426 Diseases of Economic Plants 



LARKSPUR 



A black leaf-spot due to bacteria has been noted in Massa- 

 chusetts. 

 Drop (Sclerotinia) . — See lettuce. 



LILAC 



Powdery-mildew {Microsphoera alni (Wallr.) Salm.)- — 

 The characteristic spots of the powdery-mildew, white and 

 flour-like, are frequent upon the lilac. Black perithecia are 

 abundant late in the season. 



Leaf-spot (Bacteria) is of minor consequence. 



LILY 



Gray-mold ''^^ {Dotrytis sp.). — This exceedingly destruc- 

 tive mold of the lily was noted about 1885, and was first 

 closely studied by Ward in 1888. It makes its appearance 

 in the spring as small, orange-colored spots upon the leaves 

 and buds. These enlarge, and later become coated with a 

 light brown, dusty, fuzzy mold which destroys the leaves and 

 blossoms, often leaving onl}^ the naked stalks standing. 



Sclerotia much like those described under lettuce drop 

 appear in association with the decay in its late stages. Their 

 subsequent history is like that of lettuce sclerotia. 



Bermuda lily-disease.^^'' — The plants are stunted and the 

 leaves are distorted and bear spots that are yellowish to white 

 and usually sunken. Frequently a commercial loss of from 

 20 to 60 per cent follows. No parasite is present, and the 

 actual cause of the disease is unknown. Rogueing in the 

 field to eliminate affected bulbs is necessary. 



LILY-OF-THE-VALLEY 



Drop {Sclerotinia sps.). — See lettuce, 



MIGNONETTE 



Leaf-spot ""^^ (Cercospora resedce Fcl.). — This disease 

 occasionally ruins the greenhouse crop. The spots are at 



