PEAR DISEASES 349 



The twigs, petioles and leaf-scales also exhibit signs of the 

 disease similar to those on the foliage. The lesions on the 

 twigs, however, are more elongated and become depressed, 

 and finally girdling results. 



Cause. 



The leaf-blight disease is caused by a f ungus, Fabrcea maculata. 

 Throughout the summer its conidia, developed upon the leaves, 

 fruits and twigs, are scattered to other leaves, where infec- 

 tion results. It may be that certain of these conidia pass the 

 winter on diseased twigs, producing infections the following 

 spring. The chief method of hibernation, however, is by means 

 of apothecial bodies in fallen leaves. Infected leaves, either 

 at maturity or prematurity, fall to the ground in the late 

 summer or autumn, carrying the fungus with them. Further 

 activities on the part of the pathogene in these old leaves 

 result in the formation of apothecia. In the spring, ascospores 

 are discharged from these fruiting structures, and are carried 

 to the susceptible parts. About one week later, the effects 

 of the work of the parasite within the tissues are visible to the 

 naked eye; and within a month, or less, after the ascospores 

 are discharged, a new crop of spores, conidia, is developed. 

 These conidia are borne in acervuli which are to be found in 

 the center of each spot. Conidia from this source may infect 

 the quince ; likewise, the conidia from the quince may infect 

 the pear. This is an adaptation on the part of the fungus 

 which renders its control more difficult. Furthermore, these 

 conidia may infect the hawthorn, apple and other closely 

 related plants, thus adding complications to the application of 

 remedial measures. All these plants, the quince, the apple and 

 others, must be regarded as a source of trouble to the pears. 



Control. 



For the orchard trees and pear stocks, spraying is profitable 

 and effective. Lime-sulfur 1 to 50 may be used with safety 

 and with success. It is recommended that iron-sulfate be 



