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Copyright 2005, Board of Trustees, University
UNIVERSITY OF FLORIDA
Agricultural Experiment Station
SCALY BARK OR NAIL-HEAD RUST
H. S. FAWCETT
Pepper Pub. & Ptg. o.. Gainesville, Fla..
Pepper Pub. & Ptg. o., Ga[_nsville, Flal.
Cause of Scaly Bark __-- -- ----------
Where Scaly Bark is present ...------
How to Identify Scaly Bark_-------
Control of Scaly Bark-------------
Effects of Bordeaux Mixture ----
-------- -------------- 3
.--_---....----- .-- ---------------- 3
---------------------....--- ------- 5
Distribution and History --- ------------- ------ -------------.- 13
Development of the Disease --------------.--------------------------- 14
Development of Diseased Spots ..------ .------- ---------. 14
Time of Infection --------------------------------------------------- 16
Age of Tissue infected ----.-----. ..---------------------------- 16
Investigations of the Cause .---------------------- ------- ----------. 16
Cladosporium herbarum, var. citricolum ---------------------- 16
Comparison with C. herbarum --------------------------------- 23
Inoculation Experiments------------------------- ------------- 26
Experiments for the Control of the Disease ----- ----- ----------- 29
Spraying with Bordeaux ..----. ..--------------------------- 29
Pruning ____------______ .._..._-___---- ----- 35
Heading back ----_ -. .------------------------------- 35
Spraying with Carbolineum --------------.-- 36
Copper Sulphate on the Soil_ ------ ------- -- 36
Top-working to Immune Varieties ---- .....------------- 37
Literature ____----------_ .--------------------------------------- 37
Summary___ ------. --------.-------. .- -------------------------- 40
1. Scaly Bark is a fungus disease of the sweet orange.
2. It causes serious losses by spotting the fruit and killing the
3. It is as yet confined to a few localities in Florida.
4. It may be avoided by grafting or budding to grapefruit.
5. Scaly Bark may be cured by heading back and painting with car-
bolineum or spraying with Bordeaux.
6. Scaly Bark may be controlled by thorough pruning and spraying
7. The spotting of the fruit may be prevented by spraying with
SCALY BARK OR "NAIL-HEAD RUST"
(Cladosporium herbarum, var. citricolum.)
BY H. S. FAWCETT
The first part of this bulletin is intended for those growers who desire
to find out, without the reading of unnecessary details, the cause of Scaly
Bark, the means of its prevention and cure, and enough of the distinguish-
ing characteristics to be able to identify the disease at its earliest appear-
ance. The second part is intended especially for those growers who wish to
know more in detail about the experiments and technical study on which the
reported results are based, and the nature of the fungi instrumental in caus-
ing the disease. In this respect it will be found useful also to plant patholo-
gists and other scientific investigators.
CAUSE OF SCALY BARK
Scaly Bark is a disease of the fruit and bark, and appears mainly on sweet
orange trees. The primary spots on both fruit and limbs, often known as "nail-
head rust" spots, have been found after much study and experiment to be
caused by a minute invisible parasitic fungus growth, which is so similar to a
common species well known scientifically as Cladosporium herbarum, as to be
considered a variety of it. This fungus, in common with molds, mildews,
rusts, mushrooms, and yeast, is a plant of low order. It arises from a spore
or seed-like body the shape of a pea, but so small that at least 5,000 of them
could be placed on a dot made by a sharp lead-pencil. From each of these
spores there grow out very thin cylindrical tubes or threads filled with a living
jelly, which penetrate the skin of the orange fruit or the bark of the branches,
and continually grow, branch out, and form threads or filaments which feed
on and also injure the tissues and cause diseased spots to appear. In, the
course of time, these spots on the limbs increase in number, become hard and
brittle, and finally make the bark scale off in flakes. During the progress of
the disease, the branching microscopic fungus threads are producing thou-
sands of microscopic spores like the one from which they originated. These
spores may be blown, or carried by insects or birds, or conveyed in many
other ways to the new growth of other orange trees, so that these may also
become infected. All this is going on unseen to the unaided eye, and can
only be known by the help of a compound microscope.
WHERE SCALY BARK IS PRESENT
Scaly Bark is most prevalent.in that part of Hillsboro County known as
the Pinellas Peninsula, but it hasibeen found in individual groves in several
other counties, as will be seen by examination of Fig. 10. The disease has
attracted much attention in the Pinellas Peninsula, because of its severity in
recent years. The study of Scaly Bark has shown that it is infectious, and
P1lordla Agricultural EixpcrimenW Station
there is every reason to believe that it may be easily spread from tree to tree
and from one grove to another. It should therefore receive attention in
other sections as well as in the section in which it is most prevalent, because
a.... i -D'SERNANDO
BA'o- E Q-_
A A L AC HI A
Fig. 10.-Present distribution of Scaly Bark in Florida.
of the danger of its being introduced into new regions on nursery stock or in
other ways. The advantage to the grower of being able to recognize at a
glance a disease at its earliest start can scarcely be over-estimated. There
are times when by the destruction of a single tree in a grove, or of a tree near
a house or barn, into which a disease had been carried, an entire grove may
easily be saved from being infected and ruined. It has been estimated that
the loss of fruit alone from spotting by this disease in one citrus growing
section is 20,000 to 30,000 boxes of oranges annually. The loss in badly
infected places in bad years is from 50 to 75 per cent. of the crop, and even
during favorable years it may run as high as 25 per cent. In addition to
S .. .. I C
\ .1.., ... t --. ....
other ways. The advantage to the grower of being able to recognize at a
this, there is the constant weakening of the trees from the spotting :and iscab-
bing and the dying back of the branches.
HOW TO IDENTIFY SCALY BARK
In order to identify Scaly Bark in the grove and distinguish it from other
diseases, it is necessary to look for certain characteristics.
Fig. 11.--A. Spots beginning. B. More advanced spots.
C. Scabby bark; spots have coalesced.
1.-On the smooth bark of branches 6 to 9 months old and older, will be
found more or less round or oval spots one-sixth to one-half inch broad,
raised above the surface, rusty in color, with well-marked edges (Fig. 11, A).
As the spots grow older the bark becomes glazed, then brittle, shows cracks
running lengthways, and at last breaks into small flakes and scales (Fig. 11, B).
In severe cases of Scaly Bark, these spots increase in number till they join
together, forming large patches of rusty or reddish-brown scaly and scabby
bark (Fig. 11, C).
2.-On the larger limbs, and sometimes on the trunk, will be seen
patches of rough shaggy bark, the small pieces of which shell off as the hand
is passed over them. (In some cases this shagginess of the old bark may be
3.-On the fruit will usually be found brown sunken spots, some of which
are apt to be in the form of sunken rings (Fig. 9). These spots are at first
yellowish to reddish brown on the green fruit, and finally become dark and
sunken. In ringed spots the rings first become sunken, with a higher part in-
side. This central part afterwards sinks in, and the whole area inside the ring
becomes dark. The spots vary in breadth from one-fifth to one-half inch. Fig. 9
shows fruit with both kinds of spots.
Florida Agricultural Experiment Station
The only two diseases which are at all likely to be confused with Scaly
Bark are Gummosis and Melanose, descriptions of which are here given to
make the points of difference clear.
GUMMOSIS.-The disease first makes itself apparent by the oozing out of
a thin watery gum, which sometimes runs down the bark in lines, forming
"tears." This gum comes from a crack or rupture in the bark of the trunk
or large limbs. Later on the gum thickens and collects in large quantities at
the cracked places in the bark. As the disease progresses, the bark cracks
still more, and assumes a scaly ulcerated appearance over patches a few inches
to a foot or more in length. The diseased patches may extend entirely around
the limb, or may be confined to one side of a branch. Gum may continually
ooze out all over the affected areas, or the gumming may cease for a time and
the old gum be washed away by the rain. This will leave only a scaly ap-
pearance which may easily be mistaken for Scaly Bark. In cases where the
gummosis is not too severe, new bark is formed under the old, and the surface
becomes marked by ridges, warts, and resinous-looking deposits, resulting
from the hardening of the gummy exudations. In severe cases the bark dies
to the wood, and the wood decays inward, often destroying the limb or the
Gummosis differs from Scaly Bark in the following points. Gummosis
does not affect all the tree from the trunk to the smallest twigs as does Scaly
Bark; nor does it spot the fruit. It does not appear as round or oval "nail-
head rust" spots, reddish rusty on the branches and dark brown on the
fruit, as does Scaly Bark. Gummosis presents a scaly shaggy appearance on
the trunk and larger limbs, almost identical with Scaly Bark; but lacks the
marks on the small twigs and fruit, and usually more gum is exuded. Gum-
mosis is found in severe form on grapefruit trees, as well as on other varieties
of citrus trees, while Scaly Bark is confined principally to the sweet orange
and rarely injures grapefruit trees.
In the "Florida Fruit and Produce News" for August 12, 1910, B. F.
Floyd described Melanose as follows:
Melanose is a disease that starts only on the young leaves, stems and
fruit. The individual marks or spots, caused by the disease, start as sunken
points, which grow larger and more evident as the tissue grows older.
They may reach a diameter as great as 1-16 of an inch. Frequently these
marks are so plentiful that as they grow they run together, forming a mass
or area in which the individuality of the marks will be lost. The individual
markings, and sometimes the areas, become arranged in circles, or parts of
a circle. This is characteristic of Melanose. In many cases, particularly
if the fruit hangs so that water drips on to it from a leaf or branch above,
the location of the areas will resemble withertip tear-staining.
