Bulletin 229, Diseases of Citrus in Florida


cases of gummosis started in improperly made or unprotected
pruning wounds on healthy trees within less than a year from
the time they were made. This would indicate that the infection
of wounds by certain organisms undoubtedly may initiate the
development of at least some forms of gummosis in Florida.
 On the other hand, a severe outbreak of gummosis was recently
observed on a large number of vigorously growing young grape-
fruit trees which had been given a heavy application of nitrog-
enous fertilizer. The disease had broken out at numerous points
on the trunks, larger branches, and even on the twigs, but healed
up in a few months in many cases. It was evident that in this
case no organism was responsible for initiating the trouble but
rather some excessively strong physiological stimulus which re-
sulted in the formation of a large amount of gum instead of
normal wood elements by the growing tissues. It is of interest
in this connection to state that the effect of various chemical
stimuli in inducing gum formation in citrus trees is well known.
Excessive concentrations of copper sulphate in the soil, or when
applied to the trees as injections, will induce copious gum forma-
tion. In some cases fumigation with hydrocyanic acid gas and
the spilling of cyanide or its products on the roots will also in-
duce gum formation. It is quite evident that further investiga-
tion of the gummosis problem in Florida is required, particularly
to demonstrate the different types of gummosis that may occur
and the extent to which parasitic organisms or other agencies
are responsible for each.
 CONTROL OF GUMMOSIS
 It is believed that gummosis can be prevented to a large extent
by maintaining the trees in a vigorous condition and protecting
them, as far as possible, from shocks or weakening influences
occasioned by severe storms, water injury, drought, starvation,
cold, or other adverse influences. Making pruning wounds prop-
erly and protecting the wounds by applying a disinfecting water-
proof dressing will also do much to minimize the development of
gummosis.
 Trees attacked by gummosis should not be neglected with the
hope that they will eventually recover. Although slight cases of
gummosis may do little injury and small spots may heal without
attention, in the majority of cases the gumming becomes chronic
and spreads to such an extent as to threaten the life of the tree.
All diseased trees should be located and treated promptly. Gum-