Florida Agricultural Experiment Station


was used and it was given in two applications. The affected
trees were located in a grove on high pineland in the vicinity
of Orlando and the chemicals were applied in March and May.
 During the years of 1915 and 1916 experiments were con-
ducted by the Experiment Station with severely affected trees on
high pineland in Pinellas County. Two pounds per tree was
found to be an effective preventive on budded and seedling trees
more than twenty years old, whereas one pound was not nearly
so effective. The chemical was given in one application in April.
Hardwood ashes and air-slaked lime used separately on other
plots in the same grove were without effect. During the follow-
ing year the whole grove was subjected to ammonia starvation
by omitting one application of the fertilizer and using a low am-
monia content in the others. In the fall there was very little
evidence of any new development of the disease. The fruit for
the first time in years was largely free from dieback markings.
 Bluestone is a strong poison. A number of cases of injury to
citrus trees by its use have been reported. On the other hand,
it has been used about citrus trees in rather large quantities
without injury. Grossenbacher applied as high as 16 pounds
in two applications of 8 pounds each about two months apart, and
12 pounds at a single application on another occasion without
any injury to the trees. It should probably be used with greatest
care on moist soil where it will be put into solution rapidly after
application.
 While bluestone is evidently a preventive for dieback, it is
not known how it prevents.
 Bluestone Beneath the Bark.-Another method of using
bluestone for dieback that is commonly employed by growers is
to insert a crystal varying in size from a grain of wheat to that
of a pea, beneath the bark of the tree. If the tree is large two
or three crystals are inserted at different points in the circum-
ference of the tree. It is sometimes inserted into the crown roots,
or the larger branches, but it is more often placed beneath the
bark of the trunk.
 While it appears to be an effective preventive of dieback in
some cases, especially of young trees, it is more often not effec-
tive. In experiments conducted by the Experiment Station with
affected trees on high pineland at St. Leo, Pasco County, this
method gave negative results. The chief objection to the method