Orchid Diseases 295 



cause of the disease and methods of control are as 

 yet unknown. 



Bacterial Leaf Spot of Orchids 



Caused by Bacillus cypripedii Hori. 



Symptoms. According to Hori,* this disease is 

 prevalent in Japan and is greatly feared there. The 

 disease attacks the most valuable orchids and ruins 

 them in a very short time. 



The disease is manifested as light amber-colored 

 spots on the leaf blades. The spots quickly enlarge, 

 and in a few days the entire leaf becomes invaded 

 and discolored. A few days later the diseased foli- 

 age turns brownish and later a deep chestnut 

 brown; the upper surface becomes wrinkled, with 

 loss of luster. The lower surface of the leaves, just 

 imdemeath the spots, rapidly take on a faintly pale 

 color, and only gradually assumes the same color 

 as that of the upper part. If infection takes place 

 on the lower portion of the leaf, the upper half 

 soon becomes yellowish and dies off as a result of 

 lack of food (fig. 59, d.). The rot from the leaves 

 works down to the stem, involving the entire plant. 



The disease (also known as brown rot, brown 

 spot) attacks orchids with fleshy, succulent leaves, 

 such as Phalsenopsis amabilis. Ph. schileriana Cyp- 

 ripedium haynaldium, C. philippinense, C. Iseviga- 

 tum, C. godefroyse. The more susceptible varieties 

 seem to be Phalxnopsis schilleriana and Cypripedium 



*Hori, S., Centralb. fur Bakt, 31:85-92, 1911. 



