242 Diseases of Greenhouse Crops 



dark brown spots which increase in size until they 

 meet. Affected foliage drop off prematurely. Dis- 

 eased plants become weakened and produce small 

 flowers. The disease is often introduced in the 

 greenhouse with infected cuttings. The pycnidia of 

 the fungus are minute, while the conidia are ob- 

 scurely septate. 



Control. Cuttings should be secured from healthy 

 plants. All diseased leaves and trash should be de- 

 stroyed by fire. Spraying with a standard fungicide 

 is also recommended. 



Blight 



Caused by Cylindrosporium chrysanthemi E. & D. 



Symptoms. This disease seems to work quickly 

 and affected plants are short lived. The trouble 

 appears on the leaves as dark blotches about one- 

 half of an inch to three-quarters of an inch in 

 diameter. The spore heaps are formed on the dead 

 tissue where the spots occur. The area beyond the 

 spot turns yellow, and soon the leaves shrivel, droop, 

 and cling to the stems (fig. 50, f.). 



The Organism. The acervuli of this fungus are 

 imbedded, the conidia are somewhat thick but taper 

 to the end; they are several septate and straight (fig. 

 50, e.). 



Control. Infected material should be destroyed 

 by fire. Spraying with a standard fun^cide will 

 protect the healthy plants. 



