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record of the Institute for Food and
Agricultural Sciences and should be
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Copyright 2005, Board of Trustees, University
UNIVERSITY OF FLORIDA
Agricultural Experiment Station
STEM-END ROT OF CITRUS FRUITS
H. S. FAWCETT
Fig. 1.-Stem-End Rot of Immature Grapefruit.x,.
The Station Bulletins will be sent free upon application to tile
Experiment Station. (Gainesville, Florida,
1. Stem-end Rot causes the fruit to drop, or to decay in transit and'at the
market; it also kills back the twigs of the trees.
2. Its presence is indicated when the fruit drop and soften at the stem end.
This usually begins on immature fruit in August.
'3. Scale insects at the stem end of the fruit; an exceptionally warm'fall or
winter; and a damp and shady situation, appear to favor infection by this dis-
4. Spores of the fungus which causes the disease develop in spring and
summer on dead branches and bark, and on mummified fruit. The fungus lives
in the soil under infected trees.
5. Sound picked fruit, green or mature, can be infected by contact with this
fungus. Injured branches are readily infected.
6. Fungicides did not check the fruit from dropping and rotting in transit,
nor was disinfection proved useful.
7. Remedial measures are: (1) Pruning out and destroying all dead or
diseased branches; (2) destroying all dropped or diseased fruit; (3) culling and
careful handling; (4) cooling in transit; (5) spraying against scale insects.
Introduction ................... ..... ............ ............. 3
Injury from the Fungus ...... ........... ...... .... ........... 5
How the Fungus Lives and Grows .............................. ......... 5
Description of Stem-End Rot ............................................ 6
Conditions Favoring Stem-End Rot ..................................... 7
Infection Experiments .................................................. 8
Inoculation of Green Fruit and Branches on the Tree .................. 12
Description of the Fungus .................. ............................ 13
Experim ents for Control ....................... ........... .......... 16
Disinfection of Fruit ................................. ............ 19
Control M measures ........................................... 19
Catalogue of Rots, etc. .............................................. 22
STEM-END ROT OF CITRUS FRUITS
By H. S. FAWCETT
The information contained in this bulletin is based on investigations during
the two seasons 1909-10 and 1910-11. Our knowledge of Stem-End Rot and of
its control is as yet somewhat imperfect, and the conclusions and recommenda-
tions should therefore be considered as tentative, until further experiments have
been carried out. For the percentages of Stem-End Rot in shipments of fruit
from various parts of Florida to Washington, D. C., the author is indebted to
Prof. A. V. Stubenrauch, Expert in Charge of Field Investigations in Pomology;
and also to Mr. H. J. Ramsey and other members of the field staff of investiga-
tion of the Bureau of Plant Industry, who were making investigation of the rela-
tion of handling to the occurrence of decay in citrus fruits while in transit and
after arrival in market. They also gave invaluable co-operation in experiments oi
the disinfection of fruit in packing houses. Valuable assistance was rendered by
Mr. O.'F. Burger in the inoculation experiments and in the cultural work with
In November, 1909, the attention of the Experiment Station was
first called to this new kind of decay of citrus fruits which begins at
or around the stem end of the fruit. Letters of inquiry and specimens
were received about this time from a number of growers in Volusia,
Lake, and Orange counties. At first the disease seemed to be con-
fined to these three counties, but later observations and specimens
showed that although it was apparently most prevalent there, it was
also present more or less in nearly every citrus-growing county in the
State (see Fig. 2). It has been definitely noticed as doing considerable
damage by some few growers in Volusia county for two years or more
previous to 1909. The difference between this form of decay and the
Blue Mold decay had also been noticed by Mr. L. S. Tenny of the
Bureau of Plant Industry, in the fall of 1908, in shipments of Florida
fruit to Washington: D. C.,. for experimental purposes. There are no
authentic reports of its occurrence in the State earlier than this.
A study of this disease has shown that the softening and decay is
brought about through, the growth and penetration of. the tissues of the
fruit by the microscopic filaments of a fungus, which is found to be a
new species of the genus Phomopsis. This fungus was isolated from
partially decayed oranges, grapefruit, and other citrus fruits; and waas
4 FLORIDA AGRICULTURAL EXPERIMENT STATION
Fig. 2.-Present known distribution of Stem-End-Rot in Florida. Each (d~
represents a locality known to have the disease.
grown in pure cultures in the laboratory until it produced spores. The
spores were placed in contact with sound fruits which afterwards ex-
hibited the same kind,of decay, and from the interior of which the same
kind of fungus was again isolated.
INJURY FROM THE FUNGUS
The injury to the fruit from this decay is twofold. First, it causes
the fruit to drop and rot before or after its maturity on the tree (see
Fig. 1); and, secondly, it causes a softening and rotting of the fruit
in transit, or soon after arrival at the market. Careful records, in four
different localities, showed that from 15 to 32 per cent. of all fruit
dropped from infected trees, from all causes, between October, 1910,
and February, 1911 (see Table VII). From 35 to 85 per cent. of this
dropped fruit showed the symptoms of Stem-End Rot, at or soon after
the time of dropping from the tree. Shipping tests of fruit from in-
fected groves to Washington, D. C., made in co-operation with the
Bureau of Plant Industry, showed an average stem-end rot of 1.5 per
cent. on arrival; 8.5 per cent., one week after; 22.3 per cent., two
weeks after; and 36.7 per cent., three weeks after arrival.
HOW THE FUNGUS LIVES AND GROWS
Each minute oval spore of this fungus, about 1-3000 of an inch
long and one-third as broad (see Fig. 9), gives rise to an invisible fila-
ment that enters the fruit at the stem end while the latter is still hang-
ing to the tree or after it has been picked. If the fungus enters while
the fruit is on the tree, the fruit often drops. The fungus, by the con-
tinued branching growth of its innumerable interwoven microscopic
filaments, causes the infected fruit to pass through all the stages of
decay; from a slight softening without discoloration at the stem end,
through a dull brown or muddy color, to a soft sticky mushiness, and
finally to a hard withered mummy. These stages of' decay require
from one to two or three weeks, the shortest period usually coming in
the warmest time. Fruit picked from infected trees, inspected closely,
and packed in a perfectly sound condition, will often show signs of
rapid decay in a few days. If the weather is warm, the decay will often
develop in transit, and the boxes will show a high percentage of soft
fruit on arrival at the market.
