• TABLE OF CONTENTS
HIDE
 Copyright
 Front Cover
 Table of Contents
 Summary
 Introduction
 Appearance of melanose injury
 Nature of melanose
 Cause of melanose
 Effects of melanose
 Conditions favoring melanose
 Control






Group Title: Bulletin - University of Florida. Agricultural Experiment Station - no. 145
Title: Melanose II
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027737/00001
 Material Information
Title: Melanose II
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: p. 101-116 : ill. ; 23 cm.
Language: English
Creator: Stevens, H. E ( Harold Edwin ), b. 1880
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1918
 Subjects
Subject: Citrus -- Diseases and pests   ( lcsh )
Fungal diseases of plants   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by H.E. Stevens.
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station) ;
 Record Information
Bibliographic ID: UF00027737
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 - 000922764
oclc - 18162222
notis - AEN3273

Table of Contents
    Copyright
        Copyright
    Front Cover
        Page 101
    Table of Contents
        Page 102
    Summary
        Page 102
    Introduction
        Page 103
    Appearance of melanose injury
        Page 104
        Page 105
    Nature of melanose
        Page 106
    Cause of melanose
        Page 107
        Page 108
        Page 109
    Effects of melanose
        Page 110
    Conditions favoring melanose
        Page 111
        Moisture
            Page 111
        Drouth
            Page 111
        Dead wood
            Page 112
        Susceptible growth
            Page 112
    Control
        Page 113
        Page 114
        Spraying
            Page 113
        Pruning
            Page 113
            When to prune
                Page 115
            Method of pruning
                Page 115
        Control of other agencies
            Page 116
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





February, 1918


UNIVERSITY OF FLORIDA

Agricultural Experiment Station


MELANOSE II
By H. E. STEVENS


FIG. 25.-Typical melanose injury to citrus leaves, stems, and fruit


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


Bulletin 145
















CONTENTS
PAGE
Introduction ................................................... 103
Appearance of Melanose Injury.................................... 104
Nature of Melanose.............................................. 106
Cause of M elanose ....................................... .... .. 107
Effects of Melanose........................................... 110
Conditions Favoring Melanose ................................... 111
M oisture ............................................. 111
Drouth ................................................... 111
D ead W ood ............................. .... ........... 112
Susceptible Growth ................................. .... 112
Control ................. .................................. 113
Spraying .................................................. 113
Pruning ................................................. 113
When to Prune.................................... 115
M ethod of Pruning .................................. 115
Control of Other Agencies.................................. 116


SUMMARY
1. Melanose is a disease of citrus leaves, young stems and
fruits.
2. It is abundant and widely distributed in the Florida citrus
groves.
3. It is caused by the same fungus that causes stem-end rot
of citrus fruits.
4. This fungus is found chiefly in the dead twigs and
branches of the citrus trees and this dead wood is the principal
source from which the disease spreads.
5. Melanose does not spread from the spots or markings on
the foliage and fruits.
6. Fruits may be injured by attacks of melanose during a
period of several months.
7. The removal and destruction of dead wood from the citrus
tree seems to offer the most practical method at present for
avoiding melanose.
















CONTENTS
PAGE
Introduction ................................................... 103
Appearance of Melanose Injury.................................... 104
Nature of Melanose.............................................. 106
Cause of M elanose ....................................... .... .. 107
Effects of Melanose........................................... 110
Conditions Favoring Melanose ................................... 111
M oisture ............................................. 111
Drouth ................................................... 111
D ead W ood ............................. .... ........... 112
Susceptible Growth ................................. .... 112
Control ................. .................................. 113
Spraying .................................................. 113
Pruning ................................................. 113
When to Prune.................................... 115
M ethod of Pruning .................................. 115
Control of Other Agencies.................................. 116


SUMMARY
1. Melanose is a disease of citrus leaves, young stems and
fruits.
2. It is abundant and widely distributed in the Florida citrus
groves.
3. It is caused by the same fungus that causes stem-end rot
of citrus fruits.
4. This fungus is found chiefly in the dead twigs and
branches of the citrus trees and this dead wood is the principal
source from which the disease spreads.
5. Melanose does not spread from the spots or markings on
the foliage and fruits.
6. Fruits may be injured by attacks of melanose during a
period of several months.
7. The removal and destruction of dead wood from the citrus
tree seems to offer the most practical method at present for
avoiding melanose.










