264 Diseases of Economic Plants 



pearing on the blossom end and injurious chiefly to early 

 tomatoes. It is especially harmful, owing to the high value 

 of the early fruit that it destroys. Various factors have been 

 named as the cause, and it cannot yet be said with certainty 

 which is responsible. 



The trouble is more serious upon droughty soils and can 

 to some extent be controlled by irrigation or moisture con- 

 servation, i. e., increasing the water-holding power of the 

 soils by the addition of organic matter and surface tillage. 



Early-blight {Allernaria solani (E. & M.) J. & G.). — 

 Ruin is brought to the crop in many seasons, particularly 

 in the southernmost states, by this blight, which is identical 

 with the potato early-blight. The leaves bear numerous, 

 small, usually angular spots, often concentrically marked, 

 which appear first as minute brown specks, later showing a 

 pale center with a darker border. In badly affected leaves the 

 tips dry and curl up. Petioles and stems are also attacked. 



Thorough spraying with the usual Bordeaux mixture should 

 be begun at the first indication of the disease and continued 

 weekly, or semiweekly if growth is rapid and the weather 

 damp. Often it is still better to begin spraying in the seed bed. 



Southern-blight (Sclerotium rolfsii Sacc). — This blight 

 IS often completely destructive to the tomato in the south- 

 ernmost states. The first sign is wilting of the terminal por- 

 tion of the plant, distinguishing Southern-blight from other 

 wilts, which commence with the lower leaves. 



For discussion and treatment, see pepper. 



Leak {Rhizopus nigricans). — The effect is much as on 

 strawberries and the loss during shipment is large. 



Minor diseases 



Anthracnose {Colletotrichiim phomoides (Sacc.) Chest.). — 

 This is chiefly a disease of the ripe fruit, cither upon the vines 

 or after harvest. It appears as sunken, discolored spots with 

 wrinkled surfaces and black specks, the acervuli. The disease 

 does much damage to fruit before it is picked, and also in- 

 jures the keeping quality. 



