46 FUMIGATION [INVESTIGATIONS IN CALIFORNIA. 
ERADICATION OF THE PURPLE SCALE. 
The foregoing experiments have shown that the purple scale can 
be eradicated from citrus trees, provided a dosage of sufficient 
strength be used with a sufficient exposure. This dosage strength 
is much greater than that at present used in fumigation. 
If the purple scale can be everywhere eradicated by using a dosage 
of definite strength 'which we hope to determine in due time), the 
question will immediately arise in the orchardist's mind whether it 
will be profitable to use this heavier dosage provided it can be em- 
ployed without injury to the tree and fruit. In deciding this ques- 
tion several practical considerations must be taken into account. 
The trees, as will be shown later, are in a condition to stand this 
heavy dosage without injury during but a limited portion of the year. 
It would he impossible for the number of outfits at present in exist- 
ence to fumigate the infested area within this limit of time. More- 
over, unless compelled to do so the orchardists in any locality would 
not all use this dosage. Whether it would be advisable for a grower 
to incur the additional expense for this heavier dosage in his orchard 
when the infested orchards on all sides of him are fumigated with 
lighter dosages, if at all, must be determined by large-scale tests. 
The foregoing are some of the difficulties in respect to the use of this 
heavy dosage. 
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. It will be seen in 
an examination of the data from the foregoing experiments that an 
orchardist, fumigating trees containing purple scale in its different 
stages on the fruit as well as on the leaves and branches, would, 
except with the heaviest dosages, leave on the fruit healthy eggs soon 
to hatch and infest other parts of the trees. It would be impractical 
under most circumstances to use a dosage heavy enough to destroy 
the eggs on the fruit. The cost of the extra cyanid required, above 
that necessary for the destruction of the eggs on the leaves and 
branches, would be more than the scaly fruit is worth. Therefore 
in fumigating for eradication it is advisable to remove the infested 
fruit, and 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 purple-scale eggs than all the rest of the tree, and on the 
hatching of these eggs the insect- will spread to other parts of the 
tree. The danger from old scaly fruit is evident and all such should 
be removed from the tree- before fumigating an orchard. 
