PEACH SCAB AND ITS CONTROL. 33 



Twig lesions remained quite scarce, however, throughout July, but began to appear 

 in greater numbers dm'ing early August. On August 13 they were fairly abundant 

 upon unsprayed trees in low places. On August 20 a dozen twigs were tagged and 

 noted as to scab development. On September 10 numerous additional infections 

 were evident on these twigs, while the older lesions had enlarged perceptibly. 



In 1913 sparse twig infection was observed at Cornelia on July 14. In early August 

 these lesions became much more abundant, and the subsequent development of the 

 twig disease closely paralleled that of the preceding season. 



It was planned to ol^tain exact data concerning the development of twig lesions 

 during their second season by following closely the development of the disease on 

 the twigs tagged and noted on August 20, 1912. Unfortunately, howeA^er, the experi- 

 mental trees were ' ' dehorned " before the writer returned to Georgia in 1913. Never- 

 theless, field observations in 1912 and 1913 showed beyond question that lesiojis may 

 pass the winter in any macroscopic stage of development and continue their develop- 

 ment during the next season. It was evident, further, that many late infections do 

 not become visible until the following spring. 



In the springs of 1912 and 1913 twig lesions occurred generally and abun- 

 dantly. It was difficult to find a Summerour twig which was free from infection, 

 while, in many instances, the lesions were so abundant as to become confluent. 



ON LEAVES. 



Owing to the inconspicuous nature of the leaf disease as it occurred 

 under field conditions in Georgia and to its wide variance in appear- 

 ance from previously published descriptions, the leaf lesions were 

 not identified until 1913. Therefore, the writer has not had the most 

 favorable opportunity of following closely their seasonal development 

 under natural orchard conditions. Inoculation experiments have 

 shown, however, that young or mature leaves may readily be infected 

 and that the period of incubation on the leaf closely approximates 

 that on the twig. It is evident, therefore, that the occurrence of 

 the leaf disease should parallel that on the twigs. Such field observa- 

 tions as are available accord with this view. 



Supporting record><. — Leaf infections were first observed at Corrielia on August 21, 

 1913, though they evidently had been visible for some time. The lesions were not 

 very abundant, but increased in number as the season progressed. In late September 

 and October they were quite abundant, though inconspicuous, upon the under 

 surfaces of unsprayed Summerour leaves. ^ 



On August 6, 1915, abundant infection was observed upon the lower surfaces of 

 Elberta leaves at Chevy Chase, Md. The appearance of the lesions indicated that 

 they had been visible for at least three or four weeks. 



PRODUCTION OF CONIDIA. 



Throughout the seasons of 1912 and 1913 the occurrence of conidia 

 was closely followed by means of frequent examinations of scab 

 lesions (a) directly from the field and (6) from moist chambers. 



ON FRUIT. 



Conidia are usually borne upon the fruit in the earliest macroscopic 

 stages of infection and may be produced under favorable conditions 

 48408°— Bull. 395—17 5 



