122 



FUNGOUS DISEASES OF PLANTS 



Burrill, T. J. Blight of Pear and Apple Trees. 111. Indus. Univ. Rept. 10 : 



583-597- 

 Jones, L. R. Studies upon Plum Blight. Centrbl. f. Bakt. Paras, u. Infek- 



tionskr. 9 (Abt. II): 835-841. 1902. 

 Waite, M. B. Cause and Prevention of Pear Blight. Year Book U. S. Dept. 



Agl. (1895): 295-300. 

 Waite, M. B. Pear Blight and its Control in California. State Hort. Com. 



of Calif. (Special Report) (1906): 1-20. 

 Whetzel, H. H. The Blight Canker of Apple Trees. Cornell Univ. Agl. 



Exp. Sta. Built. 236: 103-138. Jigs. 50-83. 1907. 



Pear blight has been known in the United States for more than a 

 century. Various common names have since been applied to this 



disease, determined largely 

 by the host plant upon which 

 it was found, and by the par- 

 ticular effect produced upon 

 the host. Such names there- 

 fore as fire blight, twig blight, 

 blossom blight, and other 

 more or less similar designa- 

 tions have been applied. 



Geographical. This disease 

 was first reported from the 

 northeastern United States, 

 but its occurrence was subse- 

 quently established in states 

 to the south, west, and south- 

 west, and by 1878 it was evi- 

 dently very well established 

 throughout the United States 

 east of the Mississippi. Still 

 later it became an important 

 bacterial disease in the far 

 West and Southwest. It is certainly distributed throughout the 

 United States at present, but so far as is known, it does not 

 occur in Europe or in Asia. There is every indication that the 

 disease had its original home in the eastern United States, and its 

 original host was doubtless some species of crab apple or thorn tree. 

 Its gradual spread westward, therefore, was governed by the spread 

 of civilization and the consequent greater contiguity of orchards. 



Fig. 31. Pear Tree Practically Dead 



from Severe Attack of Pear Blight 



(Photograph by H. H. Whetzel) 



