• TABLE OF CONTENTS
HIDE
 Copyright
 Front Cover
 Table of Contents
 Summary
 Introduction
 Melanose
 Cause of melanose
 Stem-end rot






Group Title: Bulletin - University of Florida. Agricultural Experiment Station - no. 111
Title: Melanose and stem-end rot
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027738/00001
 Material Information
Title: Melanose and stem-end rot
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Alternate Title: Melanose and stem end rot
Physical Description: 16 p. : ill. ; 23 cm.
Language: English
Creator: Floyd, B. F ( Bayard F )
Stevens, H. E ( Harold Edwin ), b. 1880
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1912
 Subjects
Subject: Fungal diseases of plants   ( lcsh )
Citrus -- Diseases and pests   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by B.F. Floyd and H.E. Stevens.
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station) ;
 Record Information
Bibliographic ID: UF00027738
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: aleph - 000921865
oclc - 18160463
notis - AEN2333

Table of Contents
    Copyright
        Copyright
    Front Cover
        Page 1
    Table of Contents
        Page 2
    Summary
        Page 2
    Introduction
        Page 3
    Melanose
        Page 4
        Distribution of melanose
            Page 4
        Nature of melanose
            Page 4
        Appearance of melanose
            Page 5
        Effects of melanose
            Page 6
        Relation to growth conditions
            Page 7
        Comparison with other diseases
            Page 8
    Cause of melanose
        Page 8
        Culture experiments
            Page 9
            Page 10
            Page 11
        The fungus and its habits
            Page 12
        Surface injury from the fungus
            Page 13
    Stem-end rot
        Page 14
        Description of stem-end rot
            Page 14
        Conditions favoring stem-end rot
            Page 15
        Injury from the fungus
            Page 15
        Control measures
            Page 15
            Page 16
Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida





DECEMBER, 1912


UNIVERSITY OF FLORIDA


Agricultural Experiment Station




MELANOSE AND STEM-END ROT

BY

B. F. FLOYD AND H. E. STEVENS

S 4


Fig. 1.-Grapefruit with Melanose streaking.



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


Pepper Pub. & Ptg. Co Gainesville, Fla.


BULLETIN III
















CONTENTS
PAGE
Introduction .--------------------------------------------- -- -------- 3
Melanose-------------- ------- 4
Distribution of Melanose ------------ --- --- ------------------ 4
Nature of Melanose .-------------.. -------------------------------- 4
Appearance of Melanose ---------------.-----------.- ------------- 5
Effects of Melanose ----------------------------------------------- 6
Relation to Growth Conditions ------.-- --- ----------------- 7
Comparison with other Diseases----------------------------------- 8
Cause of Melanose ..---------------..____- ------..------------------- 8
Culture Experiments -------------------------------------------- 9
Infection Experiments __---- --- --------_.--. --------------- 9
The Fungus and its Habits .------_---- ----------------------------- 12
Surface Injury from the Fungus ---------- ----- 13
Stem-End Rot -------------------- ----------..--------------- 14
Description of Stem-End Rot------- ------------------------------14
Conditions favoring Stem-End Rot-------------------------------- 15
Injury from the Fungus____ _-.------------------------------------- 15
Control Measures _---------------__.-------------------------------- 15




SUMMARY
1. Melanose and Stem-End Rot are caused by the same fungus.
2. Up to the present time this fungus has been found to produce spores only on
dead wood and mummied fruits.
3. The principal source of infection seems to be the dead branches and sprigs,
4. Melanose, whether on the leaves, the young shoots, or the fruits, seems to be
incapable of spreading the disease.
5. Bordeaux mixture and ammoniacal solution of copper carbonate prevented
Melanose, but they did not prevent StemEnd Rot.
6. Disinfectants, used in the washing tank or after the fruit comes from the
washer, have not proved effective in preventing Stem-End Rot.
7. Scale insects at the stem-end of the fruit, an exceptionally warm fall or winter,
and humid and shady situations, appear to favor Stem-End Rot.
8. The most effective method of controlling both diseases would seem to be a
thorough pruning out of all dead and diseased wood, including twigs.
















CONTENTS
PAGE
Introduction .--------------------------------------------- -- -------- 3
Melanose-------------- ------- 4
Distribution of Melanose ------------ --- --- ------------------ 4
Nature of Melanose .-------------.. -------------------------------- 4
Appearance of Melanose ---------------.-----------.- ------------- 5
Effects of Melanose ----------------------------------------------- 6
Relation to Growth Conditions ------.-- --- ----------------- 7
Comparison with other Diseases----------------------------------- 8
Cause of Melanose ..---------------..____- ------..------------------- 8
Culture Experiments -------------------------------------------- 9
Infection Experiments __---- --- --------_.--. --------------- 9
The Fungus and its Habits .------_---- ----------------------------- 12
Surface Injury from the Fungus ---------- ----- 13
Stem-End Rot -------------------- ----------..--------------- 14
Description of Stem-End Rot------- ------------------------------14
Conditions favoring Stem-End Rot-------------------------------- 15
Injury from the Fungus____ _-.------------------------------------- 15
Control Measures _---------------__.-------------------------------- 15




SUMMARY
1. Melanose and Stem-End Rot are caused by the same fungus.
2. Up to the present time this fungus has been found to produce spores only on
dead wood and mummied fruits.
3. The principal source of infection seems to be the dead branches and sprigs,
4. Melanose, whether on the leaves, the young shoots, or the fruits, seems to be
incapable of spreading the disease.
5. Bordeaux mixture and ammoniacal solution of copper carbonate prevented
Melanose, but they did not prevent StemEnd Rot.
6. Disinfectants, used in the washing tank or after the fruit comes from the
washer, have not proved effective in preventing Stem-End Rot.
7. Scale insects at the stem-end of the fruit, an exceptionally warm fall or winter,
and humid and shady situations, appear to favor Stem-End Rot.
8. The most effective method of controlling both diseases would seem to be a
thorough pruning out of all dead and diseased wood, including twigs.











MELANOSE AND STEM-END ROT
(Phomopsis citri Fawcett)

BY B. F. FLOYD AND H. E. STEVENS.


