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Copyright 2005, Board of Trustees, University
C-O-P-Y SRbtropical Evperment Station
Mimeographed Report No.- 6 October 1940
University, of Florida
SUW-T'ROPICAL EXPEBIMET STAT ION
MANGO ANTERACNOSE AND ITS CONTROL
Geo. D. Ruehle
There are a number of factors which may contribute to lack of fruitfulness
of mangos in Florida where the Haden is the lading commercial variety. Of these,
infection by the common anthracnose fungus, Colletotrichum gloeosporiddes Pensz,
has long been considered of primary importance.
The various manifestations of the disease include blossom blight, leaf-spot,
fruit russetting or staining, and fruit rot. Infections on the bloom and setting
fruits are often severe and constitute the most important phase of the disease.
Injury from the disease is closely dependent upon humidity, the prevalence of
rains or heavy dews during the critical period for infection greatly increasing
Infections on the flower panicle appear at first as minute black spots which
gradually, enlarge and often coalesce to cause the death of flowers either directly
or indirectly by invasion of the flower stalks. Very young fruits also are fre-
quently affected and seedless fruits are extremely susceptible to early infection.
Blossom blight may vary, in severity from slight to complete involvement of the
panicle according to prevailing weather conditions. Spots on young leaves are
small, dark, circular or angular, and often fall away giving the mature leaves a
ragged shot hole appearance. On nearly mature fruits black spots of varied form,
which may be sunken or show surface cracks, appear and may coalesce to cover
large areas. These infections usually penetrate deeply and either cause rotting
of the fruit on the tree or may. serve as centers of decay after the fruit is har- ,
vested. Surface staining or russetting may, result from spores being washed down,
upon the fruit from an infected twig or flower stalk.
The causal organism is one of the most widelydistributed pathogenic fungi
in Florida. It causes the well-known wither-tip of Citrus and a ripe rot of avo-,
cado, papaya, and several other sub-tropical fruits. It grows saprophytically and
sporulates abundantly, during wet weather on dead twigs and leaves of many, plants,
including the mango, avocado, and Citrus species. It seems likely that the possi-
bilities for infection are great at all times and all that is needed to produce
the disease in abundance is the presence of susceptible tissue and a favorable
period of moisture.
The widespread occurrence of the fungus on living as well as on dead mango
tissues and on other plants as well, makes it impractical in commercial groves to
attempt control of the disease bypruning. Most of the infection takes place from
the beginning of the blossoming period until the fruits are about half-grown. Re-
duction of anthracnose.can be brought about by maintaining a protective coating of
fungicide on susceptible parts during this critical period. Recent experiments in
the West Indies show that much of the decay, which develops on mature fruits has its
inception as latent infections occurring when the fruits are quite small. These
latent infections become active and serve as centers of decay, when the fruit ap-
proaches maturity. Even in relatively dry, seasons considerable latent infection
may occur, and, spraying at intervals until the mangos are half grown will increase
the percentage of first grade fruit and prevent considerable loss from decay in
Experiments conducted in Florida by the U. S, Dept. of Agriculture showed
that five applications of 8-8-100 bordeaux mixture are necessary, for satisfactory
control of blossom infection and anthracnose of the fruit in average years.
Laboratory tests conducted at the Sub-Tropical Experiment Station indicated that
weaker bordeaux mixtures and certain of the neutral or "fixed" coppers possessed
sufficient toxicity to the spores of the causal fungus to control anthracnose.
Field experiments with these fungicides were started in the 1937-38 season
and were continued until the freeze of January 1940 caused a temporary cessation
of the tests. They were conducted at the Coral Reef Nurseries, near Cutler, in
a 10-acre grove of Haden mangos. The spray, treatments were applied in a uniform
manner to duplicateplots consisting of 22 trees each. The fungicides were com-
pared in schedules which included a dormant spray in one case and no dormant spray
in another. The dormant spray, was applied when the flower buds were just beginning
to swell. The second spraying in these plots and the first spraying in all other
plots was made when the first panicles were well opened but before individual
flowers were open. Successive spraying were made at approximately, 1, 3, 7, and
11 weeks after the first bloom application.
All parts of the top were covered thoroughly at the dormant and first bloom
applications, but thereafter attention was directed to covering only the flower
clusters and fruits thoroughly Mature fruits were examined as they were harvested
and were graded according to severity, of infection into three classes, as follows:.
(1) free of anthracnose; (2) stained or russetted; and (3) showing active decay
spots. Practically, all of the fruits which set from the early or main bloom were
examined from each plot.
TShe spray, schedules and the results are shown in Table 1.
The results show that it is unnecessary, to apply, a dormant spray, in commercial
groves that have been sprayed annually for control of anthracnose. It is apparently,
more practical to delay the first spraying until the flower clusters have opened but
before individual flowers have opened.
