Ornamental Plants 421 



COSMOS 



Stem-blight^^" (Phomopsis stewartii Pk.). — The first 

 indication of disease is seen in brown discoloration of the 

 stem or jjranches, the attack often, though not always, 

 occurring at a wound. The diseased branches at the point of 

 attack are weak and frequently break off. Minute pycnidia 

 are present in the diseased parts. The disease appears only 

 on mature plants and is very destructive. 



CYCLAMEN 



Leaf-spot {Phoma cydamemB Hal.). — A disease of the 

 foliage which sometimes causes almost entire loss of the 

 crop is marked by large, dark, irregularly shaped spots 

 upon the leaf. These spots later dry, turn lighter in color, 

 and show a series of concentric light and dark bands, at the 

 same time becoming brittle and often breaking away. Dis- 

 eased leaves should be burned and the plants sprayed with 

 Bordeaux mixture or ammoniacal copper carbonate. Several 

 fungi as Ascoehyta, Botrytis, Phyllosticta, Ramularia, Sep- 

 toria, cause leaf-spots. 



Anthracnose (Glomerella cingulata var. cydaminis P. & 

 C). — The spots on the leaves are circular, watery, with 

 definite borders. Black, hairy acervuli are often present in 

 great numbers. 



Nematodes and Thielavia occur on the roots. 



DAHLIA 



Powdery-mildew (Erysiphe cormnunis Wallr, Oidium). — 

 This powdery-mildew is quite common, affecting particularly 

 the lower leaves late in the season. 



Blight {Phoma dahlia; Berk.). — The stems of the flowers 

 are the chief seats of attack. The flowers are small and are 

 often dropped before opening. Root-rot (Botrytis) occurs in 

 storage as a wet soft rot. Wilt {Verticillium dahlice Kleb.). — 

 Cf. p. 180. 



