseases


suddenly become exposed for a time to the direct rays of the sun.
Apparently a certain stage or growth condition is necessary for
sunscald to develop. The visible effect produced is a reddish-
brown stain on the part of the leaf surface affected. In some
cases the affected area on a leaf is raised and the surface is
hard and glazed. From a small part to a half or more of the
leaf may be involved. The injury is of minor importance.
LIGHTNING INJURY
Lightning occasionally causes an injury to citrus trees that
might easily be mistaken for the effects of some parasitic dis-
ease. Several cases of such injury have come to the writer's
attention within the last few years, and the trouble has been
reported from widely separated localities within the State. The
loss in this respect is usually small since few of the affected trees,
are killed and in general the injury is confined to scattering
twigs and branches over a number of trees.
When lightning strikes in a grove, from a few trees to two
or three dozen may show varying degrees of injury. Usually
one or two trees in the affected lot will be severely injured or
perhaps killed, while on those adjacent or in the immediate vicin-
ity the injury is confined to scattering twigs or branches. Clus-
ters of three or four shoots of the same age and in the same con-
dition of growth are frequently observed in which one or two
shoots will be affected and the others will appear uninjured.
Where a tree has been killed or badly damaged it should be
replaced with a new one, and severely affected branches and
twigs may be pruned from the less injured trees.
APPEARANCE
The most striking feature of the injury is the characteristic
spots or blotches produced on the surface of the young shoots
and twigs. (Fig. 53.) When first formed these occur as pale
greenish-yellow to yellowish areas on the surface of the bark
and they may vary much in size and shape. In some cases the
spots cover an area of only a fourth to a half inch in diameter,
and again specimens are observed in which the entire surface of
the twig is affected for a distance of three or four inches. The
leaf and leaf petiole in such cases seem to escape injury. Spots
are often seen encircling the base of the leaf petiole, and in cases
where the entire surface of the green twig is affected the green
petioles and leaves stand out in marked contrast against the dis-
colored areas. (Fig. 54.)







Florida Agricultural Experiment Station


In later stages the spots or blotches become yellowish-brown
and are raised above the surrounding healthy bark. The surfaces
remain smooth for a time and are covered by a thin glazed mem-


Fig. 53.-Lightning injury: Spots on citrus twigs resulting
from the injury

brane or covering which becomes more or less bleached with
age. The tissue beneath this covering is soft and spongy and
is found to be made up of a few layers of dead cells. In most
cases the injury seems to be confined to the few surface layers
of cell tissue. The deadened areas or spots are gradually ele-
vated and finally the surface covering ruptures, breaking in
longitudinal slits. The surfaces of the spots then become ragged,







Bulletin 150, Florida Citrus Diseases


and eventually slough off, leaving a brownish, roughened scar.
The first stage of the injury is the result of the effects of light-
ning on the tissue. At this time the affected spot or area is not
noticeably depressed but the affected tissue appears dry and the
cells within are more or less collapsed. Tissue thus weakened
is readily attacked
by fungi and bac-
teria which rapid-' 1
ly complete its de-
struction.
A species of Col-
letotrichum has
been found con-
stantly associated
with such injuries
and no doubt this
fungus is largely
responsible for la-
ter development of
the spots and
blotches. When a' '. "-
spot or blotch
once appears it I
does not spread ,
beyond its original
limits, and all the
spots or affected
areas on a tree ap-'
pear at about the ,.
same time. There
is no succeeding
development of
spots as is true
with a parasitic
disease. On the Fig. 54.-Lightning injury: More enlarged view
older twigs and of spots showing the green leaf petioles sur-
branches protect- rounded by the affected areas
ed by an outer corky layer, these spots and blotches are rarely
found, and the leaves seem to be little affected.
When the trunk is lightning struck the injury is usually man-
ifest by a narrow strip of dead bark extending downward to the
ground. At the base of the affected tree this strip may broaden






Florida Agricultural Experiment Station


into an area completely girdling the trunk at that point. In such
cases the affected tissue is slightly sunken and the bark is killed
down to the wood. The dead bark is soon invaded by fungi and
bacteria, which cause it to decay rapidly. Trees affected in this
way rarely recover.

