218 



THE APPLE 



one. Sometimes the proportion is even greater. The badly diseased 

 apples are small, unshapely, and often cracked and worthless. Light 

 attacks of this scab, while not always stunting or splitting the fruit, 

 lower its market value. 



Apple scab is caused by a fungus which lives in summer on the 

 leaves and fruit and, to some extent, on the twigs, and in winter 

 on fallen leaves. The character and extent of its work are well 

 known to all apple-growers. Scab appears on the fruit as roughly 

 circular, dark-gray or olive-brown spots. The size of individual 

 spots varies from tiny specks to blotches half an inch in diameter. 



Fig. 97. Scab 



Malformation and cracking resulting from a bad attack of scab. The surface of the fruit is 

 nearly covered with scab spots. (University of Maine) 



Frequently two or more scab spots join, and together extend their 

 development so that almost the entire epidermis of the apple is 

 scabbed. In such attacks the apple usually cracks deeply, and even 

 if it does not drop prematurely, it has no market value. 



The fungus also attacks the leaves, causing the same olive-brown 

 discoloration common to its early stages on the apple. Most of the 

 infections of the leaf are confined to the downy underside, the 

 fungus rooting and growing there more readily than on the glaze- 

 like upper surface. 



The development of apple scab is coincident with the appearance 

 of the foliage and fruit in early spring. The fruit buds are often 

 destroyed in large numbers at this season, and when the leaves are 



