• TABLE OF CONTENTS
HIDE
 Title Page
 Important facts
 Table of Contents
 Introduction
 Russeting due to rust mites
 Melanose
 Russeting and tear-streaking caused...
 Buckskin
 Thrips marks and silver scurf
 Sun scald
 Die-back markings
 Anthracnose
 Chemical injuries
 Nail-head rust or scaly bark...
 Splits
 Creasing
 Knots in the rind
 Mechanical injuries
 Blue mold rot
 Stem-end rot
 Diplodia rot
 Black rot














Group Title: Bulletin - University of Florida. Agricultural Experiment Stations ; no. 108
Title: Diseases of citrus fruits
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027351/00001
 Material Information
Title: Diseases of citrus fruits
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: p. 25-47 : ill. ; 23 cm.
Language: English
Creator: Rolfs, P. H ( Peter Henry ), 1865-1944
Fawcett, H. S ( Howard Samuel ), b. 1877
Floyd, B. F ( Bayard F )
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1911
 Subjects
Subject: Citrus -- Diseases and pests -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by P.H. Rolfs, H.S. Fawcett and B.F. Floyd.
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station)
 Record Information
Bibliographic ID: UF00027351
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000921860
oclc - 18160353
notis - AEN2328

Table of Contents
    Title Page
        Page 25
    Important facts
        Page 26
    Table of Contents
        Page 26
    Introduction
        Page 27
    Russeting due to rust mites
        Page 27
        Page 28
    Melanose
        Page 29
    Russeting and tear-streaking caused by withertip fungus
        Page 30
        Page 31
    Buckskin
        Page 32
    Thrips marks and silver scurf
        Page 32
    Sun scald
        Page 33
    Die-back markings
        Page 34
        Page 35
    Anthracnose
        Page 36
        Page 37
    Chemical injuries
        Page 38
        Page 39
    Nail-head rust or scaly bark spots
        Page 40
        Page 41
    Splits
        Page 42
    Creasing
        Page 42
    Knots in the rind
        Page 43
    Mechanical injuries
        Page 43
    Blue mold rot
        Page 44
    Stem-end rot
        Page 45
    Diplodia rot
        Page 46
    Black rot
        Page 47
Full Text


BULLETIN 108 NOVEMBER, 1911


UNIVERSITY OF FLORIDA

Agricultural Experiment Station


DISEASES OF CITRUS FRUITS
BY
P, H, ROLFS, H, S. FAWCETT and B. F. FLOYD


























Fig. 10.-Grapefruit tree affected with withertip.
Anthracnose on dropped fruit.

The publications of this Station will be sent free upon application to the
Experiment Station, Gainesville, Florida.
RECOxD CO., ST. AUGUSTINI, L A.

4020










IMPORTANT FACTS

1. This bulletin calls attention to the principal diseases of citrus fruits.
2. Some of the troubles can, and others cannot, be treated successfully
after the fruit has matured.
3. Some of the troubles can be overcome only by better grove sanitation
and hygiene.
4. Some troubles that are less prevalent (but at the same time severe in
individual groves) have not yet been successfully remedied.
5. Wherever possible, a disease should be prevented rather than allowed to
odcur. Remedying a disease after it is prevalent is an expensive
expedient to make the best of a bad situation.
6. No two groves are under exactly the same physical conditions, nor are
the weather and other factors exactly the same during any two
years; consequently a remedy must be applied with discretion or
it is likely to give disappointing results.






CONTENTS
PAGE
Introduction ......... ...................... .. ........... .. 27
Diseases Affecting the Epidermis-
Rust Mite Russeting, by P. H. Rolfs .. .................... ....... 27
Melanose, by B. F. Floyd ............................... ..... ...... 29
Russeting and Tear Streaking Caused by Withertip Fungus, by P. H. Rolfs 30
Buckskinning, by H. S. Fawcett ................ ... .......... 32
Silver Scurf and Thrips Marks. by H. S. Fawcett .......................... 32
Sun Scald, by B. F. Floyd ................ .............................. 33
Diseases Affecting the Peel-
Dieback (Ammoniated) Markings, by B. F. Floyd........... .......... 34
Anthracnose, by P. H. Rolfs ................................... 36
Chemical Injury, by B. F. Floyd...................... ... .......... 38
Nail-Head Rust, by H. S. Fawcett .................... ....... 40
Scab, by H. S. Fawcett .................... .. ............. 41
Splits, by B. F. Floyd ......... .... .................................... 42
Creasing, by B. F. Floyd ...................... .. ......... 42
Knots in Rind, by B. F. Floyd.......... .... .................... 43
Mechanical Injuries, by B. F. Floyd ........................ ...... 43
Diseases Affecting the Interior of the Fruit-
Blue Mold Rots, by H. S. Fawcett...................................... 44
Stem-End Rot, by H. S. Fawcett......... .. ..................... 45
Diplodia Rot, by H. S. Fawcett................ .............. 46
Black Rot, by H. S. Fawcett ................ .. ............... 47










IMPORTANT FACTS

1. This bulletin calls attention to the principal diseases of citrus fruits.
2. Some of the troubles can, and others cannot, be treated successfully
after the fruit has matured.
3. Some of the troubles can be overcome only by better grove sanitation
and hygiene.
4. Some troubles that are less prevalent (but at the same time severe in
individual groves) have not yet been successfully remedied.
5. Wherever possible, a disease should be prevented rather than allowed to
odcur. Remedying a disease after it is prevalent is an expensive
expedient to make the best of a bad situation.
6. No two groves are under exactly the same physical conditions, nor are
the weather and other factors exactly the same during any two
years; consequently a remedy must be applied with discretion or
it is likely to give disappointing results.






CONTENTS
PAGE
Introduction ......... ...................... .. ........... .. 27
Diseases Affecting the Epidermis-
Rust Mite Russeting, by P. H. Rolfs .. .................... ....... 27
Melanose, by B. F. Floyd ............................... ..... ...... 29
Russeting and Tear Streaking Caused by Withertip Fungus, by P. H. Rolfs 30
Buckskinning, by H. S. Fawcett ................ ... .......... 32
Silver Scurf and Thrips Marks. by H. S. Fawcett .......................... 32
Sun Scald, by B. F. Floyd ................ .............................. 33
Diseases Affecting the Peel-
Dieback (Ammoniated) Markings, by B. F. Floyd........... .......... 34
Anthracnose, by P. H. Rolfs ................................... 36
Chemical Injury, by B. F. Floyd...................... ... .......... 38
Nail-Head Rust, by H. S. Fawcett .................... ....... 40
Scab, by H. S. Fawcett .................... .. ............. 41
Splits, by B. F. Floyd ......... .... .................................... 42
Creasing, by B. F. Floyd ...................... .. ......... 42
Knots in Rind, by B. F. Floyd.......... .... .................... 43
Mechanical Injuries, by B. F. Floyd ........................ ...... 43
Diseases Affecting the Interior of the Fruit-
Blue Mold Rots, by H. S. Fawcett...................................... 44
Stem-End Rot, by H. S. Fawcett......... .. ..................... 45
Diplodia Rot, by H. S. Fawcett................ .............. 46
Black Rot, by H. S. Fawcett ................ .. ............... 47












DISEASES OF CITRUS FRUITS
BY
P. H. ROLFS, H. S. FAWCETT AND B. F. FLOYD



INTRODUCTION
Much of the material brought together in this bulletin by the three
writers has been obtained rather incidentally than as the result of major
projects. It is brought together in what is thought to be a convenient
form for the grower, and includes the principal diseases that occur on
the fruit after maturity. All of them must be prevented, and cannot
be cured after the fruit has become affected.

