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 Bad. 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 



