PEACH SCAB' AND ITS CONTROL. 63 
Primary infection results from conidia from overwintered twig 
lesions. Spores from lesions of the current year's production may 
induce secondary infection. 
The fungus overwinters in the mycelial stage in the lesions on living 
twigs. There is no evidence that any other type of overwintering is 
of any practical importance in the life history of the parasite, although 
it has been shown that the mycelium may survive the winter on fallen 
fruit and twigs. 
Peach scab occurs at its worst in temperate sections where the 
spring and early summer are moist and the growing season is long. 
It is much less prevalent in dry sections and in high altitudes where 
the opposite conditions obtain. 
Varieties vary markedly in the degree to which they are subject 
to scab injury. In general, early varieties are not very seriously 
affected. Midseason varieties may be moderately or severely at- 
tacked. Late varieties are usually the most severely affected. The 
period of exposure of the fruit to the attack of the fungus is a major 
factor in these differences. There are, however, varietal differences 
which are independent of the ripening period of the fruit. These 
have not been explained. 
It has been shown conclusively that the disease may be controlled 
in a highly satisfactory manner by spraying with self-boiled lime- 
sulphur or with finely divided wet table sulphur and that the scab 
treatment may be satisfactorily combined with the control of brown- 
rot and the plum curculio. (For summarized recommendations, 
see pp. 59-60.) 
Under average conditions, the cost of spraying 7-year-old to 10- 
year-old peach trees for scab, brown-rot, and the plum curculio 
(three treatments, as recommended on pp. 59-60) should not exceed 
5 cents a tree. 
In the writer's experience, the merchantable fruit from trees 
properly sprayed in accordance with the foregoing recommenda- 
tions has rarely amounted to less than 95 per cent of the total yield, 
even under severe conditions, while its quality has uniformly been 
much superior to that of the unsprayed product. 
