MARKET DISEASES OF APPLES, PEARS, QUINCES 41 



inch in diameter, with a raised nipple at the center, surrounded by a 

 depressed ring. Occasionally a very small black scale, the stage 

 that lives through the winter, is found. Underneath the covering 

 is the scale insect itself, lemon yellow in color; the females are 

 roughly circular in outline, whereas the males are elongate. 



Spots suggesting the presence of scale insects may be caused by 

 several other factors. Certain rot infections in the early stages 

 resemble scale spots, even to the red ring, but the brown or black 

 center cannot be rubbed off. A red spot similarly suggesting a 

 scale insect is sometimes caused by green aphids feeding on the fruit. 

 In this case, however, there is no light-colored center. 



The San Jose scale may be controlled by spraying at any time 

 after the leaves have dropped in the fall, or before the buds open 

 in the spring, with winter-strength lime-sulphur, with oil emulsions, 

 or with miscible oils. The oil sprays are more completely effective 

 and are preferable. For detailed information regarding control 

 measures as well as on the life history, see the following references 

 (73, 74, S3, 165, 183, m, 19 i, 201). 



SCAB 



(Venturia inaequalis (Cke.). Aderh.) 



OCCURRENCE, SYMPTOMS, AND EFFECTS 



Scab is an orchard disease that attacks the leaves, twigs, and fruits 

 of the apple. It occurs in all apple-growing sections of the United 

 States but is most destructive in the cooler regions of the Eastern 

 States, the upper Mississippi Valley, the coastal sections of the north- 

 ern Pacific Coast States, the apple-growing sections of Idaho and 

 Montana, and in the mountainous portions of Virginia, Arkansas, 

 and other Southern States. In the northern United States it is the 

 most destructive of all apple diseases. Farther south the losses 

 caused by scab are often exceeded by those caused by blotch and 

 bitter rot. The Plant Disease Survey of the United States Depart- 

 ment of Agriculture estimates the average annual loss from scab in 

 the United States during the 5-year period ended December 31, 1930, 

 as 6.5 percent, or 9,332,000 bushels. There is great variation from 

 year to year and from one section to another in the susceptibility 

 of apple varieties to scab. The commercial varieties usually most 

 susceptible are Mcintosh, Fameuse, Wealthy, Baldwin, Ben Davis, 

 Rome Beauty, Rhode Island Greening, and Oldenburg. 



Scab spots on the leaves appear first on the lower side as olive- 

 colored areas which have a tendency to spread out irregularly along 

 the veins or the midrib. In the beginning they are slightly darker 

 than the healthy leaf surface ; later they turn brown or almost black 

 and take on a velvety appearance. On the upper side the lesions have 

 at first a lighter green color than the healthy surface of the leaf, 

 but later they present the same velvety appearance described for the 

 lower side. Occasionally there is considerable distortion of the sur- 

 face ; toward the end of the season many of the diseased spots die, 

 shrink, and become cracked and ragged. In most sections the disease 

 is rare on the twigs. The bark becomes blistered and later ruptured 

 in places, so that affected twigs have a scurfy appearance very much 

 like that shown by scabby pear twigs. 



