56 HYDROCYANIC-ACID GAS FUMIGATION IX CALIFORNIA. 
Other conditions exist which take part in prohibiting this greater 
dosage. If this dosage were used in general orchard work, it is doubt- 
ful if eradication would occur in all cases. Tents not properly 
pulled down on all sides of the tree, a hole in the tent, mistake in 
measuring the trees or in reading the dosage from the schedule, 
erroneous measuring of chemicals, boiling over of a generator, over- 
turning of a generator, and numerous other considerations which will 
sometimes escape even the most careful manipulator, make the differ- 
ence between eradication and noneradication more variable in prac- 
tice than in theory. If the fumigator is inclined to be a little careless, 
some of the above errors will frequently creep in. 
Moreover, unless compelled to do so the orchardists in any one 
locality would not all use this dosage, while possibly some would not 
fumigate at all. To go to the extra expense required in an eradication 
dosage and then be subject to reinfestation from one's neighbors 
presents no special attractiveness to the grower. Supposing that 
the growers in any one locality were willing to use an eradication 
dosage, the present number of fumigation outfits is inadequate to 
meet this requirement within the limited time necessary in order to 
prevent reinfestation. These practical considerations demonstrate 
that the eradication of the purple scale from any large district is im- 
practicable at the present time. 
DIFFICULTY OF DESTROYING THE SCALE OX THE FRUIT. 
There is one more important point which must be considered in 
connection with fumigation for the purple scale. In experiments 
to which attention has been called it has been shown that destruction 
of scale is much more difficult on the fruit than on the leaves and 
branches. Careful investigation of this point for about two years 
has also shown that the susceptibility of the scale on some fruit is 
much greater than on others. Hence, no exact standard of destruc- 
tion for the scale on fruit is possible. When scales become matured 
and deposit eggs the dosage required for eradication is very much 
greater on the fruit than on the leaves and branches. It may require 
a one-fourth to one-half or in some cases an even greater increase. 
A dosage sufficient for eradication of the scale on the fruit is impracti- 
cal for the very same reasons that make eradication on the leaves 
and branches commercially impractical. A grower possessing a 
few trees on which he intends to eradicate the scale at one fumigation 
should remove all infested fruit before the operation and then use a 
1^ schedule. It is advisable to remove the old scaly fruit in any fumi- 
gation. At picking, fruit badly infested with scale is usually left on 
the tree, and frequently from one to a half dozen or more old, scale- 
infested oranges per tree remain throughout an orchard. Even after 
a good fumigation one of these old fruits might carry more healthy 