COLD INJURY
Various types of injury to the citrus tree may result from the
effects of low temperatures. The nature and extent of such in-
juries will depend largely upon the state or condition of the tree
at the time and the degree of temperature to which it is exposed.
Frosts in early fall or during the spring may cause consid-
erable injury to the tender foliage without serious permanent
damage to the tree. Freezing or excessively low temperatures
during a period when the tree is in active growth are apt to be
most disastrous. In such cases much of the hardened growth
will be killed and the bark and trunks will frequently be split.
Even when the tree is in a more dormant condition, more or less
injury is likely to result from freezing temperatures. This is
more evident on trees that are weakened by diseases, especially
those affected with foot rot or gummosis. Weakened bark ap-
pears to be more easily affected by cold, and following freezing
temperatures small patches of dead bark are often observed on
the trunks and limbs of many trees. These injuries are fre-
quently mistaken for gummosis since they usually show an
oozing of gum after a time.
A tree that has been seriously injured by freezing should re-
ceive prompt attention. The splits in the bark and trunk should
be treated with some antiseptic to prevent the invasion of fungi
and bacteria, and then bound up securely to prevent drying out.
Such trades should be immediately banked to prevent an excessive
loss of moisture. When sufficient time has elapsed to determine
to what extent the tree has been injured, all the dead twigs and
branches should be pruned out and destroyed. The dead bark
should be removed from any wounds on the trunk and limbs and
the cut surfaces treated with some antiseptic or wound covering.
Trees that have been severely cut back may need extra care for
a time in the way of cultivation and fertilizer to stimulate them
to normal growth again.
Where the young trees have been killed down to the banks,
the dead tops should be removed as soon as possible. This top
is frequently left as a support for the new shoots that put out







Bulletin 150, Florida Citrus Diseases 107

below, but this is not a safe practice since the dead wood is rap-
idly invaded by the fungus Phomopsis citri, and melanose is apt
to cause serious injury to all the new growth that develops. The
dead tops should be cut off before any new growth appears, and
be removed from the grove and destroyed. In cutting out the
dead wood it is advisable to cut an inch or so into the living wood
in order to remove all trace of the fungus. If stakes are neces-
sary for the new shoots these should be provided from some
other source.











INDEX


Algae, 94
appearance, 94
control, 95
Ammoniacal solution of copper car-
bonate, 25
formula, 26
preparation, 26
spray for anthracnose, 42
Ammoniated fruit, 71
Anthracnose, 37
Antiseptics, 32
bichloride of mercury, 32
bordeaux paste, 34
carbolineum, 33
crude carbolic acid, 32
lime and sulphur wash, 33


Bark excrescences, 70
Berger, Dr. E. W., 63
Bichloride of mercury, 32
Black melanose, 98
appearance, 99
Blight, 54
appearance, 55
cause, 56
control, 57
Bloom blight, 39
Bordeaux mixture, 23
composition, 23
formula, 24
preparation, 23
using, 24
Bordeaux paste, 34


Canker, 62
appearance, 63
cause, 66
control, 68
distinguished from other diseases,
66
Carbolineum, 33
Cassytha, 101
Cephaleuros virescens, 94
Cercospora, 91
Cladosporium citri, 82
Cladosporium herbarum, var. citri-
colum, 57
Coal tar, 34


Cold injury, 106
Colletotrichum, 105
Colletotrichum gloeosporioides, 35
Crude carbolic acid, 32
Cuscuta sp., 100