The spurs from which the fruit has dropped frequently die back to
a distance of 3 to 12 inches or more, and often show small drops of
gum near the junction of dead and live wood. Spores of the fungus
have been found in abundance on these dead branches, and pure cul-
tures have been obtained from their interiors as well as from the inte-
rior of softened fruit. The pycnidia and spores of this fungus have also
6 FLORIDA AGRICULTURAL EXPERIMENT STATION
been found in abundance on killed bark and dead patches on the large
limbs and trunks of orange and grapefruit trees during the spring and
summer. Inoculation experiments, by introducing pure cultures into
cuts made in the bark of orange and grapefruit trees in the greenhouse,
show that the organism is able to induce gumming with more or less
killing of tissue.
DESCRIPTION OF STEM-END ROT
The appearance of this decay varies somewhat according to the
maturity of the fruit, the temperature at which it takes place, and the
amount of moisture present. A second fungus, Diplodia natalensis,
produces a decay so similar in its first stages, that it cannot be dis-
Fig. 3.-Orange showing wrinkling of skin and sinking at stem end due to
Stem-End Rot. About natural size.
tinguished from that due to Phooopsis sp. In the later stages of decay
these two may easily be differentiated. (The former decay is described
later in this bulletin.)
The decay usually met with in mature packed fruit develops on
oranges as follows. A circular patch at the stem end becomes soft
(see Fig. 3). This at the very first can usually be detected only by the
pressure of the finger, as there is often no discoloration of the rind.
This stage of rotting is well described in the words of a northern sales-
man, as follows: "I noticed that the oranges are affected with some
disease that causes a rotting in a peculiar way around the stem end.
From outside appearance oranges do not show rot, but by placing your
hand on the orange at this end you readily see that the orange has
decayed from the inside and is unfit for sale." As the softening ad-
vances and enlarges to include one-third to one-half of the fruit, the
rind changes to a dull brown, drab, or dark coffee color, and becomes
soft and sometimes sticky, with or without the exudation of a sticky
brown juice. The peel, however, does not become so brittle as in the
case of Blue Mold decay. If the fruit is opened, the decay will be
found to have proceeded most rapidly along the center where the
segments join, and along the inner white part of the rind, and not so
rapidly into the juice sacs (see Fig. 1). It may easily be distinguished
from the Blue Mold decay by the absence (as the decay proceeds) of
the blue-green, or olive-green powdery spore formation so character-
istic of the latter. It may be distinguished from the Diplodia Rot by
the absence of dark bands corresponding to the divisions between the
segments. In the grove, the earliest visible appearance of Stem-End
Rot on immature fruit is a dark brown, reddish brown, to almost black
discoloration about the stem end. This is sometimes seen on fruit still
hanging on the tree, especially in infected tangerine oranges. Sweet
oranges and grapefruit are more apt to drop off before the discolora-
tion begins. The first indications of the rot are usually seen in August,
or in the first part of September.
CONDITIONS FAVORING STEM-END ROT
The conditions that appear to increase Stem-End Rot are: (1)
presence of scale insects; (2) abnormally warm weather in the fall;
(3) dampness and shade in a grove.
Observations in a number of different groves indicate that Stem-
End Rot is most apt to develop in those fruits which have a number of
scale insects clustered about the stem. The scale insects (principally
Mytilaspis citricola) in many cases are found to have crawled under
the persistent calyxes of the fruit, and to have developed in great
numbers close to the stem or stalk. These weaken the fruit and make
it more subject to the attack of the fungus. Periods of unusually
warm weather after the fruit begins to mature appear to have a ten-
dency to increase the amount and to hasten the development of the
decay. Inoculation experiments with fruits, which are discussed later
in this bulletin, showed clearly that the fungus developed more rapidly
in a warm temperature. The greatest loss from Stem-End Rot has
been observed in groves that were rather moist and shady, although
s FLORIDA AGRICULTURAL EXPERIMENT STATION
the decay has also been found in groves under every condition of
moisture, thickness of growth, o: shade.
After the fungus had been isolated repeatedly from decaying fruits
(including grapefruit, sweet oranges, sour oranges, and tangerines),
laboratory experiments were undertaken to find out to what extent
sound fruit could be infected by previously rotted fruits, or by pure cul-
tures of the fungus. As a preliminary experiment, a few grapefruits
and oranges were inoculated, some with pure cultures, and some with
pieces of diseased tissue placed at the stem end. The fruit at room
temperature (which was at that time about 70 degrees F.) began to
show softening at the stem end in about two weeks. The same siymp-
toms of decay were produced by the application of the pure culture a:;
by the pieces of diseased tissue. Isolation cultures from the former
fruit (that which had been infected from cultures), gave pure cultures
of the same fungus again.
More extensive infection experiments were then undertaken. Most
of this work was done with oranges. In one small test, lemons were
used. The oranges were picked from a grove in which no trace of
the disease could be found, and shipped immediately to the Experiment
Station. One series of tests was as follows: Five glass jars were
partly filled with tap-water, and to four of them were added respec-
tively, pure cultures of fungus, pieces of diseased oranges, 2 pounds
of soil from under an affected tree, 3 pounds of the same soil after air-
drying in the laboratory for 16 days. The fifth jar remained untreated,
as a check. In all of these 5 jars sound oranges were placed and allow-
ed to soak for 24 hours. They were then taken out and wrapped, as
one would wrap oranges for market, and kept in ant incubator at 85
degrees F. They were inspected every week. At the end of two weeks
those which had not decayed were removed and allowed to lie in the
room for a week longer. Two other glass jars contained lemons: one
with cultures in tap water, and the other with water alone, as a check.
