PRESS BULLETIN 199
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
MELANOSE AND STEM-END ROT
By H. E. Stevens
Melanose is a disease of citrus fruits that has long been known in Flor-
ida. It attacks young succulent growth and fruits of the citrus tree, causing
raised brown spots or scabs. The spots may be small, distinct and scattered,
or irregular and running together to form circular markings, irregular flakes,
streaks or bands. Sometimes the entire surface of the fruit is covered with
these spots, giving it a russeted appearance. The greatest loss to the grower
results from this russeting and marking of the fruits. The disease is wide-
spread, and is found more or less abundantly in all citrus-growing localities
In the State. Under favorable conditions it is spreading rapidly and the
loss from damaged fruit is increasing yearly.
f Preventive Measures
Prom the scientific data at hand it would seem that neither Melanose
nor Stem-End Rot could occur in a grove if all of the dead wood were eliml-
riited, it is, however, almost impossible to prune out every bit of dead
wood from a bearing tree. We have proven by laboratory experiments that
dead sprigs only four inches long will produce repeated infections. There-
fore the most successful method for controlling these diseases is to prune
out and burn all dead wood from the trees. Small twigs should be re-
moved as well as large branches, for the former are known to harbor the
fungus. Pruning can best be done during the dormant season, and should
be done before the trees bloom.
Bordeaux mixture and ammoniacal solution of copper carbonate will con-
trol Melanose; tut in using either of these sprays the grower must be pre-
pared to combat the scale insects that are likely to come afterwards. Two
thorough spraying should be made: the first just after the bloom drops,
and the second three weeks to one month later.
Oetober 5, 1912
The exact cause of Melanose was unknown until quite recently. The
J sease was first described in 1896, but no specific cause was assigned. Me-
lanose was also thought to be due to some physiological cause, or to certain
conditions in the soil. B. F. Floyd made a study of the disease along this
line, and his results led him to conclude that the disease was due to an
The writer undertook a study of the disease to determine if possible the
exact cause, and has found that Melanose is produced by the fungus Pho-
mopsis citri Fawcett, the same fungus that causes Stem-End Rot of citrus
fruits. Numerous laboratory experiments proved that this fungus was pres-
ent in dead twigs and branches taken from melanoseinfected trees, and
melanose infection was readily obtained from this dead wood. From pure
cultures of this fungus, melanose infection was readily produced, and both
Melanose and Stem-End Rot were produced from the same pure culture. A
detailed account of these experiments will appear later.
Habits of the Fungus
The fungus exists chiefly in the dead twigs and branches -of the trees.
Under favorable conditions countless numbers of fruiting bodies (pycnidia),
containing spores, are produced. When sufficient moisture is present, these
spores escape, and they are then washed down by rain or dew on to young
fruits. In four or more days the characteristic brown melanose spots may
Spores that lodge on dead twigs or branches give rise to new fruiting
bodies which produce other new spores. Thus the fungus is kept in the
groves from one season to the next by propagating in the dead wood.
Later in the season, after the fruits are pretty well matured, spores
may again be washed down, come in contact with the stem ends of the
fruit, and, if the conditions are favorable, cause Stem-End Rot. It is readily
seen that this fungus is a troublesome one and should be removed from the
grove at once.
State papers please copy.