RUSSETING DUE TO RUST MITES
Russeting of the citrus fruits may be produced by one of several
agents: rust mites (Eriophyes oleivorus), withertip fungus (Colleto-
trichum gloeosporioides), and melanose. The last-named does not
properly belong among the russeting, but frequently when fruits are
affected by melanose in a peculiar form with the specks exceedingly
minute and generally distributed, they are placed among the russets.
(See Melanose, and Withertip Russeting, in this bulletin). The rust
mite is not an insect, but is more closely related to the spider mites.
Rust-mite russeting is the most general affection of Florida citrus
fruits. It occurs on all varieties of grapefruit and oranges, including
the sour orange and even the bitter sweet (though these two varieties
are nearly free from it). When russeting is caused by rust mites, the
appearance of the fruit varies from the least tinge of darkening to a
nearly pitch black, with all intermediate grades. As a rule, the russet-
ing occurs on the side toward the light, shading off to the side of the
fruit next the interior of the tree. Not infrequently the side of the
fruit exposed to full mid-day sunlight is also free from russeting.
Fruit more or less shaded is likely to be rather evenly russeted. In
dense shade the fruit is nearly always bright.
The migration of the rust mite from the leaves to the fruit does not
normally occur before the latter part of April, and usually not until the
the middle of May. Usually much damage has been done before the
grower is aware that the mites are present. The multiplication of the












DISEASES OF CITRUS FRUITS
BY
P. H. ROLFS, H. S. FAWCETT AND B. F. FLOYD



INTRODUCTION
Much of the material brought together in this bulletin by the three
writers has been obtained rather incidentally than as the result of major
projects. It is brought together in what is thought to be a convenient
form for the grower, and includes the principal diseases that occur on
the fruit after maturity. All of them must be prevented, and cannot
be cured after the fruit has become affected.

RUSSETING DUE TO RUST MITES
Russeting of the citrus fruits may be produced by one of several
agents: rust mites (Eriophyes oleivorus), withertip fungus (Colleto-
trichum gloeosporioides), and melanose. The last-named does not
properly belong among the russeting, but frequently when fruits are
affected by melanose in a peculiar form with the specks exceedingly
minute and generally distributed, they are placed among the russets.
(See Melanose, and Withertip Russeting, in this bulletin). The rust
mite is not an insect, but is more closely related to the spider mites.
Rust-mite russeting is the most general affection of Florida citrus
fruits. It occurs on all varieties of grapefruit and oranges, including
the sour orange and even the bitter sweet (though these two varieties
are nearly free from it). When russeting is caused by rust mites, the
appearance of the fruit varies from the least tinge of darkening to a
nearly pitch black, with all intermediate grades. As a rule, the russet-
ing occurs on the side toward the light, shading off to the side of the
fruit next the interior of the tree. Not infrequently the side of the
fruit exposed to full mid-day sunlight is also free from russeting.
Fruit more or less shaded is likely to be rather evenly russeted. In
dense shade the fruit is nearly always bright.
The migration of the rust mite from the leaves to the fruit does not
normally occur before the latter part of April, and usually not until the
the middle of May. Usually much damage has been done before the
grower is aware that the mites are present. The multiplication of the





28 FLORIDA AGRICULTURAL EXPERIMENT STATION

mites is very rapid, and in the course of two or three weeks nearly all
the fruit of a grove may be affected.
Moist weather, or any condition that induces a high humidity, is
likely to cause partial or complete destruction of the mites. Dry
weather and conditions that induce low humidity are favorable to the
development of the mites. Some hammock groves are notably free
from russeting, while many pine-land groves are noted for the pro-
duction of russets.
J/The principal season for russeting occurs in late spring or early
summer. There have been notable exceptions to this rule. Last year
(1910-11) the largest amount of russeting in Dade County occurred
after the first of September, continuing until late in December. In
1907-8 the grapefruit in certain groves on the Subpeninsula remained
bright until the first of January, and after that russeted very badly.
From the studies made on the rust mites it is certain that this form of
russeting may occur at any time after the middle of April until the
fruit is gathered.
Rust-mite russeting may be distinguished from other forms by the
skin being smooth and frequently shiny; while withertip russeting is
dull-colored as a rule and rather rough to the feel. Melanose russet-
ing can always be distinguished by the discoloration occurring in
sharply defined dots. Any two or even all three may occur together on
the same fruit.
J.'REATMENT.-Much confusion and disappointment have arisen in
recent years because many have assumed that all russeting was due to
the rust mites, which is quite contrary to the facts.
Sulphur and its compounds are the substances that form the reme-
dies par excellence for the destruction of rust mites and other pests be-
longing to this group of animals.
Dry sulphur, or sulphur and lime mixed in equal parts may be ap-
plied with an air gun. This is a cheap and more or less satisfactory
remedy. The soda-sulphur and lime-sulphur compounds have long
been used and are still among the most efficient remedies. The self-
boiled lime and sulphur should also prove an excellent remedy, but
has not been tested by the writer. In using the lime sulphur solution
or the soda-sulphur solution, it is not necessary to bring the insecticide
in contact with the mites. Observations by means of the microscope
show that these liquids do not have to come into actual contact with
the mites to prove effective, the fumes being sufficient. While con-
ducting experiments in 1910 the effect of lime-sulphur on rust mites
came under observation incidentally. At the end of two and one-half
hours the effect on the rust mites could be made out by means of a
hand k [s. In four hours' time the little pests had all collapsed, some