It will be seen from the following table (Table I) that infection took
place in all the tests, while none of the checks showed infection with
Another test was made to determine whether infection would take
place through any other part of the fruit than the cut end of the stem.
For this purpose the following means were employed: (1) The cut
end and calyx were covered with grafting wax, and cultures placed on
the stylar end. (2) The cut end of the stalk was covered with grafting
wax and cultures placed on the calyx. (3) The calyx was covered with
wax and cultures placed on the cut end of the stem. (4) Fruits on
which no cultures were placed were also kept as checks. After the
culture was put on, the place was covered with a bit of (lamp sterilized
cotton. The orange was then loosely wrapped in paraffined paper and
placed in the incubator, at about 85 degrees F. (28 to 30 degrees C.).
Table II shows the result of this test.
INFECTION EXPERIMENT, I
FRLtT IN WATER FOR 24 HOURS
Oranges with cultures of fungus .... .............
Oranges with pieces of decayed fruit .............
Oranges with 2 pounds of soil from affected tree ..
Oranges with 3 pounds of soil from same place, after
drying 16 days ............................. .
Oranges in water only, as checks ..................
Lemons with cultures in water ...................
Lemons in water only, as checks ..................
INFECTION EXPERIMENT, II
STE- END ROT
After After After MoLD
1 2 3
week weeks weeks
16 34 41 25
20 90 00 10
43 64 75
0 0 12
0 0 0 17
0 43 57
0 0 0 0
FRUIT W A'EPPED After After I After
1 2 3
week weeks weeks
Stem end and calyx waxed, and cultures placed on stylar end 43 43 43
Stem end waxed, and cultures placed on calx ........... 40 60 0o
Calyx waxed, and culture placed on cut end of stem ..... 87 100 100
Not inoculated, checks ............................. ..... 0 0
A third test was made to determine whether infection could take
place through attached stems of various lengths. For this test oranges
were specially picked with stems of lengths varying from one-half to
four inches. The calyx, and in most cases the entire epidermis, was
covered with grafting wax, leaving the cut end bare for the reception
of the culture which was put on and wrapped as in the former test. A
third table (Table III) shows the result of this test.
INFECTION EXPERIMENT, III
FaI;T \ND STEMS WRAPPED After I After I After
1 1 2 3
week weeks weeks
Cultures put on ends of stems 3 inches long ... ....... 0 1 43 I 45
Cultures put on ends of stems 2 inches long .............. 0 50 50
Cultures put on ends of stems 1V2 inches long ............. 0 100 100
Cultures put on ends of stems 1 inch long .................. 33 100 100
Cultures put on ends of stems inch long ...............I 0o) 100 100
Cultures put on ends of stems, normal clip ............... S7i 1/ 100 100
No cultures put on ends. checks .......................... 0 0 0.
10 FLORIDA AGRICULTURAL EXPERIMENT STATION
RESULTS.-The experiments show that, under laboratory condi-
tions, infection of sound oranges may take place not only through the
cut ends of stems up to 3 inches long, but also through the epidermis
of the fruit, and through the calyx; and that infection of oranges or
lemons may take place in water either from cultures, pieces of diseased
orange, or contaminated soils.
In the year 1910, another set of experiments in the infection of
fruit was made. For this test, fruits were used that were still slightly
green, although mature enough to be good for eating. The experiment
was planned not only to show the possibility of the fungus producing
decay in uninjured picked fruits, as was done in the previous year, but
also to find out its effect on injured fruit, and to compare this result
with the effect of three other fungi of citrus when brought in contact
with the fruit. The three other fungi used in the test were: the wither-
tip fungus, Colletotrichum gloeosporioides; the scaly bark fungus,
Cladosporium herbarum var. citricolum; and Diplodia natalensis. The
results shown in Table IV indicate that neither the withertip fungus
nor the scaly bark fungus was able to produce softening and decay
at the stem end, but that Diplodia natalensis was able to produce a de-
cay quite similar in its initial stage to that produced by Phomopsis sp.
STEM-END ROT INFECTION ON ORANGES, NOVEMBER 25, 1910
Fungus filamelits put on stem end .............
Fungus filaments put on punctured stem end .....
Fungus filaments put on cut peel ................
Spores of fungus put on stem end ...............
Spores of fungus put on cut peel ......... ......
No fungus put on stem end ...................
:No fungus put on cut peel ......................
Withertip fungus put on stem end ...............
Withertip fungus put on punctured stem end .....
W ithertip fungus put on cut peel ................
Scaly Bark fungus put on stem end .............
Scaly Bark fungus put on cut peel ...............
Gummosis (Diplodia) fungus put on stem end ...
Gummosis (Diplodia) fungus put on punctured end
Gummosis (Diplodia) fungus put on cut peel.....
In 5 In 18 In 23
days days days
22 66 100
33 100 100
100 100 100
0 0 100
0 100 100
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 60 so80
30 70 100
100 100 100
In this test the inoculations were made in the following ways:
first, by placing the fungus in contact with the stem end, without in-
jury to the fruit; second, by inserting a sterile needle a short distance
into the center of the woody stem end left on the fruit in picking, and
placing the fungus on this puncture; and, third, by making a cut with a
scalpel partly through the peel, near the stem end, and placing the
fungus on this cut. In case of the Phomopsis Stem-End Rot fungus, bits
of mycelium and spores of the fungus were used in separate sets of
fruit. All the fruit for this test were first carefully washed in tap-
water, wiped with a cloth damp with mercuric chloride 1-1000, and
allowed to dry. The surface of the stalk, where the fruit was clipped
from the tree, was then freshly cut across with a sharp scalpel. Checks
were kept, both uninjured, and with a cut rind. The oranges, etc.,
were wrapped separately in paper and put into open aquarium jars in a
temperature of about 80 to 90 degrees F. None of the checks showed
any Stem-End Rot. The checks with the peel partially cut through
showed a gradual drying and browning along the cuts, without any
softening. Those oranges that were inoculated with Colletotrichum
and Cladosporium were not at all softened, but Colletotrichum slowly
caused a browning of the rind that developed into a large round "An-
thracnose" spot with acervuli and spores. The Colletotrichum fungus
did not penetrate through the inner part of the peel, nor into the juicy
part of the orange. The Cladosporium fungus also remained in the
outer part of the peel and did not soften the orange fruits in the least.
