122 



N. H. AQR, EXPERIMENT STATION 



[Bulletin 144 



APPLE RUST. 

 Grjmnosporangium glohosum Farl. 

 Apple rust is a widely distributed disease, and in some sections 



is quite injurious. It is of 

 common occurrence in New 

 Hampshire and, while not 

 one of the most serious apple 

 troubles, it often does con- 

 siderable damage. It some- 

 times attacks the fruit, 

 but its effects are usually- 

 confined to the foliage. Here 

 it causes yellowish spots, 

 which usually become some- 

 what elevated in the center 

 and in which are produced 

 numerous spores (Fig. 18). 

 The spots usually appear on 

 the leaves in June. The 

 spores from the leaves are 

 borne by the wind and attack 

 the twigs of cedar trees, caus- 

 ing morbid growths or swellings, the so-called "cedar apples "^ 

 (Fig. 19). The fungus passes the winter in the tissue of the 



cedar apple" and in the 

 spring produces an abun- 

 dance of spores in the gela- 

 tinous outgrowths of these 

 galls. These spores, when 

 borne back to the apple foli- 

 age, produce the rust again, 

 and thus the fungus passes 

 from one host back to the 

 other. 



Treatment. Numerous ef- 

 forts to control the disease 

 by spraying have been with- 

 out success. Since the "cedar apples" harbor the fungus thru 

 the winter the method of control is obviously to destroy them,, 

 or, when practicable, the cedar trees themselves. 



Fig. 18.— Rust on apple leaf. 



< c 



Fig. 19.— Cedar apple on Red Cedar. 



