44 BULLETIN 395, U. S. DEPARTMENT OF AGRICULTURE. 
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 mycelium 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 obtain. Likewise, in regions 
where the disease is abundant it is more prevalent in moist than in 
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 than 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 lightly 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 