Hard spots, resembling the "Nail-head rust" spots of Florida Scaly
Bark (See Bulletin 106, Fla. Agr. Exp. Sta.), were produced at the
cuts. The Diplodia softened the punctured and cut oranges rapidly,
but acted only slowly on the uninjured fruit, 20 per cent. of which re-
sisted its attack altogether. Of the inoculations with Phomopsis sp., a
hundred per cent. showed the presence of Stem-End Rot in 23 days.
Where the spores were used on the uninjured fruit the decay began
from the eighteenth to the twenty-third day; but on the fruit with cut
peel, the decay began from the eighth to the eighteenth day.
Apples were also inoculated with all of these fungi except Clados-
porium. Diplodia. iatalensis caused -rapid softening and rotting when
placed on cuts in the skin. In thirty days the numerous pycnidia with
one or two-celled Diplodia spores had pushed through the skin of the
shrunken apples. Colletotrichum gloeosporioides caused a slow rotting
resembling "bitter rot." The Stem-End Rot fungus, Phomopsis sp., ap-
peared not to affect the cut apples in the least.
Another test was made in infecting fruit by means of contact with
fungus-infected soil. The oranges were placed, stems down, in boxes
containing soil as follows: (1) soil from under trees known to be in-
fected with Stem-End Rot; (2) soil from Experiment Station grounds
where no citrus trees had been grown; (3) soil from the same
source into which cultures of the Stem-End Rot fungus, Phomopsis sp.,
had been stirred: (4) soil sterilized by steam; and (5) soil sterilized
by steam with the subsequent addition of the Stem-End Rot fungus.
The soils were kept moist and at a temperature of about 25 degrees C.
Table V shows that infection of sound oranges by contact with the soil
12 FLORIDA AGRICULTURAL EXPERIMENT STATION
was quite slow, and that a large percentage of the fruit was not at-
STEM-END ROT INFECTION OF ORANGES, NOVEMBER 29, 1910
ORANGES PLCED STErs DOWN IN Soir Oranges i
From under infected trees, Ormond Fla. .. 30
From Florida Experiment Station grounds 35
From Florida Experiment Station grounds
and fungus added ................... 40
From Florida Experiment Station grounds,
sterilized ............................ 30
From Florida Experiment Station grounds,
sterilized and fungus added .......... 60
Check, no soil .......................... 10
days 13 da.
On August 3, 1911, a set of inoculations were made by placing the
fungus on 1the stem end of green immature oranges cut from the tree.
The fruits were wiped with a cloth moistened with corrosive sublimate
1-1000. In some cases mycelium was used for infection, and in other
cases spores were placed on the stem end. The oranges were then
wrapped as for packing, and placed in an open glass jar without
moisture at a temperature of 82 to 88 F. Checks not inoculated were
wrapped and kept under the same conditions. The checks all remained
green, but some of them shriveled in a month. A representative orange
of those inoculated with spores, began to turn yellow in sixteen days,
was decaying at the stem end in twenty-two days, and had produced
pycnidia on the surface in thirty-five days (See Fig. 4). The oranges
inoculated with mycelium began to decay about a week sooner than
when spores were used. This experiment showed that the fungus is
quite active in breaking down the tissues of immature oranges as well
as that of mature ones.
INOCULATION OF GREEN FRUIT AND BRANCHES ON THE TREE
Inoculation experiments to determine the effects of the fungus
on young fast-growing orange fruits and branches were made. On
Sept. 24th, 1910, several green oranges were inoculated, both by placing
spores under the calyx, and by puncturing the rind slightly with a
needle and putting on spores. No development of the disease was ob-
served. On May 27, 1911, other inoculations were made in the same
way on fruit about half an inch in diameter, in the greenhouse. At the
punctured points were formed raised corky warts, but the fruit was
otherwise no more injured than the checks up to September, 1911. Re-
22 da. 31 da.
peated inoculation by insertion of the fungus into cuts made through
the bark of branches and twigs, with check cuts for comparison,
showed that the fungus is capable of inducing much gum under those
conditions and of killing the adjacent tissue, and killing back young
twigs; but so far all inoculations by placing fungus mycelium or spores
on the uninjured bark or rind of green fruit on orange trees, have
failed to show any effects. The fungus appears to be only semi-para-
sitic. It grows most readily and lives principally as a saprophyte.
Fig. 4.-Inmature orange showing white pycnidial pustules. Inoculated
with spores of Phomopsis sp. 35 days before. X1%.
DESCRIPTION OF THE FUNGUS
In the first stages of stem-end rot the hyphae of the fungus may be
seen extending through the tissue to the very edge of the softening.
If the fruit is still immature the juice sacs will remain intact without
the presence of a single hyphal thread, while the walls between the
segments and the tissues of the core and inner rind will be penetrated
by the branching mycelium. Only rarely are spores formed on the de-
caying fruits in the grove, until after the fruits become mummified
upon.the ground. In the laboratory, however, the formation of pyc-
14 FLORIDA AGRICULTURAL EXPERIMENT STATION
nidia .pushing through the epidermis has sometimes been observed on
immature fruit (See Fig. 4). The fungus is easily isolated from the
interior of partially decayed oranges, either by introducing minute
pieces into glucose agar on petri dishes, or by dropping small bits into
sterilized prune or orange juice. The color of the fungus growth is
white to chalky, not turning black, even with considerable age. On
glucose agar the growths become chalky white or mealy in appearance
in a few days. Aerial hyphen are produced, but no spores. Pycnidia
are seldom produced on ordinary media, such as agar or potato plugs.
