RASPBERRY DISEASES 401 



affected plant. In the roots the mycelium is found between 

 the cells of the cortex, near the cambium. As it proceeds up- 

 ward the pith of the canes is invaded. In the leaves the spongy 

 parenchyma is infected. In young stems the hyphse may be 

 found in any of the tissues. In all these attacked organs the 

 mycelium develops haustoria. These arise as side branches 

 from the mycelium. They pierce the cells to get food. As an 

 infected cane grows the fungus follows the growing-tip. In the 

 spring on the upper surface of the opening leaves sterile black 

 bodies appear. These are called spermagonia, or pycnia. Two 

 or three weeks later the orange-colored cushions develop on the 

 lower side of the leaf. Many spores are formed, which are 

 capable of germinating at once. From each spore a short 

 promycelium bearing four sporidia is protruded. These sporidia 

 cause other infections on raspberries and blackberries during 

 the growing-season. Mycelium develops from the sporidia. 

 In the winter the fungus is again dormant as mycelium in the 

 canes, crown and roots. 



Control. 



The perennial nature of this rust fungus makes it difficult 

 to control. The only known remedy for diseased plants is to 

 dig and destroy them. All wild blackberries and raspberries 

 known to be affected should be destroyed ; they may be regarded 

 as weeds in this connection. Spraying to protect healthy plants 

 from infection should be beneficial, although no experimental 

 data on which to base specific recommendations are available. 

 The fungus has definite enemies which destroy the spores in 

 large numbers. Certain insects eat quantities of spores. A 

 certain fungus, Tuberculina persicina, is parasitic on the rust 

 pathogene. 



REFERENCES 



Clinton, G. P. Orange rust of raspberry and blackberry. Illinois 

 Agr. Exp. Sta. Bui. 29 : 273-296. 1893. 



