ORNAMENTAL PLANTS 475 



by a good dormant spray. Ammoniacal copper carbonate 

 used once each week is effective after the plants are in foh- 

 age. 



Powdery mildew {Sphcerotheca pannosa (Walk.) L6v.). — 

 This is perhaps the most widespread and destructive of all 

 rose diseases both under glass and in the open, being es- 

 pecially destructive to the Rambler varieties. In mild cases 

 it occurs merely as flour-like, dusty white patches upon the 

 leaves. But when present, it usually becomes aggressive, 

 attacking the young leaves and tender shoots, which 

 become dwarfed, curled, reddened, variously deformed (Fig. 

 201), and covered with the white powder of spores and 

 si)ore stalks. The vitality of the plant is so lowered by 

 repeated attacks and even by direct attack upon the buds 

 that the plants become worthless. 



Indoors sulphur is serviceable. The house should be 

 closed and the sulphur boiled in a kettle for two to three 

 hours twice weekly, or the house may be closed in the morn- 

 ing, the temperature raised to 75° F., and the air well filled 

 with sulphur from bellows. The temperature should then 

 be raised to 85°-90° F., and then allowed to cool gradually. 



Either out doors or in, spraying with any good fungicide, 

 as potassium sulphide, 1 ounce to 2 gallons, or Bordeaux 

 mixture, is effective. 



Rust (Phragmidium subcorticum (Schrank) Wint.). — 

 This true rust is common in Europe, and is found in many 

 parts of the United States from the Atlantic to the Pacific; 

 still it is not a very common pest. 



Early in the season orange-yellow sori appear upon the 

 green parts of the plant : on the leaf as small, circular spots ; 

 on the stems and petioles often as quite large, powdery 



