4 BULLION. 1079, U/ S/ DEfcART^ENT OF AGRICULTURE. 



IT MUST *Bfi *EfFECTrv : E> -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 



