Rose Diseases 323 



or burning the diseased stems will prevent the fur- 

 ther spread of the disease. 



Other Rose Rusts. There are other species of 

 Phragmidiums which have been found by Mikio 

 Kasai.* Among them are the following: Phrag- 

 midium americanum (Pk.) Diet, found on Rosa 

 dahierica; Phragmidium fusiforme Schroet on Rosa 

 acicularis; Phragmidium Japonicum Diet, on Rosa 

 multiflora, R. wichuriana, R. lucise; Phragmidium 

 rose multiflora Diet, on Rosa multiflora, R. laevi- 

 gata; Phragmidium rosa rugose Kasai, on Rosa 

 rigosa] Phragmidium yezoense Kasai on Rosa 

 rugosa. 



Powdery Mildew 



Caused by Spherotheca pannosa Wallr. 



Symptoms. Powdery mildew is a very trouble- 

 some disease of greenhouse roses. The disease ap- 

 pears as powdery, whitish patches on the leaves, 

 stems, and blooms. The affected foliage fails to 

 develop normally, becoming uneven and twisted, 

 curled and reddened (fig. 65, d.). 



The Organism. On the rose the conidial or 

 oidium stage is most frequent. The conidia are 

 ovid, hyaline, and are borne on short conidiophores. 

 The same fungus also causes the powdery mildew 

 of the peach, in which case the ascus stage is most 

 common. 



Control. It is believed by many florists that 



* Mikio Kasai, Trans. Sapporo Nat Hist. Soc. 3: 27-51, 1909- 

 J9ia 