The markings of Melanose in its mature condition are wax-like and
reddish brown in color. They somewhat resemble a drop of melted sugar
burned to a reddish brown color. They are slightly raised above the sur-
rounding surface. Upon the stems and fruits the markings more frequently
run together, forming areas. Where the disease is severe the stems will be
more or less completely covered with the markings. Young terminal twigs,
when severely affected, will die and dry up, appearing very much the same
as the stained terminal branches in dieback. The fruit, when severely af-
fected at an early age, will be stunted. In most cases it will grow to a nor-
mal size, but will have the markings more or less completely scattered over
its surface. The markings are not attached bodies like a scale, but are a
part of the tissue of the fruit itself. Therefore they cannot be removed, and
the fruit is worthless for shipment. The development of areas is greatest on
the fruit. Very often they are large, cake-like, and cracked in lines like
CONTROL OF SCALY BARK
The remedies and preventive measures here recommended are based on
investigations covering a period of about three years. These investigations
included experiments in a badly infected grove for the control of the disease,
a laboratory study of the cause, and observations of the results of various
methods of treatment practiced by the best orange growers in the regions
where this disease is prevalent. The nature of the disease and its slow de-
velopment upon the branches make the effect of any line of treatment slow
in showing itself. As the development of the disease to its destructive stage
is slow, so the recovery of the trees after the source of infection is cut off re-
quires a long time. We cannot expect to see the beneficial effects of any
line of treatment on the branches of the trees in much less time than 8 to 10
months. In the treatment for spotting of fruit, however, the results are
shown much more quickly. The treatment to be used for Scaly Bark will
vary according to the severity of the disease in the trees, and the attitude of
the grower toward his grove; whether he be looking for merely temporary re-
lief, or be willing to sacrifice present profits for future benefits. It will also
vary according to what other fungus diseases or insect pests may be present at
the time. Because of this difference in the outlook of the different growers,
and of the variation in conditions due to other troubles, five lines of treatment
that have been used successfully are here given, one or more of which may
TOP WORKING.-The study of Scaly Bark has shown that several varie-
ties of citrus (such as grapefruit, mandarins, and tangerines) are nearly im-
mune to this disease, even when surrounded by badly affected sweet orange
trees. Diseased trees may therefore be top-worked to one of these varieties.
This might seem to be too severe a remedy, but 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 com-
pensate for the loss of crop on the top-worked trees.
During December or January, or before any spring growth has started, all
large limbs should be cut off, as for ordinary top-working. Then the trees
may be top-grafted. 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 be-
low. When these top-worked trees begin to produce a fair crop, the un-
touched trees may be treated in the same way. It has been found that only
rarely does this disease affect the grapefruit limbs, and never, as far as has
been observed, does it produce "nail-head rust" spots on the fruit of this
If the grower does not wish to be constantly removing 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.
Florida Agricultural Experiment Station
HEADING-BACK AND BORDEAUX.-If the grower does not desire to
bud over to grapefruit, there are other methods that may be employed with
good results, though with less certainty of permanent success.
Fig. 12.--Results of spraying. Sprayed tree on the right.
Both were headed back.
Fig. 13.-Badly infected tree. Not treated.
During the dormant period, preferably in December or January, cut out the
top, leaving only the trunk and the stubs of larger branches, and spray thor-
oughly with Bordeaux mixture (5 pounds rock lime and five pounds copper sul-
phate, to 50 gallons of water). This should be followed by three or four addi-
tional sprayings, about eight weeks apart, as the new growth comes on. Fig. 12
shows the results of such treatment. On the left is a tree headed back; on
the right is a similar tree, which had been in addition sprayed 5 times with
Bordeaux. Fig. 13 shows the state of a tree neither headed back nor sprayed.
Fig. 14 shows the effect on the branches of spraying with Bordeaux 6 times.
These branches grew on adjacent trees during a period of 17 months, at which
time the tree from which B was taken was sprayed 6 times and the tree from
which A was taken was not sprayed at all. Fig. 15 shows the effects of two
sprayings with Bordeaux on B; A was unsprayed.
Fig. 14.-A, unsprayed. B, sprayed six times.
Florida Agricultural Experiment Station
Fig. 15.-A, unsprayed. B, sprayed twice.
HEADING-BACK AND CARBOLINEUM.-Another method, which was
quite successful in the experiments carried out by the Station, was
the heading back of the tree, as described above, accompanied by
the painting of the entire bark and cut surfaces with an emulsion
of 1 gallon of carbolineum to 1 gallon of water to which 1 pound of
whale-oil soap had been added. In our treatment 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 scabs had disappeared, and the bark had become smooth and
free from flakes. The carbolineum, far from injuring the tree, appeared to
stimulate it to increased vigor. Unless the entire grove is treated in this way,
the young growth should be protected by spraying with a good fungicide in
May or June when the new wood will have hardened. Fig. 16 shows an
orange tree headed back and painted with carbolineum, six weeks after treat-
Fig. 16.-Headed back and painted with carbolineum (half strength)
in February, 1907. Photographed six weeks after.
ment; and Fig. 17 shows the same tree, fourteen months after treatment.
PRUNING OUT DEAD WOOD.-As the infection of the new growth takes
place from the spores of the fungus in the old scabs on dead and badly infect-
ed limbs, much good can be done by pruning out these limbs. The experi-
ments carried out in a badly infected grove showed that pruning out all dead
wood diminished the amount of spotting on the fruit very materially, as will
be seen by referring to Diagrams I, II, and III.
In pruning, not merely the dead wood, but the whole of the badly dis-
eased limbs should be cut out. Care should be taken to make smooth cuts,
usually at the base of a branch or limb, so as not to leave projecting stubs in
which infection from other fungi may occur. After pruning, paint the cut
surfaces with carbolineum or pine tar. The best time to do this is in the
dormant period between the middle of December and the middle of January,
and again in July.
While the pruning will be of considerable benefit in itself, the disease
will continue to kill new branches as they put out. In order to make this
treatment more effective it should be followed up by spraying with some good
fungicide, such as Bordeaux mixture, 3 or 4 times.
SPRAYING TO PREVENT FRUIT SPOTTING.--One of the most obvious
osses from this disease is that caused by the spotting and dropping of fruit.
This loss may vary from a small percentage to 75 per cent. of the total crop.
Florida Agricultural Experiment Station
Fig. 17.-Same tree as in Fig. 16. Fourteen months after treatment.
By reference to Diagram II, it will be seen that this spotting was successfully
controlled during 1908 by spraying with Bordeaux mixture.
As the diseased spots and scabs are located almost entirely on the
branches, large limbs, and trunk, and not on the leaves, care should be taken
to spray the interior of the tree thoroughly. Spraying should be done so as to
cover the trunk and larger limbs, and also the entire surface of the wood out
to the smallest twigs. If the spray is thrown on from the outside, most of it
will be caught by the leaves, and but little good will result.
EFFECTS OF BORDEAUX MIXTURE
It is taken for granted in suggesting this treatment that the grower
already knows quite well the effects of this mixture in allowing an increase of
scale insects, and that he uses it with a full knowledge of this disadvantage.
No one is advised to use the Bordeaux, unless the progress of the disease
makes it necessary. Such increase of scale insects is due to the parasitic
fungi that keep them in control being killed by the Bordeaux mixture. This
increase may be prevented in part, either by the use of a good contact insecti-
cide, or by hanging in the sprayed trees, two or three weeks after spraying,
pieces of branches bearing the beneficial fungi; the red-headed fungus
(Sphaerostilbe coccophila), the white-headed fungus (Ophionectria coccicola),
and the black fungus (Myriangium duriaei).
DISTRIBUTION AND HISTORY
Scaly Bark is especially destructive on the west coast of Florida, in the
district called-the Pinellas Peninsula. As far as is known, it has only been
found in a few isolated groves in other localities (see Fig. 10). This particu-
lar disease is not known to exist in any other part of the United States, nor
in any foreign country. The disease known as Scaly Bark in California ap-
pears to be a different trouble, which is apparently more like the Florida
Gummosis. The Florida Scaly Bark is confined almost entirely to the sweet
orange. Other varieties of citrus fruits seem to be only slightly affected,
even when growing in close proximity to badly diseased sweet orange trees.
These other varieties are, however, rather more affected as the trees be-
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; in the
Proceedings of the Florida State Horticultural Society for 1908, p. 101, and
for 1909, p. 77; and a preliminary report was published in Bulletin 98 of the
Florida Experiment Station in March, 1909. Previous to this, H. H. Hume,
in a paper on the diseases of citrus, in the Proceedings of the Florida Horti-
cultural Society for 1901, p. 64, spoke 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 was also made of Scaly Bark by P. H.
Rolfs, in the Proceedings of the same Society for 1905, p. 32, and the com-
mon name of the disease was given by him. In June, 1906, Mr. J. E. Kil-
gore, acting on a committee for the Pinellas Orange Growers' Association,
spent much time in finding out the destructiveness and distribution of the
disease. He reported to the Experiment Station the threatening nature of
Scaly Bark, and the work on the disease was taken up in August of the same
The history of Scaly Bark, as learned from the older growers in the
Pinellas Peninsula, is of some interest. The disease had been known to them
for at least thirty or forty years, but the damage from it is said to have been
slight until a recent date. About the year 1840 Odette Phillippi, a French-
man of royal blood, came from Key West and settled with a small company of
other Frenchmen near the large Indian shell mound at the inner edge of
Safety Harbor, on what is known as Old Tampa Bay. Phillippi brought orange
and grapefruit seeds with him, and planted the grove, now some sixty years
old, owned at the present time by Mr. Phillippi's grandson, Mr. D. J. Booth.
It was in one of these original seedling trees, after it had become some twenty
years old, that the disease was first noticed. The disease is reported to have
spread very slowly, and almost imperceptibly, over the entire grove of several
acres. Contiguous to the grove, Mr. Phillippi grew nursery stock for many
years, and many of the old seedling groves of the surrounding country were
set out with trees bought from this nursery. All of these old groves that
could be traced back to the Phillippi nursery were found to be badly affected
with the Scaly Bark disease. These observations strongly indicate that the
disease originated at Phillippi's place and spread from his nursery.
