CIRCULAR No. 27
MAY, INt
ALABAMA
Agricultural Experiment 
Station
OF THE
Alabama Polytechnic 
Institute
AUBURN
Citrus Canker
F. A. WOLF and A. B. 
MASSEY
Opelika, Ala.
Post Publishing Company
1914
COMMITTEE OF TRUSTEES ON EXPERIMENT STATION.
HON. R. F. KOLB------------------------------------- Montgomery
HON. H. L. MARTIN------------------------------------------------QOzark
HON. A. W. BELL ----------------------------------- Anniston
STATION STAFF
C. C. THACH, President of the College.
J. F. DUGGAR, Director of Experiment Station.
DEPARTMENTAL ORGANIZATION.
AGRICULTURE:
J. F. Duggar, Agriculturist.
E. F. Cauthen, Associate.
M. J. Funchess, Assistant.
J. T. Williamson, Field Agent.
0. H. Sellers, Assistant.
H. B. Tisdale, Assistant.
VETERINARY SCIENCE:
C. A. Cary, Veterinarian.
1. 5. McAdory, Assistant.
CHEMISTRY:
B. B. Ross, Chemist, State Chemist
J. T. Anderson, Chemist, Soils
and Crops.
C. L. Hare, Physiological Chemist.
T. Bragg, First Assistant.
S. Adler, Assistant.
EXTENSION :
L. N. Duncan, Superintendent*
J. B. Hobdy, Assistant.*
N. A. Negley, Assistant.*
Mrs. Birdie 1. Robinson.*
,C. S. Jones, Assistant.*
BOTANY:
J. S. Caidwell, Botanist.
A. B. Massey, Assistant.
PLANT PATHOLOGY:
F. A. Wolf, Pathologist.
HORTICULTURE:
Ernest Walker, Horticulturist.
J. C. C. Price, Associate.
G. V. Steizenmuller, Field Agent.
ENTOMOLOGY:
W. E. Hinds, Entomologist.
J. E. Buck, Assistant.
G. W. Ells, Field Agent.
ANIMAL INDUSTRY:
G. S. Templeton, Animal Hus-
bandman.
E. S. Girton, Assistant.
S. S. Jerdan, Assistant.*
A. R. Gissendanner, Assistant.
J. A. McLeod, Assistant.
*In co-operation with United States Department of Agriculture
CITRUS CANKER
By F. A. WOLF and A. B. MASSEY.
About three months ago our attention was directed
to the presence in the vicinity of Mobile, Ala., of a new
citrus disease which has received the popular name of
citrus canker. This disease was very severe in cer-
tain grape fruit groves during the previous season and
threatens to become the most serious difficulty with
which the grower will have to contend. For this rea-
son investigations were immediately begun, both in the
field and in the laboratory, to learn something of the
nature of the disease, its cause, its distribution, and
the means for its prevention and control. Sufficient
information has already been collected to warrant the
publication of this preliminary report for the purpose
of calling the attention of those interested in this in-
dustry, both as nurserymen and growers, to the pres-
ence of this malady, so that concerted efforts may
immediately be made to prevent its further spread
and development.
This circular is prepared at the request of the Citrus
Fruit Grower, the official organ of the Gulf Coast
Horticultural Society. This society has co-operated
through certain of its officers and members with the
Experiment Station in furnishing materials and facili-
ties for the prosecution of the investigations which are
being made. A complete report of these studies will
be published as soon as the work is completed. Spe-
cial thanks are extended to Mr. J. A. Dew, Insecticide
Department, Van Antwerp's Drug Co., for his hearty
and arduous co-operation and to Dr. E. W. Berger,
State Nursery Inspector of Florida for furnishing the
photograph of the diseased grape fruit from which the
illustration has been made.
DISTRIBUTION OF THE DISEASE.
