224 



FUNGOUS DISEASES OF PLANTS 



where the fungus promises to be abundant, it may be necessary 

 to repeat the spray every ten or twelve days. Recently it has 

 been reported that sulfuric acid may be used to advantage in the 

 treatment of the rose mildew, the strength employed being I part 

 of strong acid to iooo parts of water. This preparation should 

 prove serviceable, but it has not been tested for the gooseberry 

 mildew. Winter treatment with a lime-sulfur wash has been con- 

 sidered desirable as a result of some Canadian experiments. 



XXIII. MILDEW OF PEACH. ROSE MILDEW 



Spharotheca pannosa (Wallr.) Ldv. 



Smith, Erw. F. Peach Mildew. Journ. Mycology 7 : 90-91. 1892. 

 Whipple, O. B. Peach Mildew. Colo. Agl. Exp. Sta. Built. 107: 1-7. pis. 

 1, 2. 1906. 



This mildew bears the relation to the peach that Podosphcera 

 leucotricha bears to the apple, that is, it is more commonly found 



on nursery stock, and 

 then usually only when 

 the conditions are moist 

 and the stock crowded, 

 although occasionally it 

 occurs on mature trees 

 (Figs. 88 and 89). 



It is as a disease of 

 cultivated roses that this 

 fungus is best known, 

 and most destructive. It 

 is widely distributed and 

 indeed absent from very few home gardens. There is great differ- 

 ence in the susceptibility of different varieties of the rose, and selec- 

 tion should lead to resistant strains in many cases. The crimson 

 rambler is notably sensitive. 



This mildew covers the leaves, especially the young leaves and 

 the vigorous and young shoots, injuring and often arching or 

 curling the leaves and deforming the more succulent stems. 

 The oidial stage is produced in great profusion, and consequently 

 the disease spreads rapidly. Perithecia are not always present. 



Fig. 89. Mildew on Peaches 