Florida Agricultural Experiment Station
In the Report of the Florida State Horticultural Society for 1892 (p. 136),
Mr. A. L. Duncan gave the following account of this grove:
On the western side of the entrance to Safety Harbor in Hillsboro Coun-
ty, lies what is known as the Phillippi Hammock. It is a spot of rare
natural beauty ..On nearly the highest part, which is a rich shell soil,
Dr. Phillippi 50 years ago planted seed which came from Cuba. After the
war the place was neglected to a considerable extent, and the orange trees
are now dead or dying, while the grapefruit trees are in a thrifty condition,
bearing annually large crops of very excellent fruit. It would therefore ap-
pear that the grapefruit can safely be planted in shell lands where the sweet
orange, under certain conditions, is comparatively short-lived.
These "certain conditions," in the light thrown on the subject by the
Scaly Bark study, appear to have been due to this disease rather than to the
land being filled with shell, because orange trees in this same county on all
kinds of land where attacked by Scaly Bark are much injured, while grapefruit
is nearly immune.
DEVELOPMENT OF THE DISEASE
Along with the experiments for the control of the disease which are de-
scribed later, a study was made to find out, (1) the characteristic appearance,
size, and rapidity of development of the diseased areas, and the steps in their
development from their first appearance till they reach their destructive
stage; (2) at what time or times of the year the diseased areas first make their
appearance; and (3) at what age of growth of the stems the disease first
appears. For this study, copper labels, to the number of 303, were placed
in various places on branches of different ages. Notes were taken on these
at intervals of about two months for nearly two years.
The following are some of the results of this study.
DEVELOPMENT OF DISEASED SPOTS
The diameters of the spots on branches, when first noticeable to the un-
aided eye, were about 1 to 4 mm. They were circular or oval to irregularly
angled, and first became evident in the following forms: (a) faint lemon-
colored spots; (b) raised or ruptured reddish-brown portions of bark; (c) cir-
cular yellowish bands with a raised portion in the middle.
In most cases, the beginning of the spot is marked only 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 8 or 10 months the spots become rusty
in color with well defined margins (Fig. 11, B). At this stage they may be
10 to 20 mm. in diameter. The bark is raised, becomes brittle, and begins to
crack and form small flakes or scales. These spots are at first scattered, but
may increase in number to such an extent as to become joined together
(Fig. 11, C.) The branch is rarely killed the first year. During the second
year additional spots form between the old ones, and this may go on for sev-
eral years until the branch is finally girdled at some point and killed. On new
spots, only the epidermis and a few layers of cells below appear to be affect-
ed. As the spots develop, there is an increase of the parenchymal cells, and
sometimes a new bark is formed under the old as the latter cracks and flakes
off. Larger branches, when not too badly diseased, will live on for years with
the old marks of Scaly Bark upon them.
When branches in the condition of C, Fig. 11, are cut transversely, one
may often find, between the different rings of growth in the wood, tracts con-
taining loose tissue filled with a gummy substance. In many instances these
tracts seem to be entirely enclosed by a layer of healthy wood cells, while the
branch keeps on growing and forming new layers of wood and new cortical
cells at the cambium zone.
The development of the disease from its first appearance till the
branches become severely scabby, was watched on a number of stems and
branches, observations being made, as already stated, every two months.
The notes taken on two average cases from 1907 to 1909 are given below.
1.-A tender sprout, 2i feet long, growing from a large branch 5 feet
from the ground, on a tree in plot 6, was labeled on September 9, 1907.
November 4, 1907: further growth, 6 inches: no infection showing. January
8, 1908: no further growth. February 13, 1908: no further growth; no infec-
tion. April 2, 1908: growth 20 inches further than on November, 1907. July
7, 1908: a few spots developed at base of shoot. October 12, 1908: spots
well developed at base, and appearing on thorns of the newest growth.
December 2, 1908: spots many, most abundant near base, and distributed out
nearly to end of shoot. February 22, 1909: numerous spots especially on
oldest wood toward base of shoot. April 12, 1909: additional new growth
one and a half feet long: numerous new spots forming on older wood, and
some new spots also on newer growth, except the youngest. August 3. 1909:
branch extremely scabby and spotted all the way out from base. December
8, 1909: spots on oldest wood very abundant, 3 to 18 mm. in diameter, mostly
about 12 mm. The older spots, where the bark is superficially split and
cracked, in cross sections show brown gummy patches between the last two
layers of wood tissue; younger spots in cross sections show these gumming
patches just at or within the youngest layer of wood tissue.
On examination of normal branches near the outside of the tree the same
condition was found. In badly diseased stems a false cambium appears to be
formed within the bark, and some of the inner cortical cells are cut off from
the rest, leaving diseased patches inside or between the rings of wood. In
some cases darkened patches of wood were found opposite the diseased areas,
extending for a number of layers inward, indicating perhaps that the live tissue
had succeeded in cutting off the infected patches for a number of years in
2.-A new shoot, 1 foot long, recently grown from a large limb on a tree
in plot 3, was labeled on September 9, 1907. November 1, 1907: two feet ad-
ditional growth, but no spots yet seen. January 8, 1908: same. February
17: same. April 1: two feet additional growth. July 23, 1908: twelve inches
additional new growth since last observation; two spots developed. October
12, 1908: spots few, scattered along up to base of youngest growth. Decem-
ber, 1908: same. February 18, 1909: spots numerous out to base of newest
growth. April 28, 1909: new spots developing. December 8, 1909: shoot
now five feet long and one inch in diameter at the base; spots on oldest wood
6-25 mm. in diameter; on largest spots, bark cracked and broken; spots on
newest growth just beginning, 6-12 mm. in diameter. Cross section shows
the bark thicker at the spots. There appears to be formed an extra layer of
sclerenchyma cells within the bark layer. Cross sections of newest spots
show the cambium apparently not yet affected. Cross sections of older spots,
in which bark is not yet split, show a region of gum just bordering the last
well-formed wood, or sometimes apparently within it.
On the rind of green fruit the spots first appear either as round yellowish
areas, which soon become reddish to brown, or as slightly sunken rings with
an interior green area. These usually begin to appear on the fruit in July
and August. The earliest record of spots on the fruit is June 29, in 1907. By
September 6, of the same year, the spots were quite conspicuous; and by
November 5, they were well formed. As the fruit approached maturity, and
Florida Agricultural Experiment Station
while it was still green, the rings became sunken and brown, while their cen-
tral portions remained green longer. In some spots the center was marked
by a ruptured point which suggested infection from an insect puncture. The
fruit colored rapidly, the portion inside the ring sometimes remaining green
for a short time. The center was finally broken down and the whole spot
became brown. Many spots were also formed which were not ringed. The
spots varied with the variety of fruit and the thickness of the rind. The
spotted fruits colored prematurely, and dropped before the picking season.
The spots varied from 3 mm. to 15 mm. in diameter, but were mostly about
5 to 10 mm. across. They rarely extended deeply into the rind, but only af-
fected the outer portion. Spots rarely occurred on the leaves. When pres-
ent, they were somewhat similar to those on the twigs. They became reddish
rusty, while the affected leaf-tissue grew hard, glazed, and brittle, and was
surrounded by a yellowish border.
TIME OF INFECTION
It was found that new spots made their appearance on the twigs at any
time of the year, but the greater number of them first appeared between
about June 1 and December 1. During this period there was a succession of
new diseased areas, our records showing about the same number of infections
for each of the three observations made during that period. During the other
months of the year some new areas did appear, but not in such great numbers,
and they did not develop so rapidly as in the period above mentioned. The
diseased areas on the fruit first appeared about the first of July, and spots made
their appearance from that time until the fruit had ripened. They became
most apparent when the fruit began to color.
AGE OF TISSUE INFECTED
It was found that diseased areas rarely made their appearance in the
grove on twigs less than 6 months old. The most severe infection occurred
on wood 9 months to 18 months old. The disease often made its first ap-
pearance on much older wood than this, but usually such areas on vigor-
ous limbs healed over and caused no serious damage. The spots on the fruit'
made their first appearance about 4 or 5 months after the bloom had been
It will be seen that the inoculation experiment, to be described later,
showed that the fungus spores failed in the greenhouse to infect growth that
was less than 4 months old, and produced most infection on stems 5 to 8
months old at the time of inoculation. If 40 to 60 days are allowed for the
first appearance of the spot after infection, as shown by inoculation tests, the
observed, age of the earliest spotted stems in the grove agrees almost exactly
with that shown by the trees inoculated in the greenhouse.
INVESTIGATIONS OF THE CAUSE
CLADOSPORIUM HERBARUM VAR. CITRICOLUM
A fungus somewhat similar in cultures to Cladosporium herbarum has
been found when inoculated to cause spots on small orange stems, that are
identical in the early stages with spots produced by bringing the diseased
portions of branches affected with Scaly Bark into contact with healthy
branches. (See Figs. 18 and 19.)
Fig. 18.-Growth of hyphae from a stoma on a diseased
spot of an orange shoot, and spores of fungus.
(Magnified 480 times.)
Fig 19.-Hypha and stoma at very early
stage of diseased spot on orange
shoot. (Magnified 500 times.)
This was proved in the following way, details of which will be found on
a later page of this bulletin. (1) Pure cultures of the fungus were obtained
from the diseased areas. (2) Young sweet orange trees in the greenhouse
were inoculated from the pure cultures by spraying on the spores, and spots
were seen to develop upon the inoculated trees in from 40 to 60 days; while
trees not so treated were free from such spots. (3) These spots proved later
to be identical with those started by bringing diseased pieces of wood affected
with Scaly Bark into contact with healthy bark of trees in the greenhouse.
(4) Pure cultures of a fungus, identical with those from which the inoculations
were made, were isolated from these diseased areas.