MELANOSE
By H. E. STEVENS

The importance of producing citrus fruits of better appear-
ance is becoming evident to the Florida citrus grower. An at-
tractive fruit of good quality is more in demand, and strong com-
petition with outside fruit has exacted a much higher standard
for the Florida product. There are but few citrus growers
who do not realize that bright fruit is more readily disposed of
and at a considerable advance in price over unsightly fruit of
similar quality, and many realize that bright fruit cannot be
produced without considerable effort. The time has come, how-
ever, when the best and most economical methods of producing
better fruit should be sought and applied by all concerned in the
production of citrus fruits.
There can be little question regarding the quality of citrus
fruit grown in Florida, but the appearance of a large percentage
of this is far from what it should be. Several factors are respon-
sible for the unsightly fruit and a majority of them can be
largely controlled by timely efforts- on the part of the grower.
Insect pects and fungus diseases are .responsible for probably
ninety-five percent of the unsightly fruits and a greater part of
this injury might be avoided by using proper precautions at the
right time.
Melanose is responsible for perhaps a larger percentage of
permanent injury to citrus fruits than any other single agency in
the State, and the annual loss from this disease is increasing
from year to year. It is a common trouble in the Florida citrus
grove and is more generally distributed than any other citrus
disease in the State. Few groves are found in which melanose
does not occur, except perhaps those of more recent planting,
and in many localities it is becoming more abundant each season.
In- certain groves the disease is much more severe than in others
and frequently from seventy-five to one hundred percent of the
crop is injured annually.
Melanose is caused by a fungus which is usually found abun-
dant in the dead wood in citrus trees. Generally in those groves
where the trees contain a large amount of dead twigs and
branches melanose injury is most severe.






104 Florida Agricultural Experiment Station

The control of melanose will depend largely on keeping the
citrus trees free from dead wood. This will require careful and
systematic pruning and attention to all other agencies that are
likely to cause dead or weakened wood in the trees. Pruning is
expensive in many cases and often is slow and tedious work,
however, this seems at present to offer the most effective method
of reducing melanose injury. The disease may not be entirely
eliminated from the grove even by the most careful pruning;
however, with pruning such as is done by the ordinary laborer
the percentage of bright fruit can be doubled or trebled in many
groves.
APPEARANCE OF MELANOSE INJURY
The type of injury caused by melanose should not be easily
confused with that of other citrus diseases. It is a disease of the
leaves, young stems, and fruits and attacks only young and suc-






.: ?-=-






U---


SN4


FIG. 26.-Severe melanose injury. Caked masses






Bulletin 145, Melanose II


culent tissue. Melanose is sometimes referred to as "rust"
owing to the reddish-brown color produced on the affected parts,
but it bears no relation to the true rusts.
Melanose fornis characteristic injuries on the surface of the
affected parts and these are the same in general appearance
whether they occur on the fruit, leaves or stems. (Fig. 25.) The
injury is more commonly observed in the form of small, hard,
raised, reddish-brown spots or specks, scattered over the sur-
face of the leaves or fruits. In general, these spots are round
with a smooth, glazed surface. In slight attacks the spots may
be so. widely scattered as to escape notice while in severe cases
the surfaces may be thickly studded with small spots or specks,













...M .70r,





FIG. 27.-Grapefruit with melanose streaking
or these may be run together forming caked masses, streaks or
circular markings. (Fig. 26.) The surfaces of such markings
are similar in appearance to the smaller or individual spots. A
tear-staining effect is often observed on fruits in the form of
narrow streaks or bands extending from the stem end to the
blossom end. (Fig. 27.) This resembles in a measure the tear-
staining of withertip, but can easily be distinguished from it by
the rough sandpaper-like feel of the surface of the bands. In
withertip the streaks are smooth and appear more as a stain on
the surface. Circular markings, either complete or in part, are






106 Florida Agricultural Experiment Station

peculiar to melanose injury. While circles are more frequently
observed on the fruits, they are not uncommon on the leaves and
stems. They may vary from an eighth to a quarter of an inch
in diameter, being outlined by a narrow raised line, continuous
or broken into dots. In severe attacks of the disease caked
masses are found on the fruit, leaves and stems. These masses
are of irregular shape and vary from a quarter to a half inch
or more in extent. The surfaces are reddish-brown, glazed, and
frequently are fissured by small cracks. Where the injury is of
long standing the surfaces of such areas often flake off leaving
a russet scar.
NATURE OF MELANOSE
Melanose is an injury resulting from spores of a certain fun-
gus coming in contact with tender citrus foliage or fruits in the










*."i i- 4- .. "< "4
14-




>. p ,- .. ., ,.. .
.. V -{.
S. -. .- .

** ^ 4 "V .- -.
V -' )t < s i *4
FIG. 28.-Section of melanose spot, with unbroken epidermis.
(Highly magnified)

presence of sufficient moisture. Thru germination of the spores
a certain area of tissue cells in the first few layers are affected.
These cells are killed, become hardened, reddish-brown in color,
and are cut off from the living cells below by a thin corky layer.
As the living cells below continue to develop, the dead mass is
gradually pushed up forming the typical raised spots of mela-
nose. (Fig. 28.) No growth of the fungus takes place within
the affected cells and the disease is not spread from the spots or
markings on the foliage or fruits. The source of the disease is







