236 Diseases of Greenhouse Crops 



very helpful. This, however, should be done in 

 the early part of the day, so that the foliage will 

 be dry at night. Chrysanthemums are heavy feeders, 

 and this should not be lost sight of. 



Diseases of Chrysanthemums 



Chrysanthemums are subject to several important 

 diseases. These often become so troublesome as to 

 seriously interfere with the profitable culture of the 

 plant. 



Crown Gall 



Caused by Pseudomonas tumefaciens Ew. Sm. 



This disease causes swellings on the crown and 

 the roots of the plant. The trouble is seldom of any 

 economic importance under greenhouse conditions. 

 The causal organism attacks not only chrysanthe- 

 mum, but also the daisy, geranium, sugar beet, pop- 

 lar, willow, peach, etc. 



Black Speck 



Caused by Pilobolus crystallinus (Wigg.) Tode. 



The speck is often found on the leaves. Some 

 growers believe this specking due to the accumu- 

 lation of smoke settled on the leaves after fumiga- 

 tion. Others believe that it is due to a con- 

 densation of ammonia arising from fresh manure. 

 As stated for a similar case on roses (see p. 321), the 

 specking is due to the discharge of sporangia of 