Florida Agricultural Experiment Station
B. In orange agar, x 160.
This fungus occurs in cultures at ordinary room temperature in the
form of the genus Hormodendron (as does also Cladosporium herbarum). It
was therefore referred in the Annual Report of the Plant Pathologist for 1909,
p. xlvi, to Hormodendron sp. A study of the fungus has shown it to be
similar in many respects to Cladosporium herbarum Lk.; but since it shows
some distinct cultural differences, described later in this bulletin, it has been
thought advisable to regard it as a variety of C. herbarum, until a more per-
fect form of the fungus is found, if there be such. C. herbarum, as it now
stands in the literature, appears to be a rather variable species, and several
varieties of it have already been described. Some investigators have reported
Dematium pullulans De Bary, to be a form of C. herbarum. In the cultural
work with C. herbarum (from Dr. Westerdyk, Amsterdam) and the citrus
Cladosporium, this form was not produced from spores of either of these fungi.
Dematium pullulans (from Dr. Westerdyk) was grown on some of the same
media as the two last-mentioned fungi, but did not change to the Cladospo-
rium or Hormodendron form.
THE FUNGUS IN DISEASED TISSUE.-Spores of this fungus may be
found on diseased spots at any season of the year. The growth of the hyphae
and the formation of spores are usually quite different on living tissue from
their appearance in artificial cultures. The difference is so great that the
fungus would not at first be recognized as the same. On the dead tissue of
the diseased spots, the external hyphae are usually thick and closely septate,
with a tendency to constriction at the septa. The spores are one to two-
celled, being either of the Hormodendron or of the Cladosporium form. Both
spores and hyphae are straw-colored. On live tissue, on early spots, the
hyphae and spores are hyaline. The hyphae at this time may be very small
and inconspicuous and vary from 1-3 microns in diameter, without constriction
at the septa which are more distant. Although this fungus has been shown
to be the primary cause of the Scaly Bark disease, the investigations appear
also to show that the Withertip fungus, Colletotrichum gloeosporioides, is an
important secondary agent in the destruction wrought by the disease. In
numerous cases where the surface of diseased spots was sterilized, and under-
lying pieces of tissue were cut out and put into sterile test-tubes, Colletotri-
chum gloeosporioides grew up in them.
Fig. 21.-Colored hy-
pha producing a
From diseased spot
on orange shoot in
fied 430 times.)
An examination of the diseased areas at different
seasons of the year showed that both the Hormodend-
ron and Cladosporium form of spore were present. On
the youngest spots, the spores and hyphae were usual-
ly hyaline to only slightly colored (Fig. 21), but as the
spots became older the hyphae and spores became
more straw-colored or smoky. During warm weather
there were more spores of the Hormodendron form,
while during the cooler weather spores of the two-
celled Cladosporium form increased. During the fall
and winter, which is a dry season in Florida, spores of a
Coniothecium form were seen, and also microsclerotia.
The three forms of spore and the microsclerotia have
been seen in old cultures of the fungus in the laboratory, as well as on dis-
Fig. 22.--Germination of five spores of Scaly Bark fungus
in water. (Drawn from a photo-micrograph.)
eased trees. The two first mentioned forms of spore, together with the for-
mation of microsclerotia, have been observed by Bancroft in Cladosporium
herbarum on various plants in England (see Bibliography).
The spores from the spots, by numerous measurements, were found to vary
much in size. The one-celled spherical Hormodendron spores measured
from 3 to 6 microns in diameter. The Cladosporium-like spores measured,
when one-celled, 6 to 9 by 3 to 6, and the two-celled spores measured 8 to 12
by 4 to 6 microns. The small hyaline hyphae measured 1-3 microns and the
Florida Agricultural Experiment Station
older colored hyphae were 2 to 6 microns in width, with segments 6 to 9
ISOLATION OF THE FUNGUS.-The fungus (Cladosporium herbarum
var. citricolum) (Figs. 23 and 24) has been isolated repeatedly since Decem-
ber 1908 from diseased spots on branches and fruit. This has been done by
three different methods. (1) By touching a needle to the surface of diseased
spots and carrying out the usual dilution plate method of isolating organisms.
Cultures were obtained in this way both from spots just started and from
Fig 23.-Culture on standard agar. 1.5 per cent.
acid to phenolphthalein.
advanced spots. (In one series of cultures the fungus was obtained after
scraping off the surface of the diseased area with a flamed scalpel.) (2) Pieces
of branches bearing diseased spots were put into sterile test-tubes with a little
water at the bottom. The fungus was allowed to grow out from the surface,
and the spores were then sown in plates in the usual way. (3) The surface
of recently developed spots was sterilized and cut off with a flamed scalpel,
and a piece of the tissue underneath cut out, under aseptic conditions, and
put into a test-tube containing dilute sterilized prune juice or other medium.
In only a few out of many such tests were pure cultures of this fungus ob-
tained. In a majority of the tests, the withertip fungus, Colletotrichum
gloeosporioides, was also present, and in some cases no other fungus than the
Fig 24.-Culture on orange agar. Abundant spores.
withertip fungus was noticed, indicating that the withertip fungus is an im-
portant secondary agent in the damage from this disease.
CULTURES ON VARIOUS MEDIA.-The growth of this fungus on vari-
ous media was as follows:
Standard peptonized agur (1.5 per cent. acid to phthenolphthalein, tem-
perature 15 to 25 C.).-Mycelia at first white to gray in color; in 3 to 4
ays showing a dark center which enlarges as the conidiophores develop,
leaving only a white fringe of spreading hyphae. Hyphae composed of
short segments, at first hyaline, turning darker in a few days, irregularly
branched, bearing spores on upright conidiophores. Conidia in chains or
branched chains from any segment near the end of a conidiophore. Spores
spherical; 3 to 6 microns in diameter, or oval (6 to 9 by 4 to 6 microns); at
first hyaline, becoming smoky in color. (Fig. 23.)
Orange agar.-(Made by steaming young orange stems and leaves in
water at 800 C. for one hour, and adding agar to make 1.5 per cent.) Mycelia
became dark as soon as well formed. Spores were produced sooner and in
much greater abundance than on peptonized agar. Entire mycelium turning
dark olive-green to black. (Fig. 24.)
Gelatin Tubes.--Growth much as in standard agar. Gelatin was slowly
Irish potato plugs.--Growth grayish at first, usually not spreading over
entire surface, but forming sunken dun-colored patches or spots: hyphae
growing inward. In time forming dark, hard and crusty, raised, sclerotium-
Florida Agricultural Experiment Station
Sweet potato plugs.-Growth of fun-
gus very abundant, producing a velvety
dark green layer over the entire surface
of the plug with the formation of abun-
Rice tubes.-Growth less rapid than
that on sweet potato plugs. A black
velvety mycelium spreading slowly over
the surface and over exposed side of
substratum. In 5 days very abundant
growth, olive green; one month, black
growth growing into and through medi-
um. Hormodendron spores abundant.
White corn meal (Grits). -- Growth
about the same as on rice tubes.
Fig. 25.-From culture on rice,
ten days old. (Magnified 550
Orange agar tubes (Stab culture).-In 3 days, growth 6-10 mm. from
stabbed point, forming abundant spores. In 15 days, entire surface of me-
dium covered with a black matted growth; hyphae growing slightly into
medium. In one month, crust-like formation over top blackening the
medium, and small septate hyaline hyphae penetrating the medium. Hormo-
dendron-like spores abundant.
Orange wood plugs. (Pieces of live
orange branches sterilized in test-
tubes).--In 3 days, grayish growth on
surface. In 5 days, growth darker than
O' 0 on corn meal or rice. In one month,
O surface of stems covered with olive-
green growth; spores abundant, Hormo-
O O dendron-like. (Fig. 26.) After some
months, microsclerotia were observed,
Fig. 26.-Hyphae and spores from and spores were still present.
culture on sterilized orange stem. Orange peel. (Pieces in test tubes.)-
(Magnified 520 times.) In 5 days, very small amount of growth.
In 12 days, lumpy dark green growth,
sunken in spots. In one month, raised wrinkled dark mass with abundant
Hormodendron spores, hyphae in short bead-like segments.
Orange pulp.-In 5 days, a very small amount of growth on top and
edge. In one month, chains of spores formed similar to Sporodesmium.
Lemon peel.-In 5 days, small amount of gray growth. In 12 days,
raised black lumpy growth. In one month, Hormodendron spores and hy-
phae of bead-like cells present.
Lemon pulp.-In 5 days. no growth. In 12
days, a few dark specks at edge of medium. In
one month, dark growth of large swollen cells
with guttulae within, and only small amount of
true hyphae. Several months later, a black car-
bonaceous mass composed of Coniothecium spore-
masses. Spore-masses, straw-colored; with cells
6-9 microns in diameter. (Fig. 27.)
Apple plugs.-In 5 days, growth sparse. In
12 days, raised dark-green growth at points of
inoculation, but not spreading rapidly. In one Fig. 27.-Coniothecium-
month, two-celled dark spores of the shape of like growth from cul-
Diplodia spores; hyphae with enlarged cells con- ture on lemon pulp, af-
taining spherical bodies about the size of Hormo- ter 3 months. (Magni-
dendron spores. After several months, hyphae fed 560 times.)
swollen, containing dark chlamydospores 8 to 12
microns in diameter. Also larger two to three-celled club-shaped, Helminth-
osporium-like spores, 18x9 microns.
Banana plugs.--In 5 days abundant greenish growth; in 12 days a thick
olive-green mat of growth; in one month small hyaline hyphae growing well
into medium, with very small branches.
Red Beet.-In 5 days, growth gray to olive green. In one month,
abundant growth forming thick black velvety layer over surface. (Fig. 28.)