Bulletin 145, Melanose II


in the dead twigs and branches, where the fungus grows and
produces spores in abundance. These spores are washed down
from the dead wood and collect on the surfaces of the foliage and
fruits. Water contaminated with spores may collect in small
drops containing only a few spores, in which case the spots
will be small. Such a condition may occur during heavy
dews or light rains. Or spores that have lodged on the leaves
may be collected in small drops, which may account for the
small dot-like spots frequently observed. Streaks and bands are
formed from large drops heavily charged with spores. These are
carried downward by gravity, leaving a film of spores in their
wake. Circles result from the evaporation of drops charged
with spores, in which case the spores are deposited at the edge.
The injury is not visible to the unaided eye until three or four
days after the spores have come in contact with the young tis-
sue. Spots then appear as small sunken watery dots on the sur-
face which in the course of a few days develop into the typical
raised spots or markings of the disease. After the spots or
markings become visible there is no further increase in size of
the affected area other than by the gradual pushing up of the
hardened mass occasioned by growth and development of the
living cells below. The injury is mainly superficial but when
once formed the spots remain and stand out more strikingly on
the mature fruit and older leaves. On the twigs, however, these
markings slough off and disappear on the formation of the true
bark.
Rapidly growing or more succulent citrus tissue shows the in-
jury more prominently, which is especially true of the grape-
fruit. This has led to the common belief that grapefruit is more
susceptible than other citrus varieties, but observations and ex-
periments do not indicate this to be true. All the common citrus
varieties show about the same degree of susceptibility to the
disease and the intensity of attack seems to be influenced more
by the condition of growth, the presence of moisture and the
amount of fungus spores rather than by any resistant property
of the variety itself. Under favorable conditions any citrus tree
may be severely attacked by melanose.

CAUSE OF MELANOSE
Melanose is caused by the fungus Phomopsis citri, which is
widely distributed in the citrus groves thruout the State. It
propagates chiefly in dead citrus twigs and branches, the minute







Florida Agricultural Experiment Station


fruiting bodies developing abundantly in the bark. These fruit-
ing bodies (pycnidia) are embedded in the bark and are not
easily detected without the aid of a good lens. The visible por-
tion is then only represented by the neck of the pycnidium which
appears as a small light speck or pimple-like elevation on the
surface of the bark. Within the pycnidium (fig. 29) countless
spores (seed) are produced (fig. 30). These are minute, elon-
gated, oval, colorless bodies that can be detected only with a com-
pound microscope. When dead bark containing pycnidia be-
comes moist the spores are exuded in masses or stringy tendrils.
These are at first white but later become yellowish in color on ex-








FIG. 30.-Spores FIG. 31.-Germi-
and paraphyses. nating spores.
X 750. (From FIG. 29.-Diagrammatic section of X 350, about.
Bul. 107.) pycnidium. X 45. From Bul. 107.) (From Bul. 107)

posure to the air. These tendrils and masses are dissolved by
rain or dew and the spores are carried down onto the foliage and
fruits or dead wood.
If the spore (fig. 31) lodges on dead citrus bark, it germinates,
grows into the dead tissue and later forms other fruiting bodies
filled with spores. This process is repeated thruout the season,
resulting in several distinct crops of spores and a decided in-
crease of the fungus in the dead citrus bark.
If a spore or mass of spores lodges on young succulent tissue,
whether leaves, stems, or fruits, and sufficient moisture is pres-
ent, germination takes place but the fungus does not penetrate
the tissue in this case. The spores die and apparently disinte-
grate after germination but a certain number of tissue cells have
been affected and in three or four days an injured spot appears
which eventually develops into a typical melanose spot or mark-
ing.
The fungus is distributed in individual trees mainly by rain
and dew. It is carried from tree to tree or from one grove to
another probably by the wind, insects and birds. Personal ob-







Bulletin 145, Melanose II


servations indicate that wind is perhaps the principal agent in
distributing this disease over wide areas.
Phomopsis citri was first described as the cause of stem-end
rot of citrus fruits (Bul. 107, Fla. Exp. Sta.), a disease charac-
teristic and distinct from melanose. In this case the fungus
affects only the fruit that is mature or nearing maturity. It en-
ters the fruit tissue at the stem end causing a decay which re-
sults in a total loss of the fruit affected. The fungus also de-
velops pycnidia on the surface of the decayed fruits that are
allowed to mummify beneath the trees. Altho stem-end rot
causes more or less loss to the citrus crop each season, it is some-
what sporadic in occurrence.
It was later discovered by the writer that this same Phomopsis
was the cause of melanose injury (Bul. 111, Fla. Exp. Sta.). In
this case only young and succulent tissue is affected and no
growth of the fungus is detected in the tissue of the melanose
spots. Melanose injury has been repeatedly induced by applying
spores of this fungus from cultures of known purity to healthy,
succulent citrus foliage kept thoroly moistened for twenty-four to
forty-eight hours after treatment. Where similar citrus foliage
was kept under the same conditions except that no spores were
added, no such injury occurred on the checks. Spores of this
fungus have been atomized on citrus foliage and applied with
a needle to the surface of leaves and twigs previously sprayed
with sterilized water and in practically every case distinct injury
occurred which later developed into typical melanose spotting.
All attempts to re-isolate the fungus from such injuries have
given negative results and the organism has never been obtained
from spots or markings formed naturally.
A study of sections of melanose injury in various stages of de-
velopment has not revealed the presence of the mycelium of this
fungus in connection with the affected cells. Occasionally, in
the tissue of the older injuries an isolated fungus filament is
observed but'this appears to be a secondary invader rather than
the causative agent.
The inability to re-isolate the organism from the artificially
induced injuries makes it impossible in this case to strictly fol-
low the prescribed formula for proof of pathogenicity. How-
ever, it has been demonstrated beyond a doubt that spores of
Phomopsis citri, in the presence of an ample supply of moisture
will produce on succulent citrus tissue a typical injury known as
melanose. No other fungus or bacterial organism has yet been








