February, '17] BECKER: round-headed apple tree borer 69 



east or west sides than on the north. From the fact that the bark 

 appeared normal where the asphalt cracked or chipped off, it seemed 

 most likely that the presence of asphalt impaired the process of 

 respiration. 



Preliminary tests were made with two-year-old apple trees to 

 see what effect treatment would have. Twenty-four trees were 

 treated at temperatures ranging from 235 to 175 degrees C. The trees 

 were submitted to Professor Hewitt, Plant Pathologist, whose report 

 follows: "The asphaltum tests indicated that trees would stand as- 

 phaltum as hot as 203° C. without apparent injury, provided it was 

 quickly applied, though a tree treated from 140 to 150 degrees C. was 

 injured, when the application was prolonged to one-half minute. It 

 thus appears that young trees could stand a high temperature for a 

 short time better than a somewhat lower temperature unduly pro- 

 longed." 



After the preliminary tests, it was decided to try asphaltum in the 

 tests at the three different temperatures. One at the lowest tem- 

 perature at which the raw asphalt would spread efficiently (about 

 150° C.) ; another at 130° C. ; and a third at 1 15° C. The melting points 

 in the latter two instances were reduced with oils. In order to deter- 

 mine whether it would be desirable to have the oil dry out rapidly, 

 or to have it remain in combination longer, gasoline, kerosene and 

 linseed oil were used. Thus, asphalt was used in seven combinations. 



1. Asphalt applied at about 150° C. 



2. Asphalt with melting point reduced to 130° C. with gasoline. 



3. Asphalt with melting point reduced to 130° C. with kerosene. 



4. Asphalt with melting point reduced to 130° C. with raw Unseed oil. 



5. Asphalt with melting point reduced to 115° C. with gasoline. 



6. Asphalt with melting point reduced to 115° C. with kerosene. 



7. Asphalt with melting point reduced to 115° C. with raw Unseed oil. 



As before indicated, in order to see whether some varieties might 

 be more susceptible than others, tests were carried out with three 

 varieties which were considered as fairly representing tough, medium 

 and tender barks. Mammoth Black, Jonathan, and Yellow Trans- 

 parent were selected. 



Our conclusions in regard to asphaltum were : 



1. Asphaltum will not make an absolutely borer proof coat, 

 because of its tendency to crack, due, presumably, to the pressure 

 of growing bark in cool weather when the coat is brittle. Exceptions 

 should be noted here in the case of linseed oil mixtures, which remain 

 more plastic. 



2. Moisture tends to make asphalt brittle, causing it to flake off. 



3. Buds in growing, readily push through the asphalt coat, thereby 

 making it defective. 