Cassava Stems.-In 5 days, growth not so
abundant as on beets. In one month, heavy
dark-velvety growth as on beets, finally becom-
ing black. Hyphae, close-septate. Spores
4-5 microns in diameter. Sclerotium masses
SJapanese cane.-In 5 days, growth rapid and
abundant. In 12 days, sooty growth all over
surface of medium, and abundant growth on
Fig. 28.-Growth on steril- surface of liquid at bottom of tube. One month,
ized red beet. (Magni- hyphae bead-like, inside the fibers of stem.
fled 520 times.) Spores Sporodesmium-like.
Corn on the Cob.-In 5 days, abundant
growth over surface. One month, black sooty growth over surface of corn
Corn stalks. (Taken near top of plant).-In 5 days, good growth, olive
green to black. In one month, abundant sooty dark-green growth with
Onion.-In 5 days, growth fair, in spots over surface. In 12 days, dark
thick growth over inoculated surface. In one month, hyphae bead-like.
Parsley stalks.-In 5 days, growth dark greenish, spores fairly abun-
dant. In one month, spores abundant, in chains.
VYelet bean petioles.-In 5 days, growth abundant, black in color. In
one month, abundant dark growth as on parsley.
GERMINATION OF SPORES AT 25 TO 30 DEGREES C.
Hyphal tubes three
times as long as the
Agar Germination just
(1.5 acid) begun.
Orange agar Germinating fast-
er than in either
of the other media.
Hyphal tubes 60-80
microns in length,
by 2 microns wide.
Hyphae 60-210 mi-
crons long, with
formation of many
hyaline spores in
chains. Spores 3 to
Hyphal tubes Rapid growth with
broader, but not so abundance of
long as in sterile spores.
Hyphal tubes 250 1 Hyphae darker, and
microns in length. not so broad as in
agar, but with a
great abundance of
COMPARISON WITH CLADOSPORIUM HERBARUM LK.
Parallel cultures of Cladosporium herbarum var. citricolum, and of Clados-
porium herbarum were made. The material of the latter was obtained from
Dr. Westerdyk, Bureau pour la distribution de cultures de moisisseures (Asso-
ciation international des Botanistes), Amsterdam, Holland. These parallel
cultures were made on nearly all of the media already mentioned. Distinct
differences in growth and spore formation were noted. (Fig. 29, A and B.)
Florida Agricultural Ecperiment Station
Fig. 29.-(A) C. herbarum Lk. (B) C. herbarum var. citric.lumn.
In agar, 3 p. c. normal acid.
Fig. 30.-Spores of C.
herbarum var. cit-
ricolum, after 24
fied 470 times.)
In general, on all of the various
media, the diameters of the spores
and hyphae of C. herbarum var.
citricblum Lk. were slightly
smaller than those of C. herbarum
Lk. from Amsterdam. The spores
of the former were usually more
strictly Hormodendron-like, and,
under favorable conditions, many
times more abundant. The dif-
ferences of growth in standard
peptonized agar at various per-
centages of normal acid and
Fig. 31.-Spores of
Lk., after 24
from Dr. Wes-
alkali are given in Table XIII. The acid used was ned 470 times)
normal hydrochloric, and the alkali, normal sodium
hydroxide. The temperature varied between 25 and 30 C. (See Figs.
30 and 31.)
GROWTH IN STANDARD PEPTONIZED AGAR.
VAR. CITRICOLUM OF SCALY
Spores germinating to a dis-
tance of 4-6 times their
length. Hyphae branching
Colonies smaller, more
dense, lighter, with more
even margins. Hyphae more
hyaline, more branched, not
constricted at septa. Spher-
ical spores, 3 to 5 microns
diameter; oval spores, 5 to
8 by 4; hyphae, 3 to 5 mi-
crons in diameter.
Growth about same as that
of C. herbarum. Colonies
thinner and lighter on edge,
dark in center.
(4 days) Growth good, much
as in 3 per cent acid. Abun-
(4 days) No growth.
(23 days) Slight delicate
(4 days) No growth.
(13 days) No growth.
(4 days) No growth.
(13 days) No growth.
(4 days) Colonies light gray;
2 to 5 mm. (13 days) Colo-
nies lighter than other fun-
(4 days) No growth.
(13 days) Slight growth.
I(4 days) No growth.
FROM DR. WESTERDYK.
Spores germinate to a dis-
tance of 10-20 times length of
spore: unbranched as yet.
Colonies larger, more open,
with more irregular margin,
growth more on surface of
medium; hyphae more col-
ored; septa more prominent;
hyphae straighter, less
branched. Spherical spores,
5 to 6 microns diameter, oval
6-12 by 5-6. Spore heads
more open, spores not so
Growth about same but light-
er in color than same fungus
on 1.5 acid. (13 days) Colo-
nies seal-brown. Spores more
abundant than same fungus in
1.5 per cent. acid.
Growth about same amount
as var. citricolum, but spore
heads more open.
(4 days) Good growth; spore
(4 days) Fair growth on sur-
face of medium.
(13 days) Dark crust forming
on surface of medium.
(4 days) No growth.
(13 days) No growth.
(4 days) Good growth, colo-
nies 3 mm., spore production
fairly abundant. (13 days)
Colonies darker than var.
(4 days) Very abundant
growth, whitish, no spores.
(13 days) Few spores formed.
(4 days) White growth, less
abundant than same in 1.5
(13 days) Few spores, less
than same fungus in 1.5 al-
Florida Agricultural Experiment Station
Inoculation experiments with pure cultures of the fungus (C. herbarum var.
citricolum) were made on young orange trees in the greenhouse. The account
of some of these inoculations which follows was given in the annual Report
Spores were sprayed on to the trees with an atomizer; spores were painted
over the surface with a camel's hair brush; and spores were inserted into the
bark by puncturing or by scratching the bark. The trees were well watered
twice a day, to keep them as moist as ordinary greenhouse conditions would
permit. Some of the trees were kept under bell-jars for several days after in-
oculation, and branches of other trees were enclosed in oiled paper which was
removed in a few days. Untreated trees were kept as checks in every case.
Inoculation tests have been made at three different times; on Feb. 15, March
11, and May 5, 1909. At each time there have been produced, in from 40
to 60 days, Scaly Bark spots that are identical with spots produced by bring-
ing diseased bark in contact with healthy branches of trees of the same age,
kept under identical conditions of growth. Out of 24 trees inoculated with
pure cultures of the fungus, 15 developed Scaly Bark areas one to four milli-
meters in size. The spots on inoculated trees never made their appearance
on the very young growth. The stems on which the spots appeared were from
4 months to 12 months old. Spots appeared on branches that were at least
4 months old at the time the spores were sprayed on the trees. The greatest
amount of infection was upon branches 5 to 8 months old at the time of inoc-
ulation. These experiments show that infection usually takes place on hard-
ened twigs, and that tender growth is quite resistant. From spots on inocu-
lated trees pure cultures of the fungus were again obtained, by the usual iso-
lation method on agar; and these, being transferred to other media, produced
growths identical with the pure cultures first isolated from diseased spots.
Previous to these inoculation experiments with pure cultures, the infec-
tious nature of the disease had been shown by hanging diseased pieces of stems
in contact with the bark of young trees in the greenhouse. Some of these
were held in close contact with the healthy tree by means of wrappings of par-
affined paper and raffia, and others were simply hung loosely and without
wrapping. Diseased spots, identical with many of those seen in the early
stages of infection by Scaly Bark in the orange groves, were usually formed
close to the infecting material; though in some cases, they were at considera-
ble distances from the diseased piece. Only a few of the diseased spots de-
veloped to any considerable size, and this is thought to be due to the greater
resistance of young trees to this disease. In groves where Scaly Bark is
prevalent, trees only a few years old are little attacked by the disease, while
older trees near by are badly affected.
Diseased pieces of stems were placed on 32 young trees. Of these, 28
showed infected spots in from 40 to 80 days, and all but one showed infec-
tion within five months. The spots were 2 to 5 mm. in diameter, and were
formed by a raised patch of bark which became rusty colored, hard and brittle.
These spots were also identical in appearance with many of the early signs of
infection before described as naturally occurring in diseased groves. Ring-
shaped spots did not occur on the trees in the greenhouse. As already stated
the spores produced by inoculation with pure cultures proved to be of the
same kind as those which came after infection by diseased pieces of stems.
Pure cultures of Cladosporium herbarum var. citricolum were recovered from
the spots produced in this latter way, as well as from those produced by pure
INOCULATION OF UNRIPE ORANGES IN THE LABORATORY.-The
fruit was but slightly green, and had been picked and shipped about 5 days
previously. It was carefully washed and dried in the laboratory. Inocula-
tions were made in three ways. (1) By placing the fungus on the surface
of the rind without injury to the epidermis. With four tests in the moist
chamber, no infection took place. (2) By pricking the surface in a num-
ber of places over an area of about one square inch, and rubbing the spores
over this part. With three tests, all showed spots similar to Scaly Bark spots
in about 20 days. On one of these fruits an infected spot remained green
much longer than the other part of the fruit, which is characteristic of the
spots developing naturally on fruit in diseased groves. (3) By pushing a bit
of the fungus under the epidermis by means of a sharp needle. With three
tests, all developed typical sunken Scaly Bark spots, 4-6 mm. in diameter, in
14 days. Checks showed only a drying of the injured cells.
RELATION TO WITHERTIP.- Microscopical examination of diseased tis-
sue, and numerous cultures from the same, indicated that the withertip fungus
(Colletotrichum gloeosporioides) plays an important secondary part in the injury
caused by this disease. In advanced stages of Scaly Bark spots, we often find
numerous acervuli of C. gloeosporioides and often observe the characteristic
killing-back effect of this fungus on the weakened branches. From well devel-
oped spots of nearly all stages, the withertip fungus has been obtained in the
following way: The surfaces of shoots with smooth bark were thoroughly
washed, and sterilized by immersing in mercuric chloride solution 1-1000;
then washed in sterile water, and put into test-tubes with a little sterile water
at the bottom. The numbers of times in which C. gloeosporioides was ob-
served in different tests are given in Table XIV.
