Florida Agricultural Experiment Station


 DISEASES AND INJURIES DUE TO NON-
 PARASITIC CAUSES

 DISEASES DUE TO PHYSIOLOGICAL OR
 UNKNOWN CAUSES
 EXANTHEMA OR DIEBACK
 Exanthema* has been reported from most of the important
citrus-producing countries of the world, with the exception of
South Africa, and is widely distributed throughout the citrus
region of Florida. The wide use of the term diebackk" by Florida
growers for a specific disease is unfortunate since the particular
disease in question is commonly confused with the dying back of
trees from other miscellaneous causes.
 This disease was first accurately described by Fowler, from
Florida in 1875, and is known to have occurred in this state as
early as 1864. When it first appeared has never been ascertained
but it probably has been present ever since citrus trees have
been grown commercially in the state. Swingle and Webber
estimated that this disease caused an annual loss of $100,000
prior to the freezes of 1894-95. In 1907, Hume stated that it
could be found in practically every citrus grove of any size in
the state. So far as is known, no species or variety of citrus is
exempt from this disease but it is of much more frequent oc-
currence on orange than on grapefruit or tangerine trees. The
disease occurs under a great variety of soil conditions. Although
exanthema has never been described until recently on any other
than citrus trees, it has been known for a long time in California
that a similar disease is not uncommon on various kinds of fruit
trees other than citrus trees, occurring on prune, pear, apple,
and olive trees. This trouble has also been reported on Japanese
plum trees in Western Australia.
 Citrus trees of all ages may be affected but the extent of the
injury from exanthema varies greatly in different groves. The
disease checks the growth of the tree and impairs the produc-
tion and quality of the fruit. When the attack is severe or
prolonged, the affected tree may be dwarfed and stunted. Despite
the vast increase in the Florida citrus industry, however, exan-
thema today is of far less frequent occurrence and a much less
serious problem for growers than it was a generation ago. The
 *This name is from the Greek word signifying an eruption.