The information contained in this bulletin is the result of in-
dependent investigations carried on by B. F. Floyd, plant physi-
ologist, and H. E. Stevens, plant pathologist. Since the two dis-
eases are produced by the same cause, it was thought proper also
to include certain parts of Bulletin 107 on Stem-End Rot, by H.
S. Fawcett. Some of the illustrations are taken from that bulle-
tin. Work on these diseases is being continued, to ascertain un-
known facts, and to make practicable the application in the grove
of the facts already known. Further experiments are necessary
to clear up some doubtful points. However, it is believed that
the methods for prevention outlined herein will, if strictly fol-
lowed, aid materially in preventing these diseases.
Although Melanose and Stem-End Rot are caused by the
same fungus, they differ as to the frequency of their occurrence.
The trees are subject to Melanose during a comparatively long
time. Whenever there is a flush of growth, it is susceptible until
it hardens; this occurs several times during the season, from
early spring until fall. The fruit is susceptible from the time
the petals drop until late summer or early fall. With the fungus
present, and the recurring conditions favorable for infection,
Melanose may occur not only once but several times during the
growing season. On the other hand, Stem-End Rot occurs only
when the fruit is nearly mature or quite mature. This period
is comparatively short. Infection will occur only when the
fruit has been weakened by some cause (such as scale insects
around the calyx), and when the conditions are also favorable
for the growth of the fungus. This combination of circum-
stances does not occur every year during the period when the
fruit is nearly or quite mature. Thus Stem-End Rot is of less
frequent occurrence than Melanose.
Again, the two diseases differ as to the amount of damage
they cause. Melanose is only a superficial marking, and its
chief injury is the unsightliness that it produces. But owing
to its frequent occurrence the total damage amounts to many
thousands of dollars. On the other hand, Stem-End Rot pro-
duces a rotting of the matured or nearly matured fruit in the
grove, in transit, and in storage. This loss is felt keenly by
the grower; but in total it cannot be compared to the loss from
Melanose because of its less frequent occurrence.






4 Florida Agricultural Experiment Station
MELANOSE.
DISTRIBUTION OF MELANOSE.
Melanose is a disease of citrus trees. It occurs in nearly
all citrus-growing communities in the State. Few groves are
absolutely free from the disease, yet it is serious only in cer-
tain groves. Melanose is not confined to Florida. What ap-
pears to be the same disease has been reported from other
countries. It is reported from Australia by Cobb (Agricul-
tural Gazette of New South Wales, VII, No. 4, pp. 225-228),
and McAlpine (Fungus Diseases of Citrus Trees in Australia,
and their Treatment; Department of Agriculture, Vict9ria,
1899), and is considered a serious disease there. It also occurs
in Jamaica, Porto Rico, and Algeria.
The disease was first discovered in Florida by Webber and
Swingle at Citra, in 1892, (Principal Diseases of Citrus Fruits
in Florida. Div. Veg. Phys. and Path., U. S. Dep. Agr., Bull. 8).
They later found it to occur at Ocala, Stanton, and Sanford.
They concluded that it was of recent origin and local in its dis-
tribution, but was spreading rapidly. They were unable to de-
termine the cause, but predicted it to be some minute vegetable
parasite. In 1907, the senior author began a study of Melanose
from a physiological point of view. His experiments and mi-
croscopical studies led to the conclusion that it was not a physi-
ological disease (Florida Agr. Exp. Sta. Report for 1911, p.
lxxii). In the spring of 1912, a study of the disease was started
in co-operation with the plant pathologist, who speedily discov-
ered the cause of Melanose to be the fungus which also causes
the Stem-End Rot of citrus fruits.
NATURE OF MELANOSE.
Melanose has been observed on nearly all varieties of citrus
fruits. None have been found that are particularly immune.
The markings of the disease show so prominently on grapefruit
that it is sometimes thought to be more susceptible; but neither
observations nor experiments have proved this to be the case.
The leaves, stems, and fruit are the parts affected; but these
are attacked only while they are young and succulent. A flush
of growth is susceptible to attack from the time it is put out
until after the time it has attained its full growth in size, but
not when it has begun to harden. The fruit is susceptible from
the time the petals fall until it is approaching its full size. Ma-
tured tissues are never attacked anew. This information is
important in determining the proper time to spray to prevent
the disease.
The marks made by the disease are a part of the plant tissue
itself and cannot be washed or scraped off, nor can the marks be
made to disappear by any method of treatment. Therefore
the disease can be controlled only by methods that will prevent






4 Florida Agricultural Experiment Station
MELANOSE.
DISTRIBUTION OF MELANOSE.
Melanose is a disease of citrus trees. It occurs in nearly
all citrus-growing communities in the State. Few groves are
absolutely free from the disease, yet it is serious only in cer-
tain groves. Melanose is not confined to Florida. What ap-
pears to be the same disease has been reported from other
countries. It is reported from Australia by Cobb (Agricul-
tural Gazette of New South Wales, VII, No. 4, pp. 225-228),
and McAlpine (Fungus Diseases of Citrus Trees in Australia,
and their Treatment; Department of Agriculture, Vict9ria,
1899), and is considered a serious disease there. It also occurs
in Jamaica, Porto Rico, and Algeria.
The disease was first discovered in Florida by Webber and
Swingle at Citra, in 1892, (Principal Diseases of Citrus Fruits
in Florida. Div. Veg. Phys. and Path., U. S. Dep. Agr., Bull. 8).
They later found it to occur at Ocala, Stanton, and Sanford.
They concluded that it was of recent origin and local in its dis-
tribution, but was spreading rapidly. They were unable to de-
termine the cause, but predicted it to be some minute vegetable
parasite. In 1907, the senior author began a study of Melanose
from a physiological point of view. His experiments and mi-
croscopical studies led to the conclusion that it was not a physi-
ological disease (Florida Agr. Exp. Sta. Report for 1911, p.
lxxii). In the spring of 1912, a study of the disease was started
in co-operation with the plant pathologist, who speedily discov-
ered the cause of Melanose to be the fungus which also causes
the Stem-End Rot of citrus fruits.
NATURE OF MELANOSE.
Melanose has been observed on nearly all varieties of citrus
fruits. None have been found that are particularly immune.
The markings of the disease show so prominently on grapefruit
that it is sometimes thought to be more susceptible; but neither
observations nor experiments have proved this to be the case.
The leaves, stems, and fruit are the parts affected; but these
are attacked only while they are young and succulent. A flush
of growth is susceptible to attack from the time it is put out
until after the time it has attained its full growth in size, but
not when it has begun to harden. The fruit is susceptible from
the time the petals fall until it is approaching its full size. Ma-
tured tissues are never attacked anew. This information is
important in determining the proper time to spray to prevent
the disease.
The marks made by the disease are a part of the plant tissue
itself and cannot be washed or scraped off, nor can the marks be
made to disappear by any method of treatment. Therefore
the disease can be controlled only by methods that will prevent