The conclusion that Withertip is an important factor in the destructive-
ness of Scaly Bark is also indicated by the fact that the older growers had
known the disease for at least 40 years, but had only begun to consider it a
serious trouble in recent years, from about the time that Withertip began to
be prevalent and to cause much injury.
OTHER FUNGI.-The spores of a number of other fungi are of common
occurrence upon the surface of diseased spots. The most common of these
is a Diplodia with spores measuring about 24 to 27 by 12 to 14 microns.
Recent investigations in connection with gummosis have shown that there is
a common Diplodia with spores of this size, which is capable of producing
gum when put under the bark of orange trees. In a few tests, made by ster-
ilizing the surface of spots showing a slight gumming, and cutting small pieces
of diseased tissue from beneath the bark, a Diplodia grew in cultures in dilute
prune juice. As there is frequently some gum produced in various stages of
Scaly Bark, and as Diplodia spores are so common on Scaly Bark spots, it is
suspected that a species of this fungus is also frequently a factor in the de-
structiveness of this disease. Further work is needed to test this point.
Date when Number developing Clado-
Date when How made. of Colletotrichum sporium
made. tubes. gloeosporioi- herbarum
Dec. 6, 1906. Spots on fruit cut out 22 11 8*
and put into tubes.
Dec. 11, 1906. Spots on fruit washed in 24 9 6*
running water, immersed
in mercuric chloride,
1-1000,10 sec., and rinsed
in boiling water.
Mch. 9, 1907. Spots on shoots in all 26 20 1*
stages of development
washed J hour in run-
ning water, rubbed with
cloth and rinsed. Im-
mersed in mercuric chlo-
ride, 1-1000, li to 3min.,
and rinsed in 3 changes
of sterile water.
May 8,1907. Pieces of twigs and 19 14 3*
shoots 2-3 in. long con-
taining spots, rinsed in
mercuric chloride, wash-
ed and rinsed in dis-
tilled water; then into
mercuric chloride for 1
min., rinsed in 4 changes
of sterile water, and put
into test-tubes with ster-
ile water at bottom.
Same as above, but out- 8 7 0*
er layer of bark peeled
off just before going into
mercuricchloride the sec-
July 1, 1907. Pieces of shoots as be-
fore, washed, immersed
in mercuric chloride,
1-1000, and rinsed in
(a) 5 min. in mercuric
chloride. 4 3 I
(b) 3 min. in mercuric 2*
chloride. 3 2
(c) 2 min. 5 3 3*
Aug. 1, 1908. Pieces of shoots washed
in distilled water and
rinsed 5 times; then rin-
sed in 3 changes of ster- 12 8 4
ile water, and put into
sterile test-tubes with
Dec. 7, 1908. (a)Pieces of shoots wash-
ed in 3 changes of dis-
tilled water with slight
rubbing, and rinsed.
(b) Fruit washed in sev-
eral changes of distilled
water, and spots cut out
with flamed scalpel and
put on slant agar.
(c) Same, put on rice
Oct. 17, 1910. Spots on twigs and fruits
flamed, surface then cut
off, and piece underneath
put into sterile prune
(a) From twigs.
(b) From fruit.
Oct. 26, 1910. Same as above.
(a) From twigs.
(b) From fruit.
Nov.128,1910 Same as above.
Number developing Clado-
of Colletotrichum sporium
tubes. gloeosporioi- herbarum
5 0 3
6 0 4
*These records were made before Cladosporium herbal rum var. citricolum was
suspected to be the cause of the trouble, and are therefore probably more un-
certain and incomplete than they would otherwise have been.
EXPERIMENTS FOR THE CONTROL OF THE DISEASE
A badly diseased grove at Bayview, Florida, was used for experiments in
the control of this disease. One hundred and seventy-five trees, divided into
plots of six to nine trees each, were under observation and treatment. The
principal lines of experiment were: (1) Spraying with Bordeaux mixture at
various times of the year; (2) pruning out; (3) heading back, followed by
treatment with carbolineum, carbolic acid, or Bordeaux; (4) spraying with
emulsion of carbolineum in soap and water; (5) treatment of soil with cop-
per sulphate crystals.
SPRAYING WITH BORDEAUX
In the Bordeaux mixture spraying experiment, there were 10 plots of 9
trees each, and two check plots. A number of trees on one side of the
grove, which were not used in the experiments, were also good checks on the
work. The formula used for all the Bordeaux spraying was: 5 pounds of cop-
per sulphate and 5 pounds of lime to 50 gallons of water. The spraying was
Florida Agricultural Experiment Station
begun in May, 1907, and was continued at intervals of about two months
TIMES OF SPRAYING (See Diagram I)
Plot 1 was sprayed in May
S5 -- ---- July
"12 _----_.._ .-----. ....September
11 _____________________------------.__ _. November
2 May_--- ----- July
1" 0 May _--..--. __July ------September
S8 May July ------- September --------- November
7 ------------- July ------September .. ---- November
S9 _-------. September --------- November
The experiment was continued during the year 1908 on the same plots
and in the same order as in 1907. In addition, Plot 14 was sprayed in Feb-
In two months after the spraying had begun, the only effect that could
be detected was the killing of the lichens upon the trunks and larger limbs of
the trees. In five months, the leaves on the sprayed trees appeared to be
greener and more healthy than those on the unsprayed trees. In seven
months, in November, 1907, it was evident that the Bordeaux mixture had
cut down the percentage of spotted fruit upon the sprayed plots as compared
with the check plots. The number of new diseased areas formed upon the
wood was also less where the trees had been sprayed. In November of the
second year a more noticeable effect from the Bordeaux treatment was appar-
ent, as will be seen by the accompanying table and diagrams, showing the per-
centage of spotted fruit in the various plots. The average percentage of spotted
fruit on all the plots sprayed before November 1907, was 21.5, as against 36.1
per cent. on the check plots. The average percentage in 1908 for the same
plots was 0.9, as against 16 per cent. for the check plots. Plots 8 and 10
showed no spotted fruit in November 1908. A month later, a very few dis-
eased fruits were found, all of which had developed near the tops of one or
two trees on plot 8. The sprayed trees had greener foliage, and the number
of new diseased areas appearing upon the branches was greatly diminished,
while many of the spots which had begun were checked and did not develop
to any serious extent.
The percentages of spotted fruit on these plots were obtained in the fol-
lowing way: A count was made on each tree of all the fruit that could be ea-
sily examined while standing on the ground while the fruit was still hanging
to the tree, and the percentage of the fruit which had any spots at all was used
as the percentage for the entire tree. The average of the percentages for the
nine trees was then taken for the percentage of the plot.
This method of securing the percentages favors the checks, since in al-
most every case the fruit counted as spotted in the sprayed plots had fewer
spots than the fruit on the unsprayed trees. Many fruits on the check plots
were almost covered with spots, while rarely did any on the sprayed plots
have more than a few spots. For this reason, the actual results of the spray-
ing in each case were greater than the figures show. A noticeable effect of
spraying with Bordeaux was a diminishing of the amount of fruit on the spray-
ed plots. It was not possible to obtain the count of the total amount of
fruit from each plot, so that the actual loss in number of fruit could not
be learned. Generally speaking, the plots where sprayings were made in eir
their of the months of April or May appeared to show the greatest amount of
diminution, and those sprayed in July came next. The least amount of dimi-
nution appeared to result from the sprayings made in February, September or
October. A large part of this diminution early in the season was probably due
to the increase of scale insects which followed the application of Bordeaux
mixture. The gradual decrease of the Scaly Bark disease in the entire grove
from year to year, as seen from the checks, was probably due in part to more
favorable years, but was also due to better care of the grove, especially prun-
ing out of dead wood, which was done to some extent by the owner uniformly
throughout the grove. It must be kept in mind also in drawing conclusions
from the diagram of the experiment grove, that the amount of disease was
greater in untreated trees in the part represented by the upper right hand end
of the page toward plots 13 and 14, and gradually lessened toward plots 4 and
12 at the part represented by the bottom of the page.
PERCENTAGE OF SPOTTED FRUIT
Sept. ------------- 21.7
Nov. ---------- 22.1
May and July -- 18.6
May, Jul. and Sep. 22.0
May, Jul. Sep. Nov 20.6
Jul. Sept. Nov. 13.3
Sept. and Nov.--. 23.0
Pruned and spray-
ed, July--------- 30.5
Not sprayed__- 38
Pruned, July._--_ 17
Check, not sprayed 25.1
Check, not sprayed 47.1
April and July --_
April, July, Oct._
Apr. Jul. Oct. Dec.
July, Oct. Dec..--
Oct. and Dec.-_ --
Not sprayed ..--..
dS Not 2$
S- sprayed g
g > in1909. >
.5 ___----------- .3
2.5 ------.... 1.5
.5 __- ------ 1.6
.3 ___ 1.7
.2 ---------- 1.2
0 --- 1 .3
0 --- ----. .3
1.0 --- .3
2.5 -----.- i 3.5
1.0 ...... 2.2
3.4 --...- 2.2
2.1 ----- .2
12.9 ------- ---3.2
19.1 ---------- 4.6
EXPERIMENT PLOTS AT BAYVIEW, FLA.
Percentage of Spotted Fruit on Nov. 4, 1907.
EXPERIMENT PLOTS AT BAYVIEW, FLA.
Percentage of Spotted Fruit on November 13, 1908.
Plot 5. Plot 14.
ry Not Febr.,
July. 1Sprayed. 1908
2.5 18.2 3.4
EXPERIMENT PLOTS AT BAYVIEW, FLA.
Percentage of Spotted Fruit on November 13, 1909,
(No spraying had been done in 1909.)
Oct. Dec., '08.
Oct., Dec., '08.
