310 MANUAL OF FRUIT DISEASES 
the bacteria become dormant and remain so until spring, 
when the cycle begins anew. 
The weather has a rather marked effect upon the severity 
of the black-spot disease. Ordinarily an outbreak may not 
be expected until May ; however, if the spring weather is warm 
and damp, infections appear as early as April 1. A tempera- 
ture between 68° and 82° Fahrenheit is most favorable to the 
bacteria. Cold weather not only- checks the activities of the 
bacteria, but also of the insects which disseminate the bacteria. 
Heavy, driving rains of short duration, even if accompanied 
by a favorable temperature, are not conducive to the spread of 
the pathogene; for such rains carry the bacteria to the ground. 
And should the showers be followed by sunshine and breezes, it 
is unlikely that a serious outbreak will ensue on account of 
the fact that the susceptible parts would thus be quickly 
dried off and the bacteria on the surface would die. Heavy 
dews, if accompanied by proper temperatures and shaded 
locations, are favorable to the growth of the bacteria. Slight 
injury from Bact. Pruni results in dry seasons, especially if 
the spring has been cold. 
Control of black-spot. 
Reasoning from the facts and phenomena recorded above, 
treatment may be followed along several lines as tabulated 
below. 
(1) The disease affects the peach, plum, nectarine and apricot. 
Growers of all four fruits may find the problem of control more 
complicated than where, for example, only peaches are grown. 
A few old and comparatively worthless trees of plums, apricots 
or nectarines may be a constant source of trouble. These 
should be removed. 
(2) The growing of resistant varieties offers little relief at 
present. 
(3) The twigs, fruits and leaves are affected. The injury 
may be serious on any or all of these organs. The twigs furnish 