When transferred to sterilized orange stems, Y2 to 2 inches in diameter,
the fungus first forms a chalky white mat of mycelium over the sur-
face, in which the pycnidia are produced in about four weeks. If kept
to coil. X420.
Fig. 6. Ach y a-like
growth, with protrusion of
protoplasm. In dilute prune
juice. X370 about.
moist, yellowish globular masses of spores ooze out from the pycnidia.
In some cases the spores ooze out in curved light-yellow strings. In
dilute prune juice the fungus hyphae are larger than usual, and imitate
at first the growth made by certain Phycomycetous fungi. As growth
proceeds the liquid is filled with the hyphse. As the fungus gets to the
top, short aerial hyphae are formed, sometimes with close coils on their
ends (See Fig. 5). A thick gelatinous to leathery mat of small inter-
woven hyphae covers the surface of the liquid, and sterile pycnidia
have sometimes been seen in this. Before any true spores were dis-
covered, the fungus was thought to be similar to Pythiacystis citroph-
thora which causes brown rot in California; but an examination of the
two fungi in parallel cultures soon showed that there were distinct dif-
ferences. Phomopsis sp. has the peculiar habit (in either dilute prune
juice or orange juice) of producing branches with protrusion of pro-
toplasm from the ends closely imitating the genus Achlya. This mass
of protoplasm forms distinct balls, and gives the impression of spore
formation (See Fig. 6). It was this condition of the fungus that led
author into thinking that the fungus might be a species of Achlya, and
it was so stated in the Proceedings of the Florida State Horticultural
Society for 1910. (A more detailed description of the cultural char-
acters of this species will be published elsewhere.)
Having seen the pycnidia in pure cultures it was easy to find the
same bodies upon the dead twigs and dead bark of citrus trees in the
grove. Without the aid of the cultures these would scarcely have been
suspected to belong to the same fungus as that seen inside the decayed
fruits. The pycnidia (See Fig. 8) push up through the epidermis of
the twigs, and are white to gray and sometimes even dark brown. They
are formed singly and are usually somewhat scattered.
Specimens were sent to Mrs. Flora W. Patterson, Mycologist.
Bureau of Plant Industry, U. S. Dep. of Agr., who kindly made an
examination of the fungus, and came to the conclusion that it must be
classed as a Phomopsis. No species of this genus was found to have
been reported on citrus.
Fig. 7.-Spores Fig. 9.-Germi-
a n d paraphyses. Fig. 8.-Diagrammatic section nati n g spores.
X750. of pycnidium. X45. X350 about.
16 FLORIDA AGRICULTURAL EXPERIMENT STATION
EXPERIMENTS FOR CONTROL
Two kinds of experiments for the control of the Stem-End Rot
were carried out during the fall and winter of 1910-1911. First, spray-
ing the fruit on the trees with various fungicides, beginning in Octo-
ber: and, second, the disinfection of the fruit in the packing house. The
results of these experiments were largely negative, although some val-
uable data were obtained in regard to the nature of the trouble. The
plan of the spraying experiments was as follows: Five plots of ten
trees each were chosen in a grove known to have had the Stem-End
Rot the previous year. One plot of ten trees was left as a check; the
second was sprayed with Bordeaux mixture of formula 5-5-50 ; the
third with ammoniacal solution of copper carbonate (3 pints ammonia
of 2(i degrees strength and 5 ounces of copper carbonate to 50 gallons
of water) ; the fourth with commercial lime-sulphur solution (about
30 Baume), one gallon to 25 gallons of water; and a fifth with copper
sulphide made by pouring a solution of 2 pounds of copper sulphate in
5 gallons of water, into 45 gallons of self-boiled lime-sulphur mixture
(8-8-50) while stirring. The spraying was done with the special pur-
pose of covering the fruit, there being no attempt to drench the entire
trees. Three spraying were made, one during the first week in each
of the months of October, November and December. The same ex-
periment was repeated in each of four different localities. Records
were made of the total number of dropped fruit from month to month
up to February, 1911. Through the co-operation of Prof. A. V. Stu-
henrauch, Mr. H. J. Ramsey and assistants, of the Bureau of Plant In-
PERCENTAGE or STEM-END ROT THREE WEEKS AFTER ARRIVAL. IN SHIIPLINT OF
FRUIT TO WASHINGTON, D. C.
SI Amm. |Copper Commercial
ORANGcES Check| Bordeaux copper sul- lime and
Carbonate phide sulphur
Locality A, Volusia County I 45.8 :17.s
Locality B, Volusia County 41.3 64.0 43.4 44.4
Locality C, Orange County 26.5 31.6 28.0 32.1 28.8
Average of A, B, and C .. 37.0 44.4
Average of B and C ....... 34.0 47.8 35.7 38.7
Locality A, Volusia County I 22.S 26.4 15.4
Locality D, Polk County ... 3.5 10.0 4.9 6.7 2.7
Average of A and D ....... 13.1 15.6 11.0
dustry, 2 shipments of fruit from each of these experimental plots were
made. The fruit was shipped to Washington, D. C., and inspected on
arrival, and also one, two, and three weeks after arrival. As will be
seen from the table showing the average percentages of Stem-End Rot
for the different localities after holding three weeks at Washington,
none of the fruit showed any marked benefit from the spraying, and the
liordeaux appeared as if it was actually harmful (See Table VI).
The records of dropped fruit from these same plots showed that
there was no prevention of the fruit from dropping, but that in the
case of Bordeaux mixture the percentage of dropped fruit was con-
siderably increased (Sec Table VII). This is thought to be due to the
increase of scale insects which the use of this spraying mixture caused.