Florida Agricultural Experiment Station


found which will cause this same type of injury when subjected
to these same tests. Hence Phomopsis citri Fawcett must be
considered the cause of melanose.
It has not yet been fully determined just what reaction takes
place in the formation of such injuries. They may be primarily
due to chemical or enzymatic action induced by the germinating
spores and a later disintegration of the same. Experiments have
demonstrated that viable spores are required and germination
is a necessary requirement as no melanose injury resulted when
spores were killed by sterilization and applied to susceptible
citrus foliage under the same conditions that were sufficient to
induce the injury when living spores of Ph. citri were used.
As suggestive that melanose injury may be chemical in nature,
the following experiment may be of interest. Diluted lemon
juice was sprayed on susceptible citrus foliage which was kept
under humid conditions for forty-eight hours. In the course of
a few days small dot-like spots were evident and many of these
later developed into markings that were quite typical of mela-
nose.
EFFECTS OF MELANOSE
The disease is confined to the leaves, stems and fruits but per-
haps the greatest loss from melanose results from injury to the
fruit. This is more evident on mature fruit ready for market.
Melanose does not affect the quality for the markings are con-
fined to the surface, but the disease may greatly mar the appear-
ance of such fruits and make them less salable or of lower grade.
In severe attacks the fruit may be badly russeted or reduced to
culls while slight attacks will materially lessen the amount of
fruit that can be classed as bright.
Melanose may occur on the fruit at any time after the bloom
drops until the fruit is nearing maturity, which makes a rather
long period of susceptibility. Indications are that severe at-
tacks on young fruits early in the season may cause them to drop
freely or they may become stunted or weakened from the effects
of melanose and drop later under adverse conditions. Just what
percentage of immature fruits is lost in this way has not been
determined for any particular grove but in localities where the
disease is well established this loss is undoubtedly large.
While the effect on the foliage is unusually considered of less
importance, injury in this case may be very great. The spots or
injuries on the leaves and stems have a tendency to reduce the
working capacity of such by disturbing the normal functions of


110








Bulletin 145, Melanose II


the cells within the areas affected. A normal leaf tissue is essen-
tial to supply the available food material for the tree, and any-
thing that affects this tissue will have a corresponding effect on
the food supply. In severe attacks of melanose a large percent-
age of leaf tissue is affected which may result in a material de-
crease in the supply of necessary food for the tree. As a result
such trees make little new growth or make growth of a weakened
character and the fruit produced is apt to be undersized and be-
low the average in yield.
Severe attacks of the disease on young shoots, frequently cause
the leaves to drop and the twigs die later. This is more notice-
able on water sprouts or shoots appearing in the interior of the
trees.
CONDITIONS FAVORING MELANOSE
The development of melanose is dependent upon certain neces-
sary conditions. The fungus must be present; the growth must
be in a young and succulent state; and a sufficient amount of
moisture must be maintained for several hours. All of these
factors must be present at the same time before injury will oc-
cur. In Florida citrus groves there are many times during the
season that these conditions are met. The fungus is universally
present in the citrus grove, and susceptible tissue may be found
from the first flush of growth in the spring until the fall flush
has hardened. Thus the first two conditions are easily met.

MOISTURE
Moisture is the more variable factor, yet this is present with
sufficient frequency to cause more or less melanose to develop
during the entire season. A period of rain for twenty-four hours,
or a rain followed by cloudy skies for a day or two under the
foregoing conditions, will result in a severe attack of the disease.
If this should occur in the spring about the time the fruit has set
both fruit and foliage will be severely affected. This may be
repeated several times during the season, resulting in several
attacks on the fruit and subjecting the different flushes of
growth to injury.
Heavy dews, especially in groves located in moist, shady situ-
ations, may supply the needed moisture for the development of
the disease.
DROUTH
If drouthy conditions prevail during the spring and early sum-
mer the first foliage growth usually escapes injury and the fruit








