PRESS BULLETIN No. 90.
Florlda Agrlcullural Experiment sf1100n.
TREATMENT OF CITRUS DIE-BACK.
BY B. F. FLOYD.
The principal conditions recognized as bringing on die-back are; (1.) over-
fertilization with fertilizers containing cottonseed meal, blood and bone,
dried blood, and other such forms of ammonia, as well as with stable manure;
and (2.) unfavorable soil conditions. Groves set out in fields previously planted
to vegetables, and heavily fertilized with the usual vegetable fertilizers, are
often subject to the disease. Groves in which vegetables are grown between
the rows also frequently become diseased with die-back. Trees situated near
stables, chicken-yards, and similar places where an excessive amount of or-
ganic matter is allowed to accumulate in the soil, suffer from the same dis-
ease. The use of large amounts of stable manure, cow-penning and similar
practices frequently bring it on.
REMEDIES FOR EXCESS OF AMMONIA.
The remedy in these cases is to discontinue cultivation as soon as the
moisture condition of the soil will allow. In some places, it is not possible to
stop cultivation:during times of drought 'on account of the great loss of soil
moisture that would follow. The natural growth of grass and weeds that
comes on during the rainy season should be cut and removed after maturing.
The ammonia of any fertilizer used should always be in the form of nitrate
of soda or sulphate of ammonia. This treatment should continue until the
trees have recovered.
REMEDIES FOR SOIL CONDITIONS.
Die-back very frequently occurs in soils that have a tendency to keep the
water from draining off during the rainy season. Such die-back areas not in-
frequently occur in the higher portions of a grove, and a few such instances
have been known to occur on the top of a hill. To cure die-back in such
cases it is necessary to ridge the tree rows high, or to provide the
grove with other surface drainage. Trees planted on grounds where a com-
pact subsoil, such as hard-pan, marl or clay is near the surface, are often
affected with die-back. In some cases the hard-pan is thin enough to be
broken through with hand implements. In other cases it is shattered by dis-
charging a little dynamite under the tree. Both of these methods have cured
die-back when caused by hard-pan.
Die-back has been noticed to be particularly prevalent upon certain lands
in the state, such as the shell lands, the" coquina lands, and the rocky lands in
May 2, 1908.
the extreme southern part of the state. The treatment for die-back when
occurring upon the shell lands consists in mowing the weeds and grass and
preventing the accumulation of decaying vegetable matter. Any stirring of
the soil should be avoided. Such forms of ammonia as cottonseed meal, blood
and bone, and stable manure, should not be used either in combination or
separately. Most of the fertilizers sold to citrus growers contain more or less
of these forms of ammonia in their combination. (This is shown on their
tags). Sulphate of ammonia should be used in their place. When die-back
occurs in groves located on lands where the coquina rock occurs near the sur-
face the treatment consists in avoiding all cultivation. Such ammonia man-
ures as cottonseed meal, blood and bone, and dried blood should not be used
either in combination or separately. The grass and weeds should be mowed
frequently. In treatment for die-back occurring on rocky lands, snch as are
found in extreme southern Florida, such fertilizers as contain cottonseed meal,
blood and bone, or dried blood, should not be used. Stable manure, and guano
should also be avoided. Plowing should be practiced only when absolutely
necessary to conserve the soil moisture. Grass and weeds should be cut be-
fore they become rank in order to avoid accumulating much organic matter.
Stable manure, guano, cottonseed meal, dried blood, and bone meal, are
stimulating fertilizers for citrus trees and can usually be applied in small
quantities, or at infrequent intervals, with decidedly beneficial results for
making wood and leaf growth; but in large quantities, and by continued use,
they are almost certain to bring on die-back. When used on fruiting trees,
rough coarse fruit is apt to be produced, as well as splitting and premature
State papers please copy.