280 REPORT OF THE DEPARTMENT OF ENTOMOLOGY. 
From this it will be seen that the subject of cost of spraying 
is just as variable as that of fumigation. That it depends on 
cost of materials, the distance they have to be freighted, the size 
of the trees, ete. 
It has been shown under cost of fumigation that the expense 
of fumigating the largest trees that could be covered by box 
fumigators need not exceed 34 cents. The cost of spraying the 
same size of trees with crude petroleum need not exceed 12 
cents per tree. Which shows that spraying costs about one-third 
as much as fumigation. Spraying has the disadvantage of being 
an uncertain method of treatment, not only uncertain as to effect 
upon the scale insect, but also upon the trees. In fact the mar- 
gin between the amount of oil required to injure the pernicious 
scale and to injure the tree upon which the insect occurs is so 
close that it is a lottery as to what the result will be. Further- 
more, oil spraying at best is disagreeable and an undesirable 
method of controlling the pest. 