BULLETIN 1o8


of them not having been touched by the insecticide. Some fruits on
the same tree had not been touched by the solution. On these the
mites were not destroyed.
Preventive.-Use flowers of sulphur, or a mixture of equal parts
air-slaked lime and sulphur sifted together through a flour sifter. Ap-
ply by means of an air gun. This is a simple and cheap remedy, but
of varying effectiveness.
Soda-sulphur solution, or lime-sulphur solution one quart to fifty
gallons of water is usually effective. At the rate of one gallon to thirty
of water these insecticides are likely to cause chemical scalding.
MELANOSE
Melanose is a disease of the fruit, leaves and young stems. The
markings produced on these different organs are about the same. The
markings on the fruit are superficial and never extend into the rind.
Unless they are very plentiful, they do not affect the development of
the fruit. Their presence causes the fruit to be classed as a russet,
thus affecting its market value.
The markings caused by the disease are small brown spots, which
are scattered like pepper over the skin of the affected part. They are
circular to irregular in outline, and vary in size from mere points to
spots one-sixteenth of an inch in diameter. They are wax-like in ap-
pearance, and resemble small drops of melted sugar burned to a red-
dish-brown color. They are raised and cap-like, and are never conical.
Frequently where the markings are plentiful, they will grow together,
forming solid patches of irregular outline. These patches will crack
in lines like dried mud.
Some of the markings
may be arranged in lines -. -
forming circles or parts of .
circles. The borders of the "
markings that make up -
these lines are usually peel- '- ," ,
ed away. This circular ar- j.
rangement of the markings
is characteristic of melan- ''
ose. (See Fig. 11.)
Again, the markings on -
the fruit as a whole are .-
sometimes so arranged as
to resemble the tear-streak- --
ing that is due to the with-
Fig. 11.-Melanose, showing looped rows
ertip fungus. 'I'lS occurs of markings.





30 FLORIDA AGRICULTURAL EXPERIMENT STATION

where a dead twig over-hangs the fruit, so that the drip from the twig
falls upon it and runs down its side. The melanose streaking is easily
recognized by the character of the markings in the streak.
Fruit affected by melanose may also be affected by other diseases
that mark the epidermis. The mixture of the markings due to the dif-
ferent causes often gives a peculiar appearance to the fruit, making
it difficult to recognize the diseases.
Melanose starts its development in the spring after the warm
weather has well begun. Periods of cold will delay its development.
It first shows as mere sunken points, that increase in size and become
raised as the fruit develops. Owing to its early stages being so in-
conspicuous, the disease is usually not noticed until the markings have
attained some size. It shows up in its matured condition on the fruit
at any time from May to July. Only young, succulent tissue is attacked
by the disease. As the fruit approaches maturity, it becomes immune
to attack.
,/Preventive.-Since melanose begins to develop on the fruit in the
early spring, measures for its prevention must be carried out at that
time. It has been found that the disease can be controlled by the use
of either Bordeaux mixture or ammoniacal solution of copper car-
bonate. They should be first applied about two weeks after the bloom
has fallen; and again about a month later. In case periods of cold
occur late in the spring, a third spraying should be made a month
later still.
The spray should be applied in the form of a fine mist, and care
taken that all fruits are thoroughly sprayed. In groves badly diseased,
the dead wood should be carefully and thoroughly cleared out of the
trees, and burned.
Since an application of the copper sprays is quite likely to be fol-
lowed by an infestation with different scale insects, it is not advisable
to spray for melanose unless it is doing considerable damage to the
fruit. But in case spraying is done, the applications should be alter-
nated with thorough sprayings with some insecticide, the latter being
applied first. This system of spraying with both fungicide and insecti-
cide will not only control the melanose and scale, but will also control
all other fungus and insect diseases that affect the fruit while it is
young.

RUSSETING AND TEAR-STREAKING CAUSED BY
WITHERTIP FUNGUS
The withertip fungus (Collctotrichum gloeosporioides) has become
a serious parasite in citrus groves during the last fifteen years. Pre-
vious to this time its occurrence in Florida was well known to botan-





BULLETIN 1o8


ists, but no serious damage occurred from it. Its manifestations in the
grove are quite various, but only that form having the appearance of
russeting will be discussed here.
Russeting and tear-
streaking can nearly al-
ways be traced back for
their beginning to a small
dead spur or sprig. The
fungus lives in this dead
spur or sprig. Water from
rains, and moisture follow-
ing heavy dews, collect in
drops on these sprigs or
spurs, and the drops, when
they fall, carry with them
numerous fungus spores.
These spores come in con-
tact with the epidermis of
the fruits, and germinate,
causing minute lesions on
Fig. 12.-- Withertip russeting.
the epidermis too small for
complete infection and pro-
duction of anthracnose. It
requires considerable time
for withertip russeting to
appear. It has not been ob-
served to occur until the
fruit has nearly matured.
Tear-streaking may be pro-
duced at any time after the
fruit has begun to color,
and on late varieties while
they are still green. With-
ertip russeting and tear-
streaking (or streaking),
Fig. 13.--Withertip tear-streaking. being caused by the pres-
ence of fungus, can be pre-
vented by the use of a fungicide. Bordeaux mixture and ammoniacal
solution of copper carbonate are excellent for this purpose. The
grower must be prepared to fight scale insects, however, when he uses
these fungicides in his grove. In many cases the loss from russeting
and tear-streaking w ill be less than the cost of applying the fungicide
and of following that with the insecticides for destroying scale insects.





32 FLORIDA AGRICULTURAL EXPERIMENT STATION

Preventive,--(1) The proper time to begin preventive work for with-
ertip russeting and tear-streaking is in July, when all dead and weak-
ened wood should be pruned out and destroyed. This reduces the
amount of fungus spores to a minimum and saves the costly work of
spraying.
(2) Spray with ammoniacal solution of copper carbonate as soon as
russeting from withertip fungus becomes apparent. Repeat in three
weeks or a month, especially if rains have occurred in the meantime
and the fruit is continuing to russet. (See Remedy 3, under An-
thracnose.)
BUCKSKIN
On fruits affected with buckskin the rind usually presents a some-
what scurfy, grayish, slightly roughened, appearance. This most fre-
quently covers the greater part of the surface of the fruits and quite
often the entire surface. The rind often becomes abnormally thick,
an'd is pliable on maturity. The fruit is usually stunted in growth; or
if of normal size, becomes light with a small amount of juice. Buck-
skin is usually not so rough, hard, or rusty as melanose or rust-mite
russeting. It is not in definite tracts and irregular spots and lines, as
are thrips marks; and it is usually much lighter in color than the tear-
staining or withertip russeting. Buckskin appears to be most common
in grapefruits on the interior of the tree and lower branches in shaded
places. Buckskin is thought to be due to the combined effect of mites
and a surface-growing fungus. It appears to have its start in an at-
tack of mites when the fruits are very small. A fungus (which has a
Coniothecium-like spore) follows the injuries in the epidermis made
by the mites, and appears to be responsible for the further development
of the buckskin.
No recommendations based on experimental evidence are at hand,
but it would seem that lime-sulphur sprays applied as soon as the mites
make their appearance ought to remedy the trouble. (See Proc. Fla.
State Hort. Soc. 1909, p. 84.)

