412 Diseases of Economic Plants 



rust causes to cereals. Rusts from many grasses pass to 

 the common barberry though not to the Japanese bar- 

 berry. See p. 277. 



Wilt {yerticilUum alboatrum R. & B.) affects the Japanese 

 barberry. The fohage turns yellow or red; the sapwood is 

 streaked with dark lines; ultimately the wood turns black. 

 Frequently the disease is severe. 



BEGONIA 



Eel-worms in the leaves cause translucent watery spots. 

 Powdery-mildew does some harm. 



BLETIA 



Anthracnose (Colletotrichum hleticB Hals.). — The leaves 

 of this orchid are frequently disfigured by very dark, almost 

 black spots. In late stages the dead tissue falls away, leaving 

 merely shreds of veins traversing the place of disease. 



The tips of the leaves are often frayed. 



Volutella rot {Volutella concentrica Hals.). — Numerous 

 lemon-colored acervuli surrounded by concentric bluish 

 rings render these spots different from those above described. 



CALLA 



Soft-rot ^" (Bacillus carotovorus Jones). — A large annual 

 loss and frequently the abandonment of calla growing is due 

 to this disease, which is known throughout the United States. 



The affected plants rot off near the soil surface, and the 

 rot progresses from this point up into the leaves or down 

 into the corm. Usually the rot first shows at the top of the 

 corm, but in some instances it is seen first at the edge of a 

 petiole, or on the corm below ground. 



In section the diseased portion is brown, soft, and watery. 

 Leaves whose bases are diseased become pale at the edges, 

 then brown. Similar changes occur in spots on the leaf, and 

 the whole leaf eventually dies, or the rot may progress so 

 rapidly that the leaf falls before losing its green color. The 



