432 Diseases of Economic Plants 



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, va- 

 riously deformed (Fig. 220), and covered with the white 

 powder of. spores and spore 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 sulfur is serviceable. The house should be 

 closed and the sulfur 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 24° C. (75° F.), and the air 

 well filled with sulfur from bellows. The temperature 

 should then be raised to 31°-32° C. (85°-90° F.), and al- 

 lowed to cool gradually. 



Either out doors or in, dusting (sulfur 90 parts, arsenate 

 of lead 10 parts) is effective and more convenient than 

 spraying with Bordeaux mixture or lime-sulfur. 



Canker ^•'''' (Cylindrocladium scoparium Morg.). — Brown, 

 dead cankers are formed on the stems and branches, or at the 

 crown, and often encircle the stem for several centimeters. 

 Consideral)le mjury is done to roses under glass. Examine 

 new stock carefully to exclude canker. If the disease enters 

 the house remove all old soil and disinfect the benches with 

 formalin. Brown-canker ''^^ {Diaporthe wnbrina Jenk., 

 Phomopsis) also occurs on roses of many varieties. 



Rust (Phragmidium subcorticum (Schr.) 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 serious 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 

 masses. Later in the season the color of the sori changes 

 to brick red. 



Affected branches should be l)urned promptly, antl all 

 infective material should be burned in the autunni. If 