THRIPS MARKS AND SILVER SCURF

Markings on the fruit known as "thrips marks," also called "silver
scurf," are caused in most cases by thrips, but may also be caused when
the fruit is quite young by other slight injuries, such as scratches or
abrasions. (See Mechanical Injuries). The markings are grayish to
silvery irregular patches, over which is a delicate scurf made up of
minute pieces of the outer epidermis under which a new set of cells has
been formed. (See Fig. 14.) These markings, which become quite
noticeable at picking time, usually have their beginning when the fruit





32 FLORIDA AGRICULTURAL EXPERIMENT STATION

Preventive,--(1) The proper time to begin preventive work for with-
ertip russeting and tear-streaking is in July, when all dead and weak-
ened wood should be pruned out and destroyed. This reduces the
amount of fungus spores to a minimum and saves the costly work of
spraying.
(2) Spray with ammoniacal solution of copper carbonate as soon as
russeting from withertip fungus becomes apparent. Repeat in three
weeks or a month, especially if rains have occurred in the meantime
and the fruit is continuing to russet. (See Remedy 3, under An-
thracnose.)
BUCKSKIN
On fruits affected with buckskin the rind usually presents a some-
what scurfy, grayish, slightly roughened, appearance. This most fre-
quently covers the greater part of the surface of the fruits and quite
often the entire surface. The rind often becomes abnormally thick,
an'd is pliable on maturity. The fruit is usually stunted in growth; or
if of normal size, becomes light with a small amount of juice. Buck-
skin is usually not so rough, hard, or rusty as melanose or rust-mite
russeting. It is not in definite tracts and irregular spots and lines, as
are thrips marks; and it is usually much lighter in color than the tear-
staining or withertip russeting. Buckskin appears to be most common
in grapefruits on the interior of the tree and lower branches in shaded
places. Buckskin is thought to be due to the combined effect of mites
and a surface-growing fungus. It appears to have its start in an at-
tack of mites when the fruits are very small. A fungus (which has a
Coniothecium-like spore) follows the injuries in the epidermis made
by the mites, and appears to be responsible for the further development
of the buckskin.
No recommendations based on experimental evidence are at hand,
but it would seem that lime-sulphur sprays applied as soon as the mites
make their appearance ought to remedy the trouble. (See Proc. Fla.
State Hort. Soc. 1909, p. 84.)

THRIPS MARKS AND SILVER SCURF

Markings on the fruit known as "thrips marks," also called "silver
scurf," are caused in most cases by thrips, but may also be caused when
the fruit is quite young by other slight injuries, such as scratches or
abrasions. (See Mechanical Injuries). The markings are grayish to
silvery irregular patches, over which is a delicate scurf made up of
minute pieces of the outer epidermis under which a new set of cells has
been formed. (See Fig. 14.) These markings, which become quite
noticeable at picking time, usually have their beginning when the fruit






BULLETIN 1o8


is very small, just after the
bloom has shed. The
scurfed patches are at first '
small, but as the fruit en-
larges the areas become -
larger also, and a new
epidermis is formed under
the scurf. Sometimes the :
markings are so large and
deep that the fruits become
misshapen. Similar marks
are caused by slight in-
juries when fruits are quite o-
young. Spots with similar
scurf are sometimes caused
by too strong spraying Fig. 14-Thrips marks on orange.
solution when the fruits are
quite small and tender. (See Chemical Injuries.)
Preventive.-Those of the markings due to thrips may be prevented
to a large extent by spraying to kill the thrips. As a result of expe-
rience and experiment in California (Bul. No. 99, Part 1, U. S. Dept.
of Agr. Bur. Ent.) lime-sulphur with the addition of blackleaf tobac-
co extract, or blackleaf "40," was found to be an efficient spray for
thrips. The formulae are as follows:
1. Lime-sulphur (330 Baum6), 1 gallon to 75 gallons of water. To
this add blackleaf tobacco extract (23Y4 per cent. nicotine) at the rate
of 1 gallon to 100 gallons of the spraying solution.
2. Lime-sulphur, 1 gallon to 75 gallons of water. To this add
blackleaf "40" at the rate of 1 gallon to 1,800 gallons of the spraying
solution.
The first spraying should be done just after most of the bloom has
shed. This may be followed by a second spraying 10 to 14 days later,
and by a third in three or four weeks after the second. Spraying
should be thorough, as only the thrips actually hit are killed. This
spraying will also kill any rust mites that should happen to be present
at this time of year. (See Annual Report, Fla. Agr., Expt. Sta. 1910,
p. 55.)
SUN SCALD

Sun scald cannot be classed as a disease. It is an injury resulting
from some factors that are imperfectly understood. It is generally
supposed to be due to water on the fruit acting as a lens, and by col-
lecting the light rays developing enough heat to cause injury.






34 FLORIDA AGRICULTURAL EXPERIMENT STATION

This affection appears on
the fruit during the late sum-
mer or early fall. It first
shows as a premature yellow-
ing of a spot near the stem
end that is fully exposed to
the sun. The surface may be
pitted as though the oil glands
had dried out. The spot is
dry to the feel, and holds heat ,
in contrast to unaffected por-
tions of the fruit.
This affection in itself is
confined to the skin. But
owing to the weakening of the
tissues that it produces, the Fig. 15.-Sun-scald, with fungus infec-
fruit is attacked by fungi at tion at center.
this point. They penetrate the rind and cause a discoloration that
may extend to the center of the fruit.
Tangerines and Satsumas seem to be more susceptible to this trouble
than other citrus fruits. No method of treatment has been developed,
owing to lack of exact knowledge as to the cause.
DIE-BACK MARKINGS

Die-back is one of the common diseases of citrus trees. It is not
due to any organism, such as a fungus or an insect, but is caused by
improper feeding conditions. Some of the conditions known to ag-
gravate the disease are: over-feeding with organic nitrogenous fer-
tilizers, such as stable manure, cottonseed meal, and others; and un-
favorable soil conditions, such as lack of drainage, or a compact sub-
soil of hard pan, marl, or clay, that is too near the surface. The dis-
ease is common upon certain lands in Florida, such as the shell lands,
the coquina lands, and the rocky lands in the extreme southern part
of the State.
Dieback affects the fruit and young stems. The symptoms on the
stems are various. Fruits marked by dieback are usually spoken of
as "ammoniated fruit." But this may be considered as a misnomer
since it gives the impression that the disease is due to too much am-
monia in the soil; whereas, the disease is related only to certain forms
of ammonia in the soil, namely, the organic forms.
Dieback spots on the fruit are mostly confined to the epidermis.
They usually do not extend into the tissue beyond the depth of the
oil glands. They vary in size from small spots 1-16 of an inch in





