282 Diseases of Greenhouse Crops 



carrot, potato, turnip, radish, cabbage, cauliflower, 

 tomato, and in the fruit of eggplant and cucumber. 

 Control. The disease may be prevented from get- 

 ting a start by discarding diseased or spotted conns. 

 Changing the soil every third or fourth year, or 

 steam sterilizing it will prevent infection of the 

 healthy corms. Starting the plants in pots instead 

 of planting them directly in the beds is also recom- 

 mended. In this way, all diseased plants will be 

 discarded before being put finally in the bed. 



Blight 



Caused by Phyllosticta richardie Hals. 



Symptoms. This disease is characterized by large, 

 ashy spots on the leaves. Within these spots may 

 be found minute, dark fruiting bodies (pycnidia). 

 Very little is known of the causal organism. Blight 

 may often be confused with a spotting due to sun- 

 scald. In this case, however, the dead tissue is in- 

 vaded with the fungus Pestalozzia richardia Hals. 



Leaf Blight 



Caused by Cercospora richardiacola Atk. 



Symptoms. This disease was first foimd by Pro- 

 fessor Atkinson in Alabama in 1891. The spots are 

 black with small white centers, and may be formed 

 on all parts of the leaves. 



The Organism. The conidia are hyaline, and from 

 4 to 10 septate. The conidiophores are borne in 



