Bulletin 229, Diseases of Citrus in Florida


formly thickened, brownish areas of irregular outline. The
thickening of the leaf tissue on the under surface sometimes
gives the affected leaves a slightly crinkled appearance.
 CAUSE OF YELLOW SPOT
 The occurrence of the yellow spot trouble does not seem to be
limited to any particular type of soil, soil condition, or method of
grove management. The trouble may be of widespread occur-







 &-r















 Fig. 80.-Yellow spot of grapefruit leaves, showing appearance on upper
 side at left and on lower side at right.
 rence on the majority of the trees in a part of a grove and occur
 but rarely or not at all on trees in other parts of the same grove.
 In trees that are only slightly affected, certain branches may
 exhibit the spotting on the majority of the leaves, whereas the
 leaves of neighboring branches may be free from the trouble.
 According to Floyd, the trouble was found to be worst in the
 upper branches and on trees that had recently borne a heavy crop