PERCENTAGE OF FRUIT DROPPED FROM THE TREKS BETWEEN AB')UT OCTOBER 1. 11111,
AND THE MIDDLE OF JANUARY, 1911
I I Amm. Copper Commercial
ORANGES Check! Bordeaux copper sul- lime and
|I carbonate phide sulphur
Locality A, Volusia County 19.36] 18.53
Locality B, Volusia County 15.601 25.82 17.23 16.13
Locality C, Orange County.I 14.361 15.64 13.47 13.73 16.10
Average of A, B, and C ...I 16.44! 19.99
Average of B and C .......I 14.98o 20.73 15.35 14.93
Locality A, Volusia County 26.901 29.02 32.94
Locality D. Polk County.... 10.47! 14.30 0.27 10.01 16.25
Average of A and D ....... I 1S.68 19.14 21.47
In the shipping tests made from the sprayed plots, the oranges or
grapefruit picked from the upper part of the tree were kept separate
from the fruit picked from the limbs next to the ground, for the pur-
pose of finding out whether any infection came up from the soil as was
at first suspected. The results, in Table VIII, show that. in the case of
the oranges, the lower fruit averaged slightly more infection than the.
upper fruit; but that, in the case of the grapefruit, the upper fruit
averaged a little more than the lower. This appears to indicate that
no appreciable amount of infection takes place because of nearness to
the soil. The table shows the comparison for the checks or unsprayedd
STEM-END ROT IN SHIPMENTS OF FRUIT. COMPARISON OF UPPER AND LOWER
FRUIT ON TREE
OR\NGES Average of three localities. Two shipments e-ach.
Location of fruit On arrival In 1 week In 2 weeks I In 3 weeks
on tree Per cent. Per cent. Per cent. Per cent.
Upper fruit ........ ....... 1.6:1 8.10 I 19.7 33.90
Lower fruit .............. 1.3 8.80 24.8 39.50
GRAPEFRUIT Average of two localities. Two shipments each.
Upper fruit .............. 0.23 | 0.76 2.02 8.37
Lower fruit .............. 0.03 i 0.51 1.26 ) 7.84
As has already been stayed. two different sets of shipments were
made from the sprayed plots. These sets were made about one month
apart. Talle IX shows that the average percentage of Stem-End de-
18 FLORIDA AGRICULTURAL EXPERIMENT STATION
cay for the first set is much less than the average for the second set
shipped a month later, indicating that the maturity of the fruit may
have an influence on the amount of Stem-End Rot.
STEM-END ROT IN SHIPMENTS OF FRUIT SHOWING RELATION Of MATURITY TO
AMOUNT OF STEM-END DECAY
ORANGES Average percentage of three localities.
Date of shipments On arrival In 1 week In 2 weeks In 3 weeks
Dec. 30, Jan. 9, Jan. 10.... 0.7 3.4 14.3 25.3
Jan. 23, Feb. 13, Feb. 23... 3.3 15.6 35.5 53.1
GRAPEFRUIT Average percentage of two localities.
Dec. 28, Jan. 9 .......... 0.00 0.18 1.20 3.9
Jan. 16, Feb. 23 .......... 0.55 1.25 3.17 22.2
That washing the fruit appears to increase the amount of Stem-
End Rot in any sample of fruit is indicated by Table X which gives
an average comparison between washed and unwashed fruit from 37
different experiments carried out by Stubenrauch and Ramsey of the
Bureau of Plant Industry. The percentage indicates the average
amount of Stem-End decay after holding 2 weeks at the packing
STEM-END ROT AFTER R H-OLDING 2 WEEKS IN PACKING HOUSE
37 Experiments, 32 Packing Houses
SNot washed] Washed
Careful pick and pack .............................. 1.68 2.06
Commercial pick and pack ......................... .1.97 2.33
The effects of holding oranges 3 to 4 days in the packing house
before packing are brought out by Table XI which is the average of
15 series of shipments made by Stubenrauch and Ramsey. Immediate
shipments were packed and shipped as soon as possible after packing.
Delayed shipments were held in the packing house three or four days
before packing. The difference is somewhat in favor of immediate
shipment so far as this disease is concerned.
PERCENTAGE OF STEM-END ROT IN IMMEDIATE AND DELAYED SHIPMENTS
On After After Atter
arrival 1 week 2 weeks 3 weeks
Careful pick Immediate ............. .46 4.94 9.01 18.92
and pack Delayed ............... 2.30 12.21 18.64 24.90
Commercial pick Immediate ............. .61 5.54 9.57 18.47
careful pack Delayed ............... 2.72 11.13 19.25 25.30
Commercial pick Immediate ............. 1.03 6.69 16.47 23.45
and pack Delayed ............... 2.53 11.54 19.72 24.06
Averages of 13 series of shipments from Volusia, Lake and Orange counties.
DISINFECTION OF FRUIT
Experiments in disinfecting fruit in the packing hose were carried
out in two different places with the co-operation of Stubenrauch and
Ramsey. In both these localities Stem-End Rot was present. All
the oranges were washed and were afterwards treated, in lots of two
boxes each, according to the following plan:
(a) Sprayed with ammoniacal copper carbonate as the fruit came
out of the wash water.
(b) Not sprayed, as a check to (a).
(c ) Soaked in water with decayed fruit for 20 minutes, and then
sprayed with ammoniacal copper carbonate.
,(d) Soaked in water with decayed fruit for 20 minutes, and
sprayed with potassium sulphide (1 ounce to 2 gallons of water).
(e) Soaked in water with decayed fruit for 20 minutes but not
sprayed, as a check to (c), (d), (h) and (i).
(f) Soaked in water with pure cultures of the fungus for 20 min-
utes, and sprayed with ammoniacal copper carbonate.
(g) Soaked in water with pure cultures of the fungus but not
sprayed, as a check to (f).
(h) Copper sulphate (1 pound to 1000 gallons) added to water
in which decayed fruit had been placed. After the copper sulphate was
dissolved the fruit was soaked in the water.
(i) Formalin (1Y pints to 1000 gallons) added to water in which
decayed fruit had been placed, and fruit soaked as in (h).
The fruit was then packed and inspected every two weeks until the
sixth week. No conclusions could be drawn from the results since
they were not consistent. As much Stem-End Rot occurred in the di,-
infected fruit as in that not treated, and in some cases more.
