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 Historic note
 Title Page
 Table of Contents
 Important facts
 Introduction
 Description
 The disease infectious
 Technical study
 Remedies suggested














Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; no. 98
Title: Scaly bark of citrus
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00026422/00001
 Material Information
Title: Scaly bark of citrus a preliminary report
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: p. 73-80 : ill. ; 23 cm.
Language: English
Creator: Fawcett, H. S ( Howard Samuel ), b. 1877
Publisher: Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1909
 Subjects
Subject: Citrus -- Diseases and pests -- Florida   ( lcsh )
Fungal diseases of plants -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by H.S. Fawcett.
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station)
 Record Information
Bibliographic ID: UF00026422
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000921814
oclc - 18160146
notis - AEN2282

Table of Contents
    Historic note
        Historic note
    Title Page
        Page 73
    Table of Contents
        Page 74
    Important facts
        Page 74
    Introduction
        Page 75
    Description
        Page 75
        Page 76
        Page 77
    The disease infectious
        Page 78
    Technical study
        Page 78
    Remedies suggested
        Page 79
        Page 80
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





BULLETIN No. 98.


Florida


Agricultural


Experiment


Station.


SCALY


BARK OF CITRUS.


(A PRELIMINARY REPORT.)
BY
H. S. FAWCETT.


Fig. I. Scaly bark on branch of Orange.
Natural Size.


The blletins of this Station will be sent free to any address
in Florida upon application to the Director of the Experiment
Station, Gainesville, Fla.


MARCH, 1909.













CONTENTS.
Page
Introduction ........... .. ...... .......... .... .. ... 75
Description .............................. .......... 75
Scaly Bark of Branches ........................... 75
Scaly Bark of Trunk ............................. 77
Scaly Bark on the Fruit ............................ 77
The Disease Infectious ................................. 78
Technical Study ....................................... 78
Remedies Suggested ................................. 79
Top-Working Affected Trees ...................... 79
H leading Back .................................... 79
Pruning Out .................................... 80
Bordeaux Mixture ............................... 80



IMPORTANT FACTS.
I. With changed conditions, previously unknown or insignifi-
cant diseases of cultivated plants may become destructive.
2. Scaly bark, though long present, has but recently become
sufficiently important to demand attention.
3. Scaly bark did not attract much attention until after wither-
tip became general. Its destructiveness was increased through the
secondary agency of the withertip fungus.
4. The investigations of this disease have suggested four lines
of treatment, which are given in the order of their probable
efficiency.













CONTENTS.
Page
Introduction ........... .. ...... .......... .... .. ... 75
Description .............................. .......... 75
Scaly Bark of Branches ........................... 75
Scaly Bark of Trunk ............................. 77
Scaly Bark on the Fruit ............................ 77
The Disease Infectious ................................. 78
Technical Study ....................................... 78
Remedies Suggested ................................. 79
Top-Working Affected Trees ...................... 79
H leading Back .................................... 79
Pruning Out .................................... 80
Bordeaux Mixture ............................... 80



IMPORTANT FACTS.
I. With changed conditions, previously unknown or insignifi-
cant diseases of cultivated plants may become destructive.
2. Scaly bark, though long present, has but recently become
sufficiently important to demand attention.
3. Scaly bark did not attract much attention until after wither-
tip became general. Its destructiveness was increased through the
secondary agency of the withertip fungus.
4. The investigations of this disease have suggested four lines
of treatment, which are given in the order of their probable
efficiency.






SCALY BARK OF CITRUS.
(A Preliminary Report.)

BY H. S. FAWCETT.

INTRODUCTION.
Scaly bark has been found to be quite destructive to trees
of the sweet orange, in at least one of the important citrus-growing
sections of the State. The heavy losses occasioned by this disease
during the summer and fall of 1906, led the Experiment Station
to take up the investigation of this trouble, with the view of as-
certaining its cause and finding a remedy. A general account of
these investigations is given here, together with recommendations
based upon them.. A description of the disease with its relation
to withertip is also included. It is intended to follow this pre-
liminary report with a more detailed account of the work.
Scaly bark as it occurs in Florida was described under this
name in the annual Report of the Florida Experiment Station for
1907, p. xliii, and in the Proceedings of the Florida State Horti-
cultural Society for 1908, p. o10. Previous to this, H. H. Hume,
in a paper on the diseases of citrus, in the Proceedings of the
Florida Horticultural Society for 1901, p. 64, speaks of a new
disease of the orange; and it appears from his description that
the disease referred to was scaly bark as it occurs on small
branches. Mention is also made of scaly bark by P. H. Rolfs in
the Proceedings of the same Society for 1905, p. 32. A disease
of the citrus trees in California, known by the same name, has
points in common with the one in Florida (Cal. Agr. Exp. Sta.
Bul. 200).
DESCRIPTION.
This is primarily a bark and rind disease of the sweet orange.
The wood is only affected secondarily, by poisoning due to the
withertip fungus. The bark of the trunk and of branches of all
sizes may be affected; but the greatest injury is done to the younger
branches and twigs up to about one-half inch in diameter, and to
the fruit.
SCALY BARK OF BRANCHES.
On the branches and twigs there develop more or less circular
or oval spots one-sixth to one inch across, rusty in color, and with
well-defined margins. The bark becomes brittle, begins to crack,
and forms small flakes or scales. These spots are at first scattered,
but may increase in number to such an extent as to become joined
together. The branch is rarely killed in the first year. During
the second year, additional spot, form between the old ones, and






