264 Diseases of Greenhouse Crops 



Cuttings are especially susceptible and rotting usu- 

 ally starts at the cut and works upward, destroying 

 it entirely. Rooted cuttings are not as likely to be- 

 come infected as those freshly made and planted. 

 The disease is most prevalent where yoimg imma- 

 ture cuttings are made, and where the soil has been 

 excessively damp and the house poorly ventilated. 

 Little is known of the causal organism. 



Damping Off 



Caused by Pythium de Baryanum Hesse. 



This disease confines its attacks mainly to gera- 

 nium cuttings. For a description of the causal or- 

 ganism and of methods of control, see p. 17. 



Gray Mold 



Caused by Sclerotinia fuckeliana (De By.) Fckl. 



Symptoms. Gray mold is manifested as dead 

 brown spots on the leaves. Under moisture condi- 

 tions, the gray moldy growth appears. This is but 

 the Botrytis or summer fruiting stage of the fungus. 

 The trouble is prevalent in leaky houses or where 

 water is used in excess and the beds are poorly 

 drained. By proper ventilation, and by careful 

 watering the mold may be kept in check. 



Leaf Spot 



Caused by Coniothyrium trahuti Riza. 



As far as is known this disease is not known to 