BULLETIN io8


diameter, to patches covering a large portion of the surface of the
fruit. The smallest spots are usually circular in outline and conical in
shape, and of a glossy
brown or black color. The
larger spots and patches
are somewhat raised, with '
the surface irregularly
cracked. They vary con-
siderably in outline; some'
resemble thrips marks in
this respect, and others
cover the surface like rust-
mite russeting. ,
The rind of dieback
fruit frequently shows a
great increase in thickness.,
and the fruit as a whole is
coarse to the feel. This is Fig. 16.-Dieback (ammoniated) mark-
supposed to be due to a too wings on orange.
rapid growth of the fruit arising from nitrogen stimulation.
Fruit that is severely affected with dieback will show a collection
of a clear to brownish colored gum in the angles of the segments next
to the pith. This is conclusive evidence of the identity of the disease,
as this form of gumming is only known to occur in fruits affected
with dieback.
The fruit on a tree severely affected with dieback is quite likely to
become marked and to fall early. The fruit that remains on the tree
will color and ripen prematurely, and is especially subject to splitting.
The line of splitting usually develops in the discolored patches.
Dieback fruit is for the most part insipid. It is unfit for shipping
on account of the conspicuous markings. The marking on the fruit
is usually not accompanied by any other disease that would confuse
its identity.
Preventive.-The safest treatment for dieback consists of the re-
moval of the conditions that are aggravating the disease, and the de-
v,elopment of more favorable conditions for the growth of the tree. If
the disease has arisen from the feeding of too much ammonia from
organic sources, such as dried blood, cottonseed meal, stable manure,
and others, this practice should be discontinued. Only fertilizers con-
taining inorganic forms of nitrogen, such as nitrate of soda, sulphate
of ammonia, or nitrate of potash, should be used. If the grove has
been heavily fertilized, much lighter applications should be made. All
cultivation should be discontinued, excepting such as is necessary to





36 FLORIDA AGRICULTURAL EXPERIMENT STATION

conserve the moisture. The natural growth of grass and weeds that
comes on during the rainy season should be cut and removed when it
is mature. This treatment should continue until the grove has en-
tirely recovered. Under most conditions this will require from one to
several years.
If the condition aggravating the disease is the presence of a hard-
pan too near the surface, it must be broken through. This may be ac-
complished either by the use of hand implements or dynamite, accord-
ing to its thickness.
In case the water cannot be kept down by ditches where there is
lack of drainage, the tree rows should be ridged high. Lack of drain-
age sometimes occurs in localities that are high, owing to pockets being
formed by an irregular layer of hardpan. This may be determined by
systematic borings.
Where dieback occurs on shell or coquina lands, the land should
not be stirred. The grass and weeds should be mowed frequently, and
decaying vegetable matter should not be allowed to accumulate. Such
fertilizers as cottonseed meal, dried blood, guano, stable manure and
others should be avoided. This method of treatment also applies to
dieback when it occurs on the rocky lands in the southern part of the
State, excepting that cultivation is permissible when it is necessary to
conserve the moisture.
Where the fruit of a tree shows dieback marking and yet the tree
shows no particular symptom of the disease, spraying with Bordeaux
mixture will be beneficial, owing to the stimulating effect of this spray.
It should be applied once in the spring when the fruit is about walnut
size, and again in the summer.
Copper sulphate or bluestone has been used as a treatment by many
growers, either by placing a crystal smaller than a pea beneath the
bark of the trunk, or by applying less than a pound widely around the
tree. But the benefits of this method have been questioned, and it is a
dangerous practice owing to the possibility of permanently injuring
the tree from an overdose.

ANTHRACNOSE
Anthracnose, caused by Colletotrichum gloeosporioides, manifests
self by brown or dark-colored sunken patches occurring in the skin
of the fruit. The darkened spots may be regular or irregular in outline.
The lesions may occur as a number of small spots no larger than a pin-
head, or may involve a large portion of the fruit. Fruit from trees
where a considerable amount of dropping has occurred should not be
Shipped, but the trees should be treated and the disease cured before
the fruit is allowed to be picked or to come to the packing house. Not





BULLETIN ro8


only will the infected fruit become worthless in transit, but the handling
of such fruit is likely to cause infection of the healthy fruit. Infection
occurs through the skin of the
fruit, and is not transmitted
through the tissues of the tree
to the fruit. In 1902, fruit
from a certain grove near Mi-
ami was shipped from infect-
ed trees. The fruits were
picked with great care to in-
clude none that showed visible
signs of infection, yet when
the fruit arrived on the mar-
ket at Jacksonville over-70 '
per cent. of it was worthless
for commercial purposes. V
The first sign of loss from
antliracnose is the dropping
of a considerable amount of Fig. 17.-Anthracnose spots.
fruit. This is more particularly true with grapefruit than with tan-
gerines and round oranges.
This disease, caused by Colletotrichum gloeosporioidcs, does the
greatest amount of damage to grapefruit and round oranges, though it
has been observed on all edible varieties of citrus fruits, including the
lime. On the latter it appears in the form of scab.
It rarely occurs on fruit before it has begun to color, though in
some few cases, especially with tangerines, a large percentage of the
fruit has been attacked even before coloring. In such cases much fruit
has become infected before severe dropping occurs. The fruit on poor-
ly nourished and slightly debilitated trees is more subject to attack
than fruit in groves that are perfectly healthy and in full leafage.
Fruit on trees that are overloaded is likely to be attacked. Trees more
or less affected by withertip are likely to lose considerable fruit from
anthracnose. On the other hand, the fungus is not likely to make its
first appearance in a grove in the form of anthracnose. Withertip fun-
gus is present in practically every grove in the State, to a greater or
less extent. One should therefore constantly expect anthracnose to ap-
pear whenever any considerable amount of dead wood occurs in the
trees, or whenever there is any considerable loss of foliage.
This disease was especially severe during the winter of 1901-2, and
less severe during the next winter. It was again quite severe in the
winter of 1910-11.
It can be readily distinguished from the affection usually spoken of





38 FLORIDA AGRICULTURAL EXPERIMENT STATION

as "ammoniated fruits" by the fact that the anthracnose marking is
always sunken and lacks luster. Spots and patches caused by "am-
moniation" are not sunken, but are more likely to be slightly raised,
and their surface looks as if varnished or oiled. Anthracnose may be
distinguished from chemical injury by the fact that chemical injury,
when occurring as the result of spraying, always occurs on the part
of the fruit that hangs lowest, while anthracnose nearly always occurs
on the upper surface or on the sides.
Fruit affected with anthracnose is perfectly wholesome, and in the
early stages the flavor is not affected.
Preventive.-1. Keep the withertip fungus as much reduced as
possible during the summer.
2. Avoid any treatment that is likely to reduce the foliage of
the tree.
3. When withertip fungus is present in considerable abundance,
or the foliage of the trees has been considerably reduced from any
cause whatever, weekly inspections should be made, beginning about
the first of October. Any considerable dropping of fruit from a tree
calls for immediate careful inspection. If the characteristic anthrac-
nose lesions are found on the fruit, prompt and thorough spraying
with ammoniacal solution of copper carbonate is demanded. If this
work is done in a desultory manner, it might as well be left undone.
Spraying with.fungicide should be our last resort. Use eight ounces
of pure copper carbonate in a wooden or earthen jar, and add enough
water to make a thin paste. Then add three pints of twenty-six degree
ammonia. This will make a deep blue liquid. Pour this liquid into
fifty gallons of water. Spray the fruit thoroughly so as to moisten
every part of it, but avoid using so much fungicide as will cause it to
run off, which is worse than wasteful. Keep the spray from the leaves
and trunks of the trees as much as practicable. Repeat the spraying
in ten days or two weeks. It will take from two to four weeks before
the beneficial effect of the spraying can be noticed.
CHEMICAL INJURIES
Chemical injuries to fruit may arise either from a too large appli-
cation of readily soluble fertilizers, or from sprays.
An over-large application of fertilizers will cause a severe dropping
of the fruit. This fruit will show a dark brown to black discoloration
and depression of the rind in irregular patches. The fruit as a whole
will finally turn black and become mummified. Fruit thus affected
differs from the rots in the more rapid development of the affection and
in that it does not become soft.
Weakened and diseased fruit are the first to become affected and fall.