SCALY BARK OF CITRUS.
(A Preliminary Report.)

BY H. S. FAWCETT.

INTRODUCTION.
Scaly bark has been found to be quite destructive to trees
of the sweet orange, in at least one of the important citrus-growing
sections of the State. The heavy losses occasioned by this disease
during the summer and fall of 1906, led the Experiment Station
to take up the investigation of this trouble, with the view of as-
certaining its cause and finding a remedy. A general account of
these investigations is given here, together with recommendations
based upon them.. A description of the disease with its relation
to withertip is also included. It is intended to follow this pre-
liminary report with a more detailed account of the work.
Scaly bark as it occurs in Florida was described under this
name in the annual Report of the Florida Experiment Station for
1907, p. xliii, and in the Proceedings of the Florida State Horti-
cultural Society for 1908, p. o10. Previous to this, H. H. Hume,
in a paper on the diseases of citrus, in the Proceedings of the
Florida Horticultural Society for 1901, p. 64, speaks of a new
disease of the orange; and it appears from his description that
the disease referred to was scaly bark as it occurs on small
branches. Mention is also made of scaly bark by P. H. Rolfs in
the Proceedings of the same Society for 1905, p. 32. A disease
of the citrus trees in California, known by the same name, has
points in common with the one in Florida (Cal. Agr. Exp. Sta.
Bul. 200).
DESCRIPTION.
This is primarily a bark and rind disease of the sweet orange.
The wood is only affected secondarily, by poisoning due to the
withertip fungus. The bark of the trunk and of branches of all
sizes may be affected; but the greatest injury is done to the younger
branches and twigs up to about one-half inch in diameter, and to
the fruit.
SCALY BARK OF BRANCHES.
On the branches and twigs there develop more or less circular
or oval spots one-sixth to one inch across, rusty in color, and with
well-defined margins. The bark becomes brittle, begins to crack,
and forms small flakes or scales. These spots are at first scattered,
but may increase in number to such an extent as to become joined
together. The branch is rarely killed in the first year. During
the second year, additional spot, form between the old ones, and






Florida Agricultural Experiment Station.


* this may go on for several years until the branch is finally girdled
at some point and killed.





























Fig. 2. Branches of Orange affected with Scaly Bark.
Natural Size.

The development of the spots from their first appearance to
the stage just described, is slow as compared with many other
diseases. The spots first make their appearance on branches six
to nine months old, or older. On branches younger than this, spots
rarely occur. The first indication of a diseased spot on a branch
is a slightly raised band or ring one-sixth to one-quarter inch in
diameter. In many cases this band is composed of small dots or
pustules that appear to have broken out from under the green
bark. A small point also appears near the center of the spot. In
other cases the beginning of a spot is marked simply by a lemon-
colored area, which at its first appearance is nearly the size of
the fully matured spot. The bark on the affected area gradually
becomes rust-colored, hard, and brittle, and in the course of eight






Bulletin No. 98.


or ten months presents the appearance described above. On new
spots only the bark appears to be affected. A new bark is formed'
under the old as the latter cracks and flakes off. As the spots
develop, the withertip fungus comes in as a secondary agent, and
poisons the wood, causing the limbs and branches to die. Larger
branches, when not too badly diseased, may live on for many years.
The bark on these limbs becomes very rough and shaggy, so that
it shells off as the hand is passed over it. The outer bark is con-
stantly breaking up into flakes, and an irregular new bark is con-
tinually forming under the old.
SCALY BARK OF TRUNK.
This formation of rough scaly bark is also seen on the trunks
of badly diseased trees. As time goes on, the trunks present an
extremely rough and shaggy appearance. Pieces of bark one-half
inch or more in size are pushed up, sometimes over areas of several
inches in diameter, or a continuous surface of ruptured bark is
formed. New bark arises under the old, and only rarely do dead
areas on the trunk result from this disease. The exudation of
gum is a usual accompaniment.
SCALY BARK ON THE FRUIT.