4 Florida Agricultural Experiment Station
MELANOSE.
DISTRIBUTION OF MELANOSE.
Melanose is a disease of citrus trees. It occurs in nearly
all citrus-growing communities in the State. Few groves are
absolutely free from the disease, yet it is serious only in cer-
tain groves. Melanose is not confined to Florida. What ap-
pears to be the same disease has been reported from other
countries. It is reported from Australia by Cobb (Agricul-
tural Gazette of New South Wales, VII, No. 4, pp. 225-228),
and McAlpine (Fungus Diseases of Citrus Trees in Australia,
and their Treatment; Department of Agriculture, Vict9ria,
1899), and is considered a serious disease there. It also occurs
in Jamaica, Porto Rico, and Algeria.
The disease was first discovered in Florida by Webber and
Swingle at Citra, in 1892, (Principal Diseases of Citrus Fruits
in Florida. Div. Veg. Phys. and Path., U. S. Dep. Agr., Bull. 8).
They later found it to occur at Ocala, Stanton, and Sanford.
They concluded that it was of recent origin and local in its dis-
tribution, but was spreading rapidly. They were unable to de-
termine the cause, but predicted it to be some minute vegetable
parasite. In 1907, the senior author began a study of Melanose
from a physiological point of view. His experiments and mi-
croscopical studies led to the conclusion that it was not a physi-
ological disease (Florida Agr. Exp. Sta. Report for 1911, p.
lxxii). In the spring of 1912, a study of the disease was started
in co-operation with the plant pathologist, who speedily discov-
ered the cause of Melanose to be the fungus which also causes
the Stem-End Rot of citrus fruits.
NATURE OF MELANOSE.
Melanose has been observed on nearly all varieties of citrus
fruits. None have been found that are particularly immune.
The markings of the disease show so prominently on grapefruit
that it is sometimes thought to be more susceptible; but neither
observations nor experiments have proved this to be the case.
The leaves, stems, and fruit are the parts affected; but these
are attacked only while they are young and succulent. A flush
of growth is susceptible to attack from the time it is put out
until after the time it has attained its full growth in size, but
not when it has begun to harden. The fruit is susceptible from
the time the petals fall until it is approaching its full size. Ma-
tured tissues are never attacked anew. This information is
important in determining the proper time to spray to prevent
the disease.
The marks made by the disease are a part of the plant tissue
itself and cannot be washed or scraped off, nor can the marks be
made to disappear by any method of treatment. Therefore
the disease can be controlled only by methods that will prevent





Bulletin 111 5
the marks being made. The marks remain on
the leaves and fruit throughout their life, but
S those on the stems (see Fig. 2) remain only until
the true bark is formed, after which they are
sloughed off. For this reason, the symptoms of
S the disease are never found on the trunk, or on
stems more than two years old.
i APPEARANCE OF MELANOSE.
The marks produced by the fungus are near-
ly the same on the leaves, stems, and fruit.
They consist of raised areas of brown gum-filled
cells, forming dots, lines, curves, rings, and ir-
regularly shaped spots. The curves and rings
4' j (see Fig. 3) are valuable as a diagnostic charac-
ter, as they are only known to occur in connec-
S tion with this disease. Lines of breakage may
S' develop around the margins and across the sur-
"". .- faces, giving an appearance like dry cracked
....-' mud. Sometimes a slight peeling will occur, and
the surface then has a flaky appearance. The
markings may be distributed promiscuously over
Fig. 2 -Melanose the surface of the affected parts, or they may be
markings on stem arranged in streaks following the line of grav-
ity (see Fig. 1). This streaking, which is sometimes referred
to as "tear streaking," is produced by the fungus spores in
water that drips from some overhanging dead sprig that har-
bors the fungus. The markings have a wax-like appearance,
and vary from yellow to brown or black. They are frequently
spoken of as resembling
little drops or masses of
partly burnt sugar. But -
the sheen is dull and not
glossy. They give a
russet appearance to the -- _
affected part. Owing to ,.-"
their raised position they
produce a roughness that
is like sand-paper to the .. '
touch. 9.
The origin of the mark- :
ings is in an injury to the
epidermal and sub-epi-
dermal cells, whereby the
cells are killed and be-
come filled with a homo-
geneous gum-like sub-
stance. This substance
determines the color of Fig. 3.-Melanose, showingllooped rows of
determines the color markings.
the spots. It probably is a
mixed gum and is insoluble in water. It is apparently a product





6 Florida Agricultural Experiment Station
of the protoplasm, collected in the vacuole. The cell-walls re-
main intact. Before the accumulation of the material in the
cells becomes too great, the nucleus can still be seen, and is ap-
parently in an active condition. In late stages the protoplasm
is dead.
In the early stages
the injured areas are
slightly depressed (see
Fig. 4). This depres- ." '.."P
sion is caused by the
shrinking of the in- "a
jured cells. But in the
later stages the injured
cells are raised above
the surrounding sur-
face by the develop-
ment of a corky tissue"
beneath (see Fig. 5),
and the marks are com-
plete. .
Particles of fungus
hyphae can sometimes
be distinguished in the
affected tissue. But it Fig. 4.-Early stage of Melanose marking,
has not been demon- showing depressed area. (Much magnified.)
strated whether these are parts of the causal organism, or
are accidental.








' "t ', "' "




.. ,
-- _.I-. -- .. I. _.

: *y ... C b.- *
Fig. 5.-Section of Melanose spot, with unbroken epidermis.
(Much magnified.)
EFFECTS OF MELANOSE.
The markings produced by the fungus are superficial, seldom
extending to a greater depth than five or six cell-layers beneath





Bulletin 111 7
the epidermis. Therefore, the direct injury is confined to the
growth and functioning of the epidermal and sub-epidermal tis-
sues. The parts affected are seldom killed. However, excep-
tions have been noticed in cases where the terminal growth was
very young and the infection severe.
From a practical standpoint the greatest injury done by the
markings is to the fruit. If they are plentiful while the fruit is
young, it is likely to be stunted and weakened. Under adverse
conditions, these fruits will be amongst the first to fall. If the
fruit develops to maturity, the russet appearance either makes
it unsalable or classes it in the lower grades.
The effect of Melanose upon the leaves and stems is to re-
duce their working ability by closing up the breathing pores
and disturbing the normal cellular activity in these regions.
RELATION TO GROWTH CONDITIONS.
The occurrence of Melanose has no direct relation to either
soil, or such soil conditions as moisture and plant food. Trees
planted on high pine-land and on hammock land are equally af-
fected; those on dry soils are affected as much as those on wet
soils; and the disease is as prevalent in well fed groves as in
neglected ones. But the disease has been noted by observation
and proved by experiment to have a direct relation to the pres-
ence of dead wood in the tree. The reason for this is that the
markings are produced by a fungus that lives in dead wood.
Therefore conditions that lead to the production of dead wood,
and conditions that affect the growth of the fungus necessarily
affect Melanose. One such growth condition is temperature.
Low temperatures affect the disease by the production of dead
wood that affords a place for the growth and reproduction of
the causal organism. The disease has been noticed to be worse
in the growing seasons following severe winters. The older
growers in the State report it to have been very injurious the
year following the freeze of 1895. It was more prevalent in
the northern portion of the citrus belt in the spring following
the cold winter of 1909-10 than in the southern part.
Conditions favorable to the growth and distribution of the
fungus that produces the markings are warm temperatures and
moisture in the air. Moisture in the form of heavy dews or
rain encourages the growth of the fungus, putting it into an ac-
tive condition whereby it is able to produce the markings. The
trickling of rain or dewdrops spreads the fungus from its seat
of growth in the dead wood to the parts susceptible to injury.
Therefore, given dead wood harboring the fungus, and young
succulent growth in the trees, accompanied by warm moist condi-
tions (such as heavy dews or rain), and Melanose is pretty cer-
tain to follow. Of course, Melanose does not occur unless the
fungus that causes it is present in the dead wood, but this fungus
appears to be so widely distributed that it is present in nearly
every grove. The growing season of 1912 has been marked by
heavy rains. Coincident with this there has been a marked
increase in the distribution and prevalence of Melanose.





