Rose Diseases 



321 



difficult to control, because the causal organism 

 lives within the tissue of its hosts. This mildew 

 resembles that of the grape, potato, bean, etc. It 

 usually appears in irregular spots. On the lower 

 surface of the leaves, the fruiting of the fungus 

 resembles a downy white to purple coating. It is 

 fortunate that this disease is uncommon in the 

 United States, and even more so under greenhouse 

 conditions. 



The Organism. The conidiophores are nine 

 times branched; the branchlets are reflexed. The 

 conidia are pale gray, subelliptic in form. 



Control, The removal and burning of infected 

 material and the spraying of the plants with a stand- 

 ard fungicide will keep it in check. 



Mechanical Spotting 



Caused by Piloholus crystallinus (Wigg.) Tode. 



Symptoms. The trouble, if such it may be called, 

 is a small specking resembling fly speck on the 

 leaves and flowers. There is but one case on record 

 reported by Clinton.'^ It appeared on two benches 

 in a rose house. The infected benches were heavily 

 mulched with cow manure, while the others did not 

 receive this treatment. A careful inquiry revealed 

 the fact that on the two manured beds the fungus 

 Filobolus crystallinus was very abundant. The 



* Clinton, G. P., Conn. Agr. Expt. Sta., 38th Ann. Rept.: 24-25, 

 1914. 



