36 BULLETIN 847, U. S. DEPARTMENT OF AGRICULTURE. 



Considering the ease with which white-lead paint can be procured, 

 the nominal cost of applying it, its noninjurious effect upon the tree, 

 its frequent deterring effect upon the young borers, and its degree 

 of efficiency in preventing oviposition in the tree, the observations 

 of the writer indicate that where protectors of this general class are 

 desired this paint is preferable to other materials. Such paints or 

 protectors as are described above should be applied to the lower 

 portions of the trunks of trees soon after the blossoming time of the 

 apple. 



APPLICATIONS FOR KILLING BORERS IN THE TREE. 



Various attempts were made to kill the borers, especially while they 

 were 3 r oung and near the surface, by applying penetrating poisonous 

 and irritating liquids to the bark. With the same object in view, 

 gaseous liquids were also injected into the burrows of larvae in all 

 stages of development. The details of several of these treatments 

 follow. 



NICOTINE SULPHATE. 



In September, 1918, 26 apple trees infested with rountiheaded 

 apple-tree borers were located, all the burrows opened with a knife, 

 and about a teaspoonful of 40 per cent nicotine sulphate, at a strength 

 of 1 part to 20 parts of water, injected into the opening with a medi- 

 cine dropper. In all, 67 burrows were treated. An examination 

 made a month later showed that 26 small borers had been killed and 

 41 of all sizes were alive and active. It was apparent that where the 

 liquid had come into direct contact with the borer death resulted, but 

 where the liquid did not reach the insect no effect was discernible. 

 In another test 29 burrows were treated in a similar manner with 40 

 per cent nicotine sulphate undiluted. A later examination showed 

 that 21 borers were killed and 8 were uninjured. Of those killed all 

 except one was of small size and all had apparently been doused 

 with the liquid at the time of the application. 



In making the opening into the burrow through which to inject 

 the liquid, care had always to be exercised to avoid killing the smaller 

 borers with the knife. The results of the tests showed that this treat- 

 ment is impracticable. Further data regarding the effect of nicotine 

 sulphate upon the borers when applied to the bark of infested trees 

 are given in Table XII (p. 38). 



CARBON DISULPHID. 



Tests were made of the practicability of using a veterinary hypo- 

 dermic syringe and needle for injecting carbon disulphid through 

 the bark into the burrows of the borers. Considerable difficulty was 

 encountered in inserting the needle, and especially in determining 

 when the point of the needle was in proper position for the dis- 