It would seem that the experimental facts at hand give little en-
couragement to spray (with the fungicides named above) for Stem-
End Rot after October. There is moreover no encouragement toward
the use of these fungicides or disinfectants in the packing house, in
the two experiments already carried out. These tests should, however,
be repeated several times before definite conclusions are drawn. The
figures accumulated by Prof. A. V. Stubenrauch and his associates in
regard to Stem-End Rot (See Table X) show that careful handling
has a perceptible, though rather slight, influence on the percentage of
decay. It would seem. therefore, that although infection can undoubt-
edly take place af:er the fruit is picked from the tree, the evidence at
hand indicates that in actual practice most of the germs of decay are on
20 FLORIDA AGRICULTURAL EXPERIMENT STATION
or in the fruit at the time of picking from the tree. Since the spores
of this fungus have been found in large numbers on dead and dying
branches and on dead patches of bark on the trunk and large limbs
throughout the spring, summer and fall, it would appear probable that
these spores fall down upon the oranges and result in infection of the
fruit. That the development of decay in the fruit often proceeds quite
slowly after infection by the spores has been shown by infecting picked
oranges. It is probable that, on the tree, the length of time between
actual infection and appearance of rot may be much prolonged. It is
not improbable that the mycelium remains in a comparatively quiescent
condition in the epidermis of the stem or calyx of the orange while the
fruit is immature, and on its maturity grows rapidly, causing the
The measures toward control suggested by the results of the experi-
ments described on previous pages would be:
1. Pruning out and destruction of all dead and diseased twigs and
branches as early as possible after the crop is matured. The best time
to prune is in the dormant season, in December and January. The
next best time (especially if withertip is present) is in the summer
after the first flush of growth has thoroughly hardened. This is usu-
ally towards the end of June and through July. It would be well to
prune at both times in order to get the trees as free as possible from
How to Prune.-It is of the first importance in this pruning to re-
move as much as possible of the dead twigs and branches, and to prune
right back into the live healthy wood. To prune only half-heartedly
makes matters worse rather than better. When pruning, care should
be taken to make smooth cuts, usually at the base of a branch br limb,
so as not to leave any projecting stubs. This precaution should be
rigidly carried out, because infection is almost certain to occur in such
stubs when the withertip fungus is present. After pruning, paint the
larger cut surfaces with carbolineum (one-half strength), pine tar, or
liquid grafting wax.
The grove should be given unusual care after a severe pruning of
this kind. It should be supplied with a fertilizer of well-proportioned
formula, so as to bring about a vigorous and healthy growth, and to
render the trees resistant to further attacks of the fungus. Do .not
prune while new growth is putting out vigorously; for, if withertip
is present, such pruning is apt to result in injury rather than benefit.
Gathering up and destroying the prunings should be (lone without
2. Destruction of all dropped fruit to get rid of the possible
sources of infection. Not only the recently dropped fruit, but all de-
cayed or dried-up mummified fruit should be destroyed.
3. Culling and careful handling. As far as known there is no
sure way of telling that an orange is infected until it begins to soften
.at the stem end. Infection is sometimes indicated on immature fruit by a
deeper yellow color about the stem end. The Stem-End Rot, how-
ever, as well as the Blue Mold, is- most apt to develop on defective
fruit. It is therefore important to cull out closely all clipper cuts.
long stems, and fruit injured in any way, and to handle all fruit
4. Keeping fruit at low temperature. Since it has been shown by
laboratory experiments that rise in temperature greatly shortens the
time for decay to appear, the decay might be greatly lessened by re-
frigeration on the way to market and while the fruit is being held for
.. Spraying to keep down the scale insects. As has been pointed
out. the accumulation of scale insects under the calyx appears to
render the fruit more susceptible to Stem-End Rot. In case scale in-
sects are abundant, spraying with some good insecticide should be prac-
ticed. The first spraying should probably take place in April or May,
and be followed by one or two other sprayings, depending on the
amount of scale insects present.
22 FLORIDA AGRICULTURAL EXPERIMENT STATION
ROTS, SPOTS AND BLEMISHES ON
CITRUS FRUITS IN FLORIDA
1. STEM-END ROT (Phomnopsis sp.).-Decay beginning in a circular patch
about the stem end (see Fig. 3). At first light brown or very little discolored on
mature fruit, dark brown to leather colored on immature fruit on tree. Rind re-
maining fairly firm at first. Discoloration proceeding slowly from stem end in
more or less uniform circle, not in bands. Causing slow and at first only slight
discoloration of the center and inner peel and partitions. Juice sacs often re-
maining untouched for some time. The oranges when entirely decayed and soft.
still keeping their form, but not turning black until dried up. Causing much
dropping of fruit. (Fla. Agr. Exp. Sta. Report, 1910.)
2. DJPLODIA ROT (Diplodia natalensis).-In the early stage the rot shows a
patch about the stem end similar to that caused by Phomopsis sp. The discoloration
becomes darker as the decay proceeds, and shows as dark wide bands corres-
ponding to the divisions between the segments. The fruit becomes black as
the decay advances and very light in weight. The rot often advances quickly
through to the-blossom or stylar end, where a patch of discoloration shows be-
fore.all the peel is involved. It often starts in punctures or worm holes or
other injuries. Usually accompanied by the exudation of a small amount of thin
gum, or a considerable amount of amber colored sticky juice. This amber colored
juice also less frequently accompanies the Stem-End Rot. (Transvaal Dept. of
Agr. Science Bul. 4. 1910.)
3. BLACK ROT (Alternaria citri).-Rot beginning at blossom (stylar) end,
especially in navel oranges, sometimes in other varieties if there be a defect
at the blossom end. Fruit ripening prematurely with a deep color. Decay caus-
ing a blackening along the central core of the fruit where the segments meet.
Not softening the fruit so rapidly as the previous rots. Decay more confined to
the interior of the fruit and darker in color.
