Bulletin 140, Dieback of Citrus Trees


is that it produces a trunk wound and may split the bark upward
a considerable distance. The use of this method is not recom-
mended.
 Bordeaux Mixture.-Bordeaux mixture sprayed upon the
fruit and foliage of dieback trees has been found to be an efficient
preventive for dieback. Grove experience and experiments car-
ried out by the Experiment Station (Florida Agr. Exp. Sta. Rep.
1913, p. xxvii) have demonstrated its effectiveness. To be most
effective it should be applied just prior to the flush of growth in






 I'i









 FIG. 15.-Distorted S-shaped growth of terminal branches

which the dieback may develop. Therefore, it may be applied in
the late winter, late spring, or late summer. To prevent the
marking and dropping of the fruit the spraying should be done
in March or April after the fruit has set and begun to grow
rapidly.
 A 3-3-40 bordeaux has been found to beof sufficient strength
for the purpose. It is not known how the bordeaux prevents
the disease. It is supposed to be on account of the stimulating
effect which the copper of the spray has upon the leaf and stem
tissues.
 The objection to the use of bordeaux mixture is that it kills
the fungus enemies of the scale insects and whitefly and allows
these insects to become plentiful. When numerous, they will
defoliate the trees and kill the branches back quickly. Therefore,
a nozzle should be used that will direct the spray downward. The
spray should be confined as much as possible to the upper surface