Recent Results of Spraying Experiments for the 
Control of the Whitefly on Citrus 
W. W. Yothens, Bureau of Entomology, Orlando. 
Mr. President, Ladies and Gentlemen : 
It is not my intention to recommend 
spraying as a panacea for the control 
of the whitefly, nor to recommend it 
in preference to other methods of con¬ 
trol. It is my belief that the grower 
should decide which method or combi¬ 
nation of methods is best adapted to his 
circumstances. I wish only to present 
the results obtained recently as a study, 
and I hope the information may be 
helpful to those who intend to spray 
and to those who have already adopted 
spraying as a method of control. 
According to my ideas, an insecti¬ 
cide, to be valuable for the control of 
the whitefly, should be of such a na¬ 
ture that it can be used strong enough 
to kill the larvae and pupae without in¬ 
jury to the trees. There are many in¬ 
secticides which will kill the insects but 
which do so much damage to the tree 
that they cannot be used. Again, there 
are insecticides which harm the trees 
and do not kill the insects, and then 
there are those which neither harm the 
tree nor the insect. It also increases 
the value of the insecticide if it will 
loosen the sooty mold. It is my opin¬ 
ion, however, that the whitefly should 
be so kept under control that there will 
be little or no sooty mold. This is an 
ideal condition, and the fact remains 
that many groves have sooty mold 
which should be loosened. 
Then I believe also an insecticide 
should have stable qualities. By this I 
mean it should remain on the tree a 
considerable length of time without do¬ 
ing any injury. It has been a problem 
to get an insecticide with all the quali¬ 
ties which it should have and adapt it 
to this climate. The rains during the 
summer prohibit the use of many good 
insecticides which may be valuable in a 
dry, arid climate. The reverse may 
also be true, an insecticide adapted for 
rainy weather may remain too long on 
the trees if it is used in a country where 
it seldom rains. 
I should also state that insecticides 
adapted primarily for deciduous trees 
may or may not be valuable for orange 
trees. In several instances the most 
popular and valuable insecticides for 
the San Jose Scale have proven inju¬ 
rious to orange trees, even when used 
at a strength which would not kill the 
larvae and pupae of the whitefly. 
Last fall we began compounding an 
