APPLE DISEASES 



older the delicate fungal coating becomes extinct at the center, 

 and exposed at this point is the brown corky layer of the host- 

 tissue. This frequently becomes checked and cracked. In 

 some cases the whole spot thus becomes corky so that the 

 pathogene disappears entirely, leaving a russeted scar on the 

 side of the fruit. Scab spots often cause a dwarfing of the 

 side of the apple on which they occur. When the attack is 

 severe, the fruit shrivels and falls. The removal of the cuticle 

 permits the entrance of 

 rot-producing pathogenes, 

 and consequently decay 

 of the apple-flesh appears 

 beneath scab spots. Late 

 infections, which appear 

 at picking time, are much 

 smaller, being scarcely 

 more than mere specks; 

 they are also very black 

 and no marked depres- 

 sion nor dwarfing of the 

 fruit accompanies such in- 

 fections. The scab spots 

 twigs vary with the 



on 



FIG. 2. Apple-scab, margins of spota 

 showing uplifted cuticle. Lesions about 

 blossom-end. 



variety affected. In some 

 cases the affected portion 

 becomes somewhat swollen, and the twig as a whole becomes 

 prominently blistered. Severely attacked young twigs may ap- 

 pear blistered over the surface to such an extent that the bark 

 will subsequently peel in flakes. This type of injury is common 

 in Europe, and is. called grind or scurf by the Germans. In 

 other cases the shoots are not swollen and do not present a 

 blistered appearance. A third type of symptom on the twigs 

 is found in cases where the scab spots are isolated, pock-like 

 markings. 



