98 PLANT DISEASES 



mildew, which at a later stage becomes covered with a 

 delicate white powder, due to the formation of myriads of 

 conidia. During the early summer the diseased leaves 

 become brown and dead. The young fruit is also attacked, 

 usually becoming distorted and dwarfed. 



Preventive Means. — Spraying with potassium sulphide 

 has given satisfactory results ; the first application should 

 be made before the buds expand, and continued at intervals 

 of ten or fifteen days as required. 



Halsted, Rep. U.S. Dept. Agric, 1887, p. 373. 



HAZEL LEAF MILDEW 



{Phyllactiiiia suffulta, Sacc.) 



The under surface of hazel and filbert leaves is not 

 unfrequently more or less covered with a delicate white 

 mildew, which commences as scattered patches ; these 

 under favourable conditions grow into each other and 

 cover the entire surface of the leaf. 



Numerous minute, blackish perithecia are formed during 

 the summer. The appendages of the perithecia are spine- 

 like, straight, unbranched, and have a swollen base. 



Preventive Means. — Similar to those given under 

 gooseberry leaf mildew. The fungus is also parasitic upon 

 the leaves of hawthorn, elm, ash, beech, birch, alder, 

 willow, oak, hornbeam, honeysuckle, spindle-tree, cornel, 

 and sea-buckthorn. 



POWDERY MILDEW OF CHERRY 



{Podosphaera oxyacantha, De Bary. ) 



This pest is more especially injurious to young cherry- 

 trees, but also attacks the apple, peach, quince, and other 



