PRESS BULLETIN 164
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
PRUNING FOR STEM-END ROT OF CITRUS
By H. S. Fawcett
Trees from which a large amount of fruit has dropped on account of Stem-
End Rot will be seen to have numerous dead twigs sticking out in places
where diseased fruit .had been attached. Quite often drops of gum will be
visible near the border between the dead and live wood of these twigs. The
fruits on the ground, after passing through stages of decay from slight
softening at the stem end to brown mushiness, gradually dry up to small,
hard, dark-brown or black "mummies." The whole process may require 4
to 8 weeks or more, depending on the moisture and temperature. Spores
of the fungus causing the disease have been found in great numbers on
these dead twigs and on these mummified fruit. It is therefore recommended,
where the tree has not yet begun to put out new growth, to prune out and
burn these dead branches. All diseased or mummified fruit should be picked
up and destroyed at once.
How to Prune
It is of the first importance in this pruning to remove as much as possi-
ble of the dead twigs and branches, and to prune right back into the live
healthy wood. To prune only half-heartedly makes matters worse rather than
better. When pruning, care should be taken to make smooth cuts, usually
at the base of a branch or limb, so as not to leave any projecting stubs.
This precaution should be rigidly carried out, because infection in such stubs
is almost certain to occur when the withertip fungus is present. After prun-
ing, paint the larger cut surfaces with carbolineum, pine tar, or grafting wax.
The grove should be given unusual care af er a severe pruning of this
kind. It should be supplied with a fertilizer o well-proportioned formula so
as to bring about a vigorous and healthy growth, and to render the trees
resistant to further attacks of the fungus.
February 4, 1911
When to Prune
Do not prune while new growth is putting out vigorously; for, if wither-
tip is present, such pruning is apt to result in injury rather than benefit. If
the young growth is too far advanced now, it will be advisable to wait until
July, when the growth will have hardened. Gathering up and destroying the
dropped fruit should be done without delay.
Symptoms of Stem-End Rot
The presence of this disease is indicated by the dropping of the fruit, fol-
lowed 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. As the fallen fruit
dries up on the ground, the fungus produces innumerable spores in little
pustules over the surface of the mummified fruit. The twigs from which the
fruit falls often die, somewhat in the same manner as when infected with
State papers please copy.