Bulletin 145, Melanose II


the cells within the areas affected. A normal leaf tissue is essen-
tial to supply the available food material for the tree, and any-
thing that affects this tissue will have a corresponding effect on
the food supply. In severe attacks of melanose a large percent-
age of leaf tissue is affected which may result in a material de-
crease in the supply of necessary food for the tree. As a result
such trees make little new growth or make growth of a weakened
character and the fruit produced is apt to be undersized and be-
low the average in yield.
Severe attacks of the disease on young shoots, frequently cause
the leaves to drop and the twigs die later. This is more notice-
able on water sprouts or shoots appearing in the interior of the
trees.
CONDITIONS FAVORING MELANOSE
The development of melanose is dependent upon certain neces-
sary conditions. The fungus must be present; the growth must
be in a young and succulent state; and a sufficient amount of
moisture must be maintained for several hours. All of these
factors must be present at the same time before injury will oc-
cur. In Florida citrus groves there are many times during the
season that these conditions are met. The fungus is universally
present in the citrus grove, and susceptible tissue may be found
from the first flush of growth in the spring until the fall flush
has hardened. Thus the first two conditions are easily met.

MOISTURE
Moisture is the more variable factor, yet this is present with
sufficient frequency to cause more or less melanose to develop
during the entire season. A period of rain for twenty-four hours,
or a rain followed by cloudy skies for a day or two under the
foregoing conditions, will result in a severe attack of the disease.
If this should occur in the spring about the time the fruit has set
both fruit and foliage will be severely affected. This may be
repeated several times during the season, resulting in several
attacks on the fruit and subjecting the different flushes of
growth to injury.
Heavy dews, especially in groves located in moist, shady situ-
ations, may supply the needed moisture for the development of
the disease.
DROUTH
If drouthy conditions prevail during the spring and early sum-
mer the first foliage growth usually escapes injury and the fruit








Bulletin 145, Melanose II


the cells within the areas affected. A normal leaf tissue is essen-
tial to supply the available food material for the tree, and any-
thing that affects this tissue will have a corresponding effect on
the food supply. In severe attacks of melanose a large percent-
age of leaf tissue is affected which may result in a material de-
crease in the supply of necessary food for the tree. As a result
such trees make little new growth or make growth of a weakened
character and the fruit produced is apt to be undersized and be-
low the average in yield.
Severe attacks of the disease on young shoots, frequently cause
the leaves to drop and the twigs die later. This is more notice-
able on water sprouts or shoots appearing in the interior of the
trees.
CONDITIONS FAVORING MELANOSE
The development of melanose is dependent upon certain neces-
sary conditions. The fungus must be present; the growth must
be in a young and succulent state; and a sufficient amount of
moisture must be maintained for several hours. All of these
factors must be present at the same time before injury will oc-
cur. In Florida citrus groves there are many times during the
season that these conditions are met. The fungus is universally
present in the citrus grove, and susceptible tissue may be found
from the first flush of growth in the spring until the fall flush
has hardened. Thus the first two conditions are easily met.

MOISTURE
Moisture is the more variable factor, yet this is present with
sufficient frequency to cause more or less melanose to develop
during the entire season. A period of rain for twenty-four hours,
or a rain followed by cloudy skies for a day or two under the
foregoing conditions, will result in a severe attack of the disease.
If this should occur in the spring about the time the fruit has set
both fruit and foliage will be severely affected. This may be
repeated several times during the season, resulting in several
attacks on the fruit and subjecting the different flushes of
growth to injury.
Heavy dews, especially in groves located in moist, shady situ-
ations, may supply the needed moisture for the development of
the disease.
DROUTH
If drouthy conditions prevail during the spring and early sum-
mer the first foliage growth usually escapes injury and the fruit







Florida Agricultural Experiment Station


will be little affected during the early stages of development.
Later, however, when the rainy season begins this fruit may be
severely injured. Severe attacks on fruit frequently occur dur-
ing June and July.
DEAD WOOD
The fungus will be found in varying amounts in any dead
wood in the citrus tree, from the smallest terminal twigs to
larger branches and limbs. An abundance of pycnidia often de-
velops in small patches of dead bark on the trunk and main
branches of the tree. Sickly or weakened wood may be invaded
by the fungus which soon kills the affected parts and these be-
come fruitful sources in the production of pycnidia. The fungus
readily follows the attacks of other diseases and wood that has
been killed by withertip or the attack of insect pests is soon in-
vaded by Ph. citri. Scale insects and whitefly are responsible
for a large amount of dead wood each season and this rapidly be-
comes a harboring place for the fungus. Any agency that tends
to weaken the growth or cause dead wood in the citrus tree will
aid materially in establishing and propagating the fungus in
such trees.
The prevalence of the fungus in a grove will. depend largely
upon the amount of dead wood in the trees and the length of
time this has been allowed to accumulate. It has been the cus-
tom of many growers in the past to do just as little pruning in
the citrus grove as possible, allowing nature to take care of the
dead wood. As a result there has been an accumulation of dead
wood in the trees year after year affording favorable conditions
for the melanose fungus.

