PRESS BULLETIN No. 84.
florida Agrlcullural Experiment Station.
CITRUS BLOOM DROPPING.
BY P. H. ROLFS.
An early spring drought following a moist winter frequently causes a
wide-spread and general dropping of bloom. The only way to prevent
such dropping of bloom is to be equipped with an irrigating plant.
In some cases, a late freeze, and even chills during the blooming per-
iod, may cause a very considerable shedding of the bloom. When this
occurs as a result of too low temperature we can do nothing to prevent it.
Another cause of the shedding of bloom is the occurrence during the
blooming period of heavy rain-storms and winds. These, however, are not
as serious as either cold or drought, since the rains and winds that cause
shedding of bloom are usually confined to limited areas.
DROPPING DUE TO WITHERTIP.
The most serious shedding of bloom occurs as the result of an attack of a
parasitic fungus, Colletotrichum gloeosporioides. This is a serious trouble,
for only too frequently its cause is not recognized, the shedding of the bloom
being ascribed to one of the before-mentioned causes, or to the presence
of thrips or other insects.
The first sign that we notice in connection with the withertip dropping
of bloom is that a great number of unopened flower-buds have fallen from
the tree. As this same effect may be the result of other causes, the mere
fact that we find unopened flower-buds on the ground should not be con-
sidered as proving that we have a case of withertip bloom dropping.' Upon
closer examination, however, we find that where the bloom has dropped on
account of being affected with the withertip fungus, there are little red
markings upon it; and the buds or blossoms may be partially, or even en-
tirely, covered by these red patches. By examining such flower-buds or
petals in the laboratory it can be easily demonstrated that they are affected
by the withertip fungus. By using a strong hand lens one is able to see
the minute pustules in which the spores are produced. Such diseased flower-
buds and petals, however, differ so strikingly from those that have fallen
naturally, that almost every one whose attention has been called to the
point is able to distinguish between them, without the aid of a lens. When
much bloom has dropped as a result of being affected wihh the withertip
fungus, one almost invariably finds the typical signs of withertip on the
tree. The most prominent of these are the dying back of small sprigs, and
the very characteristic want of leaves on the Inside of the tree. Whenever
one sees a tree in the orchard that has no interior foliage, it should be
noted as a suspicious specimen.
March 9, 1908.
The withertip fungus which causes the dropping of the flower-buds lives
over the winter in the leaves: or in the twigs of the tree, or on fallen fruit.
From these sources some of the spores find their way to an open bud, where
the fungus grows very rapidly and produces myriads of spores. Bees, flies
and other honey-loving insects, visit the affected blossoms, and coming
into contact with the fresh spores, not .only carry them on their bodies
to almost every open blossom on the tree, but in crawling over the un-
opened buds they convey the spores to these as well. But worse still, the
insects which have visited an infected tree carry the spores to other trees
in the grove, and from these secondary infections numerous other infec-
tions occur in time; so that hundreds of trees that were free from the wither-
tip fungus may become infected from one single tree with diseased blos-
The remedy here suggested has been tried and found sufficient and prac-
tical. It is recommended only for cases where one is obliged to use it in
order to get a good setting of fruit. The use of this fungicide kills off so
many of our friendly fungi that a severe attack of scale insects is very
likely to follow.
Spray with Bordeaux mixture (for complete directions for making Bor-
deaux mixture see Bulletin 76 of the Florida Experiment Station), directing
the spray against the open bloom, avoiding as far as possible the spray-
ing of the foliage, and also avoiding an over-dose. If so much Bordeaux mix-
ture is used that it runs down the limbs, it will kill a great many of our
fungus friends that are there preying on scale insects. Under ordinary cir-
cumstances, no one would recommend that Bordeaux mixture should be
sprayed directly into the bloom. In doing this we know that a certain
quantity of the bloom will be killed by the fungicide, but so much is saved
from the ravages of the withertip fungus that there need be no hesitation
when one has to apply it.
DROPPING OF NEWLY-SET FRUIT.
Sometimes this fungus does not attack the bloom, but attacks the new-
ly-set fruit after the blooming period is over. Not unfrequently one may
see the ground under a citrus tree strewn with thousands of small fruits,
every one attacked by withertip fungus. In this case the same remedy
used for the shedding of bloom will be found useful.
State papers please copy.