8 Florida Agricultural Experiment Station
COMPARISON WITH OTHER DISEASES.
Melanose has certain resemblances to phases of other citrus
diseases that often lead to mistakes in identification. Such dis-
eases are Dieback, Scab, and Yellow Spotting of citrus leaves.
The gum-like deposits in the affected cells of Melanose are
similar to those of the "ammoniated" fruits and stained termi-
nal branches of trees affected with Dieback. But in Dieback,
these marks are not sharply raised, hence the surface of the
affected part does not have the "sand-paper" feeling. The Die-
back markings are likely to be glossy, whereas Melanose mark-
ings are of a dull appearance. Sometimes fruits slightly affected
by Dieback are marked with Melanose. In such cases, the Mela-
nose markings are more highly raised, and sometimes in be-
tween them may be seen the glossy unraised stained surface of
Dieback.
The marks caused by the citrus-scab fungus, Cladosporium
citri Massee, are raised, and are usually more prominent than
Melanose markings. But they seldom have the appearance charac-
teristic of Melanose spots. Again, the sweet orange is almost
immune to Scab, but is quite susceptible to Melanose. Grape-
fruit may be affected by both, but is much less frequently at-
tacked by Scab. Melanose is more likely to be confused with
Scab in its early stages than with any other disease. The rea-
son for this is that both diseases affect the same trees, at about
the same time, and in a somewhat similar manner.
The spots on the under surfaces of leaves affected with Yel-
low Spotting often develop a Melanose-like appearance at ma-
turity; but they can be distinguished from Melanose because
these spots extend entirely through the leaf and show on the
upper surface.
CAUSE OF MELANOSE.
Melanose is caused by Phomopsis citri Fawcett, the same
fungus that causes Stem-End Rot in citrus fruits. This fact
has been recently demonstrated by numerous infection experi-
ments with spores from pure cultures of the fungus. It seems
as if only the spores (and possibly the paraphyses) are capable
of producing Melanose spotting. No spotting has yet resulted
by using the vegetative portion or mycelium of this fungus in
infecting young tissue. When the spores come in contact with
young succulent tissue and sufficient moisture is present, Mela-
nose spotting results in four to five days.
The close relationship between Melanose and Stem-End Rot
was not at first suspected. The fungus, Phomopsis citri, had been
previously described as the cause of Stem-End Rot (Fla. Agr.
Exp. Sta. Bul. 107, 1911). It was found abundantly in the dead
twigs and branches collected from Melanose-infected trees, but
it was not then anticipated that this fungus might also be the
cause of Melanose. This connection was only established after
numerous infection experiments had been tried, and a careful
study made of the dead twigs. The fact that Melanose and
Stem-End Rot are both caused by the same fungus should mean
much to the citrus grower. This fungus is capable of producing





8 Florida Agricultural Experiment Station
COMPARISON WITH OTHER DISEASES.
Melanose has certain resemblances to phases of other citrus
diseases that often lead to mistakes in identification. Such dis-
eases are Dieback, Scab, and Yellow Spotting of citrus leaves.
The gum-like deposits in the affected cells of Melanose are
similar to those of the "ammoniated" fruits and stained termi-
nal branches of trees affected with Dieback. But in Dieback,
these marks are not sharply raised, hence the surface of the
affected part does not have the "sand-paper" feeling. The Die-
back markings are likely to be glossy, whereas Melanose mark-
ings are of a dull appearance. Sometimes fruits slightly affected
by Dieback are marked with Melanose. In such cases, the Mela-
nose markings are more highly raised, and sometimes in be-
tween them may be seen the glossy unraised stained surface of
Dieback.
The marks caused by the citrus-scab fungus, Cladosporium
citri Massee, are raised, and are usually more prominent than
Melanose markings. But they seldom have the appearance charac-
teristic of Melanose spots. Again, the sweet orange is almost
immune to Scab, but is quite susceptible to Melanose. Grape-
fruit may be affected by both, but is much less frequently at-
tacked by Scab. Melanose is more likely to be confused with
Scab in its early stages than with any other disease. The rea-
son for this is that both diseases affect the same trees, at about
the same time, and in a somewhat similar manner.
The spots on the under surfaces of leaves affected with Yel-
low Spotting often develop a Melanose-like appearance at ma-
turity; but they can be distinguished from Melanose because
these spots extend entirely through the leaf and show on the
upper surface.
CAUSE OF MELANOSE.
Melanose is caused by Phomopsis citri Fawcett, the same
fungus that causes Stem-End Rot in citrus fruits. This fact
has been recently demonstrated by numerous infection experi-
ments with spores from pure cultures of the fungus. It seems
as if only the spores (and possibly the paraphyses) are capable
of producing Melanose spotting. No spotting has yet resulted
by using the vegetative portion or mycelium of this fungus in
infecting young tissue. When the spores come in contact with
young succulent tissue and sufficient moisture is present, Mela-
nose spotting results in four to five days.
The close relationship between Melanose and Stem-End Rot
was not at first suspected. The fungus, Phomopsis citri, had been
previously described as the cause of Stem-End Rot (Fla. Agr.
Exp. Sta. Bul. 107, 1911). It was found abundantly in the dead
twigs and branches collected from Melanose-infected trees, but
it was not then anticipated that this fungus might also be the
cause of Melanose. This connection was only established after
numerous infection experiments had been tried, and a careful
study made of the dead twigs. The fact that Melanose and
Stem-End Rot are both caused by the same fungus should mean
much to the citrus grower. This fungus is capable of producing