The results of these experiments with Bordeaux, together with the ob-
servations as to the time of greatest infection, would lead us to conclude that
four applications of Bordeaux mixture the first in the dormant period in De-
cember, the second a little while before the bloom opens, the third after the
fruit is fairly set, and the fourth in the latter part of July or early in August-
would be quite effective in preventing the fruit from spotting, and would ma-
terially lessen the injury caused by the disease to the branches of the tree,
provided that scale insects were at the same time kept under control. During
the first year of the experiment, scale insects increased to such an extent on
those plots which were sprayed more than once, that the benefit from the
spraying was counteracted by injury from these insects. In fact these scale
insects became so abundant on plots 2, 7, 8, and 10, that an application of
whale-oil soap was used to control them. During the second year, the para-
sitic scale fungi (Sphaerostilbe coccophila, Ophionectria coccicola, and Myrian-
gium duriaei) were introduced into the tops of the sprayed trees, by hanging
in the trees pieces of stems about four inches long containing these fungi.
These were tied into the trees about one week after the spraying, three pieces
in each tree-top. During the second year, there were comparatively few
scale insects on any of the sprayed trees. This was attributed to the bring-
ing in of the parasitic fungi.
One plot was pruned out thoroughly, taking out as far as possible all
dead wood and badly diseased branches. The effect of this treatment was
clearly beneficial in lessening the sources of infection the first year, but the
disease gradually came back into the trees thus treated. In November, 1908,
while the pruned plot showed less spotted fruit than the check plot, yet it
had much more spotted fruit than the sprayed plots that were not pruned
out, and twice as much in November, 1908, as plot 3 next to it, which was
pruned and sprayed only in July of the year before. This would indicate
that thorough pruning out followed by spraying with Bordeaux would be more
beneficial than either alone.
A number of trees were headed back and treated in various ways. In
heading back, the tops were cut out, leaving only the trunks and the stubs of
the larger limbs. All the foliage and small suckers were removed. Two
trees were so cut about July, 1907: one was left as a check, and the other
was sprayed six times, during a period of 17 months, at the following dates:
October, 1907; February, 1908; April, 1908; July, 1908; October, 1908;
and February, 1909. An examination of the trees in November, 1908,
showed that no new diseased spots were forming on the sprayed tree (Fig.
14, B), while the growth 6 to 12 months old, on the check tree, was covered
with new spots (Fig. 14, A).
Branches of the same age were taken from each tree in March, 1910,
and photographed (Fig. 14). Each represents fairly the conditions of its
respective tree. Other trees headed back in February, 1908, and sprayed
5 times during the next year, showed as complete a recovery as this by March,
1910. A recovery, not quite so thorough, was well marked in other cases
where only one or two sprayings had been made.
In February, 1908, ten more trees were headed back. Two were painted
Florida Agriculth-al Expcirinrnt S'tation
with Avenarius' carbolineum, full strength; two with carbolineum one part,
to one part of water; and two with 25 per cent. crude carbolic acid, 1 part to
3 parts of water; two were sprayed with Bordeaux mixture five times, at in-
tervals of two months during the next year, and two were left without treat-
ment, as checks. The entire surface of the bark and the cut ends of the
limbs were painted over with the carbolineum in February. The full strength
appeared to cause some slight injury, but when diluted with an equal amount
of water, it was harmless. (The carbolineum may be made to mix with hard
water by first dissolving soap in the water.) As the growing season came on,
the trees put out new shoots, and by the end of the summer they had grown
vigorous, healthy tops. By that time the old scabs had disappeared, and the
bark had become smooth and free from flakes. The dilute carbolineum, far
from injuring the trees, appeared to stimulate them to increased vigor. An
examination of the trees in 14 months showed no scabby breaking out on
trunks or limbs; while check trees which had been headed back in the same
manner, but not treated, showed fresh ruptures on the bark and much less
vigorous growth. (Fig. 17 shows the appearance of a tree 14 months after
heading back.) In March, 1910, two years after heading back, a few spots
were coming back on the limbs. This was to be expected, since the new
growth had not been protected by spraying, and there were badly infected
trees standing near by.
On the trees painted in a similar manner with crude carbolic acid (25
per cent. pure), 1 part to 3 parts of water, the scabs did not heal up so com-
pletely, and the growth, though much more vigorous than that of the checks,
was not so vigorous as on those treated with carbolineum. The new scabs
also began to appear sooner on the new branches.
The trees sprayed 5 times with Bordeaux mixture (Feb., Apr., July,
Oct., 1908, and Feb., 1909) made a vigorous growth about equal to that
from the carbolineum-treated tree of Fig. 17. Two years after heading back,
the limbs were nearly free from spots, while the unsprayed checks showed
diseased and dying limbs throughout the tree. (Fig. 12.)
The recovery, though not so thorough, was quite marked in other cases
where only one or two sprayings had been made. Fig. 15 illustrates fairly
well the effect of spraying on trees not headed back. The branch (B) was
from a tree in plot No. 1, sprayed in April, 1907, and May, 1908, and the
branch (A) was from the new growth on a tree not sprayed, as a check. (Both
had originated since the sprayings began.) They were photographed in
March, 1910. The specimens were selected to show fairly the condition of
each tree. Two or three Scaly-Bark spots will be noticed on the sprayed
SPRAYING WITH CARBOLINEUM
One plot of nine trees was sprayed with a mixture of 2 quarts of Avena-
rius' carbolineum to 40 gallons of water in which had been dissolved 3 pounds
of whale-oil soap. This was done on October, 1908, December, 1908, and
February, 1909. By March, 1910, no effect from this spraying could be
COPPER SULPHATE ON THE SOIL
A number of growers were of the opinion that copper sulphate spread on
the ground, one pound to each large tree, was a preventive of Scaly Bark. A
plot of six trees was used to test any influence of copper sulphate. Beginning
with February, 1908, one and a half pound of copper sulphate, in the form of
small crystals, was scattered under each tree, in each of the months of Febru-
ary, April, July, September, December, 1908, and February, 1909; making
9 pounds in all to each tree in 12 months. In April, 1909, no influence,
either in checking the spotting on the fruit, or on the progress of the disease
on the branches, could be made out. These trees (which were next to plot 5)
showed many more spotted fruits than did plot 5, and about the same number
as upon the check plots. Subsequent examinations showed no difference be-
tween the checks and the treated trees. The copper sulphate as far as could
be detected had neither injured nor benefited the trees in any way.
TOP-WORKING TO IMMUNE VARIETIES
No experiments were carried out by the Station in this line, but observa-
tions of work of this kind done by experienced growers showed that the dis-
ease could be largely gotten rid of in this way. Here and there in the same
grove where the above experiments were carried on were standing grapefruit
trees entirely surrounded by diseased orange trees. Only after much searching
could even a few spots be found on the branches of these trees, and these ap-
parently caused but slight injury. Tangerine trees in the same grove showed no
Scaly Bark spots either on fruit or branches.
CONCLUSIONS.-Some conclusions to be drawn from these experiments
(1) The disease yields to spraying with Bordeaux mixture.
(2) Pruning out of the dead wood lessens the subsequent infection.
(3) Carbolineum one-half strength painted over the bark after heading
back is followed by a vigorous growth free from the disease.
(4) Spraying with one per cent. solution of carbolineum is of no practical
(5) Spreading copper sulphate in the form of crystals on the ground is of
LITERATURE OF CLADOSPORIUM HERBARUM
This is probably one of tte most common species of fungus known. It
has been reported from all parts of the world on a great variety of plants.
Much has been written in regard to it both as a parasite and a saprophyte.
Its morphology and biology have been extensively studied. Much has also
been written in regard to the polymorphism of this species, and it has been
considered at different times as a form of various perfect and imperfect
Bancroft (2), in 1910. showed that this species was able to cause the for-
mation of holes in green leaves of various plants, such as cabbage, cucum-
her, Arctimn lNppo, ( Catolpa bignonioides, Althuea. rose, and JITalra syl/vstris.
He found that the hyphae were colorless when young, becoming darker with
age. On living leaves, only the Hormodendron form of spore was produced,
but as the leaves died the Cladosporium spores were formed. These Clados-
porium spores on germination in water in a culture cell gave rise to the
Chittenden (9), in 1908, proved, by infection experiments with spores,
that this fungus was capable of attacking healthy leaves of some varieties of
apple. He was of the opinion that the infection takes place mainly through
the stomata. He found microsclerotia just below the epidermis of the leaf.
P~,lrida Agriculturaal lE.xp)crinmetct Station
L. Lopriore (25), in 1893, reported infection of wheat plants by sowing on
them spores of Cladosporium herbarum. Many other authors have consid-
ered this fungus a parasite. Kosmahl (22), in 1892, found it killing seed-
lings of Pinus rigid. Cavara (8), in 1891, considered it a parasite of rasp-
berries, Agaves, Fourcroya gigantea, and Cycas revoluta. R. Aderhold (1)
found it on Apricot leaves, and thought it might be the cause of disease.
Muth (27) in 1907, found it affecting bean seedlings in seed-beds. Cobb (10),
in 1892, considered this fungus a parasite of the wheat plant, and J. Ritzema
Bos (31) considered it a parasite of rye and wheat. F. L. Harvey (16) report-
ed it as blighting oats in Maine in 1894, and J. E. Humphrey (17) as attack-
ing winter rye in Massachusetts, in 1891. Numerous other authors have con-
sidered this fungus a parasite of wheat, rye, and other cereals and grasses.
Penzig (28), in 1887, in Italy, found this fungus on orange trees, assuming
many forms; and considered it a true parasite of the young parts of orange
A great deal has been written as to the polymorphism of this fungus.
It was considered by Janczewski (20), in 1893, as a conidial form of
Sphaerella tulasnei. Later, G. Lopriore (25),- in 1895, made an extensive
study of the fungus, and was of the opinion that Dematium pullulans and
Hormodendron cladosporioides were only forms of C/adosporium herbarum.
