Carnation Diseases 227 



the joints. On the leaves, infection seems to be 

 more localized on the lower than on the upper half, 

 and it is particularly frequent on the broad sheath- 

 ing base of the leaf (fig. 46, h.). Affected foliage is 

 often bent downwards. A leaf with numerous spots 

 may be bent at various places, downward as well as 

 sideways. The spots are usually indefinite in size 

 and outline. Within the dead area may be found 

 numerous minute fruiting bodies (pycnidia). 



Powdery Mildew 

 Caused by Oidium sp. 



Mention of this disease is made by Mercer,^ who 

 found it on greenhouse carnations in England. It 

 has not yet proved of economic importance in the 

 United States. This trouble appears as white, pow- 

 dery patches on the leaves, calyx, and corolla. The 

 English varieties most susceptible are "Lady Arling- 

 ton," ''Bridesmaid," and especially "British Tri- 

 umph." So far only the conidial or Oidium (fig. 

 46, g) stage of the fungus is in evidence. The ascus 

 or winter spore stage may probably appear on other 

 hosts. The trouble may be kept in check by dust- 

 ing with flowers of sulphur or by spraying with 

 potassium sulphide as recommended for the rose 

 mildew (see p. 323). 



♦Mercer, W. B., Jour. Roy. Hort. Soc. 41: 227-229, 1915. 



