Minnesota Plant Diseases. ,- 



375 



the sunflower has been raised in large quanti- 

 ties, this rust has often proved very injurious. 



The leaves and all parts affected by the 

 fungus should be burned in autumn to destroy 

 the winter spores and to prevent the recurrence 

 of the disease in the following spring. (See 

 Fig. 206.) 



The rose leaf rust [Phragmidium subcor- 

 ticium (Schrk.) Wint.}. This is a very com- 

 mon disease of both cultivated and wild roses. 

 All three important spore-forms are formed 

 upon the same host plant. The cluster-cup 

 stage appears in early summer, or late spring, 

 and causes a distortion of the attacked parts. 

 These are usually swollen and badly bent and 

 become bright orange in color. The summer 

 spores appear later and are also brightly col- 

 ored. The winter spores appear last and are 

 formed in small, round, blackish patches on the 

 under surface of the leaf. These spores form 

 a fine, small, powdery mass. The spores are 

 long and are divided into a number of cells, 

 often about seven or eight, arranged in one 

 row, and have a long club-shaped stalk. 



Care should first be taken to prevent the 

 wintering over of the disease. This can be 

 clone by destroying the old leaves, particularly 

 those of diseased plants. Late fall or early 

 spring treatment with a strong copper sulphate 

 solution will also aid in destroying the winter 

 spores. The dormant bushes and the ground 

 near them should be drenched. The spread 

 of the cluster-cup and summer-spores can be 

 Fl G f rosei. stem wStfa prevented by spraying after the buds open with 



groups of cluster- 1 i 



cups. Original. bordeaux or ammoniacal copper carbonate. 

 The rose stem rust (Phragmidium speciosum Fr.) This rust 

 is a near relative of the leaf rust of roses but is not identical with 

 it. The attacked stem of the rose becomes swollen and distort- 

 ed, and soon a large winter spore pustule is formed which looks 



