330 Diseases of Greenhouse Crops 



attachment to the root. Affected plants linger for a 

 long time, but they produce only a few stunted 

 blossoms. 



The Organism. The causal organism produces 

 fertile and sterile hyphse. The spores are borne in 

 fascicles, are cut off from the short conidiophores 

 by a constriction, and are held together by a sticky 

 substance, but separate quickly when placed in 

 water. The spores are cylindric, one septate, and 

 hyaline (fig. 67, c to e.). 



Control. Since the causal organism lives in the 

 soil, steam sterilization is recommended. All dead 

 or infected material should be destroyed by fire. 

 The disease may also be avoided to some extent 

 by placing grafted plants with the graft union above 

 the soil. This will prevent infection at the wounded 

 surface. Attention should also be given to the 

 watering of the plants. Crown rot is worse in over- 

 watered beds. 



■4 Cercospora Leaf Spot 



Caused by Cercospora roskola Pass. 



Symptoms. This disease is characterized by 

 roundish spots, gray in color, with a dark border 

 separating the healthy from the diseased tissue. 



The Organism. The conidiophores grow in tufts, 

 are densely gregarious, small and dark colored. 

 Conidia are straight, short, cylindric, and hyaline. 

 Spraying with a standard fungicide is recommended. 



