PEACH SCAB AND ITS CONTROL. 
45 
disease before early varieties are harvested*. On midseason varieties 
under conditions favoring the development of the disease, there is 
time for very serious injury to result. On late varieties the great 
increase in opportunities for infection and incubation are attended 
by consequent increment in the severity of the disease. The earlier 
varieties as a group are thus more properly designated as disease- 
escaping than as resistant, since they may be quite seriously scabbed 
when conditions unusually favor the early development of the disease. 
While the period of exposure of the fruit to the attack of the 
iungus appears to be a major factor in these varietal differences, it 
is evident that other causes are involved. It has been noted that 
certain varieties growing in adjacent rows and ripening at about 
the same time have been attacked by scab in very different degrees 
and that certain of the earlier varieties are commonly more seriously 
affected than some of those which ripen later (Table IX). It is also 
a matter of common observation that seedlings are often especially 
severely attacked. No attempt has been made to investigate the 
further causes underlying these variations. 
At the writer's request Mr. M. B. Waite, Pathologist in Charge of 
Fruit-Disease Investigations, Bureau of Plant Industry, has prepared 
a list of important commercial varieties of peaches grown in the Mid- 
dle States, with estimates concerning the degrees in which they are 
subject to scab injury in this territory. These estimates, which are 
based upon more than 25 years of experience and observations 
extending over all the important peach-producing districts of the 
area in question, are incorporated in Table IX. 
Table IX. — List of important commercial peach varieties, with estimates of the compara- 
tive degrees in which they are subject to injury by Cladosporium carpophilum in the 
Middle States. 
Variety. 
Estimated decrease 
in market value 
of unsprayed 
crop due to scab 
injury (per cent). 
Variety. 
Estimated decrease 
in market value 
of unsprayed 
crop due to scab 
injury (per cent). 
In aver- 
age 
seasons. 
In bad 
seasons. 
In aver- 
age 
seasons. 
In bad 
seasons. 
Alexander 
25 
40 
15 
30 
30 
40 
15 
10 
30 
15 
25 
35 
30 
50 
80 
30 
60 
60 
80 
30 
20 
60 
30 
50 
70 
60 
Oldmixon 
40 
35 
35 
25 
25 
30 
25 
40 
50 
60 
70 
75 
80 
Rivers 
Elberta 
70 
Hale Early 
70 
Waddell 
50 
Carman 
50 
Mountain Rose 
60 
Hiley 
50 
St, Johns 
70 
Champion 
Heath 
90 
Early Crawford 
90 
Belle 
95 
Reeves 
100 
Stump 
