Florida Agricultural Experiment Station


growth of weeds about the lower branches of the trees. The oc-
currence of these fungi is not of sufficient frequency to warrant
control measures.
 THREAD BLIGHT
 Caused by Corticum stevensii Burt
 Thread blight is one of the minor citrus diseases in Florida,
which rarely causes the grower any trouble. The causal fungus
occurs on several different woody plants scattered over the
state. It forms long brown threads or strands on the twigs and
 fruit (Fig. 51). These
 often spread out on the
 under sides of the leaves,
 forming a thin, whitish
 weft of fungous fila-
 ments. Here and there
 along the twigs small,
 round, hard bodies, called
 sclerotia, are formed. By
 means of these bodies
 the fungus is enabled to
 live through unfavorable
 periods and perpetuate
 itself in more favorable
 seasons. Spores are de-
 veloped from the f u n-
 Fig. 51.-Thread blight on grapefruit. gous wefts on the attack-
 ed leaves. In some in-
stances the fungous filaments penetrate the leaves and cause
their death. The fruit may have several threads or strands run-
ning over the surface or, at times, it may be covered with a cob-
webby weft of brown fungous filaments.
 The thread blight fungus is restricted to rather limited lo-
calities in the southeastern United States, apparently because
of the high humidity and high temperature required for its de-
velopment. In Florida, these favorable conditions occur chiefly
in groves which are surrounded by heavily wooded swamps or
hammock forests. In case this disease becomes of sufficient im-
portance to justify control measures, its development can easily
be checked by a single application of bordeaux-oil emulsion at
the beginning of the rainy season.