PLANT DISEASES 389 



the brown rot are also successful with the scab, and the im- 

 mense losses of past years are not apt to occur in the future. 

 393. Early Blight of the Potato. — This disease may at 

 times cause almost as much damage as the more dreaded late 

 blight already described. It causes brownislj spots on the 

 leaves, around which appear concentric lighter rings. When 

 the spots become enlarged the leaf dies, and thus, since the 

 food supply is reduced, the tubers produced are usually 

 small. The same fungus also attacks the tomato, causing 

 a smaller crop of this fruit. Spraying will check the disease 

 except under very unfavorable conditions. The peach leaf 

 curl, stem rot of the clover, root rot of tobacco, canker of 

 currant and gooseberry, ergot of rye and timothy, leaf spot 

 of the strawberry, apple scab, bitter rot of the apple, blight of 

 ginseng, dry rot of the potato, flax wilt, and the anthracnose 

 of the bean are other plant diseases of considerable economic 

 importance. 