It has thus far been impossible to make a careful sur-
vey of the area in which citrus plantings have been
made to determine the distribution within Alabama of
citrus canker, but it is believed to be quite widely dis-
tributed. Diseased specimens have been received and
examined from Mobile, Grand Bay, Axis, Bay Minette,
Fairhope, Robertsdale, and Calvert, Alabama. It is
reported in a recent bulletin (1) as having been intro-
(1). Stevens, H. E. Citrus canker. Florida Agricultural
Experiment Station, Bulletin 122; 113-118, figs. 4, 1914.
98
duced into two localities in Florida, and beyond doubt
it exists in other of the Gulf States.
HOST PLANTS.
Citrus canker is productive of more injury to grape
fruit than to any other citrus fruit. Leaves, young twigs,
older branches, and fruits are all subject to attack.
On Citrus trifoliata, this disease is thus far known to
attack only the twigs and branches. The injury to the
Satsuma seems to be slight, appearing to cause only a
spotting of the leaves. The native round or sweet
orange exhibits even more resistance than the Satsuma
but leaves have been found upon which a few spots had
formed. The kumquat is apparently free from attack.
SYMPTOMS.
The first indication of the disease upon the leaves
is the appearance of very small, circular, oily or wat-
ery dots. Within a short time these diseased areas ex-
tend through the leaf, appearing on the opposite leaf
surface as small yellowish or brownish spots. The
spots increase in size, becoming about one-sixteenth
of an inch in diameter and are elevated (Fig. 1).
These corky, elevated spots change to a light brown
color, maintaining an oily border. At this stage they
might, to the untrained eye, appear to be sour scab
infections. They may occur singly or in case the spots
are numerous they may grow together, making more
or less irregular areas. They may appear on either
surface of the leaf, being far more abundant, however,
on the lower surface. The leaf tissue surrounding the
diseased areas is paler green than the normal leaf tis-
sue (Fig 1.) and as the spots mature it becomes chlor-
otic or yellowish. Oftentimes the same spot will be ob-
served to be elevated on both sides of the leaf. Mature
spots on both the Satsuma (Fig. 2.) and the grape fruit
(Fig. 5.) are one-quarter of an inch or more in diam-
eter. They are dark brown in color, becoming at
length, grayish brown at the center. This grayish
color is imparted by the elevation and rupture of the
outer membrane of the leaf, resulting from the forma-
tion of the dark fruit-bodies (pycnidia) of the fungus
within the leaf. The pycnidia are scattered or formed
in more or less concentric zones (Fig. 5.). Consider-
able defoliation, in the case of the grap6 fruit, may
result at this stage.
The spots on the fruits of the grape fruit have much
the appearance of those on the leaves. They are
99
scurfy elevations and for the most part circular in
outline. The corky, diseased tissues, which remain
quite superficial, become variously fissured and brok-
en. The spots may unite by continued growth, form-
ing irregular, scaly areas. Affected fruits are thus
rendered very unsightly and unattractive (Fig. 3.).
The only species of citrus, of which the twigs and
branches seem to be subject to attack, are the grape
fruit and the trifoliate orange. On grape fruit stems
the disease first appears as oily, light brown blisters.
These enlarge, forming prominently projecting, irregu-
lar, corky outgrowths, which become, at length, fis-
sured and cankerous (Fig. 4.). Frequently, too, there
are no such outgrowths on the twigs but grayish areas,
dotted with the dark fruit bodies of the fungus, as
shown in Fig. 4, are formed. Stems may be complete-
ly girdled resulting in the death of the twig. Only
the outer tissues of the bark are destroyed and the
spots do not penetrate to the wood.
The disease is very severe upon the stems of Citrus
trifoliata. The base of the thorns is most commonly
the initial seat of infection. Circular spots of an oily,
dark brown color are formed. These spots gradually
increase in size, becoming zonate, with different shades
of brown, and possess a slightly elevated, darker mar-
gin. The diseased areas may become united so that
large portions of the branches are involved in a single
canker, thereby girdling them and causing their death
In advanced stages of the canker, the outer membrane
of the bark becomes frayed and torn, giving the gray-
ish appearance shown in Fig. 6. This rupture exposes
the corky, cankerous tisues below.