Fig. 3. Orange showing rings and spots due to Scaly Bark Disease.

On the rind of the fruit the spots develop somewhat similarly
to those on the small branches. The disease affects only the outer





Florida Agricultural Experiment Station.


portion of the rind. The spots start either as rings, like those on
the small branches, or as round yellowish areas. These usually
begin to appear on the fruit in July and August. As the fruit
appr.,aches maturity, and while it is still green, the rings become
sunken and brown, because of the entrance of the withertip fungus,
while their central p:.rti:on, remain green. The fruit then colors
rapidly, the portion inside the ring sometimes remaining green
for a short time. The center is finally broken down by the wither-
tip fungus, and the whole spot becomes brown. Some spots are
formed which are not ringed. Fruits spotted by scaly bark color
prematurely, and drop before the picking season. Occasionally
gummy exudations occur at the spots on the fruit.

THE DISEASE INFECTIOUS.

'Scaly bark appears to be infectious. There are reasons to
believe that it may spread from tree to tree, and be carried from
one grove to another. The history of the disease, as told by several
old citrus gra:~\ver, also points to, this conclusion. The disease
was first known at Safety Harbor about the year 1860, and in one
grove only. At this place one nursery furnished the seedling trees
from which most of the oldest groves in the sub-peninsula of Hills-
boro County were planted. It is noticeable that nearly all .of these
old groves in that section of the State are diseased -with scaly bark,
while in no other part of the State, ex,:ept in one isolated grove,
has the disease as Yet been noticed.

TECHNICAL STUDY,

Studies both in the lab:ratitrv and in the field have been carried
on to determine the primary cause and to find a remedy for the
trouble. Studies of the diseased areas with the microscope and
in cultures have so far failed to reveal any organism regularly
present thinhn the diceaerj;' tissue, except the withertip fungus
(Ccllct..lrichImi j7.'-'osp'.i'io'I._), and this only in advanced spots.
It would appear that rn't until withertip began to be general in
the State, di.l the scaly bark disease assume an\' importance. Ex-
periments for the control- of the 1die.'e have been sytematically
carried on at FB:i:vie\- for the past two years. The results
obtained have been deemed of suficiellt value to be placed before
the citrus-growers for their .consideratricn. The nature of the
disease and its slow development upon the limbs and trunks, make
the effect of any line of treatment slow in showing itself. As the
de\el-lpmlent of the disease to its destructive f.:.rm is slow, so the
recovery of the tree after the ,Iource of infection is cut off requires





Florida Agricultural Experiment Station.


portion of the rind. The spots start either as rings, like those on
the small branches, or as round yellowish areas. These usually
begin to appear on the fruit in July and August. As the fruit
appr.,aches maturity, and while it is still green, the rings become
sunken and brown, because of the entrance of the withertip fungus,
while their central p:.rti:on, remain green. The fruit then colors
rapidly, the portion inside the ring sometimes remaining green
for a short time. The center is finally broken down by the wither-
tip fungus, and the whole spot becomes brown. Some spots are
formed which are not ringed. Fruits spotted by scaly bark color
prematurely, and drop before the picking season. Occasionally
gummy exudations occur at the spots on the fruit.

THE DISEASE INFECTIOUS.

'Scaly bark appears to be infectious. There are reasons to
believe that it may spread from tree to tree, and be carried from
one grove to another. The history of the disease, as told by several
old citrus gra:~\ver, also points to, this conclusion. The disease
was first known at Safety Harbor about the year 1860, and in one
grove only. At this place one nursery furnished the seedling trees
from which most of the oldest groves in the sub-peninsula of Hills-
boro County were planted. It is noticeable that nearly all .of these
old groves in that section of the State are diseased -with scaly bark,
while in no other part of the State, ex,:ept in one isolated grove,
has the disease as Yet been noticed.

TECHNICAL STUDY,

Studies both in the lab:ratitrv and in the field have been carried
on to determine the primary cause and to find a remedy for the
trouble. Studies of the diseased areas with the microscope and
in cultures have so far failed to reveal any organism regularly
present thinhn the diceaerj;' tissue, except the withertip fungus
(Ccllct..lrichImi j7.'-'osp'.i'io'I._), and this only in advanced spots.
It would appear that rn't until withertip began to be general in
the State, di.l the scaly bark disease assume an\' importance. Ex-
periments for the control- of the 1die.'e have been sytematically
carried on at FB:i:vie\- for the past two years. The results
obtained have been deemed of suficiellt value to be placed before
the citrus-growers for their .consideratricn. The nature of the
disease and its slow development upon the limbs and trunks, make
the effect of any line of treatment slow in showing itself. As the
de\el-lpmlent of the disease to its destructive f.:.rm is slow, so the
recovery of the tree after the ,Iource of infection is cut off requires





