226 THE FORAGE AND FIBER CROPS IN AMERICA 



270. DISEASES. Three diseases occur rather commonly on field beans. In 

 order of their abundance and destruction they are: anthracnose or pod spot 

 (Colletotrichum lindemuthianum (Sacc. and Magn.) Bri. and Cav.); bean 

 blight (Bacterium phaseoli Erw. Sm.) and bean rust (Uromyces appendicularis 

 (Pers.) Link.). 



Anthracnose is a fungous disease known by its brown or black spots on 

 stems, pods, or leaves. The disease also affects the seeds, which show reddish- 

 brown or black spots and are often shrunken or shriveled. The seed harbors 



dCoat 



Stardi Grains 



The relation of the anthracnose fungus to the tissues of the bean. To the left above is 

 diagram of a section across a bean pod through an anthracnose canker. The large draw- 

 ing below is a much enlarged view of a portion of this same section. It is largely dia- 

 grammatic. It shows how the mycelial threads of the fungus may penetrate the seed coat 

 and enter the starchy tissue of the seed, there to remain dormant until the following 

 season. On the left of the large drawing is shown a spore germinating and penetrating 

 the epidermis. This germ tube branches, spreads through the tissues of the pod and 

 so gives rise to a new spot or canker. To the right above is shown a magnified view of 

 some of the spores of the anthracnose fungus. One has germinated. 

 (After Whetzel) 



the fungus, which develops on the cotyledons of the young seedling, from 

 which it may spread to older and healthy plants. It is a destructive and 

 much-dreaded disease. Three steps in combating this disease are recommended: 

 the selection of disease-free seed, the removal of diseased seedlings, and 

 spraying with Bordeaux mixture. Seeds themselves have not been successfully 

 treated, because the fungus is embedded in the seed, and thus far no sub- 

 stance has been found which will destroy the fungus without injury to the 

 germination of the seed. Since the disease is from without and local to the 

 spot attacked, as shown in the illustration, spraying with a fungicide is the 

 best means of preventing this disease. The Cornell Station recommends 5 



