958 



MICROBIAL DISEASES OF PLANTS 



plantings are the worst affected. As a control measure, planting from 

 two to three weeks later is suggested. 



PEAR BLIGHT 



Bacillus amylovorus (Burrill) De Toni 



HISTORY AND DISTRIBUTION. As early as 1780, William Denning, 

 a fruit grower, who lived on the Highlands of the Hudson River, ob- 

 served pear blight in the trees of his neighborhood. It is very probable 



FIG. 196. Two pear twigs. The upper one affected with Fire Blight, the lower one 

 healthy. (After Sackett, Mich. Agr. Exp. Sla.) 



that blight existed many years before this in eastern North America on 

 some of our native wild crabs, hawthorns, and wild plums, and with the 

 introduction of cultivated varieties, it found a new field for attack. As 

 the farming communities became more thickly populated, and the 

 orchards more numerous, it has spread gradually westward over the 



