8o PLANT DISEASES 



VIOLET MILDEW 



(Peronospora violae, De Bary.) 



This pest is not uncommon on the leaves of Heartsease 

 ( Viola tricolor), and has of late years done considerable 

 injury to the cultivated Neapolitan violet. The under 

 surface of the leaves is more or less covered with a 

 somewhat dense, dingy, pale violet-grey felt, and later 

 in the season oospores are formed in the dying parts of 

 the host. 



The fungus is most abundant during damp weather. 



PREVENTIVE MEANS. So far as I am aware, no liquid 

 fungicides have been experimented with. Probably 

 potassium sulphide spray might prove beneficial. Plenty 

 of air and not too much water retards the spread of the 

 fungus. 



CUCUMBER AND MELON MILDEW 



(Peronospora cubensis, Berk, and Curt.) 



Forms a very delicate white mould on the under surface 

 of various cucurbitaceous plants under cultivation, as 

 cucumber, melon, squash, etc. Often proves very destruc- 

 tive if allowed to run its course unchecked. Known in 

 the United States, and recently in England. I have also 

 seen the fungus on leaves of Cucurbita pepo, and Cucumis 

 sativa from Tokyo, Japan. 



PREVENTIVE MEANS. Spray with dilute Bordeaux mix- 

 ture, taking care to reach and wet the under surface of the 

 leaves, which is not an easy matter, but it must be done. 



