Group Title: Press bulletin
Title: When to spray for whitefly
Full Citation
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 Material Information
Title: When to spray for whitefly
Series Title: Press bulletin
Physical Description: 2 leaves : ; 21 cm.
Language: English
Creator: Berger, E. W ( Edward William ), b. 1869
University of Florida -- Agricultural Experiment Station
Publisher: Florida Agricultural Experiment Station
Place of Publication: Gainesville
Publication Date: 1909
Subject: Citrus whitefly -- Control -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: by E.W. Berger.
General Note: Caption title.
General Note: "September 25, 1909."
 Record Information
Bibliographic ID: UF00090485
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 79001240

Full Text


Florida Agrlcullural Experiment Stallon

This bulletin has been written to meet the requirements of those who pre-
fer to spray with insecticides, and for those who find it necessary to use spray-
ing solutions when fungus is difficult to obtain, or during periods of protracted
dry weather when the fungi spread but little.
The young of the citrus whitefly (sometimes incorrectly called eggs,) are
scale-like, and pass through five stages of development, increasing from about
one-eightieth of an inch to about one-eighteenth of an inch in length. The
first four stages are spoken of by numbers (first, second, third, and fourth
larval stages); but the fifth, the transformation stage from which the winged
whitefly emerges, is called the pupa. The best time to spray with contact in-
secticides is when these insects are mostly in the first three larval stages, or
the thin flat fourth stage. Those in the thick fourth, or in the pupal stage,
are less easily killed, and require a stronger insecticide. The eggs of the
whitefly cannot be destroyed by ordinary insecticides, and it is useless to spray
the winged adults.
There are two principal periods when the whitefly is in the younger stages.
The first period is in April or May, and begins about two weeks after the
winged whiteflies have ceased swarming and have disappeared. The advan-
tages of spraying at this time may be summed up as follows: (1) The white-
flies are in the young larval stages and are easily killed; (2) they are mainly
on the new growth and more easily sprayed; (3) the larvae are destroyed be-
fore sapping the strength of the new growth, and before much sooty mold has
developed; (4) there is little rain to interfere with the spraying.
Spraying may also be carried on any time during the summer after the
second brood of adult whiteflies has been out for several weeks; but since dur-
ing this time the whitefly develops irregularly, there being all stages present
in considerable numbers at all times, and since rains are generally abundant,
spraying at this time is not advised, except when the trees are suffering
The second best period for spraying is in October or November, or soon
after the adult whiteflies have wholly or nearly disappeared, and after the last
layings of eggs have hatched. Groves sprayed in the early part of last No-
vember with a spraying mixture whose principal ingredient was whale-oil soap
(about 1 pound to 10 gallons of water), showed that about 90 per cent. of the

September 25, 1909

larvae had been killed. The advantages of fall spraying may be summed up
as follows: (1) The young larvae are abundant and easily killed; (2) they are
killed before they wax fat on the trees; (3) there are few rains to interfere
with spraying.
Since spraying for the young whitefly larvae must be done in spring, sum-
mar, or fall, when either tender leaves or fruit are on the trees, it is evident
that a spraying solution must be employed which will not injure the foliage or
fruit. Any good contact insecticide can be employed, provided it is sufficient-
ly diluted.
It has been found that soap solutions of 1 pound of soap to 6 gallons of
water, destroyed all the larvae in the first three stages, and most of those in
the fourth and pupal stages. Thorough spraying resulted in destroying be-
tween 90 and 96 per cent. of all the larvae on the leaves. Soap solutions of 1
pound of soap to 9 gallons of water destroyed about 90 per cent. Good's pot-
ash whale-oil soap No. 3 was used, and also Octagon soap. It is probable that
any kind of soap will be effective against these young larvae. In winter it
would probably be necessary to use the soap stronger, say 1 pound to 4 gallons
of water; but a weak solution when used in spring, summer, or fall, will give
better results than the strong solution in winter.
"Golddust" was also used on young larvae at the rate of 1 pound to 4
gallons of water, and 90 to 95 per cent. were killed. Preliminary chemical ex-
amination of Golddust showed that it consisted of about 25 per cent. of soap,
62 per cent. of washing soda, and about 13 per cent. of water. Golddust is an
expensive mixture to use for spraying. One part of whale-oil soap with three
parts of washing soda gave practically the same result as Golddust, when each
was used in the proportion of 1 pound to 4 gallons of water. One pound of
whale-oil soap to 9 gallons of water gave practically the same results as the
whale-oil soap and soda mixture, at about the same cost, which was a little
less than half a cent per gallon. Whale-oil soap is therefore a cheaper mate-
rial to use for spraying than Golddust. A mixture equally as good as Gold-
dust can be made from whale-oil soap and washing soda, at about one-half the

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