PEARS— PEAR DISEASES 



iai5 



Productiftn of Pears in United States 

 Trees, Production and Value 



Peaks. Grade Rules. See under Apple 

 Packing. 



Pears, Pollination of. See under 

 Apple. 



Peaks, Self-Fertile and Self-Sterile 

 Varieties. See Pollination, under Apple. 



PEAR DI.SE,4SES 



Anthracnose. See Apple Diseases. 

 Black Leaf 



In this disease one side or one limb 

 of the pear tree dies and the leaves turn 

 black and hang on for some time. The 

 effect is quite similar in a general way 

 to that of pear blight, but there is no 

 sign of the presence of the pear-blight- 

 causing organism as indicated by the red, 

 .iuicy inner bark of limbs and twigs af- 

 fected with the real blight. Sometimes 

 there is connected with black leaf a dy- 

 ing of the bark extending in a narrow 

 strip of uniform width down the trunk 

 to the ground. All phases of this disease 

 are distinguished from the true blight 

 by the fact mentioned that there is not 

 present the red, juicy condition of the 

 inner bark, but the bark simply dies 

 down and becomes very hard and dry 

 from the first. This trouble also often 

 occurs in orchards where the blight is 

 not present and does not show the char- 

 acteristic spreading of blight from tree to 

 tree through the blossoms or by infec- 

 tion of young shoots and suckers. 



The disease appears to be more of the 

 nature of sour sap, connected most com- 

 monly with an excessive amount of 



moisture in the ground during the win- 

 ter and spring. Where individual limbs 

 are affected or narrow strips of bark on 

 the side of the trunk, it appears that cer- 

 tain roots have been badly injured and 

 that the portions affected above ground 

 correspond with such roots. 



R. E. Smith, 



California Experiment Station Bulletin LIIS. 



Black Rot. See Apple Diseases. 



Blight 



The Bacterial Blight of Apples, Pears, 

 Quinces and Other Pome Fruits 



Bacillus amylovorus (Burrill) De Toni 



P. J. 0'G.iRA 



Pathologist 

 In the preparation of this article on 

 pear blight the writer has in mind the 

 many requests that have been made for 

 a complete discussion of this subject. 

 Although a large number of pathologists 

 have studied pear blight from the labora- 

 tory standpoint, very few have ever car- 

 ried out successful experiments in its 

 control. To the United States Depart- 

 ment of Agriculture belongs the credit 

 of working out the methods of control 

 and putting them into practice. The field 

 work has been carried out in the East 

 and South, and on the Pacific coast in 

 California and Oregon, where excellent 

 results have been obtained. 



Early History and Native Origin 



In going over the literature on pear 

 blight we find a long array of articles 

 which describe the disease fairly well. 