The number of bloom applications necessary for good control depends largely,
upon the prevailing weather conditions and the uniformity with which the flower
clusters open. They, do not all open at the same time in the main bloom and in
some seasons lack of uniformity of opening is more evident than in others. It may
be necessary in some seasons to apply only two bloom sprays, while in others three
or four bloom sprays may, be desirable.
The results show that 4-4-100 bordeaux mixture is as effective as the
6-6-100 formula, and it is probable that stronger mixtures would give no better
results. There has been no opportunity, however, to compare these formulas during
a season in which abundant rains occur during the critical period for infection.
Red cuprous oxide gave the best results of the three neutral coppers tested. Tri-
basic copper sulfate gave fairly good results in the 1938-39 season and is worthy,
of further trial. Scale insects have been found to increase at a faster rate
after bordeaux mixture than after the neutral copper sprays.
S. Control Recommendations
Results of the spraying experiments to date indicate that blossom blight and
anthracnose of the fruit can be controlled effectively by five applications of
copper fungicide in groves where spraying is practiced annually. It is doubtful
whether additional sprays would prove practical even in extremely wet seasons.
Table 1. Mango spraying experiments, Coral Reef Nurseries
Number of sprays 1937-38 1938-39
Fungicide Dorm. Bloom Post- No. of Free of Stained Decay No. of Free of Stained Decay
bloom fruits disease of fruits disease or
S russetted russetted
-------------- ^ --^ r
3-3-100 (Dorm. 6-6-100)
4 4-100 (Dorm. 6-6-100)
37.3 50.7 12.0
88.2 9.9 1.9
87.8 9.9 2.3
82.6 15.3 2.1
81.7 15.5 2.8
Red cuprous oxide 2-100
Red cuprous oxide 2-100
Red cuprous oxide 3-100
Red cuprous oxide 3-100
Copper silicate 3-100 (Dorm.6-100)
Copper silicate 3-100
Tri-basic copper sulfate 3-100
Tri-basic copper sulfate 3-100
If bordeaux mixture is used it need never be stronger than the 6-6-100
formula and .4-100 bordeaux has given good results thus far. Indications are
that 3-3-100 bordeaux is not strong enough to give good control. Red cuprous oxide
(49 copper as metallic) 3-100 and tri-basic copper sulfate (53% copper as metallic)
3-100 may, be substituted for bordeaux mixture with nearly equal results. It is
essential that the sprays be timed properly,. The following spray,schedule is recom-
mended for the present but may, be modified later depending on information developed.
from further experiments:
1. First bloom spray applied when the first bloom clusters have appeared
but before individual flowers have opened..
2. Second bloom spray applied 7 to 10 days after 1.
3. Third spray, applied three to four weeks after 1, At this time the last
of the main bloom clusters will be open and many, fruits will have
set from the first panicles to open.
4. One month after 3,
5. One month after 4.
This schedule applies to the first bloom which is normally, the main bloom and
generally ,produces the more desirable fruit., Changes in time of making applications.
may, be necessitated by, variations in seasonal conditions. Occasionally, the first
bloom is light and sets little or no fruit, in which case a second later bloom may,
be heavy, and produce the main crop. When this occurs the spray schedule should be
shifted to apply to the later bloom. The first spray, should be applied thoroughly
to all parts of the tree top. Attention need be directed to covering only/,tle' bloom
clusters and fruits in later applications. It is desirable to add an efficient
Spreader to the fungicide in all applications if one is not already incorporated
with the fungicide.
S Zinc sulfate 5-100 with sufficient lime added for neutralization (half the
amount of zinc sulfate) if a fixed copper is used, may, be added to one of the late
sprays in the above schedule for correction of zinc deficiency, should this trouble
be manifest on the foliage.
Control of Insects
Mango blossoms are sometimes injured by the blossom anomala, a small dark-
colored beetle which feeds at night. The best means of control is by, spraying
with arsenate of lead. The poison may be added at the rate of l 1/2 pounds to 50
gallons of the copper fungicide in 'the first or second bloom application or as soon
as possible after feeding by the beetles becomes evident.
At the first indication of red spider damage, which is usually greatest from
December to March, measures should be taken to control these pests which confine
their feeding to the upper surfaces of the leaves. They may, be readily ,controlled
by adding wettable sulfur (6-10 pounds to 100 gallons) to one of the copper sprays:
in the above schedulee and covering the leaves thoroughly. Should red spiders
appear on the trees before or after the time for spraying with copper fungicides,
they may, be controlled by, applying either sulfur dust or by, spraying with lime-
sulfur solution i.-60o.
Several scale insects infest the mango tree in Florida and generally, increase
rapidly after copper fungicides have been applied. It is therefore advisable to
Sapply,oil emulsion throughly, at high pressures to trees sprayed with copper sprays
shortly, after the crop has been harvested. Emilsions containing 1.1/2 to 1 3/4
percent actual oil are usually, necessary, for a good clean-up of these pests.