18 
are its availability and its cheapness, kerosene spreading very rapidly 
and much less of it being required to wet the tree than of a soap and 
water spray. Pure kerosene is more apt to be injurious to peach and 
plum than to pear and apple trees, and the treatment of the former as 
with the soap wash should be deferred until spring, just before the 
buds swell. With young trees especially, it is well to mound up about 
the trunk a few inches of earth to catch the downflow of oil, removing 
the oil-soaked earth immediately after treatment. 
The crude-petroleum treatment.—Crude petroleum is used in exactly 
the same way as is the common illuminating oil referred to above. 
Its advantage over kerosene is that, as it contains a very large per- 
centage of the heavy oils and paraffin, it does not penetrate the bark so 
readily, and, on the other hand, only the light oils evaporate, leaving a 
coating of the heavy oils on the bark, which remains in evidence for 
months and prevents any young scale which may have escaped from 
the individuals that were not reached by the spray from getting a 
foothold. Crude petroleum comes in a great many different forms, 
depending upon the locality, the grade successfully experimented with 
in the work of this Division showing 43° Baumé. The experience of 
Prof. J. B. Smith indicates that crude oil showing a lower Baumé than 
3° is unsafe and more than 45° is unnecessarily high. The lower 
specific gravity indicated (43°) is substantially that of the refined 
product, the removal of the lighter oils in refining practically offsetting 
the removal of the paraffin. The same cautions and warnings apply 
to the crude as to the refined oil. 
The oil-water treatment.—Various pump manufacturers have now 
placed on the market spraying machines which mechanically mix kero- 
sene or crude petroleum with water in the act of spraying. The pro- 
portion of kerosene can be regulated so that any desirable percentage 
of oil can be thrown out with the water. <A 10-per-cent-strength 
kerosene can be used for a summer spray on trees where the San Jose 
scale is multiplying rapidly and it is not desirable to let it go unchecked 
until the time for the winter treatment. The winter treatment with 
the water-kerosene sprays may be made at a strength of 20 per cent of 
the oil. Applications of the oil-water spray should be attended with 
the same precautions as with the pure oil, and there is even somewhat 
greater risk, owing to the natural tendency one has to apply the dilute 
mixture much more freely than the pure oil. The application should 
be merely enough to wet the bark and should not, to any extent, at 
least, run down the trunk. The collection of water and oil about the 
trunk is just as dangerous to the tree as the pure oil. 
In the use of the oil sprays noted above, one who has not had experi- 
ence with them is advised to make some careful preliminary tests to 
fuliy master the process. It is wellalso, with the oil-water mixtures, 
to test the pump from time to time, spraying into a glass Jar or bottle 
Se 
