PRESS BULLETIN 165
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
TREATMENT OF MELANOSE
By B. F. Floyd
Where the citrus crop was considerably injured by melanose during the
summers of the last two years, it is advisable to spray during the spring
(f 1911. Spraying with either Bordeaux mixture or ammoniacal solution of
copper carbonate will prevent this injury. Two sprayings should be made;
the first about two weeks after the flowers have fallen; and the second,
four weeks later. A nozzle of 45 degrees angle should be used for applying
the spray. With such a nozzle the solution can be directed downward,
thereby preventing, more or less, the wetting of the under surfaces of the
leaves where the friendly fungi thrive on the scales and whitefly.
Wherever it is found necessary to spray for the prevention of melanose,
the grove should be carefully inspected at short intervals. If scale insects
show any tendency to become abundant, they should be kept in check by
the use of some good insecticide until the friendly fungi have developed
Cause of Melanose
From our most recent investigations it is concluded that melanose is
not a disease which is due to malnutrition; but that .it is caused by some
unknown organism. Some of the reasons for this conclusion are as follows:
1. The markings that the disease makes upon the fruit, stems and
leaves are superficial. They extend to only a small distance beneath the
skin, and are separated from the healthy tissue by layers of cork tissue.
2. The markings are small and individual. They have no connection
with each other, excepting where they occur so close together as to unite
3. The disease injures the tree by affecting the functioning of the
outer tissues, such as the breathing pores, and the cells containing the green
of the plant.
4. Only young succulent tissue becomes infected. The place of in-
fection is a mere point that increases in size with the growth of the affected
FebruaryU 11, 7911
5. The distribution of the disease throughout the tree and through
the grove is much like that of diseases which are known to be caused by
6. The disease is found on all varieties of citrus fruits. It affects trees
growing under opposite conditions, such as, trees that are starved, and
trees that are well-fed; trees growing on acid soils, and trees on alkaline
soils; trees growing on hammock soil, and trees on high pine land.
7. Any condition or treatment that tends to reduce the vitality of the
tree makes it more susceptible to the disease. Trees that are affected with
other diseases, such as gummosis, blight, yellow spotting, and scaly bark,
are particularly susceptible. Trees that have been injured by cold are easily
infected. Data at hand show the disease to be more prevalent north of
the frost line; but it is not all confined to this region. Attempts have been
made to cure the disease by the application of fertilizers. These were
doubtless of benefit by making the tree less susceptible to infection.
8. In some cases the disease is associated with dead wood in the tree.
It is probable that the dead wood is a source of infection.
Symptoms of Melanose
The markings that melanose makes upon the fruit, stems and leaves
are essentially the same. They consist of groups of gum-filled cells that
have been cut off and raised from the healthy tissue of the plant by a
The markings start as sunken points in the young succulent tissue, and
these grow larger and more evident as the tissue grows older. They become
elevated and wax-like and reddish-brown in color in their mature condition.
They somewhat resemble drops of melted sugar burned to a reddish-brown
The markings are in most cases scattered like pepper over the affected
surface. Often patches of them will interlace, surrounding little fields of
green. They are sometimes arranged In circles or parts of circles. This
is a characteristic symptom.
In most cases, the damage done to the leaves and stems is negligible.
But when the fruit is marked by the disease, its market value is reduced,
and it may be a total loss.
State papers please copy.