Press Bulletiin No. 5(.
UNIVERSITY OF FLORIDA.
LAKE CITY, FLA.
WHITE FLY CONDITIONS IN
The unusually low temperatures of January 26 to 29 of the
present year resulted, in the northern part of the State, in a
partial defoliation of citrus trees. Orange growers are now
looking with interest to the effect that these conditions will
have upon the white fly. It will add to the clearness of the
discussion to have clearly in mind, first of all, the condition in
which the insect passes the winter. The eggs of the fall brood
are hatched during October and November. All are hatched
certainly by the end of December. A few hours after hatching
the young attach themselves on the under side of the leaves.
From this time on through the winter they are growing insects,
and as such require, and are taking, nourishment from the
leaves. During the months of January and February we have,
then, to deal, not with eggs, but with insects which are alive
and feeding, but immovably attached to the leaves. These
facts should be kept in mina in order to clearly understand the
effect upon the insect of.defoliation of the trees.
The cold has not of itself killed the larvee. as will be quick-
ly seen by an examination, in an infested region, of any of the
several hardy non-deciduous plants on which the insect feeds.
The white fly is fond of privet. The larvee on hedge rows of
Feb. 28, 1995.
privet on the Station grounds at Lake City, where the ther-
mometer went to sixteen degrees above zero, are alive, having
apparently suffered not at all from the cold. The same is true
of larvae on cape jessamine. Living larvae may also be found
in abundance on the green leaves still clinging to the orange
The real injury and check to the insect at this time comes
from the more or less complete defoliation of the trees result-
ingfrom thefreeze. The young, as has been mentioned, are in a
growing stage. If the leaf dries and the flow of sap ceases the
insect must necessarily perish. The larvae at the time of the
freeze were in varying stages of development. Some of them
were comparatively small. If the leaf falls the case of these
is clearly hopeless. They must die for the lack of food. On the
other hand, some of the larvae were practically full grown.
These require very little additional food. They must, however,
have moisture to prevent drying of the body, and unless the
leaf falls in a damp place even these will die. It seems, then,
barely possible that on those leaves falling in damp places
some few larvae may live to escape as adults. It has been gen-
erally belie%"L that the white fly is to oe found on the leaves
only. It is evident, however, that in rare instances they oc-
cur on the stems also. A single pupa case of last summer's
brood was found attached to the stem of a badly-infested orange
tree on the Station grounds. During the summer the growing
tips are tender, and it is to be expected that eggs may be occa-
sionally deposited on them. At the time the eggs of the win-
ter brood are deposited the stems are harder and the young
even less likely to occur on them.
Neither from the piles of dead leaves, nor from any occa-
sional larve found on the branches, will the new brood of white
fly come, but from the few leaves still clinging to the trees
and from the hardy non-deciduous plants round -about the
grove on which the insect feeds.
Whatever precautions are taken at this time against the
white fly, the presence of these hardy plants on which the in-
sect is taking its normal course uninjured by the cold must not
be forgotten. The fly is known to feed on cape jessamine, privet,
and mock orange, and to some extent on water oak and on
scrub palmetto. The first three of these can usually be dealt
with successfully. They should be either defoliated or de-
stroyed. If, however, the insect has spread to the water oak
and scrub palmetto, extermination in that locality becomes
hopeless. This need not, however, prevent the pest being
brought under control; and the practical question now before
the orange grower is how best to take advantage of the present
favorable opportunity. In case the grove or nursery contains
only small trees already partially defoliated, it may be found
practicable to complete defoliation. If such method is adopt-
ed, care should be used not to leave clinging to the trees the
basal part of the leaves,to which not infrequently larvae are at-
tached. Those citrus varieties which have leaves with winged
petioles often break above the base, the wing remaiining attach-
ed, harboring for some time larvee which may thus survive and
emerge. If, on the other hand, the grove has large trees defoli-
ation will usually be found impracticable. In such cases, if
the insect is to be effectually checked,spraying must be resort-
ed to. The scanty foliage at this time gives an especially fa-
vorable opportunity for successful spraying.
The adult insects of the spring brood issue, according to
those who have watched them most closely, largely during
March, April, and May, depending to some extent upon the
weather conditions, and varying from the northern to the
southern part of the State. Measures for their control .should
be put in operation, if possible, before any.,of thr'adults emerge.
If sprays are to be applied proper attention must also be given
to the condition of the trees.
Regarding the most desirable spray, opinions are by no
means uniform. The resin wash has long been a favorite espec-
ially as a spray during the dormant season when it may be used
fullstrength according to the standard formula. It is, however,
reported unsafe during April, May, and June, and during the
summer is used with safety only in the weaker solution. Pro-
fessor H. A. Gossard, in his standard publication on the white
fly, Bulletin 67 of this Station, page 634, says: "Spra'ving
should cease when the blossoms commence opening, but may
be continued until the buds are swollen and ready to burst."
Whale oil soap has been found an efficient spray. The
following formula for the preparation of a whale oil soap is
taken from Bulletin 76 of this Station:
"True potash lye .......... ..............I lb.
F ish oil .......... ........................3 pts.
Rain water...... .... ............ ...3 gals.
Dissolve the lye in boiling water, then add the oil and boil
for at least two hours longer. When boiling is finished, there
should be two gallons of soap; if necessary, add water to make
two gallons. For insects, such as plant lice, use this soap at
the rate of 1 lb. in 9 or 10 gallons of water; for scale insects,
one lb. in five to six gallons of water."
Various prepared whale oil soaps are on the market.
Good's potash whale oil soap No. 3 has given in Florida ex-
ceptionally satisfactory results, and has a mild effect upon the
tree. Of this soap Professor Gossard says: "Used at the rate of
one pound to four gallons ot water it will kill about sixty per
cent. of the grown larva in March; and, when used at the
rate of one pound to tree gallons of water on half grown lar-
va in May or early June, from eighty-five to ninety-fiv, per cent,
of them are killed." When spraying for the white fly.especial
effort should be made to reach the under side of the leaves.
Whatever spray is used, too much emphasis cannot be put
upon the necessity of thorough application.
E. H. SELLARDS, Entomologist.
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