A. N. Berlese (3), in the same year, as the result of a long investigation with
pure cultures, concluded that Cladosporium herbarum and Dematium pullu-
lans had no connection. P. Planchon (29), in 1900, grew 20 species of
Dematieae in different culture media. He found that diverse media affected
the form of the vegetable cells much more than that of the reproductive
organs. The results of this extensive work by Planchon (29) was to show
that Hormodendron cladosporioides is a form of Cladosporium herbarnum,
but that Dematium pullulans and Cladosporium herbarum are distinct spe-
cies. He found, however, that C. herbarum under certain cultural
conditions assumed a form somewhat resembling D. pullulans. Sac-
cardo (32), however, assumes that C. herbarum and Dematiumnpullulans are
synonyms. The work of the author and 0. F. Burger with pure cultures of
Cladosporium herbarum Lk., C. herbarum var. citricolum and Dematiumn put.
lulans indicates, as does the work of Planchon (29), that C. herbarum and
D. pullulans are distinct species.
It has not not been attempted to get a complete bibliography of ('lald,-
porittumi hlrbarum. The following list, however, is thought to contain many of
the most important works on this fungus. In some of the publications given
will be found bibliographies containing still other references. In all cases
where the author was unable to consult any given publication, the place
where it was found reviewed or abstracted is indicated. Where possible, the
host plants, and the nature of the contents of the publication, are indi-
cated in brackets.
1.-ADERHOLD, R. (Landw. Jahrb. XXII, 3: 435-467. 1893.) Abstract
in Bot. Centrbl. LVI: 153-155. [On apricot.]
2.-BANCROFT, C. K. Annals of Botany XXIV: 359-372. 1910. Bib-
liography. [On various plants.]
3.-BERLESE, A. N. Rivista di Patologia vegetable (Firenze) IV: 2-45.
1896. With 6 plates. [On Euonymus japonicus. Morphology and
biology in cultures. C. herbarum distinct from Dematiumpullulans.]
4.-BRIOSI, G. and FARNETI, R. Atti Istit. Bot. Pavia, N. S., X: 1-60.
1904. With 11 plates. [Cladosporium, Ovularia, Haplaria, Pseudo-
fumago and Pseudosaccharomyces, are conidial forms of Rhynchodiplo-
dia citri. On citrus.]
5.-BRIZI, U. (Bollettino di notiz. agrar. XV: 563, 564. 1893.) Ab-
stract in Zeitsch. f. Pflanzenkr. IV: 348. 1894. [On maize leaves.]
6.--CARRUTHERS, J. B. Tropical Agriculturist (Ceylon) XX: 708. 1900-
1901. [On tea leaves.]
7.-CARRUTHERS, W. Jour. of Roy. Agric. Soc. X: 685. 1899. [On
8.- CAVARA, F. (Revue Mycol. XIII: 177-180. 1891.) Abstract in
Zeitsch. f. Pflanzenkr. II: 366-367. [On raspberry and other plants.J
9.-CHITTENDEN, F. J. Jour. of Roy. Hort. Soc. XXXIII: 500-511.
1908. [Infection experiments with apples.]
10.-COBB, N. A. Agr. Gaz. N. S. Wales III: 994-997, 1000. 1892.
[Parasitic on wheat.]
11.-COMES, O. (Atti del R. Istit. d'Incoraggiamento, (Napoli) VI.
1893.) Abstract in Bot. Jahresber. 1893. [On tobacco roots, with
12.-DELACROIX, G. (Bull. mensuel de 1' Office de renseignement agri-
cole. April, 1905.) Abstract in Zeitsch. f. Pflanzenkr. XVII: 52.
[Attacks peas. Culture experiments.]
13.-FRANK, A. B. Die Krankheiten der Pflanzen. Breslau. 1896. Pp.
290-296. [On grain.]
14.-FROELICH, H. (Pringsheims Jahrb. f. wiss. Botanik, XLV: 256-
301. 1907.) Abstract inBot. Jahresber., 1907; and in Exp. Sta.
Record XX: 17. [Fixes nitrogen.]
15 -HABERLANDT, F. (Wiener landwirthsch. Zeitung XXI; 245. 1878.)
Reference in Bot. Jahresber. 1878. [On rye.]
16.-HARVEY, F. L. Rept. Maine. Agr. Exp. Sta. for 1894. Part II, p. 96.
1895. [On oats.]
17.- HUMPHREY, J. E. Rept. Mass. State Agr. Exp. Sta. IX: 229. 1892.
[Attacks rye weakened by rust.]
18-IPPOLITO, G. d'. Staz. Sper. Agrar. Ital. (Modena) XXXVII: 664. 1904.
[In seed-coats of wheat.]
19.-IWANOFF, K. S. Zeitsch. f. Pflanzenkr. X: 97. 1900. [On rye
20. -JANCZEWSKI, E. Bull. de 1' Academie des Sc. de Cracovie, July,
1893. [C. herbarum the same as Sphaerella tulasnei.]
21.-KIRCHNER, O Die Krankheiten und Beschaedigungen unserer
landwirtschaftlichen Kulturpflanzen. Stuttgart. 1906. Pp. 36 & 68.
22.-KOSMAHL, A. (Ber. d. deutsch. bot. Ges. X: 422. 1892.) Abstract
in Zeitsch. f. Pflanzenkr. 1893; and in Bot. Jahresber. 1892.
[Attacks Pinus rigida.]
23.-KUEHN, J. (Fuehling's deutsche landw. Zeitung. 1876. Pp.
734-736.) Abstract in Bot. Jahresber. 1876.
24.-LAURENT, E. (Ann. de l'inst. Pasteur II: 558-566, 581-603.
1888.) Abstract in Bot. Jahresber. 1888. [Polymorphism in cultures.]
25.- LOPRIORE, G. Landw. Jahrb. XXIII: 969-1008. 1895. Extensive
bibliography. [On seedling wheat. C. herbarum not distinct from
26.-MCALPINE, D Fungus Diseases of Stone Fruits in Australia.
Melbourne. 1902. Pp. 99-100. [On margins of leaves affected with
27.-MUTH, F. (Sond. Jahresber. Ver. f. Botanik. 1907-1908. Pp. 49-
82.) Abstract in Zeitsch. f. Pflanzenkr. XIX: 358. 1909. [On bean.]
28.-PENZIG, O. Studi botanici sugli agrumi. Roma. 1887. P. 407.
[On all parts of citrus plants.]
29.-PLANCHON, P. Annales des Sci. Nat. (Botanique) XI, 1-248.
1900. [Twenty forms of Dematieae were grown on various media.
C. herbarum was identical with Hormodendron cladosporioides, but dis-
tinct from Dematium pullulans.]
30.--PRILLIEUX, E. Maladies des plants agricoles. Paris. .II: 252-263.
1897. [On cereals.
31.-RITZEMA-BOS, J. Zeitsch. f. Pflanzenkr. IV: 146. 1894. [Parasitic
on cereals in several European countries.]
32 -SACCARDO, P. A. Sylloge Fungorum XIX: 298-300. 1910. Bibli-
ography. [C. herbarum the same as Demalium pullulans.]
33. SCHNEIDER-ORELLI, O. Centralbl. f. Bakt. XXI, 2: 365 374.
1908. [On fruit of citrus.]
34 SCHOEYEN, W. M. (Beretning om Skadeinsekter og Plantesygdomme
i 1898. Kristiania, 1899 ) Abstract in Zeitsch. f. Pflanzenkr. X:
343. 1900. [On barley in Norway.]
35.-SORAUER, P. Zeitsch, f Pflanzenkr. II: 402. 1886. [On peas,
lilies and hyacinths.]
36.-SORAUER, P. Zeitsch. f. Pflanzenkr. V: 335, and VII: 223. [On rye and
wheat.] VII:4. [On potatoes with Alternaria.]
37.-STEVENS, F. L., and HALL, J. G. Diseases of Economic Plants. New
York, 1910. P. 447. [Attacks pine needles.]
38.--TUBEUF, K. VON. Diseases of Plants induced by Cryptogamic Para-
sites. English edition by W. G. Smith. London, 1897. P. 509.
39.--THUEMEN, F. V. (Fuehling's Landw. Zeitung. 1886. Pp. 606-
609.) Abstract in Bot. Jahresber. 1896. [On cereals.]
40.--WHITEHEAD, C. (Report on insects and fungi London, 1893. P.
60.) Abstract in Exp. Sta. Record VI: 65. [Causes black mold of
1. Scaly Bark is a disease of the fruit and bark mainly of sweet orange
trees, and occurs in only a few localities in Florida.
2. A species of fungus, which has been designated Cladosporium herba-
rum var. citricolum, has been isolated repeatedly from diseased spots, and when
inoculated into sweet orange trees was found to produce the early stages of
3. A study of the fungus has shown that its growth in cultures is similar
to, yet distinct from, Cladosporium herbarum Lk., obtained in cultures from
Dr. John Westerdyk, Amsterdam, Holland.
F~lorida~ IfI~ricultaral EI J)jperihnodL Stationl
Bulletin 106 41
4. The withertip fungus, Colletotrichum gloeosporioides, has been found
so constantly associated with C. herbarum var. citricolum as to be considered
an important secondary agent in the destruction produced by the disease.
5. It was found that the disease could be gotten rid of by budding or
grafting to resistant varieties of citrus, such as Pomelo (Grapefruit, Citrus decu-
mana), or Mandarin and Tangerine (Citrus nobilis).
6. It was found that the disease could be controlled by heading back
the trees, and either painting the bark with carbolineum, or spraying five to
six times with Bordeaux mixture.
7. Spraying with a two per cent. emulsion of carbolineum was of no
8. Spreading copper sulphate on the soil, one and one-half pounds in
alternate months six times, making nine pounds in all, proved of no practical