178 Diseases of Economic Plants 



tinued at ten-day to fourteen-day intervals throughout the 

 growing period. All spore-bearing refuse should be burned. 



Minor diseases 



Leaf -spot (Phyllosticta apii Halst.). — -A dull brown, cir- 

 cular pycnidia-bearing patch, not to be confused with the 

 light, ashen-colored, angular Cercospora spot, is charac- 

 teristic. Soft-rot (Bacillus carotovorus) consists of a soft, 

 light-brown rot of the central bud, sometimes of the leaf 

 or leaf stalks. It occurs on celery, also on parsley, and 

 is probably identical with the carrot soft-rot. Rust {Puc- 

 cinia bullata (Pers.) Wint.) has not yet been destructive in 

 America. Damping-ofif due to Sclerotinia, Rhizoctonia, and 

 Fusarium have caused much loss in the South on both celery 

 and parsley. See also p. 19. Pithiness. -^'^ — The stalks and 

 hearts are pithy, a condition attributed to the parent plant 

 and heredity, not to parasites or environment. As high as 

 30 per cent of pithy plants have resulted from certain lots of 

 seed. Proper rogueing of seed plants is recommended. Scab 

 due to Phoma apiicola Kleb. consists of rotting of the roots, 

 leaving the plant with a conical rotten base. 



CHARD. See beet. 



CHIVE. See onion. 



COLLARD. See cabbage. 



CUCURBITS: CUCUMBER, ^^s MUSKMELON, MELONS, 



WATERMELON, PUMPKIN, SQUASH 



Downy-mildew ^^^ (Peronoplasmopara cubensis (B. & C.) 

 Clint.). — Downy-mildew first shows its presence by yellowish 

 angular spots, 3-6 mm. in diameter, upon the leaves as seen 

 from above. These appear first upon the older leaves at 

 the center of the plant. The spots become more distinct, 

 enlarge, increase in number, and soon the whole leaf be- 

 comes pale, sickly, and dies. If the weather is moist, the 



