1 62 



Bulletin 2'/1. 



of introduction of the causal organism into the tree precludes this as 

 an effective means of control. If we were able to determine definitely 

 what insects are responsible for the dissemination of the bacteria in 

 each case, it might be possible to control the disease by destroying the 

 insects. Thus far we believe this method has not been tried. 



Making the trees immune by the introduction of different substances 

 into the sap has not as yet been definitely proved to be successful despite 

 the claims made by many manufacturers of Blight remedies. The 



Fig. 1 8. — Pear tree in autumn after having been treated with Callahan's Blight Spe- 

 cific the previous winter. Note the dead leaves clinging to the limbs that blighted 

 during the ■summer. 



senior writer has had this phase of the problem under investigation 

 for several years. One of these so-called remedies, viz., Callahan's 

 Blight Specific, has been thoroughly tested and proved to be not only 

 absolutely worthless as a preventive of Blight (Fig. i8) in pears, but 

 positively injurious to the trees, as shown in Fig. 19. This remedy 

 consists of a gray, green powder, which is to be inserted into a hole 

 bored in the base of the tree, firmly tamped down and confined with 

 a soft wooden plug tightly driven into the mouth of the hole. Following 

 directions explicitly, during the early winter of 1908 six large pear 



