= BULLETIN 1079, U. S. DEPARTMENT OF AGRICULTURE. 
IT MUST BE EFFECTIVE ON VARIOUS SPECIES OF WOOD. 
The type of bark makes considerable difference in the application 
of a spray. A bark which is very absorbent, such as that of ash or 
juniper, readily takes a spray; on the other hand, a smooth bark, 
such as beech or hickory, will absorb scarcely any of it. Such smooth 
bark does not hold the spray well but allows it to be easily washed 
off in the rain. In the latter case poison sprays would hardly be 
effective. The irregularities of the bark and all crevices must be 
thoroughly covered. 
IT MUST NOT BE LEACHED OFF BY RAIN OR OTHER WEATHER CONDITIONS. 
One of the greatest difficulties in the experiments to find an 
effective spray has been that the solutions are soon washed off by 
rain. Many of those tried were effective for a few weeks, or until 
the first hard rain, after which the trees were immediately attacked. 
IT MUST NOT BE EXPENSIVE. 
Since a considerable quantity of liquid is required to cover a 
large log by spraying, it naturally follows that the material must 
be inexpensive or it can not be used. Creosote oil, the most effective 
material so far tried, is far too expensive. It can be diluted, how- 
ever, with as much as 4 parts of kerosene, thus materially reducing 
the cost of the spray without diminishing its effectiveness. For rus- 
tic work a much more costly spray can be used than on logging op- 
erations. | 
IT MUST FIRST PREVENT ALL INSECT INJURY FOR FROM ONE TO THREE 
MONTHS AT LEAST. 
Three months’ protection by the spray would be sufficient for most 
purposes. It is usually possible to get logs to the mill or into a 
place of safety within that time. If it were sufficiently cheap so 
that a second and perhaps a third application could be made, the 
solution would need to be effective for only one month; the necessity 
for more than one application, however, would of course be a handi- 
cap. In many cases three months’ prevention of damage would carry 
the tree or log through the danger period—that in which the insect 
is flying—and natural seasoning during the ensuing winter would 
prevent further injury. 
EXPERIMENTS WITH PREVENTIVE SPRAYS. 
During the period of insect activities in the years 1916 to 1920, 
inclusive, series of experiments were conducted at the Eastern Field 
Station of the Bureau of Entomology, East Falls Church, Va., to 
determine the effectiveness of various solutions. These were 
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