CAUSE OF THE DISEASE.
Several different fungi have been found associated
with the spots and cankers, but it has been determined
that the disease is caused by a species of i homa*.
Since several different species of Phoma have pre-
viously been reported on Citrus the specific name re-
mains to be determined only after further study. This
Phoma has been isolated in pure culture from grape
fruit leaves and twigs, from Citrus trifoliata twigs,
and from Satsuma leaves. Inoculations have been
made with pure cultures into grape fruit twigs and
* This is beyond doubt the same organism as the one which
:Stevens calls Phyllosticta, but the question of proper termi-
nology is reserved for consideration in the complete report.
100
leaves and into the twigs of Citrus trifoliata. The in-
oculations made on grape fruit twigs and leaves on
April 23rd, had developed the characteristic symptoms
of the disease by May 12th. The fungus fruited on the
artificially inoculated trifoliate twigs about two weeks
after the date of inoculation and the Phoma has been
reisolated. It exhibited the same appearance and
characteristic growth in culture as the organism orig-
inally isolated, which was used in making these inocu-
lations. This leaves no doubt that the Phoma, which is
being studied, is the cause of the disease.
TIME OF INFECTION.
The first appearance of citrus canker in the field,
during the present season, was noted on May 11th.
No infections were apparent in this grove when it was
visited on May 1st. Judging from this and the period
of incubation found in the artificial inoculation experi-
ments, infection must have occurred about two weeks
prior to May 11th. Infections must have taken place
earlier in 1913, than in the present season, since com-
parable seasonal conditions came about two weeks ear-
lier and since certain growers reported that consider-
able defoliation had occurred by May 11th, 1913, as a
result of the attacks of citrus canker.
CONTROL.
Experiments are being conducted in a grove of 98
grape fruit trees on the effectiveness of Bordeaux mix-
ture, ammoniacal copper carbonate and soluble sul-
phur in the control of this disease. The plan of these
experiments will not be described at this time, but
suffice it to say that very encouraging indications of
successful control have been obtained by the use of
each of these fungicides. In case, however, it is learn-
ed that mature parts are equally as susceptible as young
growth, it will be impractical to depend on the use of
fungicides, since it would require repeated sprayings
throughout the entire season. This point cannot be de-
termined until the experiments have progressed furth-
er. It seems quite probable that young trees, which
are only slightly attacked can be made to overcome the
disease by protecting their new growth with fungi-
cides and removing the limb cankers or covering them
over with Bordeaux paste.
Every effort should be made to avoid the further dis-
semination of the disease in new plantings. Young
grape fruit trees should be carefully examined before
101
being planted, to see that they are free from disease.
Subsequently, the grove should be occasionally inspect-
ed, as the disease can be much more easily eradicated
if it has not been permitted to become thoroughly es-
tablished. If the twigs of older trees are seriously
cankered it is probably advisable to prune off the dis-
eased parts, even though this necessitates cutting back
the trees rather severely. All of the disease parts
which have been removed should be burned. Judging
from the indications as regards the effectiveness of
fungicides, the new growth of the trees, thus pruned,
should be protected by spraying at intervals of several
weeks.
It is quite probable that the disease will not become
a menace to the Satsuma. In cise it is found to be al-
ready present in older groves, it will likely be most
economical to pick the diseased leaves and destroy
them. Since defoliation of citrus nursery stock is
required, there is little danger of the introduction of
citrus canker in new plantings of Satsuma. The trees
should be inspected from time to time, however, dur-
ing the first year, to guard them against infection from
nearby trees.
It will be a great aid in learning of the distribution
of citrus canker, if any grower finding the disease will
send specimens of the same to the Plant Pathologist of
the Alabama Experiment Station.
I
V 9 
-
, 
j