Florida Agricultural Experiment Station


from discoloration, except for a slight yellowish tint. As the
disease progresses, which often occurs very slowly at first, the
original scaly spot enlarges from year to year and is accompanied
by additional bark scaling. Even in the intermediate stages,
psorosis may completely encircle the trunk or limb without caus-
ing serious injury to the underlying wood.
 Up to a certain point in the development of psorosis, new
 bark forms under the
 outer bark that loos-
 ens and scales off
 but, instead of re-
 maining healthy, the
 disease breaks o u t
 anew in this bark
 and the scaling pro-
 cess continues. The
 bark within the af-
 fected area thus be-
 S comes considerably
 thickened, rough and
 brownish, giving this
 area a more or less
 swollen and distinct-
 ly ulcerated appear-
 ance. In this stage
 the lesions are very
 conspicuous because
 of the pronounced
 .. breaking up of the
 i.t outer bark into large
 flakes, sca 1 e s, or
 shaggy strips which
 curl away from the
 trunks or branches
 as they slough off
 (Fig. 29). After the
 lesions encircle the
 trunk or branch they
 Fig. 29.-Psorosis on orange tree, showing well continue to increase
 advanced stage in which the disease has
 spread entirely around the divisions of the in l e n g t h. Scaly
 trunk. bands are thus form-
ed which vary in length from a few inches on the smaller