Bulletin 229, Diseases of Citrus in Florida


marked decrease in the prevalence of this disease appears to be
largely correlated with the general discontinuance of deep plow-
ing and cultivation and the improvement of cultural methods
generally.
 SYMPTOMS OF EXANTHEMA
 Exanthema causes an abnormal development of the smaller
branches, twigs, leaves, and fruit and the formation of more or
less gum. With the exception of very young trees, the disease
seldom affects directly the mature tissues of the older branches
and trunks, although the abnormalities developed on the young
woody parts may persist for some years. The trouble is
more likely to occur on rapidly growing trees than on those of
moderate to slow growth. As was pointed out by Floyd, the root
systems of severely affected trees are strikingly deficient in
fibrous feeding roots.
 The disease manifests itself in a num-
ber of ways, depending upon the sever-
ity and duration of the deranged con-
ditions in a given tree. Its course is
progressive and all the symptoms are
produced only after several months of
development in the chronic form. The
five most common and conspicuous
symptoms are bark eruption, stained
terminal branches, stained or marked
fruit, gum pockets in the twig, and mul-
tiple buds. In addition to these symp-
toms, there may be S-shaped shoots,
coarse, large, dark-green leaves, dying
back of the terminal branches, bushy
growth, splitting and premature drop-
ping of fruit, and gum at the center of
the fruit in the angles of the segments.
 On the Twigs and Branches:-The Fig. 61.-Gum pocket on
 citrus twig (indicated
development of gum pockets on the by arrow) resulting
young shoots is one of the earliest from exanthema.
symptoms. These appear before the twigs or branches have be-
come fully hardened. They appear like small blisters under the
bark, being formed by the accumulation of a clear, light-colored,
liquid gum between the bark and the wood. They usually occur
at or near where a leaf comes out from the stem (Fig. 61) and