Bulletin No. 98.


a long time. We cannot expect to see the beneficial effect of any
treatment on the branches in much less time than eight to ten
months. Twenty experiment plots, each receiving different treat-
ment, were laid out. These have been continuously under observa-
tion, and form the basis for our conclusions.
REMEDIES SUGGESTED.
From the results of our observations and experiments we are
prepared to suggest one of the four following remedies.
I. TOP WORKING AFFECTED TREES.
Grapefruit, mandarins, and tangerines appear to be nearly im-
mune to scaly bark, even when surrounded by badly affected sweet
orange trees. Diseased trees may therefore be top-worked to one
of these varieties. At first sight this would seem to be too severe
a remedy; but, as a matter of fact, it can be carried out without
serious loss at any one time. This can be done by treating only
alternate trees in a row, or by treating alternate rows. In this
way the untreated trees will be found to produce a much larger
crop, and this will in a measure compensate for the loss of crop
on the top-worked trees.
During December or January, before any spring growth has
started, cut off all the large limbs as for ordinary top-working. Then
top-graft the trees. If the grafts fail to take, the sprouts that
start from the large limbs and body of the tree can be budded at
the proper time. Top-working has already been practiced by some
growers. As a further precaution, the trunks and branches may
be treated with carbolineum as suggested in remedy No. 2. When
thie.e top-worked trees begin to produce a fair crop, the untouched
trees may be treated in the same way.
If the grower does nbt wish to be constantly annoyed by sprouts
coming from the lower part of the tree, the trunk may be sawed
off at the ground and crown grafts put in. This, however, will
require a year or more longer to secure a tree in good bearing.
2. HEADING BACK.
During the dormant period, preferably in December or Jan-
uary, cut out the top, leaving only the trunk and the stubs of the
larger branches. Then paint the entire. bark and the cut surfaces
with one part of carbolineum to one part of water. In our treat-
ment of the disease in this way, which began in February, the bark
assumed a dark-red color. In a few weeks, as the growing season
came on, the tree put out new shoots, and by the end of summer
had grown a vigorous, healthy top. By that time the old scabs
had disappeared, and the bark had become smooth and free from
flakes. The carbolineum, far from injuring the tree, appeared to





Florida Agricultural Experiment Station.


stimulate it to increased vigor. Unless the entire grove is treated
in this way the young growth should be protected by spraying
with a I per cent. solution of carbolineum in May or June, when
the wood will have hardened.

3. PRUNING OUT.

This is a less drastic and less effective method. Prune out
thoroughly all dead branches and weak 'inijih. and spray with a
dilute solution of carbolineum. Use a I per cent. solution during
the growing -e: :.n Any strength up to 5 per cent. may be used
in the dormant season. The I per cent. solution is made as fol-
lows: Dissolve 3 pounds of soap in 2 gallons of water, add one-
half gallon of the best grade -of carbolineum, and make up to 50
gallons. The carbolineum diluted in this way is not at all injurious
to the hands or face.

4. BORDEAUX MIXTURE.

The use of Bordeaux mixture has been attended with beneficial
results in diminishing the number of.spotted fruits, but with bad
results in all..,,ini the increase of scale insects. A thorough test
was made as to the effects of this spraying mixture at different
times of the year, and with ;'i ff,:-'clt numbers of sprayings through-
out the year. The most marked result has been the diminished
number of spotted oranges on the sprayed plots, as c.i ma!,-rie with
the unsprayed plots. This test was repeated in the second year
on the same plots and in the same way as at first. During the
first year some effect was noticed, oin.ci;ily on those plots where
the spraying had begun early in the summer, but the results were
not 1 "i'.ii.i:c.1. During the -c'-..'il year a great diminution of
spotted fruit was seen in nearly all of the sprayed trees. The
amount of fruit, however, was con-iblcl:. 1-i diminished on the
plots sprayed at or near the 1-1l...:.;ing season. Our experiments
indicate that one Ih., i.-~ l.i la;.:iii at any time between November
and February is almost as efficient in diminishing the amount of
spotted fruit in the f.ll.-,\ i,- crop, as three or four -., .,in.i ;
during any other part of the year. It is also attended with a smaller
increase in scale insects.
Extreme caution must be taken in using Bordeaux mixture
for orange trees, since it kills the fungi that are useful in keeping
scale insects in check. If Bordeaux is applied it should be followed
by a good insecticide, or twigs from unsprayed trees bearing the
proper fungi should be hung in the tops of the sprayed trees a
week or two after the treatment. (See Bulletin 94 for the use of
the fungi, and Bulletin 76 for the making of Bordeaux mixture.)




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