44 BULLETIN 395, U. S. DEPAETMENT OF AGEICULTUKE. 



In connection with this work, careful watch was kept for a possible 

 ascigerous stage of the fungus, but no positive results were secured. 



As has been shown in preceding topics, the primarily important 

 overwintering of the fungus is accomplished by the mycehum in lesions 

 on living twigs. Here the organism passes the winter safely, and 

 with the advent of favorable conditions in spring it produces conidia 

 abundantly. 



CLIMATE IN RELATION TO THE DISEASE. 



Published records from the more important peach-producing dis- 

 tricts of the world indicate that scab occurs at its worst in temperate 

 sections where the spring and early summer are moist and the growing 

 season is long, while it is much less prevalent in dry sections or in high 

 altitudes, where the opposite conditions obtam. Likewise, in regions 

 where the disease is abundant it is more prevalent in moist than m 

 dry seasons and on low than on high ground. 



In the light of the foregoing life-history studies, the reasons under- 

 lying these conditions are evident. Abundant moisture is necessary 

 for spore production, spore dissemination, and infection, while the 

 long growing season increases the period during which these processes 

 may occur. 



VARIETIES IN RELATION TO THE DISEASE. 



Among writers on this aspect of peach scab, there appears to be a 

 consensus of opinion that varieties differ markedly in the degree in 

 which they are subject to the disease. Selby (1898, p. 221) writes — 



Certain varieties of peaches appear more susceptible to scab tban others, just as 

 certain varieties of apples suffer more than others from the apple scab. 



Scott and Quaintance (1911, p. 11-12) state — 



In general, the late varieties are much more susceptible than the early varieties. 

 This is due, in part at least, to the fact that the fruit of the late-maturing varieties is 

 exposed to infection over a longer period and the opportunity for the development of 

 the disease is greater. 



While the writer has made no detailed study of these varietal 

 differences, field observations and the life-history work previously 

 reported accord well with the views of Scott and Quaintance. In 

 general, the fruit of the earlier varieties, such as the Greensboro, 

 Carman, and Hiley, is relatively Hghtly attacked. The midseason 

 varieties, such as the Belle and Elberta, may be moderately or severely 

 diseased, depending upon conditions. Late varieties, such as the 

 Heath, Salway, and Bilyeu, are the most severely attacked. 



These conditions are partly explained in the light of the life-history 

 studies. The lateness of infection and the long period of incubation 

 ordinarily preclude very seriously injurious development of the 



