PRESS BULLETIN 151
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
SUMMER PRUNING FOR WITHERTIP
BY H. S. FAWCETT
Withertip is one of the worst fungus diseases of citrus trees in Florida.
In the summer, trees affected by it may be distinguished by the yellowing and
falling of leaves on certain branches. If the disease is in an active condition,
the bare limbs from which the leaves have recently fallen will be seen to be
gradually dying back, suggestive of a slow poisoning. The inside bark and
cambium, nearer the body of the tree than the part already killed, will be ab-
normally yellow, and sometimes the limbs will be considerably stained.. The
calyxes and peduncles of fruit dropped in the spring turn brown, and under
the hand lens show small raised points.
HOw TO PRUNE
It is of the highest importance in pruning for withertip to cut out so much
of the wood as to get rid, not only of the bare branches, but also of all the
branches that show even a slight sign of the disease. In severe cases of
withertip there are seen, in addition to bare branches, many limbs on which
the yellowish leaves are about to.fall. Close examination will show that the
disease is slowly making its way back and poisoning these limbs. This poison-
ing may start from an infection at the tip, or from an infection on a side
branch lower down, from which the poisonous effect has spread to the main
limb. Sometimes only one side of a tree, or only one branch, is severely
affected; while the remaining part of the tree is uninjured. The distance to
which the disease has progressed can frequently be seen by the presence of
new shoots with a sickly yellow color. Frequently the leaves fall from such
shoots before they are half grown, leaving the bare young shoots to dry up.
Whatever may be the conditions, it is important to get rid of all these poisoned
limbs. To prune only half-heartedly usually makes matters worse, rather
than better. When pruning, care should be taken to make smooth cuts, us-
ually at the base of a branch or limb, so as not to leave any projecting stubs.
This precaution should bp rigidly carried out, because infection in these stubs
is almost certain to occur when the withertip fungus is present. After prun-
Julyl 2, 1910
ing, paint the larger cut surfaces with carbolineum, pine tar, or grafting
The grove should be given unusual care after a severe pruning of this
kind. It should be vell fertilized with a well proportioned formula so as to
bring about a vigorous healthy growth, and to render the trees resistant to
further attacks of the fungus.
WHEN TO PRUNE
Summer pruning for withertip should be done in July. It is important
not to delay the work beyond this date. Do not prune while new growth is
putting out vigorously, for this is almost sure to result in injury rather than
benefit. Begin the work at once, and do not consider the looks of the trees,
but take out everything that shows the presence of the disease.
The beneficial results already obtained on hundreds of acres of groves
treated in this way, under the direction of Experiment Station workers, have
proved the effectiveness of this treatment.
OTHER EFFECTS OF WITHERTIP
Different results of the attack of the withertip fungus are seen at other
seasons of the year. These vary according to weather conditions and the part
of the tree affected, and need different treatment. Some of these effects of
the disease are: (1) dropping of bloom; (2) browning of tender leaves; (3)
brown spotting of older leaves;-(4) spotting of fruit anthracnosee); (5) tear-
staining of fruit; and (6) yellowing and dropping of leaves and killing back of
State papers please copy.