4. OLIVE GREEN MOLD (Penicilliun digitatu n).-Decay beginning at any
point on the fruit, especially at some injury or abrasion of the rind, causing a
soft watery decay with extreme brittleness of the peel. Much softer and mushier
than the previously described rots. Decayed areas showing white mold which
turns olive green from the center out, giving off smoky dust when disturbed.
Surface mold extending nearly to extreme edges of the softened area as fast as
the decay proceeds.
5. BLuE GREE rI MoI (Penicilliint italicunn).--Softening similar to the
Olive Green Mold. Not so much surface mold. A patch of blue green with a
narrow edge of white in the center of a much larger softened area. This mold
is often accompanied by or followed by the Olive Green Mold. (Bul. 190, Cal.
Exp. Sta., 1907; Bul. 121. U. S. Dep. Agr. Bur. of Plant Industry, 1908; and Circ.
1i), U. S. Dep. Agr. Bur. of Plant Industry, 1908.)
6. ANTHR \CNOS i ( Collctoltr ichu gloesporioides).-Causing excessive drop-
ping in the fall. Fruit showing hard spots more or less sunken, into the outer
peel. Starting as irregular brownish discolorations on the surface. Later
changing to grayish and then to dirty brown or black, variable in size, V4 to 1
inch or more in diameter. Common on lemons and grapefruit. Not so common
on oranges. (See Bul. 52, U. S. Dep. of Agr. Bur. of Plant Industry, by P. H.
Rolfs, 1904; and Bul. 74, Fla. Agr. Exp. Sta., by H. H. Hume, 1904.)
7. SCALY BARK OR NAIL-HEAD RUST SPOTS (Cladosporium herbarunt var.
citricolunm).-Causing premature coloring and dropping of fruit. Spots at first
yellowish to reddish brown on green fruit. Spots often showing as dark sunken
rings with green centers which become very hard, tough, corky, sunken, and dry,
without much enlargement, extending only into outer peel. Spots one-fifth to
one-half inch in diameter. Confined almost exclusively to sweet oranges. Not
found on grapefruit or tangerines, even when exposed to infection. Spots also on
the twigs and branches of the trees. Principally in Hillsboro county, Florida.
(Bul. 106, Fla. Agr. Exp. Sta., 1911.)
8. SCAB (Cladosporium ci:ri).-Causing warts and irregular light brown
corky projections from the surface of the fruit. Fruit often irregular and un-
sightly. Projections hard, gray to reddish tan colored, making very rough sur-
face; area between warts of normal color. Also affecting leaves and very young
shoots, causing them to become warped and contorted. Areas often coalescing
into large corky or warty scabs. Especially common on sour oranges and lemons.
Found also on Satsuma and grapefruit, but only rarely on sweet oranges.
9. TEAR STAINING AND WITHERTIP RUSSETING (Colletotrichum gloeospori-
oides).-Causing reddish brown stains on surface of the rind in form of streaks.
The bands or blotches appear to follow the lines made by the washing down of
little streamlets of water during rains. Sometimes staining one side, or almost
the entire surface of fruit. Sometimes traceable to an overhanging dead twig.
Especially common on grapefruit. Affecting merely the skin on the surface of
10. RUST MITE RUSSETING.--Surface of rind reddish brown, dark brown or
rusty colored finely chapped and roughened, which is caused by the feeding of the
rust mite on the oil cells of the surface of the rind. Rind of mature fruit becom-
ing hardened and toughened. Often covering only part of the fruit, leaving one
or two large circular or oval patches untouched. Causing fruit to become
sweeter. (Hubbard, H. G., Insects Affecting the Orange, U. S. Dep. of Agr.,
11. "THRIPS MARKS" OR SILVER SCURF.-Grayish to silvery irregular patches
with delicate scurf made of minute pieces of the outer epidermis under which a
new set of cells has been formed. Irregular blemishes on surface. Not injuring
interior in the least. Similar marks are caused by slight injuries when oranges,
etc., are quite young. Also similar marks are caused by too strong spraying solu-
tions when oranges, etc., are quite small and tender. Fla. Agr. Exp. Sta. Report.
12. BUCKSKIN.-Entire surface of fruit presenting a somewhat scurfy gray-
ish and roughened appearance. Not so hard and rusty as melanose or rust mite
russeting. The rind often becomes abnormally thick and is pliable on maturity.
Fruit usually stunted in growth; or, if of normal size, very light with but a small
amount of juice. Most common on grapefruit on the interior of the tree and
lower branches in shady places. Thought to be due to combined effect of mites
and a surface-growing fungus. (Proc. Fla. State Hort. Soc., 1908.)
13. MELANosE.-Somewhat resembling rust mite russeting in general appear-
ance, but rougher and rasping the fingers when touched. Surface of rind dotted
with minute, nearly round, slightly elevated spots. Usually only the elevated
spot is discolored, the surrounding tissue being of normal color. Spots somewhat
resembling a drop of sugar burned to a reddish brown color. Very small, only
1-100 to 1-16 of an inch in diameter. Often running together, so that individual
marks are lost, and forming large cake-like areas cracked in lines like dried mud.
Spots often arranged in parts of circles or ovals. (Press Bulletin 142, Fla. Agr.
Exp. Sta., 1910; and Bul. 8, Div. of Veg. Phys. & Path., U. S. D. A., 1896.)
14. "AMMONIATED" OR DIEBACK FRUITS.-Young fruits taking on a pale
green appearance and dropping off. Rind becoming stained in reddish brown ir-
regular areas, with or without splitting. Areas not depressed. Sometimes ac-
com:panied by slight gumming secretions on or in surface of the rind. Usually
accompanied by deposits of a clear gummy substance in the inner angles of the
sections at the center of the fruit. Mostly on oranges, accompanying Dicback.
( Press Bul. 93, Fla. Agr. Exp. Sta., 190S; and Bul. S, Div. Veg. Phys. & Path, U.
S. D. of Agr., 1896.)