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or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
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Copyright 2005, Board of Trustees, University
PRESS BULLETIN 145
florida Agrcullural kxperlmenI Stalion
CITRUS SCALES AND WHITEFLY
By E. W. Berger
When there is a great increase of scales, whether or not whitefly is also
present, it is evident that the fungus diseases of these insects are absent
or are not thriving. In this case spraying with some good contact insecti-
cide, or fumigation, should be employed to give immediate relief.
When to Spray
In the spring, summer, and fall it is not possible to use strong spraying
mixtures, and It may be advisable to spray the infested trees several times
at intervals of some weeks. It will not always be necessary to spray the
whole grove, but only the most infested trees. When whitefly is present,
the spray should of course be applied to its larvae as well as to the scales.
The following, precautions should be kept in mind when spraying for
scales in spring, summer, or fall.
1. Spray when many young scales can be seen with a lens to be crawl-
ing about, or to have just attached themselves. These young scales appear
either as oval moving specks or as round whitish dots. They are easily
destroyed by a weak spraying solution which will not injure the fruit or
foliage in any stage of growth.
2. Any contact insecticide may be employed, such as soap solutions,
emulsions of oils, or good proprietary insecticides. Soap solutions of 1
pound of soap to 6-9 gallons of water will destroy the crawling scales and
those just set, together with the young whitefly larvae, without injuring the
3. Avoid insecticides which are recommended as useful for fungus dis-
eases of citrus, because they also destroy the fungus diseases of the scales
and whitefly. Whale-oil soap causes little or no injury to these fungi, and
the same is true of some of the best proprietary insecticides.
4. During the period of summer rains the fungus diseases of the scales
and whitefly should be distributed to those trees in which they do not occur
in sufficient quantity.
5. The eggs of the scale insects, being sheltered beneath the old scales,
March 5, 1910
are not easily destroyed by sprays. The old scales are protected by their
waxy covering, and are not destroyed in great numbers b'y spraying solu-\
tions, unless of extra strength. Hence spraying in warm weather, when
the young are hatching, may be made more effective than winter sprayingJ
Whitefly and Increase of Scales
During the past two or three years scale insects have in some instances
increased abnormally in citrus trees that were infested with whitefly. It
was thought that this increase of scales had been somehow brought about
by the latter insect. That the whitefly cannot be the cause is indicated by
the facts that increase of scales has not always been preceded by whitefly,-
and that whitefly infestation is not always accompanied by increased nu -m
bers of scales. The worst cases of infestation by scales, causing partial or
complete defoliation and much loss of small twigs, are in localities suffeijngJ
from lack of moisture. It appears that this lack of moisture is the primary
factor, and that the whitefly made a bad condition worse by further exhaust-
ing the sap of the trees. The lack of sufficient moisture weakened the trees.
It also checked the development of the fungus diseases which normally
keep the scales under control. Had the trees been supplied with sufficient
moisture they would have been able to put on a fairly good growth. The
new leaves would have supplied more food to the trees. (Leaves are not
only the lungs of the tree, but also the organs in which food is elaborated.)
This food would have gone partly to feed the scales and whitefly, and partly
to maintain the vigor of the trees. These leaves would also have supplied
more moisture to the air. Their shade would have kept the interior of the
trees moister. This would have resulted in a thrifty growth of the almost
universally present fungus diseases of the scales and whitefly. It has been
noticed that scale fungi and whitefly fungi often thrive remarkably well,
even in dry localities, in vigorously growing trees with abundant foliage.
The better the condition in which a grove is kept, the less likely is it
to suffer from the depredations of insects.
State papers please copy.