Bulletin 229, Diseases of Citrus in Florida


locality an area of about a half-acre had been located previously
in a grove under different management where several trees were
attacked by mushroom root rot and occasional trees had been
dying during the last few years from a trouble thought to be
foot rot.
 From the widespread distribution of the Clitocybe root rot
fungus throughout a large part of the state and the numerous
records obtained of its occurrence on citrus trees during 1930
and the early part of 1931 it is undoubtedly likely that this dis-
ease will eventually be found to be of fairly widespread and com-
mon occurrence on citrus trees, especially throughout the central
portion of the peninsula where the rough lemon rootstock is
universally used and oak trees are prevalent. It is quite evident
that this mushroom root rot of citrus trees is no new trouble
but that it simply has not been distinguished heretofore from
foot rot, which it closely resembles in the behavior of the at-
tacked trees.

 SYMPTOMS OF MUSHROOM ROOT ROT
 The symptoms exhibited by the attacked trees vary greatly
 with the age and progress of the disease. In the 70 attacked trees
 treated in one locality in Polk County the disease, with but two
 exceptions, had not attained sufficient headway to cause a decline
 of the tops and these trees, with the exceptions noted, appeared
 as good and as productive as the adjoining trees which were not
 attacked. With but three or four exceptions where trees were
 known to have been treated previously for dead roots, the at-
 tacked trees in this locality were located solely by finding either
 fresh or old clusters of the mushrooms which had fruited at the
 bases. Upon excavating the soil under the bases of these trees,
 however, to examine the root system and prepare them for treat-
 ment, a number of the lateral roots were found to be dead in all
 cases, these often being dead clear back to the root crown and
 with the terminal portions disintegrated. In all but four of
 these trees the taproots were also dead. In some cases an area
 of bark was found to be dead at one side of the base of the trunk
 (Fig. 21, left) and a slight exudation of gum occurred just above.
 These areas of dead bark frequently marked the point where a
 large lateral root had been killed back to the trunk and usually
 were the places at which a cluster of the fruiting bodies of the
 fungus had developed. (Fig. 21, right).