342 THE CULTIVATED EVERGREENS 



excessive transpiration when the roots are unable to absorb 

 water freely, and partly due to direct killing of the tissues by 

 low temperature. 



Growth in the late fall should not be encouraged, in order 

 that the tissues may have time to mature before severe frosts 

 appear. The protection of the roots with a mulch when there 

 is little snow would be advisable. 



Fungous diseases of rhododendron. 



Bud-rot is caused by the fungus Sporocybe azalece, Sacc. 

 The bud-scales first become light brown in color and finally a 

 dark brown, standing out in contrast with the healthy buds. 

 The rot may also extend down the stem, killing it back for some 

 distance. Later the fruit bodies of the fungus appear on the 

 outside of the dead buds as small, dark-colored, hair-like pro- 

 jections, the tips of which are slightly swollen and consist of 

 a mass of spores. For control, the removal of all diseased buds 

 is recommended. 



In leaf -blotch irregular dead areas appear on the leaves and 

 sometimes the killing extends around the whole margin of the 

 leaves. It is caused by the fungus Coryneum rhododendri, S., 

 infection taking place through injuries such as those inflicted 

 by aphids. A similar disease, caused by Coryneum heijerincHi, 

 Oud., has also been reported upon leaves of cherry -laurel. 

 When occurring abundantly, this blotch may cause defoliation. 

 Several sprayings during the season with a 4-4-50 bordeaux 

 mixture will probably hold the disease in check. 



In leaf-spot the fungus Pestalozzia guepini, Desm., causes 

 the death of small areas of the leaves, these areas becoming 

 grayish in color. This fungus probably also follows the attack 

 of aphids. Although no control measures have been recom- 

 mended, spraying with bordeaux mixture might be tried. 