BULLETIN izo


The old leaves will show the same sort of discoloration and will fall.
If the injury is not great enough
to kill the branches back, the new
leaves on the tree will escape in-
jury for the most part.
The chemicals and fertilizers
most commonly used that will
cause this sort of injury are
nitrate of soda, nitrate of potash,
sulphate of ammonia, and copper
sulphate.
Direct chemical injury to fruit
frequently happens from the use
of sprays that have been improp-
erly mixed, or are used in a too Fig. Is.-Chemical injury on fruit.
concentrated condition. In general, the injury from the different chem-
ical sprays is about the same. They produce a killing and depression of
the tissue in the spots affected. These spots will resemble those pro-
duced by anthracnose, but are usually located at the blossom or lowest
end, from the collection of the spray at this point. These spots once
produced may become infected with fungi'that grow inward and pro-
duce a rotting of the fruit.
Another form of spotting that is entirely different sometimes occurs
where improperly mixed oil sprays have been used. This consists of
a mere discoloration of the skin that shows as a circular spot of light
green against the deep green of the unaffected portion of the fruit.
Sometimes a form of chemical injury occurs on young fruit from
the use of sprays, which, when the fruit has matured, resembles me-
,chanical injury. This is due to the fact that the chemical injury was
slight, and the formation of the new skin and the development in size
were identical with what occurs in mechanical injury.
The application of a spray in the fall may be attended by a falling
of the fruit if the tree is in a weakened condition from disease or un-
favorable growth conditions.
Preventive.--There is no method of treatment for chemical injuries
to the fruit after they have occurred. If the injury is due to feeding
too much of readily soluble fertilizers, further application of these
should be avoided until the tree recovers. Chemical injury due to over-
feeding most commonly follows a heavy application of a readily solu-
ble fertilizer followed by heavy rain; or where too large a quantity of
-copper sulphate has been applied to the soil or placed beneath the bark
to attempt the cure of dieback in the trees.





40 FLORIDA AGRICULTURAL EXPERIMENT STATION

Sprays should be mixed carefully, and applied according to di-
rections.
NAIL-HEAD RUST OR SCALY BARK SPOTS (Cladosporium
herbarum var. citricolum and Colletotrichum gloeosporioides)
The spots on fruit that accompany the Florida scaly bark (also
known as "nail-head rust") are hard, circular, sunken, more or less
corky spots, causing premature coloring and dropping of fruit (see
Fig, 19). The spots are at first --S"
yellowish to reddish-brown on
green fruit, and finally become W.
dark and sunken. In ringed
spots the rings first become
sunken with a higher part inside
(see Fig 9, Bul. 106, Fla. Agr.
Exp. Sta.). This central part
afterwards sinks in, and the
whole area inside the ring is in-
volved. The spots vary in
breadth from one-fifth to one-
half inch. These spots are found
only on sweet oranges. They Fig. 19.-Scaly-bark spots.
are not known to occur on grapefruit or tangerines. Some of the spots
are quite similar to anthracnose, or to some spots produced by chemi-
cal injuries; but they may be distinguished (1) by some of the spots
starting as sunken rings, (2) by grapefruits or citrus fruits other than
sweet oranges not being affected even when exposed to infection. Two
fungi (named above) are constantly associated with the spots. (See
Bul. 106, Fla. Exp. Sta., 1911.)
Preventive.-The method of treatment for this disease will vary
according to the severity of the disease and the attitude of the grower
toward his grove, whether he be aiming for temporary results or be
willing to sacrifice present profits for future benefits. The various
lines of treatment found by experiment to be successful in controlling
the trouble may be summed up as follows:
1. Top-working to grapefruit or other resistant varieties.
2. Heading back and spraying with Bordeaux, followed by an,
insecticide.
3. Heading back and painting with carbolineum (half strength).
4. Pruning out dead wood.
5. Spraying the fruit with fungicides, followed by insecticides.
(For details under the five heads, see Bul. 106, Fla. Agr. Exp. Sta.,.
pp. 7-12, 1911.)





BULLETIN io8


SCAB (Cladosporium citri)
This disease, which is especially common on sour oranges and
lemons, makes its appearance on the fruit as irregular light brown or
corky projections from
the surface. It is caused
by a fungus which at-
tacks the fruit or leaves
when quite young. Its
attack on sour oranges
and lemons (and some-
times on Satsumas and
grapefruit) often results
in making them mis-
shapen and unsightly. In
severe attacks, projec-
tions of a dark gray to
corky or even tan color
will be seen extending
out from the surface. Fig. 20.-Scab on young oranges.
The surface of the fruit between the warts is usually of a normal color.
Often these irregular corky projections coalesce to form a large raised
corky scab. In less severe attacks, especially when scab occurs on grape-
fruit and on tangerines (or rarely on sweet oranges), the warty ir-
regular projections are wanting, and there will be seen more or less
raised platform-like patches variable in shape and extent (see Fig. 20).
The surface of the raised portion is finely scabbed or lightly scurfed, as
is seen in the case of thrips marks or silver scurf. In this milder form
it can usually be distinguished from thrips marks or other forms of
scurf, by its being raised, but can be distinguished with certainty only
by the use of the compound microscope.
Preventive.-The scab can be completely controlled by the use of
weak Bordeaux mixture (3-3-50). Since the use of Bordeaux on
orange trees, however, kills the friendly fungi and allows a rapid in-
crease of scale insects or whitefly, this spray is not recommended ex-
cept when it is absolutely necessary. When it must be resorted to, a
good insecticide should be used as soon as the scale insects begin to
increase rapidly. Some of the harm from increase of scale insects
may be prevented by spraying the Bordeaux as much as possible only
on the fruit, and keeping the spray off of the larger limbs and the
inside of the tree where the friendly fungi may be left alive.