Bulletin 111 9
two phases of disease very different from one another in ex-
ternal appearance and character, and serious damage to the
fruit may be caused by either form. The fungus is active nearly
the entire year. Melanose may occur at any time when new
growth is present. Stem-End Rot usually occurs when the fruit
is approaching maturity, or after it is picked and shipped. Thus
the appearance of a heavy Melanose infection in the spring
should serve as a warning that the Stem-End Rot fungus is pres-
ent, and the grower should be prepared to take the necessary
precautions to prevent a probable outbreak of Stem-End Rot
later in the season.
CULTURE EXPERIMENTS.
As a preliminary to the culture work on this disease, a care-
ful study was made of the Melanose spots on leaves, twigs, and
fruits. Numerous specimens were collected showing the spots
in various stages of development. Microscopical examinations
were made of these, but in no case was a fungus or a bacterial
organism found connected with the spots which could be consid-
ered a cause of the disease. Occasionally superficial mycelia
or isolated spores were found associated with some of the older
spots, but they were apparently saprophytic or accidental forms,
and bore no direct relation to the spots themselves. The cracked
and open nature of the infected areas allows an easy entrance
to saprophytic fungi and a convenient place where spores may
lodge. Stained sections of diseased tissues failed to show the
presence of fungus growth within the affected or adjoining cells.
Attempts were then made to isolate an organism from the
spots by the use of culture media. Cultures were made under
aseptic conditions in standard peptone agar, prune juice, and
standard bouillon. The diseased tissue was first soaked in mer-
curic chloride solution, 1-1000, from three to five minutes;
washed thoroughly in sterile water; and the spots removed
and transferred to the different culture media. Growth was
usually obtained in all these cultures in from twenty-four to
forty-eight hours of incubation at room temperature (80 deg.
F.). In nearly every case only Colletotrichum appeared in the
cultures. The presence of this fungus was regarded as acci-
dental and not as a cause of the spotting, since Colletotrichum
is widely distributed and prevalent in nearly every locality, and
the injuries caused by this fungus are different from Melanose.
In a short time Colletotrichum overran the cultures, and this
made it impossible to isolate any other fungus that might have
been present. Repeated attempts with cultures failed to give
satisfactory results, and experiments were begun along another
line.
INFECTION EXPERIMENTS.
Attention was next directed to the dead wood in the trees.
It had been noted before that there seemed to be a close rela-
tion between the presence of dead twigs and dead branches in the
trees and the extent of Melanose infection (Fla. Agr. Exp. Sta.
Report for 1911, p. lxxx). Observations were made on a num-
ber of orange and grapefruit trees in a grove where Melanose





10 Florida Agricultural Experiment Station
spotting was very heavy. It was found that just beneath a
cluster of dead twigs a heavier spotting of leaves and fruit oc-
curred. In many cases this was so evident that dead twigs
were readily located by the heavy spotting of the foliage just
beneath. It was also noted that the spotting of leaves and fruit
was relatively less near the tops of the trees. The streaked and
tear-stained appearance of badly infected leaves and fruit strong-
ly suggested that the infection was washed down by rain or dew.
Some dead twigs and branches were collected from an orange
tree just above a badly spotted area of foliage. This dead wood
was brought to the laboratory and carefully examined. A num-
ber of different species of fungi were found. Phomopsis citri
was found in abundance, and two undetermined species were
present in sufficient quantities to attract attention. Numerous
saprophytic species were also found.
Some experiments were tried with this dead wood to see
if the infection could be transferred to new citrus growth. A
number of small orange trees in pots were selected in the green-
house, and their tops were pruned back. In the coarse of five
or six weeks new shoots, five or six inches in length, developed
on these. Two trees were selected from the lot and treated as
follows. A small bundle was made from the twigs previously
collected. This was suspended above one of the trees just over
the young shoots. Sterile water was then sprayed on this bun-
dle from an atomizer, and the drippings were allowed to trickle
down over the shoots until they were thoroughly drenched. The
second tree was treated in the same manner, receiving the drip-
pings from the same bundle. One tree was covered with a bell-
jar for thirty-six hours to conserve the moisture. The other
was left uncovered. At the end of five days, characteristic
Melanose spotting had developed on the shoots of the tree placed
under the bell-jar. No spotting developed on the tree that was
not covered. This experiment was repeated, and it was evi-
dent that the cause of the spotting came from the dead twigs.
In each case where young shoots were so treated and kept under
moist conditions for twenty-four hours, Melanose spots appeared
in four or five days. It was also found that by soaking the dead
twigs in sterile Water for an hour or two, and then spraying
this water on young orange shoots, similar spotting was pro-
duced.
The above experiments proved that the cause of the spotting
came from the dead wood, and to determine whether this spot-
ting was due to some toxic principle, or to some parasitic organ-
ism, was the next step. Experiments were tried with this ob-
ject in view. Washings were made from a quantity of dead
twigs, and the liquid divided into three parts. One part was
filtered through a Berkefeld filter to remove the fungus spores
and bacteria. A second part was filtered through heavy filter-
paper to exclude the fungus spores but allow the bacteria to pass.
The third part was not filtered. Agar plate-cultures were made
from each of the three. Three potted orange trees with young
shoots were selected. The unfiltered liquid was sprayed on





Bulletin 111 11
one tree: the filtrate from the filter-paper on a second; and the
filtrate from the Berkefeld filter on the third. Each tree was
covered with a bell-jar for twenty-four hours. At the end of
four days, a heavy Melanose spotting was produced on the young
shoots sprayed with the unfiltered washings. No spotting oc-
curred on the two trees sprayed with the two filtered washings.
In the agar-plate cultures made from the unfiltered washings,
numerous fungus and bacterial colonies developed. In the plate
cultures made from washings filtered through filter paper, only
bacterial colonies developed. In the plate cultures made from
washings filtered through the Berkefeld filter, no growth of any
kind appeared. Similar results were obtained by repeating
these experiments several times. In one or two cases bacteria
passed through the Berkefeld filter, but in no case was spotting
produced from the washings after they had passed through this
filter.
These experiments indicated: First, that the spotting was
not caused by any soluble toxin in the dead wood (if such had
been the case the trees treated with the filtered washings would
have developed Melanose spotting, the same as those treated
with the unfiltered washings); second, that the disease was due
to some organism, probably a fungus or bacterium.
A study of the agar plate-cultures from the unfiltered wash-
ings showed that a half-dozen different species of bacteria were
present, and probably twice that number of fungus species.
The bacteria were discarded for the present, as well as several
species of fungi that were not thought to be the cause of the spot-
ting. Two undetermined species of fungus were selected and
grown in cultures until spores were produced. Repeated at-
tempts to produce spotting on young orange shoots with spores
from these cultures gave negative results.
Spotting was repeatedly produced by tying small pieces of
dead twigs, from one inch to four or five inches in length, to
young shoots under proper moisture conditions. A number of
these small pieces were examined microscopically. Phomopsis
citri was found on all of the pieces from which infection was pro-
duced, and in some cases it was the only fungus found. This
led to a series of infection experiments with Phomopsis citri.
Spores were taken from a pure culture of the fungus that had
been growing in the laboratory for some time. A suspension
of the spores was made in sterile water, and this was sprayed
on young orange shoots. The trees were placed under a bell-
jar for twenty-four hours. At the end of four days Melanose
spotting appeared on the treated shoots. Shoots not treated and
left as checks showed no spotting. This was repeated several
times, using cultures of the fungus from different sources, and
in each case Melanose spotting was produced when spores of
this fungus (Phomopsis citri) were sprayed on young orange
shoots, and the moisture conditions were favorable.
In another set of experiments, spores from a pure culture
of this fungus were sprayed on young shoots, and at the same
time spores from the same culture were introduced into the





