Florida Agricultural Experiment Station


stages, the affected terminal branches may die back. New
growth is made from the nodes farther back, and in some cases
from the multiple buds. The result is a tree with a more or less
rounded, thick, bushy head that is typical of the disease. (See
 frontispiece.) With successive flushes
 of growth, a new development of the
 symptoms occurs.
 **A complete development of the dis-
 ease will not occur in the course of one
 Sflush of growth in the tree, but usually
 requires several. Such a course of de-
 velopment more often occurs in the
 chronic cases than in the acute cases of
 the disease.

 FACTORS SUGGESTED AS CAUSAL
 AGENTS
 The absolute cause of dieback in cit-
 rus trees is not definitely known. It is
 apparently very closely associated with
 the organic matter in the soil. In prac-
 tice it has long been known that the use
 of stable manure or organic ammonia
 fertilizers in excessive quantities on the
 sandy or rocky soils of Florida will of-
 ten bring on a dieback condition in the
 citrus trees. Groves set out in fields
 previously planted to vegetables and
 heavily fertilized with the usual vege-
 table fertilizers are often subject to the
 disease. Groves in which vegetables are
 grown between the rows frequently be-
 come affected. Trees near stables, out-
 houses, cesspools, poultry yards, and
 dFc. 5Lef yainieng kitchens where the roots are able to
 feed in the manures, garbage, and other
 organic refuse, often develop the trouble. Trees about which
 urine and night-soil from the home are placed, and trees border-
 ing middles where dead animals and other offal are buried often
 become affected. The growing and turning under of large quan-
 tities of legumes and other crops in the grove may give a rank
 type of growth in.the trees, that may develop dieback.