ISTew York Agricultural, Experiment Station. 401 



an inch. In July, several black specks of the size of a small pin 

 head appear at the center of some of the spots, on the upper side 

 of the leaf. Many spots, however, never show the black specks. 



Affected leaves fall prematurely. In severe attacks the trees 

 may be almost completely defoliated by July 1. The disease is 

 most troublesome in Avet seasons. It is more prevalent on Long 

 Island and in the Hudson Valley than in other parts of the State. 



Treatment. — Leaf -spot is only partially prevented by the treat- 

 ment recommended for scab. See page 404. Where the disease 

 is troublesome we suggest that this treatment be preceded by a 

 spraying with Bordeaux mixture (1-to-ll formula) just as the 

 buds show green at the tips. 



rust. 

 {Gymnosporangium spp. Syn. Roestelia spp.) 



Description^ etc. — Kust is a disease in which circular, orange- 

 colored spots about one-fourth of an inch in diameter appear on 

 the leaves in June. It also produces yellow spots on the fruit at 

 about the same time. 



It may be caused by several species of fungi belonging to the 

 genus Gymnosporangium. The species of this genus are peculiar 

 in that in one stage of their life cycle they live upon the apple 

 and some other closely related plants, while in another stage they 

 inhabit the red cedar and its relatives. Gymnosporangium macro- 

 pus is the most common cause of apple rust. Its other stage oc- 

 curs on the red cedar where it produces the so-called cedar apples. 



In [N'ew England and some parts of the South apple rust is a 

 destructive disease, but in N'ew York it is of rare occurrence ex- 

 cept on Long Island. Some varieties are attacked much more 

 severely than others. Kust should not be confused with russeting. 



Treatment. — Rust is difficult to combat. Spraying seems to 

 check it but little. Since the red cedar harbors one stage of the 

 fungus which is the chief cause of rust, it is good policy to destroy, 

 so far as practicable, all red cedars in the vicinity of the orchard. 



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