12 Florida Agricultural Experiment Station
stem ends of immature oranges. The outer surface of the fruits
was thoroughly sterilized, and the inoculations made under asep-
tic conditions. The fruits were slit at the stem ends and a small
mass of the spores introduced. The fruits were wrapped sep-
arately in sterilized paper and placed in open aquarium jars
at room temperature. Twenty-four fruits were inoculated.
Ten fruits, kept as checks, were treated in the same manner,
except that no spores were introduced into the slit stem ends.
Melanose spotting appeared on the treated shoots in four days.
In seven to ten days typical cases of Stem-End Rot developed in
the inoculated fruits. At the end of three weeks all inoculated
fruits had completely rotted, were brown in color and shriveled
at the stem ends. Some began to show the formation of pycnidia
on the outer surface. None of the checks showed any indication
of decay.
These experiments proved beyond a doubt that Melanose and
Stem-End Rot were caused by the same fungus. Spotting was
readily produced under field conditions by tying dead twigs to
young succulent shoots. The infection appeared in from four to
eleven days, depending on the weather conditions. No transfer of
infection has yet resulted from the spots themselves, or from
diseased areas on leaves, fruits or living water-sprouts. Appar-
ently no further spread of the disease takes place after the
spots are formed. The formation of the spots or diseased areas
seems to end all active growth of the fungus in this phase of de-
velopment.
THE FUNGUS AND ITS HABITS.
The fungus belongs to the group known as imperfect forms
(Fungi Imperfecti). Several members of this group are well-
known parasites, and cause serious diseases of plants. Pho-
mopsis citri, however, is a comparatively weak parasite, and is
apparently better adapted to living in dead tissue. From our
present knowledge of its habits it lives chiefly in the dead wood of
citrus trees, where it is carried over from one season to the next.
In the dead branches, and even in very small twigs, countless
numbers of fruiting bodies (pycnidia) may be found. The
pycnidia are black, very minute and. embedded in the bark, and
so may easily escape detection.
To the unaided eye they appear
Sas small dark specks or minute
S- pustules on the surface of the
bark. They are usually round,
oval, or somewhat flattened,
with a slightly elongated neck or
point that protrudes through
the outer surface of the bark.
Through the middle of this neck
Fig. 6.-Diagrammatic section of or point is a small opening
pycnidium. X45. (FromBul.107.) through which the spores es-
cape. The interior of each pycnidium is a cavity, in which
thousands of minute, oval-shaped, colorless spores are produced.





Bulletin 111 13
Mingled with the spores are other bodies called paraphyses.
These are several times longer than the spores, slender and color-
less, and usually crooked at one end.
Under moist conditions the spores and para-
physes are discharged through the necks of the
pycnidia in yellowish sticky masses or threads.
The spore masses are dissolved by rain and dew,
and washed down on young growth, fruit, and
dead twigs. Spores that come in contact with
dead wood form new pycnidia, and these later
produce more spores. This process may be con-
tinued through the spring, summer and fall Fi. 7.-Sp ores
months, depending upon weather conditions. It and paraphyses.
is probable that the fungus produces and matures x 750. (From
the pycnidia much earlier under natural condi- Bul. 107.)
tions than when grown in the laboratory. In pure cultures
grown under laboratory conditions, pycnidia are produced and
discharge spores in from four to six weeks. Under conditions
met with in the ordinary grove, and especially during a wet
season, several different crops of pycnidia may be produced
during a single season. This results in the dead twigs and
branches becoming filled with the fungus, and countless numbers
of spores being present to infect the new growth or fruits when-
ever favorable weather conditions occur.
The fungus is spread in the tree chiefly by rain and dew.
Spores are washed down from the dead wood upon the leaves,
and from leaf to leaf, until the entire new growth and all the
fruits are infected. Birds and insects are no doubt the agents
that carry the fungus from one tree to another, and from grove
to grove. By lighting on dead twigs that are covered with sticky
spore-masses birds may carry away any quantity of spores on
their feet and deposit them on other dead wood in new localities,.
and thus start new centers of infection from which the fungus
is rapidly spread. The wind probably plays a minor part in dis-
tributing this fungus.
SURFACE INJURY FROM THE FUNGUS.
In causing Melanose spotting apparently no
Vegetative growth of the fungus takes place with-
0 in the infected tissue. The spores come in con-
tact with the outer surface of young tissue, and in
the presence of moisture, after two or three days'
time, minute watery, sunken spots begin to appear.
Just what process takes place to cause the forma-
tion of these spots is not known at present. They
Fig. 8. Germi- may be caused by some stimulating or toxic ef-
nating spores. feet produced by the germination or death of the
X 350 about, spores. This, however, remains to be further
(From Bul.107.) investigated. Only the outer layers of cell tissue
seem to be affected. These cells are killed and the contents be-
come hardened. As the spots become older, they turn brown and






14 Florida Agricultural Experiment Station

become raised, and rough or cracked in appearance, forming the
characteristic markings of the disease.

STEM-END ROT.
DESCRIPTION.
The appearance of this decay varies somewhat according to the maturity
of the fruit, the temperature at which it takes place, and the amount
of moisture present. A second fungus, Diplodia natalensis, produces a de-
cay so similar in its first stages, that it cannot be distinguished from
that due to Phomopsis sp. In the later stages of decay these two may
easily be differentiated.


N.


Fig. 9.-Orange showing wrinkling of skin and sinking at stem end due
to Stem-End Rot. About natural size. (From Bul. 107.)

The decay usually met with in mature packed fruit develops on oranges
as follows. A circular patch at the stem end becomes soft. This at the
very first can usually be detected only by the pressure of the finger, as
there is often no discoloration of the rind. This stage of rotting is well
described in the words of a northern salesman, as follows: "I noticed that
the oranges are affected with some disease that causes a rotting in a
peculiar way around the stem end. From outside appearance oranges do
not show rot, but by placing your hand on the orange at this end you
readily see that the orange has decayed from the inside and is unfit for
sale." As the softening advances and enlarges to include one-third to one-
half of the fruit, the rind changes to a dull brown, drab, or dark coffee
color, and becomes soft and sometimes sticky, with or without the exuda-
tion of a sticky brown juice. The peel, however, does not become so
brittle as in the case of Blue Mold decay. If the fruit is opened, the decay
will be found to have proceeded most rapidly along the center where the
segments join, and along the inner white part of the rind, and not so rap-
idly into the juice sacs. It may easily be distinguished from the Blue Mold
decay by the absence (as the decay proceeds) of the blue-green, or olive-






14 Florida Agricultural Experiment Station

become raised, and rough or cracked in appearance, forming the
characteristic markings of the disease.

