PRESS BULLETIN 157
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
STEM-END ROT OF CITRUS FRUITS-IV
By H. S. Fawcett
Both Bordeaux mixture, in the usual strength of 5 pounds of rock lime
and 5 pounds of copper sulphate to 50 gallons of water, and ammoniacal solu-
tion of copper carbonate in the proportion of 3 ounces of copper carbonate
and 5 pints of ammonia (26 degrees) to 50 gallons of water, have proved
effective in checking this disease. Spraying should be done -with the aim
of hitting the fruit, keeping the spray as much as is practicable from the
leaves, branches, and trunk, where beneficial fungi may be present.
Although the complete results of experiments now being carried on
in six different groves by the Experiment Station, or under its direction,
will not be at hand until the end of the picking season, the following
beneficial effects have already been noticed from the use of either Bordeaux
mixture or ammoniacal solution of copper carbonate.
The fruit on one lot of badly diseased grapefruit trees was sprayed
three times with Bordeaux mixture, on September 5, 12, and 29. A similar
lot of diseased trees, next to these, was left unsprayed until September 29,
when it was also sprayed. On October 11, at which time it was too soon for
much of a result from the last spraying to appear, it was found, by counting,
that four times as many fruit had dropped from those trees which had been
sprayed only once, as from the same number of trees which had been sprayed
In a second experiment in the same grove, ten orange, trees were sprayed
with Bordeaux mixture on September 12 and 29, and ten similar trees next
to them were left unsprayed. On October 11 there were counted nearly twice
as many dropped fruit under the ten unsprayed trees as under the ten
sprayed trees. Later counts are expected to show still greater effects from
Last year every alternate tree of a. block of forty grapefruit trees was
sprayed twice with ammoniacal solution of copper carbonate, on December 4,
and on December 14. On December 21 there were one-third more dropped
Otober 29, 1910
frpit (counted), picked up from under the unsprayed trees than from the
sprayed trees. Considering the lateness of the time, this was a rather good
showing in favor of the spraying.
These experiments show that both the sprays are useful in checking this
disease. The sprays are most effective when used early, while the fruit is
still green; but they will do much good even when used at this late season.
Among other experiments which are being conducted, is a test with a com-
bined fungicide and insecticide, to find out whether it can be substituted for
the Bordeaux mixture or the ammoniacal solution of copper carbonate. It is
desirable that such a substitute should be found, because of the damage done
by these two sprays in allowing an increase of scale insects.
Observations In Citrus Groves.
As the season advances there is an increased amount of Stem-end Rot
showing in some localities, while in others there appears to be less than
last year. Previous to the storm of October 18, in some groves as many as
5 to 10 per cent. of the grapefruit and oranges had already dropped from
Stem-end Rot is present and destructive on all characters of soil, and in
groves fertilized in all sorts of ways, providing the fungus causing it is present.
It is, however, noticeably worse in low damp groves than in higher and drier
land. Although laboratory experiments show that the fungus may penetrate
the skin of healthy fruit, observations in the grove indicate that those fruits
which are weakened near the stem by any cause, such as scale insects, are
most likely to be attacked. Even in the grove, however, perfectly sound fruit
may also be attacked.
Symptoms of Stem-End Rot
The presence of this disease is indicated by the dropping of the fruit,
followed by a softening at the stem end, which softening takes place within
a few days to three weeks after the fruit has fallen. Only in rare cases
does the softening at the stem end occur before the fruit drops. Dropping
of the fruit may, however, take place from other causes, such as withertip,
thorn punctures, etc. Decay of fruit may also occur without the presence
of- stem-end rot. But dropping of fruit together with a large percentage of
softening and decay at the stem end, are signs of the presence of Stem-end
Rot. Sometimes a premature coloring at the stem end is an indication that
this part of the fruit will in time soften and decay. On unripe fruit the
decay progresses rather slowly, advancing inward most rapidly along the
central core and the inner white part of the peel, and finally breaking down
the juice sacs. The diseased portion of the fruit becomes brownish or
coffee-colored. In ripe fruit the discoloration lags behind the softening.
State papers please copy.