PRESS BULLETIN No. 297
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
THE PURPLE SCALE
J. R. WATSON
Next to the whitefly, the purple scale probably does more
damage to Florida citrus groves than any other insect. It is cer-
tainly the most abundant scale, altho scale for scale it is not so
injurious as the Florida red scale.
Like all armored scales, the female lays eggs under a hard
cover where they hatch in about a week in summer. The young
crawlers wander for a few hours, after which they become
attached and never move again. It then takes two months to
complete their growth. There is a tendency toward broods in
Florida groves. The crawlers are especially abundant in March
and April and again in May and June. Other things being equal,
these are the best times to spray for the scale. However, purple
scale, in most groves, is accompanied by whitefly. Indeed, these
two insects form one problem for most growers. The honey-dew
which is given off by the whitefly, enables the sooty mold to grow
and form a partial protection for the purple scale from its natural
enemies. The result is that the purple scale is more abundant in
groves heavily infested with the whitefly.
The insecticides which are used against the whitefly are
the very best with which to fight the purple scale. In groves
which are regularly sprayed for whitefly, purple scale will ordi-
narily be controlled. The best sprays are emulsions of the par-
affin oils, including the formulae originated by W. W. Others of
the Bureau of Entomology U. S. D. A. Ordinarily three spray-
ings a year, if thoro, are sufficient to control these two insects.
Two of these sprayings should be with paraffin oils and one with
fungi. The best time to spray with paraffin oils is about the first
of May and again sometime in September (or the last of August
in south Florida). It is necessary, of course, to spray thoroly to
do efficient work.
Early in the rainy season, groves that have large numbers
of scales, should be sprayed with spores of fungi. If possible one
should use the red-headed, the gray-headed, and the black scale
fungi, all in the same water. Material with these fungi on it is
soaked in water about half an hour and then thoroly agitated to
wash off the spores. The water from this material is strained to
remove all matter that may clog the spray pump. It is then ready
October 26, 1918
to be sprayed into the trees. Use a spray outfit that has never
contained Bordeaux mixture or lime-sulphur. The tank should
not be made of copper, as that metal is injurious to the spores of
the fungi. It is better to keep a knap-sack sprayer especially for
this and no other purpose.
If one has sufficient material, it is better to spray the water
containing the spores all over the whole of the scale infested
trees; otherwise, the spray may be confined to a portion of
each tree. In this case it should be the north or shady side of the
tree, as it is here that the fungi thrive best, and the scales are
usually more abundant. These fungi will grow into the bodies of
the scales and destroy them.
If whitefly is in the grove, the brown and red whitefly fungi
and also Microcera, if it is readily obtained, should be applied
with the scale fungi.
The purple scale is often particularly injurious in young
groves because the fungi do not thrive well in such sunny places.
In such cases, it may be necessary to spray the grove with the oil
emulsion more than twice a year. July is a good time for the
In case of a severe infestation of the purple scale, it may be
necessary to spray twice, with an interval of about a month be-
tween. The first application does not kill the eggs under the old
females. In a month these will have hatched and the young scales
will be killed by the second spraying. For the second application
one can either use one of the oils, or substitute a solution of
whale-oil or some other soap of a concentration of one pound to
five gallons of hard water, or six gallons of soft water.
State papers please copy.