STEM-END ROT.
DESCRIPTION.
The appearance of this decay varies somewhat according to the maturity
of the fruit, the temperature at which it takes place, and the amount
of moisture present. A second fungus, Diplodia natalensis, produces a de-
cay so similar in its first stages, that it cannot be distinguished from
that due to Phomopsis sp. In the later stages of decay these two may
easily be differentiated.


N.


Fig. 9.-Orange showing wrinkling of skin and sinking at stem end due
to Stem-End Rot. About natural size. (From Bul. 107.)

The decay usually met with in mature packed fruit develops on oranges
as follows. A circular patch at the stem end becomes soft. This at the
very first can usually be detected only by the pressure of the finger, as
there is often no discoloration of the rind. This stage of rotting is well
described in the words of a northern salesman, as follows: "I noticed that
the oranges are affected with some disease that causes a rotting in a
peculiar way around the stem end. From outside appearance oranges do
not show rot, but by placing your hand on the orange at this end you
readily see that the orange has decayed from the inside and is unfit for
sale." As the softening advances and enlarges to include one-third to one-
half of the fruit, the rind changes to a dull brown, drab, or dark coffee
color, and becomes soft and sometimes sticky, with or without the exuda-
tion of a sticky brown juice. The peel, however, does not become so
brittle as in the case of Blue Mold decay. If the fruit is opened, the decay
will be found to have proceeded most rapidly along the center where the
segments join, and along the inner white part of the rind, and not so rap-
idly into the juice sacs. It may easily be distinguished from the Blue Mold
decay by the absence (as the decay proceeds) of the blue-green, or olive-






Bulletin 111 15
green powdery spore formation so characteristic of the latter. It may be
distinguished from the Diplodia Rot by the absence of dark bands corre-
sponding to the divisions between the segments. In the grove, the earliest
visible appearance of Stem-End Rot on immature fruit is a dark brown,
reddish brown, to almost black discoloration about the stem end. This
is sometimes seen on fruit still hanging on the tree, especially in infected
tangerine oranges. Sweet oranges and grapefruit are more apt to drop
off before the discoloration begins. The first indications of the rot are
usually seen in August, or in the first part of September.
CONDITIONS FAVORING STEM-END ROT.
The conditions that appear to increase Stem-End Rot are: (1) pres-
ence of scale insects; (2) abnormally warm weather in the fall; (3) damp-
ness and shade in a grove.
Observations in a number of different groves indicate that Stem-End
Rot is most apt to develop in those fruits which have a number of scale
insects clustered about the stem. The scale insects (principally Mytilaspis
citricola) in many cases are found to have crawled under the persistent
calyxes of the fruit, and to have developed in great numbers close to the
stem or stalk. These weaken the fruit and make it more subject to the
attack of the fungus. Periods of unusually warm weather after the fruit
begins to mature appear to have a tendency to increase the amount and
to hasten the development of the decay. Inoculation experiments with
fruits showed clearly that the fungus developed more rapidly in a warm
temperature. The greatest loss from Stem-End Rot has been observed in
groves that were rather moist and shady, although the decay has also been
found in groves under every condition of moisture, thickness of growth, or
shade.
INJURY FROM THE FUNGUS.
The injury to the fruit from this decay is twofold. First, it causes
the fruit to drop and rot before or after its maturity on the tree, and, sec-
ondly, it causes a softening and rotting of the fruit in transit, or soon after
arrival at the market. Careful records, in four different localities, showed
that from 15 to 32 per cent. of all fruit dropped from infected trees, from
all causes, between October, 1910, and February, 1911. From 35 to 85 per
cent. of this dropped fruit showed the symptoms of Stem-End Rot, at or
soon after the time of dropping from the tree. Shipping tests of fruit
from infected groves to Washington, D. C., made in co-operation with the
Bureau of Plant Industry, showed an average stem-end rot of 1.5 per cent.
on arrival; 8.5 per cent., one week after; 22.3 per cent., two weeks after;
and 36.7 per cent, three weeks after arrival.

CONTROL MEASURES.
From our present knowledge of the two diseases and the
scientific data at hand, it would seem that neither Melanose nor
Stem-End Rot could occur in a grove if all the dead wood were
eliminated. The fungus causing these diseases lives in the dead
wood and produces countless spores. These spores are present
during the entire season and form a constant source of infection.
Small twigs contain the fungus, as well as the larger branches.
Laboratory experiments have proved that dead twigs only four
inches in length are capable of producing repeated infections.
The fungus also produces spores on decaying and mummified
fruits under the trees, and these may become a source of infec-
tion. Fungicides have been used with success in controlling
Melanose, but their use is usually attended with a heavy infesta-
tion of scale-insects. Our experiments indicate that fungicides






Bulletin 111 15
green powdery spore formation so characteristic of the latter. It may be
distinguished from the Diplodia Rot by the absence of dark bands corre-
sponding to the divisions between the segments. In the grove, the earliest
visible appearance of Stem-End Rot on immature fruit is a dark brown,
reddish brown, to almost black discoloration about the stem end. This
is sometimes seen on fruit still hanging on the tree, especially in infected
tangerine oranges. Sweet oranges and grapefruit are more apt to drop
off before the discoloration begins. The first indications of the rot are
usually seen in August, or in the first part of September.
CONDITIONS FAVORING STEM-END ROT.
The conditions that appear to increase Stem-End Rot are: (1) pres-
ence of scale insects; (2) abnormally warm weather in the fall; (3) damp-
ness and shade in a grove.
Observations in a number of different groves indicate that Stem-End
Rot is most apt to develop in those fruits which have a number of scale
insects clustered about the stem. The scale insects (principally Mytilaspis
citricola) in many cases are found to have crawled under the persistent
calyxes of the fruit, and to have developed in great numbers close to the
stem or stalk. These weaken the fruit and make it more subject to the
attack of the fungus. Periods of unusually warm weather after the fruit
begins to mature appear to have a tendency to increase the amount and
to hasten the development of the decay. Inoculation experiments with
fruits showed clearly that the fungus developed more rapidly in a warm
temperature. The greatest loss from Stem-End Rot has been observed in
groves that were rather moist and shady, although the decay has also been
found in groves under every condition of moisture, thickness of growth, or
shade.
INJURY FROM THE FUNGUS.
The injury to the fruit from this decay is twofold. First, it causes
the fruit to drop and rot before or after its maturity on the tree, and, sec-
ondly, it causes a softening and rotting of the fruit in transit, or soon after
arrival at the market. Careful records, in four different localities, showed
that from 15 to 32 per cent. of all fruit dropped from infected trees, from
all causes, between October, 1910, and February, 1911. From 35 to 85 per
cent. of this dropped fruit showed the symptoms of Stem-End Rot, at or
soon after the time of dropping from the tree. Shipping tests of fruit
from infected groves to Washington, D. C., made in co-operation with the
Bureau of Plant Industry, showed an average stem-end rot of 1.5 per cent.
on arrival; 8.5 per cent., one week after; 22.3 per cent., two weeks after;
and 36.7 per cent, three weeks after arrival.

