Bulletin 229, Diseases of Citrus in Florida


important a factor in citrus culture as formerly because its
nature and means of control are now understood and because of
the fact that sweet seedling orange groves are no longer planted
and no longer constitute such a large proportion of the total
citrus acreage.
 In Florida, foot rot has been confined largely to the old sweet
seedling orange groves and to trees budded on this and other
especially susceptible stocks. Even where resistant stocks are
used, however, the disease may occur above the bud union on
low-budded trees. Sour orange and bitter-sweet orange stocks
are highly resistant to the disease but not immune. The order
of resistance of citrus stocks to foot rot in Florida appears to be
about as follows: sour and bitter-sweet orange, Cleopatra man-
darin, rough lemon, trifoliate orange, grapefruit, lemon, and
sweet orange. The first four of these stocks may be classed
as decidedly resistant while the last two, together with the citron,
which is not used as a stock in Florida, are very subject to the
disease.
 SYMPTOMS OF FOOT ROT
 Foot rot is a type of gum disease which affects the bark of the
crown roots and base of the trunk, usually at or just below the
surface of the soil. The first symptom of the disease is a small
area of decayed bark, from which there is a slight exudation of
gum, generally in small drops. The decayed bark at first has a
watersoaked appearance and a watery gum is sometimes found
beneath it. Both the diseased bark and the underlying wood fre-
quently have an ill-smelling, fermented odor. As the disease
progresses, gum exudes from other portions of the bark, which
in turn die. The exudation of gum accompanying the early
stage of this disease is rarely abundant. It develops most abun-
dantly in late spring and early summer and the exuded gum may
be washed away by rains.
 Foot rot may manifest itself at one or more places on the
trunk. The patches of bark which first become diseased are
irregular in shape and variable in size. They later dry out and
sink below the level of the healthy bark and are thus sharply
demarked (Fig. 15). The bark remaining alive in advance of
the lesions often develops a callus formation which tends to de-
limit the disease and check its further spread, especially in an
upward direction. Following this, the old patches of diseased