SUSCEPTIBLE GROWTH
A leaf or a young twig is susceptible to melanose injury for a
comparatively short time, perhaps during a period of five to
seven weeks. When the tissues of the leaves and twigs begin to
harden they are past the stage where the fungus can cause them
injury. It is different, however, with the fruits and injury may
occur at any time thru a much longer period. Our experiments
and observations have shown that fruit is susceptible to injury
thru a period of several months. On fruits that resulted from an
early March bloom, melanose injury was induced as late as the
first of August, showing a susceptible period in this particular
case of about five months. The lengthy period during which the
growing fruit may be injured is an important point for consider-







Florida Agricultural Experiment Station


will be little affected during the early stages of development.
Later, however, when the rainy season begins this fruit may be
severely injured. Severe attacks on fruit frequently occur dur-
ing June and July.
DEAD WOOD
The fungus will be found in varying amounts in any dead
wood in the citrus tree, from the smallest terminal twigs to
larger branches and limbs. An abundance of pycnidia often de-
velops in small patches of dead bark on the trunk and main
branches of the tree. Sickly or weakened wood may be invaded
by the fungus which soon kills the affected parts and these be-
come fruitful sources in the production of pycnidia. The fungus
readily follows the attacks of other diseases and wood that has
been killed by withertip or the attack of insect pests is soon in-
vaded by Ph. citri. Scale insects and whitefly are responsible
for a large amount of dead wood each season and this rapidly be-
comes a harboring place for the fungus. Any agency that tends
to weaken the growth or cause dead wood in the citrus tree will
aid materially in establishing and propagating the fungus in
such trees.
The prevalence of the fungus in a grove will. depend largely
upon the amount of dead wood in the trees and the length of
time this has been allowed to accumulate. It has been the cus-
tom of many growers in the past to do just as little pruning in
the citrus grove as possible, allowing nature to take care of the
dead wood. As a result there has been an accumulation of dead
wood in the trees year after year affording favorable conditions
for the melanose fungus.

SUSCEPTIBLE GROWTH
A leaf or a young twig is susceptible to melanose injury for a
comparatively short time, perhaps during a period of five to
seven weeks. When the tissues of the leaves and twigs begin to
harden they are past the stage where the fungus can cause them
injury. It is different, however, with the fruits and injury may
occur at any time thru a much longer period. Our experiments
and observations have shown that fruit is susceptible to injury
thru a period of several months. On fruits that resulted from an
early March bloom, melanose injury was induced as late as the
first of August, showing a susceptible period in this particular
case of about five months. The lengthy period during which the
growing fruit may be injured is an important point for consider-






Bulletin 145, Melanose II


action in adopting any effective control measures against this
disease.
CONTROL
It will be no easy task to control melanose and persistent and
systematic efforts will be required to reduce the injury in groves
-where the disease has become well established. The nature and
growth habits of the fungus causing melanose and the extended
period during which the fruit is susceptible to attack offer little
encouragement for relying upon fungicides alone to eliminate
the disease.
SPRAYING
An application of any fungicide gives protection for a limited
period only. It does not remove the cause and spraying must be
repeated at frequent intervals to be effective. Melanose seems
to yield readily to the standard fungicides such as bordeaux mix-
ture and ammoniacal solution of copper carbonate and with fre-
quent applications of either of these the disease may be kept
under control. However,. the number of spraying operations re-
quired to give full protection to the fruit thruout the season
would doubtless prove so costly as to make this method of con-
trol in most cases prohibitive.
PRUNING
Thoro and systematic pruning seems to offer a more practica-
ble method of control and has the added advantage of removing
the source and cause of the trouble. As has been pointed out the
dead twigs and branches are the chief sources from which mela-
nose is spread. This dead wood harbors and propagates the
fungus from one season to the next and so long as it is allowed
to remain in the tree it will be an active source from which the
disease may spread at favorable opportunities. Every period of
rain causes a discharge of spores and a more active growth of
the fungus within the dead wood. Even tho the surfaces of the
dead twigs may be covered with a coating of fungicide, this will
not affect the growth of the fungus or its spore production in the
dead bark tissue beneath. Neither will it affect the discharge of
spores for the neck of the pycnidium is capable of penetrating
this covering and protruding far enough above the surface to
discharge its mass of spores beyond danger. Thus attempts at
control which do not remove or eliminate the source of the
trouble will be only temporary in nature and must be repeated
frequently.
Where the dead wood is removed from the trees and destroyed






