70 PRACTICAL TREE REPAIR 



must be investigated, until the true signs are mas- 

 tered. If the whole tree is infested and an effort 

 is made, nevertheless, to save it, the trunk should 

 be done thoroughly, whether there is time to do 

 the limbs or not. 



In his important work on forest insects (Fifth 

 Report of the United States Entomological Com- 

 mission, 1890) Prof. A. S. Packard describes a 

 method of combating bark borers which had been 

 tried, apparently with success, in Belgium. It 

 was discovered that a full flow of sap killed the 

 larvae, doubtless the reason the insects prefer 

 weak trees. Insomuch as removing bark pressure 

 increases sap flow, particularly in spring, the ex- 

 periment was tried of paring off the outer layers 

 of the cortex, down to say a quarter of an inch 

 or a little less of the cambium, over the affected 

 areas in old elms. The resultant flood of sap 

 killed the grubs. The writer has had no personal 

 experience with this method. He would suppose 

 that it would be hard to say just which trees and 

 what parts of them were invaded by the borers 

 until it was too late for the work to be effective. 

 A protective covering of cement paint would prob- 

 ably be necessary to prevent undue drying of the 

 exposed inner bark. 



Such measures as this, and not less the usual 

 curative operations, ought invariably to be supple- 

 mented by the use of stimulating manures. 



