20 II. E. Thomas and W. D. Mills 



sulfur) before blossoming', followed by the calyx and two later appli- 

 cations. The other block received only one application of fungicide 

 (sulfur dust) during the entire season. The percentages of fruit infec- 

 tion on September 12, 1928, were 1 and 12, respectively. It is evident, 

 then, that a considerable reduction in fruit infection may be expected 

 when experiments are made with the timely application of fungicides. 

 In this connection, more information is urgently needed concerning 

 the time of maximum susceptibility of the fruit. 



summary 



It has been shown that the cultivated apple in the Hudson River 

 Valley of New York is affected by three distinct rust diseases. These 

 diseases are designated as apple rust caused by Gymnosporangium 

 junijyeri-virginianae' Schw., hawthorn rust caused by G. globosum 

 Farl., and quince rust caused by G. germinale (Schw.) Kern. 



Both the quince and the apple rust cause direct and serious losses 

 by infection of the fruit. 



Hawthorn rust is occasionally destructive on apple foliage. 



Varieties of apples show marked variation in their response to the 

 diseases, both in type of symptoms and in severity of the disease. 



Symptoms of the diseases and morphological character of the fungi 

 are presented as aids to diagnosis. The terminal peridial cells of the 

 fungi offer a means of rapid determination of the fungi. 



Good germination of aeciospores was obtained after exposure to low 

 temperatures. 



Inoculation experiments were made with the three fungi on Mcintosh 

 and Wealthy foliage. No infection was obtained with G. germinale. 

 G. jiiniperi-virginianae easily effected ingress into the Mcintosh leaf 

 as well as that of Wealthy, but was usually checked in the Mcintosh 

 before pycnia were formed. G. globosum infected Mcintosh fairly 

 readily, and Wealthy only with difficulty. 



Eradication of red cedars seems to be the best method of control 

 for all of these diseases. 



The application of fungicides offers some promise in the control of 

 fruit infection. 