CONTROL MEASURES.
From our present knowledge of the two diseases and the
scientific data at hand, it would seem that neither Melanose nor
Stem-End Rot could occur in a grove if all the dead wood were
eliminated. The fungus causing these diseases lives in the dead
wood and produces countless spores. These spores are present
during the entire season and form a constant source of infection.
Small twigs contain the fungus, as well as the larger branches.
Laboratory experiments have proved that dead twigs only four
inches in length are capable of producing repeated infections.
The fungus also produces spores on decaying and mummified
fruits under the trees, and these may become a source of infec-
tion. Fungicides have been used with success in controlling
Melanose, but their use is usually attended with a heavy infesta-
tion of scale-insects. Our experiments indicate that fungicides






Bulletin 111 15
green powdery spore formation so characteristic of the latter. It may be
distinguished from the Diplodia Rot by the absence of dark bands corre-
sponding to the divisions between the segments. In the grove, the earliest
visible appearance of Stem-End Rot on immature fruit is a dark brown,
reddish brown, to almost black discoloration about the stem end. This
is sometimes seen on fruit still hanging on the tree, especially in infected
tangerine oranges. Sweet oranges and grapefruit are more apt to drop
off before the discoloration begins. The first indications of the rot are
usually seen in August, or in the first part of September.
CONDITIONS FAVORING STEM-END ROT.
The conditions that appear to increase Stem-End Rot are: (1) pres-
ence of scale insects; (2) abnormally warm weather in the fall; (3) damp-
ness and shade in a grove.
Observations in a number of different groves indicate that Stem-End
Rot is most apt to develop in those fruits which have a number of scale
insects clustered about the stem. The scale insects (principally Mytilaspis
citricola) in many cases are found to have crawled under the persistent
calyxes of the fruit, and to have developed in great numbers close to the
stem or stalk. These weaken the fruit and make it more subject to the
attack of the fungus. Periods of unusually warm weather after the fruit
begins to mature appear to have a tendency to increase the amount and
to hasten the development of the decay. Inoculation experiments with
fruits showed clearly that the fungus developed more rapidly in a warm
temperature. The greatest loss from Stem-End Rot has been observed in
groves that were rather moist and shady, although the decay has also been
found in groves under every condition of moisture, thickness of growth, or
shade.
INJURY FROM THE FUNGUS.
The injury to the fruit from this decay is twofold. First, it causes
the fruit to drop and rot before or after its maturity on the tree, and, sec-
ondly, it causes a softening and rotting of the fruit in transit, or soon after
arrival at the market. Careful records, in four different localities, showed
that from 15 to 32 per cent. of all fruit dropped from infected trees, from
all causes, between October, 1910, and February, 1911. From 35 to 85 per
cent. of this dropped fruit showed the symptoms of Stem-End Rot, at or
soon after the time of dropping from the tree. Shipping tests of fruit
from infected groves to Washington, D. C., made in co-operation with the
Bureau of Plant Industry, showed an average stem-end rot of 1.5 per cent.
on arrival; 8.5 per cent., one week after; 22.3 per cent., two weeks after;
and 36.7 per cent, three weeks after arrival.

CONTROL MEASURES.
From our present knowledge of the two diseases and the
scientific data at hand, it would seem that neither Melanose nor
Stem-End Rot could occur in a grove if all the dead wood were
eliminated. The fungus causing these diseases lives in the dead
wood and produces countless spores. These spores are present
during the entire season and form a constant source of infection.
Small twigs contain the fungus, as well as the larger branches.
Laboratory experiments have proved that dead twigs only four
inches in length are capable of producing repeated infections.
The fungus also produces spores on decaying and mummified
fruits under the trees, and these may become a source of infec-
tion. Fungicides have been used with success in controlling
Melanose, but their use is usually attended with a heavy infesta-
tion of scale-insects. Our experiments indicate that fungicides





16 Florida Agricultural Experiment Station
are of little value in controlling Stem-End Rot. Neither has the
use of disinfectants in the washing tank, or after the fruit comes
from the washer, proved effective in preventing the rot. There-
fore it would seem that the most successful method for controll-
ing these diseases would be to destroy all sources of infection
and remove as far as possible all conditions favoring infection.
The following recommendations are suggested for control:
1. Pruning. Prune out and burn all dead wood from the
trees, small twigs as well as large branches. It is almost impos-
sible to prune out every bit of dead wood from a bearing tree;
but by systematic pruning each year, removing all the larger
branches and as many small ones as possible, the amount of dead
wood can soon be reduced to a minimum. The best time to prune
is during the dormant season, in December and January. The
next best time is during the summer after the first flush of
growth has hardened, which is usually towards the end of June
and through July. Pruning may be done to advantage during
both of these periods. When pruning, care should be taken to
make smooth cuts, usually at the base of the branch or limb, so
as not to leave projecting stubs. After pruning, paint the larger
cut surfaces with carbolineum (diluted to one-half with water),
or pine tar.
2. Spraying. For Melanose, spray with Bordeaux mixture
or ammoniacal solution of copper carbonate. At least two thor-
ough sprayings should be made; the first just after the bloom
drops, and the second three weeks to one month later. As a
large increase of scale-insects usually follows an application of
these fungicides, it will be necessary to spray with some good
insecticide, to keep down the scale-insects. In spraying for
Stem-End Rot the use of fungicides does not seem advisable.
Spraying, however, should be practiced to keep down the scale-
insects. It has been noted that the accumulation of scale-insects
under the calyx appears to render the fruit susceptible to Stem-
End Rot. In case scale-insects are abundant, spray with some
good contact insecticide. The first spraying should probably be
made in April or May, and be followed by one or two other spray-
ings, depending on the amount of scale present.
3. All drops, or rotten and mummified fruits, should be re-
moved from under the trees and destroyed.
4. Culling and careful handling. As far as known there is no sure
way of telling that an orange is infected until it begins to soften at the
stem end. Infection is sometimes indicated on immature fruit by a deeper
yellow color about the stem end. The Stem-End Rot, however, as well as
the Blue Mold, is most apt to develop on defective fruit. It is therefore
important to cull out closely all clipper cuts, long stems, and fruit injured
in any way, and to handle all fruit carefully.




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