Dieback, 68
ammoniated-.fruit, 71
appearance, 69
associated with frenching, 97
bark excrescences, 70
control, 71
cultivation and cover crops, 73
curative method, 76
excessive cultivation, 75
irregular moisture conditions, 75
lack of drainage, 74
preventive methods, 72
spruce pineland, 75
gum pockets, 70
multiple buds, 71
stained terminal branches, 71
Disease control, 19
Diseases, important, 35
blight, 54
canker, 62
dieback, 68
foot rot, 43
gummosis, 48
melanose, 76
scab, 82
scaly bark, 57
withertip, 35
Diseases, minor, 87
algae, 94
black melanose, 98
cassytha, 101
cold injury, 106
dodder, 100
frenching, 97
knot, 87
leaf spots, 90
lichens, 95
lightning injury, 103
septobasidium, 93
sooty mold, 92
sunscald, 102








Bulletin 150, Florida Citrus Diseases


Diseases of bark
bark excrescences, 70
gummosis, 48
scaly bark, 57
Diseases of branches
blight, 54
gum pockets, 70
stained terminal branches, 71
Disease of buds
multiple buds, 71
Diseases of foliage
canker, 64
melanose, 76
scab, 82
Diseases of fruit
ammoniated fruit, 71
anthracnose, 37
canker, 64
dieback, 69
melanose, 76
nail-head rust, 59
scab, 82
teal staining, 38
Disease of roots
foot rot, 43
Diseases of twigs and branches
canker, 66
dieback, 69
withertip, 35
Diseases of young twigs
canker, 66
melanose, 76
scab, 82
Dodder, 100


Fertilizer, general
18
Foot rot, 43


suggestions, 17,


appearance, 43
cause, 45
control, 46
Frenching, 97
appearance, 98
control, 98
Fungicides, 22
ammoniacal solution of copper
carbonate, 25
bordeaux mixture, 23
lime-sulphur solutions, 26
Fungicides and insects, 29


Fusisporium limoni, 45

"Greasy spot", 100
Grove location, 16
Gummosis, 48
appearance, 48
cause, 52
control, 54
gummosis type, 50
psorosis type, 51
Gum pockets, of dieback, 70

Heading back, for scaly bark, 61

Insect control, 20.
Insects and insecticides, 29
Insects, scale, 30

Knot, 87
appearance, 87
cause, 88
control, 89

Leaf curl, 54
Leaf spots, 90
Lichens, 95
control, 96
Lightning injury, 103
appearance, 103
Lime and sulphur wash, 33
Lime-sulphur solutions, 26
commercial, 27
home-made, 27
Location to control diseases, 16

Matz, J., 15
McKay, Hayden M., 15
Melanose, 76
appearance, 78
control, 81
Mottle leaf, 97

O'Byrne, F. M., 16

Pine tar, 34
Phomopsis citri, 76
Phytophthora terrestria, 43
Pruning, 30
for algae, 95
for cold injury, 106








Florida Agricultural Experiment Station


for dodder, 101
for melanose, 81
for scab, 86
for scaly bark, 62
for withertip, 40
for septobasidium, 93
Pseudomonas citri, 62
Psorosis type, 51

Rolfs, P. H., 101
Rust, nail-head, 59

Scab, 82'
appearance, 83
cause, 84
control, 85
Scaly bark, 57
appearance, 58
cause, 60
control, 60
heading back, 61
pruning, 62
spraying, 62
top working, 61
Septobasidium, 93
Septobasidium pedicillatum, 93
Sooty mold, 92
control, 93
Sphaeropsis tumefaciens, 87


Spraying, 20
for algae, 95
for anthracnose, 38
for bloom blight, 39
for nail-head rust, 62
for scab, 85
Stained terminal branches, 71
State Plant Board, 15, 100
Sunscald, 102
Tar, coal, 34
pine, 34
Tear staining, 38
Top working, 61

Wilt, 54
Withertip, 35
appearance, 36
anthracnose, 38
associated with frenching, 97
bloom blight, 39
cause, 39
control, 40
tear staining, 38
White lead paint, 34
Wound coverings
bordeaux paste, 34
coal tar, 34
lime and sulphur wash, 33
pine tar, 34
white lead paint, 34




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