Bulletin 140, Dieback of Citrus Trees


 CONDITIONS COMPLICATING THE CONNECTION OF DIEBACK
 WITH SOIL ORGANIC MATTER
 Dieback occurs in citrus trees planted in locations and grow-
ing under conditions which make it less easy to establish the
connection between the cause of the disease and the organic
material in the soil. Trees subject to a lack of drainage are very
often affected. The fact that organic hardpans are formed in
sandy soils at the level of the water-table indicates an accumula-
tion of these materials at this point. The feeding of the roots
in these materials may be a factor in the development of the
disease. Water-logging of the soil will give rise to anaerobic
decomposition of the residual organic matter in the soil. The





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 FIG. 6-Dieback marked, or ammoniated fruit

feeding of the tree upon these products may be a causal factor.
 Trees planted on lands underlaid by hardpans are often af-
fected with dieback. These hardpans may be the organic hard-
pans that occur on the flatwoods land, layers of clay, marl, rock,
or even the layers of compact sand. The hardpans interfere
with the ready movement downward of materials leached from
the more open soils above. The accumulation of soluble organic
materials above these hardpans, and the feeding of the roots
therein is a possible factor in the development of the disease.
Irregularities in the surface of the hardpan may form pockets
deficient in drainage and lead to the development of the disease
in trees planted thereon.
 Excessive cultivation of the soil is apparently conducive to
the development of dieback. It has been observed repeatedly
that healthy groves on pineland which has been cultivated vig-
orously to kill out Bermuda grass, have become affected. Clean
cultivation thruout the year is favorable to its development. Any
considerable stirring of the soil in groves planted on shell ham-