PRESS BULLETIN, NO. 60.
FALL DROPPING OF CITRUS FRUIT.
BY P. H. ROLFS.
The dropping of citrus fruit in the fall of the year may
he due to one of several or-all the causes working together.
The citrus grower, therefore, must be able to diagnose the
difficulty before he can be able to determine with a certainty
what remedy to apply or if any is available.
WITHER TIP DROPPING.
This disease has been described a number of times in
various publications, in the agricultural papers of the State,
proceedings of the Florida Horticultural Society, and more
fully in publications from the United States Department of
Agriculture and the Florida Experiment Station. This
trouble is not confined to any portion of the citrus-growing
area. Wherever this disease is present in a citrus orchard it
usually causes the most severe trouble, the fruit sometimes
dropping to as much -as seventy-five to ninety per cent. In the
aggregate it causes more loss from dropping than all the
others put together.
It may be readily and certainly distinguished from other
fours by the fact that the trouble starts with a minute bJrown
speck, gradually this forms a depression and the size of the
speck increases. Sometimes a number of these occur on a
single fruit, most frequently the fruit drops before the brown'
OCT. 15, 1906.
specks have attained the size of a five cent piece. The cause of
the brown speck is due to an attack of a fungus, which is
known scientifically as Colletotrichum gloeosporioides.
The remedy -for this form of dropping is simple and
singularly effective. The fruit does not drop until after it
has been infected for some time by the fungus, or until the
spot has attained considerable size, consequently when the
remedy is applied it does not prove immediately effective,
because those fruits which have become inoculated later suc-
cumb to the disease and the remedy merely prevents other
fruits from becoming infected.
As soon as the citrus grower detects any appreciable
amount of dropping, he should at once examine the fruit to'
find out whether it is caused by the withertip fungus. If this
be the case he should at once spray with a preparation of
ammoniacal solution of copper carbonate which is made as
Put three gallons of water in a wooden or an earthen
vessel, pour three pints of ammonia (twenty-six degrees B.)
into this, and stir it to mix evenly. Take eight ounces of
copper carbonate and shake it into the ammonia water, stirring
the-liquid for a while. If a considerable part of the copper
carbonate remains undissolved, the liquid may be left to settle:
if, however, all or nearly all of the copper carbonate is dis-
solved, more of it should be added in the manner previously
described until a considerable amount remains undissolved:
then it is set aside as stated before. After the precipitate has
settled, use the clear blue liquid. The undissolved copper car-
bonate may then be treated with mdreammonia and water,
fresh copper carbonate being added whenever the residue be-
comes less than an ounce. The solution should not be kept for
more than a day or two. and when used one gallon should be
diluted with fifteen or twenty gallons of water.
In spraying to prevent this dropping care should be taken
to apply the solution only to the fruit, since the solution will
kill fungi regardless of whether they are our friends or ene-
mies. A thorough spraying of the tree would destroy the
fungus enemies of the scale insects.
Immediately after the spraying has been completed, all
dropped fruit, no matter how good or had or rotten they may
be, should be raked up and carted from- the field. These
drops should either be covered in a pit or disposed of in some
other way that would insure that none of the fungus got back
to the grove.
This fungus is present in the citrus grove and does
considerable damage throughout the entire year. The great-
est amount of damage is done to the fruit from about the
time it begins to ripen until it reaches its maximum ripeness,
gradually increasing in severity, and in some cases destroying
nearly the entire crop. Repeated experiments in controlling
this form of dropping shows that it ordinarily takes about two
weeks from the time of spraying until decided diminution
may be noticed. During the first week after spraying the
dropping is apt to increase in severity, since fruits once
infected will drop, and spraying only prevents infection. We
have proven by leaving trees unsprayed that the dropping on
sprayed trees is no more severe than on trees that were not
This same fungus causes very severe loss in a great
many orchards during the time of blooming; Severe shedding
also frequently occurs from this disease before the fruit has
reached the size of hazel-nuts. After the fruit reaches about
the size of English walnuts it is fairly safe from the attack
of this disease until the ripening season.
Splitting of citrus fruit frequently follows heavy rains
when these occur just about the ripening season especially
during the latter portion of October. When splitting is due
to purely physical conditions the fruit splits open
from the bloom end, usually, and leaves a very sharp and well
defined edge on sides of the wound. As the conditions which,
cause this splitting are beyond our control the remedy for it
likewise seems to be beyond our ability.
Trees that are severely effected with die-back lose nearly
all their fruit from dropping before it ripens. Sometimes
trees are slightlyaffected with die-back and the ordinary symp-
toms are not apparent. Such trees produce fruit with large
brown specks, frequently becoming very smooth and taking on
the appearance as if the spots had been varnished.
This diesase may be readily distinguished from the
withertip specks from the fact that the affected area on the
epidermis of the fruit is raised in the place of being depressed.
Some times die-back fruit is covered with very minute specks
not as large as a pin head, scattered over the entire or a portion
of the rind. If one is in doubt as to whether this is a case-of
incipient die-back or not, it can be verified by cutting the fruit
in two crosswise. If it is a case of incipient die-back transpar-
ent gum will be found on the inner angles of one or more of the
As die-back is a constitutional disease of the tree, it is
self-evident that no remedy will produce any radical relief
promptly. We are, therefore, in a position where ire must
lose more or less of the fruit from an incipient case of dieback
when it begins to drop. Some good can be done by spraying
the tree with Bordeaux mixture but the curative process will
require weeks and even months. Such trees should be marked
and put through a course of die-back treatment during the suc-
ceeding season to prevent loss from this source when the next
crop shall mature.
Where groves are exposed to high winds very consider-
able fruit is lost from thorning, also from scratching. Insects,
especially the cotton stainer, are apt to cause considerable
loss by puncturing the epidermis and causing the fruit to
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