6 BULLETIN 395, U. S. DEPARTMENT OF AGEICrLTUEE. 
DESCRIPTION. 
On fruit. — The earliest macroscopic evidences of infection upon the 
gTeen surfaces of the fruit appear as imperfectly denned, greenish to 
olivaceous,, circular areas, usually less than hah a millimeter in diam- 
eter. This effect is due to the appearance of the olivaceous conid- 
iophores and conidia of the fungus among the hairs of the fruit. 
Upon blush surfaces, the early development of olivaceous color may 
be accompanied or preceded by the disappearance of the normal pink 
from the invaded areas, which remain much paler than normal until 
masked by the development of the fungus. In such cases a narrow 
peripheral zone of pale or yellowish green may mark the advance of 
each diseased area. The developing lesions gradually become larger, 
darker, and more clearly defined, owing to the death and disappear- 
ance of many of the obscuring hairs of the fruit and to growth and 
pigmentation of the fungus. When fully developed they are fairlv 
well defined, circular, olivaceous to black areas with an average diam- 
eter of 2 to 3 millimeters, though under veiy favorable conditions 
they may attain a diameter of 4 or 5 mill im eters (PL I, figs. 1 and 2, 
and PL II). The direct injury is superficial, involving at most onlv 
a few layers of cells, which typically become separated from the adja- 
cent normal tissues by the formation of cork. The infectious occur 
practically exclusively upon the areas which are subject to thorough 
wetting. The lesions are. thus, generally most abundant about the 
peduncle and upon the upper portion of the wettable 1 surface (PL 
III, fig. 1, a\ They may be more or less uniformly scattered over 
the entire wettable surface, or they may be so abundant as to become 
confluent over large patches, frequently covering practically one-half 
of the surface of the fruit. The protected surfaces of even the most 
severely attacked fruits are usually free from infection (PL III, iig. 
1, l). As the peaches grow rapidly just prior to maturity, the corked 
areas can not expand so readily as the normal tissues. This condi- 
tion may result in mere inequalities of development between badly 
diseased and normal areas, but more commonly the growth stresses 
occasion the cracking of the cork layers. These cracks may appear 
upon individual lesions as small rifts extending slightly into the flesh, 
but upon very badly affected specimens they may extend the length 
of the fruit and penetrate to the pit (PL I, fig. 1). Badly scabbed 
fruits do not ripen evenly and are frequently inferior in flavor. Those 
which are severely scabbed about the attachment of the peduncle 
may be shed prematurely. 
i In the earlier stages of development of the peach, its hairy surface is very resistant to wetting. With 
growth and weathering, however, that portion which is exposed to the action of falling meteoric water 
becomes more easily wettable, while the area protected from such action, usually the opposite side of the 
fruit, remains difficultly wettable throughout the important period of scab infection. For the sake of 
convenience, these areas subsequently will be referred to as '-wettable" and "protected, " though it should 
be realized, of course, that these terms are relative, not absolute. 
