PRESS BULLETIN 135
florida Agricultural Experiment Station
THE PROTECTION OF CITRUS TiEES FROM DROUGHT
BY B. F. FLOY1
During the last month (November), the drought has been causing damage
to citrus groves in different parts of the State. Some groves, however, are
being irrigated, and in other groves differeAt forms of mulch are being used to
conserve the moisture. But, in too many cases, the growers have been leav-
ing their groves alone, hoping.for the rain that was long in coming. As a re-
sult bad conditions have developed.
RESULTS OF LACK OF WATER
The leaves and small branches have withered; the fruit has become stunted
and in some cases is falling; and the trees, being weakened generally, are in a
condition to be further injured by diseases such as withertip, and the stem-
end rot which has caused the loss of much fruit. Another result of the
drought is a splitting of the fruit. The poor supply of moisture has allowed
the fruit to mature its rind, more or less. With an increased supply of mois-
ture, the interior makes a more rapid growth, and the resulting pressure
causes the splitting.
It is well known that the citrus tree is giving off moisture all the time.
The under sides of the leaves, the green stems, and the fruits are covered
'with minute openings, known as stomates or breathing pores. These are so
constructed that the state of the plant controls their opening and closing. It
is through these that the water vapor passes out, and the exchange of gases
between the air and the plant occurs. In time of drought, these openings
close more or less, so that the amount of moisture given off nearly corres-
ponds to the amount supplied by the roots. During and after wet weather,
the openings will be wide open, and large amounts of water will be given off.
Experiments with different kinds of fruit have shown that the leaves of fruit-
ing trees may draw upon the fruits for moisture in case the, tree is suffering
from lack of water. This accounts for the stunting and dropping of the or-
anges during the late drought.
The question uppermost in the mind of the grower who has no irrigation
is how to conserve the moisture in his grove. Without irrigation, the grower
December 27, 1909
must resort to some form of mulch. This may be either a dust mulch, or a
mulch of dead weeds, grass, vines, leaves, or moss.
To obtain a dust mulch the grower plows under the grass and weeds, and
follows this with shallow cultivation once every week or two during the dry
weather, and if possible after each shower. On April 18 and 24, 1908, the
Experiment Station made a determination of the difference in the moisture
contained in' cultivated and in uncultivated land, The determinations were
made for each foot, to the depth of four feet. .It was found that there was a
difference of 175.2 tons of water, equivalent to one and a half inches of rain-
fall, in favor of the cultivated land. In groves suffering from a lack of
moisture, a dense growth of weeds and grass should not be allowed, because
these plants are continually pumping from the soil the water that should be
The other system of mulching is that of covering the ground around the
trees with large quantities of vines, moss, leaves, weeds, or grass. This not
only protects the soil from drying out, but also provides material from which
humus may be formed. It has been found that where soil contains plenty of
humus, less cultivation is required. In case young trees are beginning to
show the effect of the drought before the mulch has been applied, it may be
profitable to moisten the soil around the trees just before applying the mulch.
During the late drought, young citrus trees on the Agricultural Experiment
Station ground which were beginning to wilt were given a few buckets of
water and mulched with moss and vines. They immediately revived, and have
since showed no sign of wilting.
There are objections to both of these methods. In the fall of the year, if
a rain should occur, the plowing under of the weeds and grass and the subse-
quent cultivation may cause the trees to put forth new growth. This may
prove disastrous if cold weather comes on before the growth has had time to
harden. The objection'to the other system of mulching is that the mulch be-
ing dry would easily catch fire from a lighted match dropped accidentally, a
cigar stub, or a wad from a discharged gun. But if the grower does not have
irrigation, and would conserve the moisture in his soil, he must resort to one
or both of these methods.
State papers please copy.