PEAR DISEASES 



329 



FIG. 90. Fire-blight on apple fruit ; drops 

 of bacterial ooze on the surface. 



Suckers which arise from 



the crown, at or below 



the surface of the soil, 



are often blighted, allow- 

 ing the bacteria entrance 



into the bark of the roots. 



Trees may die from such 



a form of attack . Grafts 



are especially disposed to 



blight during the first 



year or so on account of 



their rapid and succu- 

 lent growth. Wounds 



in the larger limbs or 



the body of the tree 



may serve as centers of 



cankers. Here the bacteria are carried by the bark-boring 



beetle and deposited in their borings. In these cankers and 



blighted limbs and twigs the bac- 

 teria pass the winter. With the 

 return of the warm weather and 

 rains of the spring the rise of sap 

 encourages the growth and multi- 

 plication of the bacteria, which 

 ooze out and afford the source 

 of the inoculum for the opening 

 blossoms. 



Weather conditions should not 

 be confused with the causal factor 

 of fire-blight. On the other hand, 

 the weather is correlated to some 

 extent with epiphytotics of the 

 **\ Lf frosts may stop 



fruit right. blight by killing certain 01 the dis- 



