304 Diseases of Greenhouse Crops 



Leaf Spot of Orchids 



Caused by Cercospora angreci Roum. 



Symptoms. This disease is usually manifested as 

 spots which are more prominent on the underside 

 of the leaves. As the affected foliage turns pale 

 and loses its green color, the spots become covered 

 with a chocolate-colored mold. The latter growth 

 consists of the fruiting stalks and conidia of the 

 fungus. Cercospora angreci is found on foliage of 

 Odontoglossum alexandrse. Little is now known of 

 the causal organism and of methods of control. 



Bletia Leaf Spot 



Caused by Volutella concentrica Hals. 



Associated with the anthracnose ( Colletotrichum 

 bleti(z) is often found a leaf spot which may be 

 mistaken for it. The characteristic of this disease 

 is the formation of large dark spots (fig. 59, a.). 

 Each spot is made up of numerous bluish-colored 

 concentric rings. The fruitings of the fungus ap- 

 pear as lemon-colored balls. It is not definitely 

 known whether the Volutella fungus is an active 

 or a weak parasite merely following some injury, 

 or the attacks of a bacterial organism. In fact little 

 study was given to this trouble and the only record 

 that exists is a note by Halsted."^ 



•Halsted, B. D., New Jersey Agr. Expt. Sta., Fourteenth Ann. 

 Kept.: 417, 1893. 



