Florida Agricultural Experiment Station


them properly when they occur, since these bark attacking fungi
often gain entrance through injured places.
 GUMMOSIS
 Caused by various fungi, chemical injuries, and
 physiological stimuli
 Gummosis has been regarded as an extremely important dis-
ease in virtually all citrus-growing countries of the world, be-
ing mentioned as early as 1646 in the Latin work on Citrus by
Ferrarius. This disease, in its various forms, .has caused wide-
spread destruction in many of the older citrus-growing coun-
tries. The forms of gummosis mentioned in the earlier lit-
erature, however, are not described with sufficient accuracy to
identify each with certainty.
 Records place the appearance of gum diseases of Citrus in the
United States at about the year 1875 in California, and 1876 in
Florida. In the former state gummosis was a serious trouble
in nearly every citrus locality by 1878. The horticultural litera-
ture of this period indicates that the discontinuance of the use
of the common lemon, lime, and citron stocks in California was
due to this disease.
 Gummosis, today, is one of the more important citrus dis-
eases in Florida. Of the citrus trees commonly cultivated, the
lemon is most susceptible and the sour orange the most resistant.
The grapefruit is also very susceptible, the sweet orange quite
so, while the tangerine is very resistant to true gummosis. Trees
on rough lemon stock appear to gum worse than those on sour
orange stock.
 SYMPTOMS OF GUMMOSIS
 Gummosis in Florida is chiefly confined to trees that have
 reached the age where they are capable of bearing good-sized
 crops of fruit. A form of this disease which commonly attacks
 cultivated lemon trees as soon as they attain good bearing size
 is characterized by the disease starting just above the bud union,
 from which point it spreads up the trunk and involves the basal
 portions of the main limbs (Fig. 24). In the grapefruit and
 orange trees, however, the disease rarely starts at the bud union
 but usually at various points higher up on the trunk or on the
 larger branches. In addition to these forms of gummosis, minor
 forms of gumming may occur on different parts of trees in con-