Minnesota Plant Diseases. 



377 



Cedar apples of red cedar (Gymnosporangium macropus Link, 

 and G. glohosiLw, Fart.). See Leaf Rust of Apples. Diseases of 

 Orchards and Vineyards. 



The powdery mildew of lilac [Microsphcera alni {Walk.) 

 IVint.]. This is the very common blight of lilacs which, in the 

 fall, covers lilac leaves with a conspicuous white mycelial coating. 

 The same blight is apparently found on many other plants, as 

 alder, birches, high bush cranberry and others. Summer spores 

 are produced in the usual manner for powdery mildews and the 



Fig. 202. — Powdery mildew of lilac, showing the white patches of the fungus mycelium. 



Original. 



sac capsules appear in the fall. Tlie latter are furnished with 

 appendages similar in shape to those of the apple powdery mil- 

 dew. Unlike this blight, however, the sac-capsule of the lilac 

 mildew contains more than one sac. The presence of the blight 

 on the lilac, though it undoubtedly draws some nourishment from 

 its host, does not seem to exert any serious influence upon it. 



Burning of the fallen leaves in the autumn has been recom- 

 mended. Spraying is usually not practiced since the disease or- 

 dinarily does no serious injury. Ammoniacal copper carbonate 

 or potassium sulphide would probably prove effective against it. 