42 FLORIDA AGRICULTURAL EXPERIMENT STATION

SPLITS
Splits are fruits in which the skin and rind have broken in a line,
exposing the interior of the fruit. They are caused by a development
of growth pressure within
the fruit accompanied by a
lack of expansion of the
skin and rind. This lack
of expansion is due either
to disease markings as in
the case of fruit marked by
dieback, or to a too early
maturity of the skin and
rind on account of unfav-
orable growth conditions.
The splitting occurs when
some point of weakness de-
velops in the skin and rind
that releases the pressure.
The conditions that bring M
on the growth pressure ,..
within the fruit are un-
known. tFig. 21.--Split, after chemical injury.
known.
A case of splitting occurred on fruit growing in the greenhouse.
The point of weakness in the rind was made by a chemical injury. (See
Fig. 21.) The tree on which the fruit grew had been watered daily
with a given amount during the period of development of the fruit.
It is observed that if heavy rains follow a period of drought in the
fall, the number of splits will be greatly increased. During the drought
the fruit is soft to the feel, indicating a lack of turgidity in the cells.
Following the rains, the fruit becomes quite solid, indicating a rapid in-
crease of liquid in the fruit.
Preventive.-Splitting is commonly associated with disease or
drought in the grove. The prevention of disease conditions will pre-
vent the splits that develop with these conditions. Drought conditions
in the grove can be avoided by the use of irrigation, and of cultivation
to conserve the moisture.
CREASING
Creasing is a form of splitting in which the peel breaks only par-
tially, the skin remaining whole and covering the break. It is easily
recognized by the feel, and can be followed with the eye by the depres-
sion of the skin along the line of break. The conditions causing creas-
ing are probably closely related to those causing splits. Creasing has





42 FLORIDA AGRICULTURAL EXPERIMENT STATION

SPLITS
Splits are fruits in which the skin and rind have broken in a line,
exposing the interior of the fruit. They are caused by a development
of growth pressure within
the fruit accompanied by a
lack of expansion of the
skin and rind. This lack
of expansion is due either
to disease markings as in
the case of fruit marked by
dieback, or to a too early
maturity of the skin and
rind on account of unfav-
orable growth conditions.
The splitting occurs when
some point of weakness de-
velops in the skin and rind
that releases the pressure.
The conditions that bring M
on the growth pressure ,..
within the fruit are un-
known. tFig. 21.--Split, after chemical injury.
known.
A case of splitting occurred on fruit growing in the greenhouse.
The point of weakness in the rind was made by a chemical injury. (See
Fig. 21.) The tree on which the fruit grew had been watered daily
with a given amount during the period of development of the fruit.
It is observed that if heavy rains follow a period of drought in the
fall, the number of splits will be greatly increased. During the drought
the fruit is soft to the feel, indicating a lack of turgidity in the cells.
Following the rains, the fruit becomes quite solid, indicating a rapid in-
crease of liquid in the fruit.
Preventive.-Splitting is commonly associated with disease or
drought in the grove. The prevention of disease conditions will pre-
vent the splits that develop with these conditions. Drought conditions
in the grove can be avoided by the use of irrigation, and of cultivation
to conserve the moisture.
CREASING
Creasing is a form of splitting in which the peel breaks only par-
tially, the skin remaining whole and covering the break. It is easily
recognized by the feel, and can be followed with the eye by the depres-
sion of the skin along the line of break. The conditions causing creas-
ing are probably closely related to those causing splits. Creasing has





BULLETIN 108


been found in abundance on trees showing a severe splitting of the
fruit. On the other hand, it is found independent of fruit splitting.
Preventive.-The remedy for creasing is essentially the same as that
recommended for splitting, but it seldom becomes so serious a trouble
as to require treatment.
Some of the most successful growers in the State who have been
troubled with this malady on their fruit have noticed that it disappears
after a large application of potash.

KNOTS IN THE RIND

Knots in the rind is a malady that affects both grapefruit and
oranges, but has not been found in other citrus fruits. The knots
show on the surface of the fruit as a slight raising of the skin, and
are easily identified by their hard feel. They are gum-infiltrated spots
in a thickened portion of the rind. Sometimes a gum pocket filled with
a clear gum will be found in them. Nothing is known as to their origin.
They occur in what are otherwise healthy fruit, and are surrounded by.
apparently perfectly healthy tissue.
Where the knots are very prevalent and well developed in the rind,
the market value of the fruit is affected. No method of treatment or
prevention has been developed, owing to lack of knowledge of the
factors that cause or influence the disease.
MECHANICAL INJURIES

Mechanical injuries are those markings on the fruit that are due
to wounds. They may
be grouped into two
classes: those made
when the fruit is young,
which show on the ma-
ture fruit as prominent
markings; and those in
which the mold fungi
gain entrance and cause '
a rotting of the fruit.
Superficial wounds
may heal or dry down
leaving a scar. If these
wounds are made when
the fruit is young, the
scar increases in size
with the growth of the
Fig. 22.-Result of wound made by
fruit. A grasshopper grasshopper on the young fruit.





BULLETIN 108


been found in abundance on trees showing a severe splitting of the
fruit. On the other hand, it is found independent of fruit splitting.
Preventive.-The remedy for creasing is essentially the same as that
recommended for splitting, but it seldom becomes so serious a trouble
as to require treatment.
Some of the most successful growers in the State who have been
troubled with this malady on their fruit have noticed that it disappears
after a large application of potash.

KNOTS IN THE RIND

Knots in the rind is a malady that affects both grapefruit and
oranges, but has not been found in other citrus fruits. The knots
show on the surface of the fruit as a slight raising of the skin, and
are easily identified by their hard feel. They are gum-infiltrated spots
in a thickened portion of the rind. Sometimes a gum pocket filled with
a clear gum will be found in them. Nothing is known as to their origin.
They occur in what are otherwise healthy fruit, and are surrounded by.
apparently perfectly healthy tissue.
Where the knots are very prevalent and well developed in the rind,
the market value of the fruit is affected. No method of treatment or
prevention has been developed, owing to lack of knowledge of the
factors that cause or influence the disease.
MECHANICAL INJURIES

Mechanical injuries are those markings on the fruit that are due
to wounds. They may
be grouped into two
classes: those made
when the fruit is young,
which show on the ma-
ture fruit as prominent
markings; and those in
which the mold fungi
gain entrance and cause '
a rotting of the fruit.
Superficial wounds
may heal or dry down
leaving a scar. If these
wounds are made when
the fruit is young, the
scar increases in size
with the growth of the
Fig. 22.-Result of wound made by
fruit. A grasshopper grasshopper on the young fruit.





