PRESS BULLETIN 149 April 16, 1910
Florida Agricullural Experimenl Slallon
SPRING TREATMENT FOR WHITEFLY
By E. W. Berger
The spring brood of whiteflies is now on the wing and the problem
of how to check these pests again presents itself. Though the spring is
doubtless not so good a season in which to spray the whitefly as fall and
winter, it is easy to reduce its numbers considerably by spraying the young
scale-like larvae soon after they have hatched.
In localities where the fungi have not given satisfactory results and
the trees are out of condition, or where the owners have. a preference
for using insecticidal sprays, soap solutions or emulsions of oils can be
employed with satisfactory results. As stated in former bulletins, whale-oil
soap, 1 pound to 9 gallons of water, gave good results when applied to the
just-hatched whitefly larvae, and to young larvae less than about three
weeks old. For larvae three weeks old or more, the stronger solution of
1 pound to 6 gallons is to be preferred.
Common laundry soap, such as Octagon soap, gave slightly better re-
sults than soft whale-oil soap. Common soap may be employed when only
a small number of trees are to be treated, as in a house lot.
Golddust washing powder has been used by some growers, apparently
with good results; but my experiments show that 1 pound of good whale-
oil soap to 9 gallons of water is as effective as 1 pound of Golddust
to 4 gallons of water. Golddust consists of washing soda and soap, and a
similar and equally effective mixture may be made from 1 pound of whale-
oil or laundry soap with 3 pounds of washing soda (or sal soda), dissolved
in 16 gallons of water.
Several miscible oils have given excellent results for spring and sum-
mer spraying, when sufficiently diluted so as not to injure the fruit or
foliage; and these are at the same time somewhat more effective than
soaps against scales.
Spraying should not be done when large numbers of the winged white-
flies are swarming, nor before the eggs have hatched; for many of the
adults would fly away uninjured, and return later on to deposit their eggs.
The egga are not destroyed to any large extent by spraying solutions. Ten
to fourteen days after the disappearance of the spring brood of adult
whiteflies! the eggs laid by this brood will have hatched, and the young
larvae will then be quite readily killed by insecticides. By careful spraying
a grower can destroy up to 95 per cent. of these young larvae. He there-
fore has it in his power to nearly free his grove from the pest, for the time
being. With large trees, the percentage killed will of course be less, owing
to the difficulty of spraying; but should only 75 per cent. of the larvae be
destroyed, it will be sufficient to save the trees from serious injury.
Such spraying as is here recommended is not intended to eradicate
the whitefly, but to reduce it to a comparatively insignificant remnant at
each spraying. It is hardly practicable to eradicate it by any means yet
known, but it is possible to control it.
If the splaying is done thoroughly this spring, it may not be necessary
to do any further repressive work before next October or November, except
that the fungi may be spread during the period of summer rains if the
whitefly gets abundant.
In October or November, or soon after the fall brood of adults has
wholly disappeared, the trees may be sprayed again; unless the fungi have
succeeded in keeping the insects sufficiently in check during the summer.
After the fall spraying, it will not be necessary to spray until the following
April or May. By following out these recommendations the grower can pro-
tect his trees against injury from whitefly fairly well, whether the pests
in neighboring groves are controlled or not. The secret consists simply in
destroying the greater number of each and every brood of larvae as soon
as it develops, whether the whiteflies that laid the eggs migrated from ad-
joining groves or developed from larvae bred in the trees. This can be
done by spraying in April or May; again, if necessary, in June or July; and
again in October or November. Spray each brood of young larvae as soon
as it is hatched, which is about ten to fourteen days after each brood
of winged whiteflies has disappeared.
The Fungus Diseases
In localities where the fungus diseases of whitefly have given definite
results, growers will probably prefer to depend upon these and should bear
in mind that they can greatly assist the fungi by artificially introducing and
spreading them, especially during the period of summer rains. If it is in-
tended to introduce fungus in April or May, periods of rain should be
selected; otherwise it is generally best to wait until the time of the sum-
State papers please copy.