Florida Agricultural Experiment Station


and such trees are afterward kept free from dead wood little
trouble should be experienced from melanose. It is not possible
by the most careful pruning to entirely eradicate the fungus
from a grove, but by pruning regularly each season, removing
all visible dead wood and sickly or weakened growth the amount
of fungus can be kept down to a minimum which will materially
decrease the injury from melanose.
The results from an experiment of four consecutive years of
pruning for the control of melanose indicate that the injury can
be materially reduced by this method where the work is done
even by ordinary laborers. In table 49 is given the percentage of
the different grades of fruit from two blocks of trees, one of
which was pruned regularly each season and the other not
pruned. Each block contained the same number of trees and all
tiees were under the same cultural and soil conditions and loca-
tion. They were all of the same variety and age and as near the
same in size as could be expected. The first pruning was made
in 1913, about the middle of June, by.ordinary negro laborers
who were instructed to remove all visible dead wood. Each suc-
ceeding year these same trees were pruned in June by ordinary
farm laborers. The experiment was conducted in a grove where
melanose was very abundant and it had been prevalent for a
number of years. The trees had not been pruned for several
years preceding the experiment and all trees contained an
abundance of dead twigs and branches. When the fruit was
picked that from each tree was carefully graded according to
the following standards. All fruits that were free from mela-
nose or showed less than one percent of the surface affected were
classed as "brights." Those showing from one to twenty-five
percent of the surface affected were graded as "seconds," and all
fruits showing more than twenty-five percent of their surfaces
affected were classed as "russets."
TABLE 49.-Results of Four Years' Pruning to Control Melanose Injury to
S Citrus Fruits
Percentage of
Year Block
SBrights Seconds Russets
1913 Pruned .................. 34 I 62 4
Not Pruned .............. 23 74 3
1914 Pruned .................. 45 53 2
Not Pruned .............. 12 73 15
1915 Pruned .................. 31 52 17
I Not Pruned .............. .0 62 38
1916 Pruned .................. 34 62 4
S Not Pruned .............. 5 67 28






Bulletin 145, Melanose II


action in adopting any effective control measures against this
disease.
CONTROL
It will be no easy task to control melanose and persistent and
systematic efforts will be required to reduce the injury in groves
-where the disease has become well established. The nature and
growth habits of the fungus causing melanose and the extended
period during which the fruit is susceptible to attack offer little
encouragement for relying upon fungicides alone to eliminate
the disease.
SPRAYING
An application of any fungicide gives protection for a limited
period only. It does not remove the cause and spraying must be
repeated at frequent intervals to be effective. Melanose seems
to yield readily to the standard fungicides such as bordeaux mix-
ture and ammoniacal solution of copper carbonate and with fre-
quent applications of either of these the disease may be kept
under control. However,. the number of spraying operations re-
quired to give full protection to the fruit thruout the season
would doubtless prove so costly as to make this method of con-
trol in most cases prohibitive.
PRUNING
Thoro and systematic pruning seems to offer a more practica-
ble method of control and has the added advantage of removing
the source and cause of the trouble. As has been pointed out the
dead twigs and branches are the chief sources from which mela-
nose is spread. This dead wood harbors and propagates the
fungus from one season to the next and so long as it is allowed
to remain in the tree it will be an active source from which the
disease may spread at favorable opportunities. Every period of
rain causes a discharge of spores and a more active growth of
the fungus within the dead wood. Even tho the surfaces of the
dead twigs may be covered with a coating of fungicide, this will
not affect the growth of the fungus or its spore production in the
dead bark tissue beneath. Neither will it affect the discharge of
spores for the neck of the pycnidium is capable of penetrating
this covering and protruding far enough above the surface to
discharge its mass of spores beyond danger. Thus attempts at
control which do not remove or eliminate the source of the
trouble will be only temporary in nature and must be repeated
frequently.
Where the dead wood is removed from the trees and destroyed






Bulletin 145, Melanose II


action in adopting any effective control measures against this
disease.
CONTROL
It will be no easy task to control melanose and persistent and
systematic efforts will be required to reduce the injury in groves
-where the disease has become well established. The nature and
growth habits of the fungus causing melanose and the extended
period during which the fruit is susceptible to attack offer little
encouragement for relying upon fungicides alone to eliminate
the disease.
SPRAYING
An application of any fungicide gives protection for a limited
period only. It does not remove the cause and spraying must be
repeated at frequent intervals to be effective. Melanose seems
to yield readily to the standard fungicides such as bordeaux mix-
ture and ammoniacal solution of copper carbonate and with fre-
quent applications of either of these the disease may be kept
under control. However,. the number of spraying operations re-
quired to give full protection to the fruit thruout the season
would doubtless prove so costly as to make this method of con-
trol in most cases prohibitive.
PRUNING
Thoro and systematic pruning seems to offer a more practica-
ble method of control and has the added advantage of removing
the source and cause of the trouble. As has been pointed out the
dead twigs and branches are the chief sources from which mela-
nose is spread. This dead wood harbors and propagates the
fungus from one season to the next and so long as it is allowed
to remain in the tree it will be an active source from which the
disease may spread at favorable opportunities. Every period of
rain causes a discharge of spores and a more active growth of
the fungus within the dead wood. Even tho the surfaces of the
dead twigs may be covered with a coating of fungicide, this will
not affect the growth of the fungus or its spore production in the
dead bark tissue beneath. Neither will it affect the discharge of
spores for the neck of the pycnidium is capable of penetrating
this covering and protruding far enough above the surface to
discharge its mass of spores beyond danger. Thus attempts at
control which do not remove or eliminate the source of the
trouble will be only temporary in nature and must be repeated
frequently.
Where the dead wood is removed from the trees and destroyed






