312 DISEASES OF ECONOMIC PLANTS 



Protective spraying with 5-5-50 Bordeaux mixture, as 

 recommended for the potato, will probably serve in case of 

 this disease. In regions of infrequent rainfall it is neces- 

 sary to spray only after each rain. 



Blossom-end rot, point rot. — Readily recognized from its 

 name, this very troublesome disease is essentially a dry, 

 black rot appearing 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 fungi and bacteria have been named as the cause, 

 and it cannot yet be said with certainty which is the 

 guilty one. Perhaps it is one, perhaps several. In any 

 event it seems to be an infective disease that is probably 

 carried by insects. 



The trouble is more serious upon drought}^ soils and can 

 be to some extent controlled by irrigation or moisture 

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

 the soils by the addition of organic matter and surface 

 tillage. 



Black spot, rust {Macrosporium Solani Ell. & Mart.). — • 

 Ruin is brought to the crop in many seasons, particularly 

 in the southernmost states, by black spot, which is possibly 

 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 semi-weekly if growth is rapid and 



