Bulletin 229, Diseases of Citrus in Florida


 DIPLODIA COLLAR ROT AND OTHER BASAL BARK DISEASES
 Caused by Diplodia natalensis Evans, and other fungi
 Instances have been noted occasionally in Florida citrus groves
where the bark at the bases of young to moderately young trees
dies rapidly, as a result of which the trees suddenly become
girdled. A slight amount of gumming usually accompanies this
collar-rot type of girdling at the margins of the lesions and Dip-
lodia has been found associated with the early stages of this
trouble in various localities in the central portion of the pen-
insular section of the state. Diplodin has been found associated
with this type of trouble also in the Satsuma district of West
Florida. Young trees seem to be attacked most frequently. In
many cases only a single tree may be affected while, in others,
a group of from a few to several trees may be involved. Un-
fortunately, this trouble is rarely observed by growers until the
trees have become more or less completely girdled. When ex-
amined at this stage, the entire root systems of young trees are
often found to be more or less dead and with the bark so far dis-
integrated that no pathogenic organism is in evidence. Grow-
ers often attribute this trouble to foot rot or to lightning injury.
Further observation and study will be required before the exact
cause is demonstrated conclusively.
 Other basal bark diseases of older citrus trees have also been
encountered from time to time in Florida groves. In some cases
these appear to be caused by a form of gummosis while in other
cases the trouble is an inconspicuous dying of the bark with
little or no gum formation. These diseases have one point in
common, however, in that they frequently girdle trees rapidly
and may result in considerable loss unless detected and treated
in time. Unfortunately, but little is known concerning them.
 Trees attacked by the collar rot type of girdling or other basal
bark diseases should be treated promptly if discovered before
they are too seriously girdled. The diseased bark should be cut
out to a point slightly in advance of the discoloration on the
underlying wood. After this bark has been removed down to the
underlying wood the treated place should be painted with some
good disinfectant such as lime-sulphur solution. When the wood
has again dried, all exposed surfaces should be painted with a
durable waterproof wound dressing. Care should be taken at all
times to prevent the occurrence of bark wounds and to treat