16 



N. H. AGR. EXPERIMENT STATION. 



[Bulletin 157 



APPLE RUST. 



Gym n osporangium spp. 



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

 is quite injurious. It is of common occurrence in New Hamp- 



shire 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 con- 

 fined to the foliage. Here it 

 causes yellowish spots (Fig. 

 18) which usually become 

 somewhat elevated in the 

 center and in which are pro- 

 duced numerous spores. The 

 spots usually appear on the 

 leaves in June. The spores 

 from these spots are borne by 

 the wind and attack the twigs 

 of Junipers, causing morbid 

 growths or swellings. One 

 of the most characteristic 

 effects produced is the so-called "cedar apples" (Fig. 19). The 

 fungus passes the winter on 

 the Juniper and in the spring 

 produces gelatinous out- 

 growths that contain numer- 

 ous spores. These spores, 

 when borne back to the 

 apple foliage, produce the 

 rust again, and thus the 

 fungus passes from one host 

 back to the other. 



Treatment. Spraying has 

 not usually been very effec- 

 tive in controlling the dis- 

 ease. Since the Junipers harbor the fungus thru the winter the 

 method of control is, obviously, to destroy them. 



Fig. IS. — Rust on apple leaf. 



Fig. 19. — Cedar Apple on red cedar. 



I 



