APPLE DISEASES 5 



The losses are greatest in epiphytotic years, but these occur 

 with sufficient frequency to make apple-growing unprofitable 

 unless preventive measures are taken. The nature of the 

 losses may be indicated as follows : (1) Reduction in or destruc- 

 tion of the set of fruit. Heavy losses of fruit, in some cases 

 total, are incurred under conditions favorable to scab at blossom- 

 ing-time. (2) Impairing the efficiency of the foliage. Affected 

 leaves are often smaller than normal ones and they may fall 

 prematurely. (3) Reduction in size of the fruit. Scabby 

 apples are almost always smaller than healthy ones. (4) Re- 

 duction in quality of the fruit. This is usually regarded as the 

 chief consideration, but obviously other types of losses are nearly 

 of equal importance. (5) The keeping qualities of the fruit 

 are diminished. Pink-rot and other storage troubles com- 

 monly follow scab on stored apples. (6) The number of wind- 

 falls is increased just before picking time. Scabby fruit does 

 not cling well to the trees. 



Symptoms. 



The disease affects the leaves, flowers and fruit. On cer- 

 tain varieties, such as the Lady, scab is found on the twigs; 

 but this form of the disease is rare in America. 



On the leaves the disease usually makes its first appearance 

 in the spring on the lower surface, since that side is first ex- 

 posed as the leaf emerges from the bud. These hypophyllous 

 spots are as a rule smaller and less prominent than those on the 

 upper surface. The former lesions are brownish or olivaceous, 

 of a webby appearance, with margins indefinite, fimbriate, and 

 commonly tending to follow the veins of the leaf (Fig. 1). The 

 spots on the upper surface (Fig. 1) are similar to those below, 

 but are more definite in outline, darker, more velvety and larger. 

 When a great number of lesions occur on a leaf, each spot is 

 smaller than where fewer, lesions prevail. The spots on the 

 upper surface often cause the affected area to become convex 

 above and concave below. Near the end of the season the 



