APPLE DISEASES 61 



Cause of blotch. 



The fungus causing the various lesions just described has 

 been known since 1895, at which time it was found on the leaves 

 of wild crab ; it was then named Phyllosticta solitaria E. & E. 

 Two years later it was discovered on the apple, but not until 

 1907 was it known that the fungus on the apple was the same 

 as that previously found on crab. 



The pathogene hibernates in the cankers as mycelium. In 

 the spring about the time the petals fall pycnidia appear 

 along the margin of the lesion. Within three to six weeks, 

 spores ooze forth from the pycnidia in great quantities, this 

 period of spore-discharge extending from about the middle or 

 last of May until the end of August. It is thought that wind, 

 possibly insects, and certainly rain, act in carrying the spores 

 from their spring quarters to the leaves, fruits and other twigs. 

 Although the spores are disseminated as early as the middle of 

 May, first signs of the disease do not ordinarily appear before 

 some time in June. This means that approximately one 

 month is consumed by the pathogene in getting established in 

 its new environment. During this time the spores germinate, 

 which process requires from twelve to eighteen hours; and 

 assuming that moisture is present at the time of inoculation, 

 then the remaining time is spent in developing mycelium and 

 producing an injury of sufficient extent to become evident to 

 the naked eye. The fungus grows superficially on the fruit, 

 and in many cases the effect is not of serious nature beyond that 

 of marring the appearance. On the other hand the attacks are 

 often of a more detrimental character. Early in the develop- 

 ment of lesions on the leaves, fruits and twigs, pycnidia appear. 

 Spores are developed within these pycnidia on the fruits and 

 twigs, although on the leaves the fruiting bodies seem to be 

 sterile. However, the spores produced on the fruit and twigs 

 are readily spread to other fruits, leaves and twigs. This 

 phenomenon of secondary spread of the fungus appears to de- 



