THREE RUST DISEASES OF THE APPLE 

 H. E. Thomas and W. D. Mills 



The severity of rust on apples in the Hudson River Valley during 

 1927 and 1928 has led to a reawakening: of interest in this problem. 

 Concern is felt more particularly for the reason that abundant infec- 

 tions on the fruit have added enormously to the usual losses caused by 

 foliage infection. The attention of the writers was especially drawn 

 to the problem in the summer of 1927 by the appearance of numerous 

 fruit infections on the variety Mcintosh, which formerly had been 

 regarded as highly resistant. The need for additional study of cedar 

 rust was emphasized by the fact that the symptoms on Mcintosh and 

 other varieties were so unusual as to place in question the identity of 

 the disease on these varieties. 



As these studies have progressed, it has become evident that not one, 

 but Ihree, rust diseases are destructive among the varieties of apples 

 grown in the Hudson River Valley. Since these three diseases and no 

 others are found extensively on both cedars and apples in this region, 

 and since no other rust disease is known to be prevalent on the apple 

 in eastern North America, we shall assume that the rust problem in 

 apples in the Hudson River Valley is fully represented by them. 

 Accordingly, in this paper the three diseases are considered more or less 

 in parallel rather than consecutively, in order to facilitate comparison 

 and diagnosis. To avoid confusion the three rust diseases are desig- 

 nated as apple rust caused by Gymnosporangium jiiniperi-virginianae 

 Schw., hawthorn rust caused by G. globosum Farl., and quince rust 

 caused by G. germinal e (Schw.) Kern. 



PLANTS AFFECTED 



Weimer (1917) has studied these three diseases on cedars and certain 

 rosaceous plants in New York, but apparently found only the apple 

 rust on apples. He did not, however, make extensive observations in 

 orchards. Stewart (1910), in earlier observations in eastern New York 

 during the period from 1895 to 1910, records only the apple rust on 

 cultivated apples. 



Authors' acknowledgments. Several workers have been very helpful in supplying 

 specimens and Information ami in some of the inoculation experiments. In addition 

 to those named in the body of this paper, we mention especially Professor W. L. Doran 

 and Messrs A. I!. Iiuchhol'z. A. I'.. Burrell, E. .1. llamhleton, S. C. Jones, A. S. Mills, 

 and E. V. Shear. 



