Orchid Diseases 301 



great masses of spores formed in the acervuli. The 

 ascus or winter stage was discovered by Stoneman.* 

 The perithecia are flask-shaped, the asci are clavate. 

 The ascospores vary from elliptic to curved in shape. 

 Control. Before attempting anything else, the 

 source of infection should be removed. All infected 

 plants should be destroyed by fire. Spraying with 

 Bordeaux mixture 4-4-50 will help to protect the 

 plants from becoming infected. 



Bletia Anthracnose 



Caused by Colletotrichum bletia Hals, 



The beautiful Bletia orchid is often subject to 

 the attacks of an anthracnose, the cause of which is 

 due to a closely associated organism of the Sobralia 

 anthracnose. On the Bletia, the trouble is mani- 

 fested as a spotting that disfigures the leaves and 

 reduces their usefulness. The spots are almost black 

 and very soft. As this disease progresses, the soft 

 tissue rots and breaks away the fibrous portions. 

 Usually the trouble begins at the tender tips, and 

 causes affected foliage to have a ragged appearance. 



The Organism. In structure the organism resem- 

 bles other Colletotrichums. The acervuli are light 

 brown in color and possess numerous dark setae. 



Control. The trouble may be kept in check by 

 spraying with Bordeaux mixture. It is also essen- 

 tial to destroy by fire all dead and diseased material 



* Stoneman, B., Bot. Gaz. 26: 69-120, 1898. 