44 FLORIDA AGRICULTURAL EXPERIMENT STATION

was noticed biting a fruit on a tree in the greenhouse. The fruit was
one and one-half inches in diameter, and the wound made was one-half
inch across. The fruit was allowed to develop. When it was almost
mature, the fruit was three inches in diameter, and the spot made by
the grasshopper was one and one-fourth inches across. The new skin
that developed over the wound had become scurfy, making the surface
resemble silver scurf. (See Fig. 22.)
An experiment of a similar nature to the grasshopper bite was
made by Mr. H. S. Fawcett of this Station in studying the nature of
silver scurf. He made a figure 4 on a young fruit by means of pin
scratches. He found that the figure increased in size with the develop-
ment of the fruit, the breadth of the scratches increased and a scurfi-
ness developed in the lines. Thus slight mechanical injuries made on
the fruit while small will become conspicuous by the time the fruit
attains maturity. Such marks seriously affect the market value of the
fruit, causing them to be classed low or as culls.
The fruit is subject to mechanical injury from the time it is picked
to the time it reaches the consumer. These wounds are nearly always
followed by a rotting of the fruit due to the different molds. (See
Blue Mold Rots, in this bulletin.)
Preventive.-The minute injuries made on the fruit during its prep-
aration for market cause the growers a loss of many thousands of
dollars every year. It has been demonstrated that these injuries can
be avoided. Use gloves on the hands whenever the fruit must be
touched. Handle the fruit with the greatest of care. See that all sur-
faces that touch the fruit are perfectly smooth and that all corners are
rounded. The fruit must be handled with as much care as a high
explosive.
(See article on "Preparing Citrus Fruits for Market," by W. C.
Temple, in the Proceedings of the Florida State Horticultural Society,
1911.)

BLUE MOLD ROT (Penicillium italicumn and Pc',- .i'.;. digitatum)

This is the most prevalent kind of rot in citrus fruits of all kinds.
It begins as a softening and decay at any point on the rind that has
been punctured, scratched, or injured in any way. It almost never ap-
pears as long as the rind is perfectly sound and uninjured.
The skin on the softened area becomes extremely soft and weak,
and is covered first with a white mold, which later produces a blue-
green or olive-green powdery layer of spores, giving off a smoky dust
when disturbed.
There are two closely related fungi, either one of which is able to





BULLETIN 1o8


produce the rot known as "blue mold" of citrus fruits, and quite often
the two species are found together in the same decayed fruit. These
two forms may be distinguished as follows: (1) Penicillium italicum
is blue-green in color; and Penicillium digitatum is olive-green as seen
after producing spores. (2) Penicillium italicum produces a patch of
blue-green with only a narrow edge of white in the center of a much
larger softened area not molded; while Penicillium digitatum produces
white surface mold nearly to the extreme edges of the softened area
as fast as the decay proceeds, and an olive-green patch begins at the
center and enlarges.
Preventive.-Since the blue mold follows injuries to fruits, it may
be largely prevented by extreme care in picking, handling and packing.
The wounds through which the blue mold fungus is able to cause
decay must be guarded against all along the line, from the time the fruit
is being picked until it is loaded into the cars. Clipper cuts, long stems,
fingernail scratches, and bruises from pouring into the field boxes,
are to be avoided. In hauling, the injuries from splinters and rough
edges in the boxes, bruises from the bottom of one box being in con-
tact with the top fruit of the box below, and bruises from the jostling
of the fruit over a rough road, or in wagons without springs, should
be avoided. At the packing house, the further injuries that may result
from rough handling, as careless emptying of the field crate from too
great a height, and sharp corners of the machinery in washing, sizing
and packing, are to be constantly guarded against. Poorly constructed
washers, sizers and bins in such a position that the fruit is put into too
violent motion, are to be avoided. In wrapping and packing, finger-
nail scratches are to be avoided by wearing gloves. (See Mechanical
Injuries.) Not only must the slight injuries to the fruit be guarded
against at every turn, but the field boxes, wagons, packing houses, and
all machinery should be kept clean and free from contamination with
blue mold spores from rotted fruits lying about. Packing houses in
which culls or other inferior and worthless fruit are permitted to remain
for even a part of a day, are pretty certain to become badly contam-
inated with blue mold spores. These invisible spores are carried to all
parts of the structure by means of the ordinary air currents. Groves
in which drops are allowed to remain also become permeated with
these spores. Under the conditions which ordinarily prevail, it is al-
most literally true to say that blue mold spores occur everywhere.
STEM-END ROT (Phomopsis sp.)
Like anthracnose this disease makes its presence evident by an
unusual amount of dropping. This rot begins in a circular patch about
the stem end. At first the circular area is light brown or very little





46 FLORIDA AGRICULTURAL EXPERIMENT STATION

discolored on mature fruit, but dark brown to leather colored on im-
mature fruit on the tree.
The rind remains fairly
firm at first, and the dis-

from the stem end in a
more or less uniform circle,
and does not extend in
bands. (See Fig. 23.) It
causes a slow, and at first
only slight, discoloration of
the center and inner peel
and partitions, and the juice
sacs often remain unaffect-
ed for some time. The Fig. 23.-Stem-end Rot on grapefruit.
fruits, when entirely decayed, still keep their form more or less, but
do not turn black until dried up. This rot is caused by a species of
fungus hitherto undescribed. It attacks all varieties of citrus fruits,
and appears to gain entrance chiefly at the stem end. It is most de-
structive when accompanied by scale insects under the calyx next to
the stem.
Preventive.-The recommendations based on experiment and ob-
servation during two seasons may be summarized as follows:
(1.) Pruning out and destruction of dead and diseased branches.
(2.) The removal and destruction of all dropped and decayed
fruits.
(3.) Care at all stages of picking and handling to avoid infection
from the fungus.
(4.) Keeping fruit at low temperature in transit and in storage.
(5.) Spraying with insecticides to keep scale insects from at-
tacking fruit.
(See'Bul. 107, Fla. Agr. Exp. Sta., 1911.)
DIPLODIA ROT (Diplodia natalensis).
In the early stage this rot shows as a patch about the stem end
similar to stem-end rot. The discoloration becomes darker as the decay
proceeds, and appears as dark wide bands corresponding to the divi-
sions between the segments. The fruit becomes black as the decay
advances and very light in weight. The rot often advances quickly
through to the "blossom" end, and a patch of discoloration shows
there before all the peel is involved. The Diplodia rot often starts
also in thorn punctures or similar injuries. It is usually accompanied
by the exudation of a small amount of thin gum, or a considerable





BULLETIN 1o8


amount of amber-colored sticky juice. This amber-colored juice less
frequently accompanies the stem-end rot. Many of the characteristics
of the two rots are so similar that for practical purposes they may be
classed together. The citrus fruits are much more resistant to Diplodia
rot than to stem-end rot. Diplodia rot.appears to be less common on
immature fruits on the tree, and the fungus causing it is less parasitic.
Preventive.-The same line of treatment given for stem-end rot
holds good for Diplodia rot.

BLACK ROT (Alternaria citri).
This rot begins at the blossom (or stylar) end, especially in navel
oranges, but sometimes in other varieties if there be a defect at the
blossom end. The fruit attacked ripens prematurely with a deep red
color. This decay causes a blackening along the central core of the
fruit where the segments meet and does not soften the fruit so rapidly
as the previous rots. The decay is more confined to the interior of
the fruit and is darker in color. The fungus enters by means of slight
imperfections at the blossom end, and produces most of the decay
under the skin. All diseased fruits should be destroyed.




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