ROUNDHEADED APPLE-TREE BORER. 37 



charge of the liquid. About 30 burrows were treated in one test 

 and a subsequent examination showed that most of the borers had 

 been killed by the resultant gas. The bark, however, was injured 

 by the treatment. Where the liquid was injected into shallow bur- 

 rows and came into contact with considerable areas of the inner 

 bark more injury was done the tree than usually results from the 

 direct work of a single borer. 



Carbon disulphid can be injected with good results and with no 

 apparent injury to the tree, into burrows that extend deep into the 

 wood. Borers that penetrate beyond the reach of knife and wire 

 can often be killed by discharging a little of the liquid into the open 

 burrow and then plugging the opening with moist clay or some 

 other substance. For injecting the liquid into such galleries, nothing 

 is better than a medicine dropper with a curved point. 



KEROSENE. 



In September, 1914, 29 apple trees infested with roundheaded 

 apple-tree borers were treated with kerosene, the liquid being ap- 

 plied liberally to the bark with a paintbrush over the regions where 

 the borers were feeding. Four weeks later the trees were examined 

 and 64 borers removed. Of these, 25 were dead and 39 alive. Severe 

 injuries to the cambium and bark were beginning to show. A year 

 later two of the treated trees were dead as a result of the oil appli- 

 cation and others had large dead areas near the ground and around 

 the base of the roots. 



The conclusions derived from this test were that kerosene applied 

 to the surface does not penetrate through the bark in sufficient quan- 

 tities to kill all the borers and that its use in this way is dangerous 

 to the health of the tree. 



SODIUM ARSENATE WITH MISCIBLE-OLL CARRIER. 



Late in the summer of 1918 a 10 per cent solution of sodium 

 arsenate was mixed with a miscible-oil carrier and applied with a 

 spray pump to the trunks of infested apple trees. The treatment 

 was applied to 15 trees that averaged about 4 inches in diameter 

 and contained borers of various ages and sizes. Early during the 

 following spring the borers were removed from the trees, 28 speci- 

 mens being obtained. Of these, 2 were dead and 26 alive and active. 

 It could not be determined whether the two had died as a result 

 of the treatment or from some other cause, and the treatment was 

 considered of no practical value. 



TESTS OF OTHER PENETRATING LIQUIDS. 



In the summer and fall of 1917 a number of different penetrating 

 liquids were used on infested apple trees in the experiment orchard 