Bulletin 145, Melanose II


The first year there was very little gain in the percentage of
bright fruit from the pruned block over that of the check. It
must be remembered, however, that this fruit had been exposed
to injury for several weeks before the pruning was made.
The total average of bright fruit from the pruned block
amounted to thirty-eight percent for the four-year period while
from the check block during the same period the total average
was ten percent. This gives an annual average increase of
twenty-eight percent of bright fruit in favor of the pruned trees.
In many cases pruning will be difficult and expensive, especi-
ally if the trees are large and well-filled with dead wood. In such
cases the first pruning is apt to be costly, but if the trees are
thoroly pruned at first and pruned regularly each season, later
prunings should be made at a nominal cost.
WHEN TO PRUNE.-There are two seasons of the year when
pruning for melanose can be made to advantage. The best time
is in the winter when the trees are in the most nearly dormant
state. If the dead wood can be removed in December or January
the new foliage and fruit will not be exposed to injury during
the early period of development. Where the winter pruning is
made and the trees contain much dead wood it may also be ad-
visable to spray such trees with bordeaux mixture before any
new growth comes out in the spring. This spraying should be
thoro, using the 4-4-50 formula. This will serve as a clean up
spray ard kill any of the fungus spores that may have lodged on
the surface of the old foliage or branches. The ammoniacal solu-
tion of copper carbonate may be substituted for bordeaux mix-
ture. In using either of these fungicides there is likely to be an
increase of scale insects and one should be prepared to combat
them when they appear.
It is not advisable to prune citrus trees that are putting out
new growth or bloom. More harm may be done at this time than
good. Experiments have shown that trees pruned during Feb-
ruary, March and April were more or less weakened by such
prunings. Where it is not possible to prune during the winter
season the work may be done during the summer, preferably in
June and July.
METHOD OF PRUNING.-In taking out the dead wood it is well
to cut back into the living wood an inch or two. Clean, smooth
cuts should be made and no projecting stubs left. Where large
cut surfaces are exposed these should be covered with some anti-






Bulletin 145, Melanose II


The first year there was very little gain in the percentage of
bright fruit from the pruned block over that of the check. It
must be remembered, however, that this fruit had been exposed
to injury for several weeks before the pruning was made.
The total average of bright fruit from the pruned block
amounted to thirty-eight percent for the four-year period while
from the check block during the same period the total average
was ten percent. This gives an annual average increase of
twenty-eight percent of bright fruit in favor of the pruned trees.
In many cases pruning will be difficult and expensive, especi-
ally if the trees are large and well-filled with dead wood. In such
cases the first pruning is apt to be costly, but if the trees are
thoroly pruned at first and pruned regularly each season, later
prunings should be made at a nominal cost.
WHEN TO PRUNE.-There are two seasons of the year when
pruning for melanose can be made to advantage. The best time
is in the winter when the trees are in the most nearly dormant
state. If the dead wood can be removed in December or January
the new foliage and fruit will not be exposed to injury during
the early period of development. Where the winter pruning is
made and the trees contain much dead wood it may also be ad-
visable to spray such trees with bordeaux mixture before any
new growth comes out in the spring. This spraying should be
thoro, using the 4-4-50 formula. This will serve as a clean up
spray ard kill any of the fungus spores that may have lodged on
the surface of the old foliage or branches. The ammoniacal solu-
tion of copper carbonate may be substituted for bordeaux mix-
ture. In using either of these fungicides there is likely to be an
increase of scale insects and one should be prepared to combat
them when they appear.
It is not advisable to prune citrus trees that are putting out
new growth or bloom. More harm may be done at this time than
good. Experiments have shown that trees pruned during Feb-
ruary, March and April were more or less weakened by such
prunings. Where it is not possible to prune during the winter
season the work may be done during the summer, preferably in
June and July.
METHOD OF PRUNING.-In taking out the dead wood it is well
to cut back into the living wood an inch or two. Clean, smooth
cuts should be made and no projecting stubs left. Where large
cut surfaces are exposed these should be covered with some anti-






116 Florida Agricultural Experiment Station

septic such as Avenarius carbolineum or be painted with white
lead, or pine tar.
All prunings and rubbish should be removed from under the
trees and be either burned or buried to destroy the fungus. It is
also advisable to remove and destroy all drops that collect under
the trees.
CONTROL OF OTHER AGENCIES
Pruning alone will not be sufficient to keep down the dead
wood and other agencies that are liable to cause weakened
growth or dead wood should be looked after. By keeping down
the scale and whitefly and supplying the trees with the necessary
food material at.the proper time the occurrence of a very large
amount of dead wood may be prevented.




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