MARKET DISEASES OF FRUITS AND VEGETABLES 45 



areas is usually a light-colored spot, marking the place occupied 

 by the tiny scale insect before it was rubbed off in the handling 

 of the fruit at harvest or later. In depressed areas, such as the 

 calyx or stem ends, the scales may still be present. The scale 

 covering is gray to grayish brown, less than y 16 inch in diam- 

 eter, with a minute 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 their centers are 

 brown or black and cannot be rubbed off. A red spot suggesting 

 the scale insect is sometimes caused by green aphids feeding on 

 the fruit, but this has no light-colored center. 



The San Jose scale can be controlled by spraying — at any time 

 after the leaves drop in the fall and before the buds open in the 

 spring — with winter-strength lime-sulfur, 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 the life history of the scale, the references 

 cited should be consulted. 



(See W 9 48, 93, 101.) 



Scab 



(Venturia inaeqaalis (Cke.) Wint.) 



OCCURRENCE AND SYMPTOMS 



Scab is an orchard disease that affects the leaves, twigs, and 

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

 United States where there is appreciable rainfall during the 

 growing season. It is destructive in the cooler parts of the Eastern 

 States, the upper Mississippi Valley, the coastal districts of the 

 northern Pacific Coast States, and the mountainous parts of 

 Virginia, Arkansas, and other Southern States. In most sections 

 east of the Rocky Mountains it "is the most destructive of all 

 apple diseases. 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, Delicious, Fameuse, Wealthy, Baldwin, Rome Beauty, 

 Rhode Island Greening, and Oldenburg (Duchess). 



On the leaves scab appears first on the lower side as olive- 

 colored spots, 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 at first have a lighter green color than the healthy 

 surface of the leaf, but later they present the same velvety ap- 

 pearance as on the lower side. Occasionally there is considerable 

 distortion of the surface; 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. When it occurs 

 there, the bark becomes blistered and later ruptures in places, so 



