REPORT OF THE SOCIETY 89 



In England and Ireland the organism is known as Sclerotinia sclerotiorum, 

 but for the sclerotinia found by Lachaine in New Brunswick, no definite name 

 ■can yet be given, although it appears to be S. libertiana. 



Control 



The only satisfactory means of control are crop rotation so that susceptible 

 plants are not available to the fungus and careful removal and destruction of 

 diseased plant parts. 



In England, Cotton finds that late planting has proved successful since 

 iewer old leaves are available at the time of spore discharge. 



GROUP 6 

 Disease Caused by a Basldiomycete. — Dry Stem-Rot an d Black Scurf 



This disease is known under a variety of common names of which the chief 

 are: — dry stem-rot, black scurf, black scab, russet scab, Rhizoctonia disease, 

 little potato, aerial potato, rosette, black speck scab and collar fungus. 



The first description of Rhizoctonia was given b}' Duhamel in 1728 as caus- 

 ing a disease of saffron in France. De CandoUe in 1815 gave the fungus the 

 name Rhizoctonia when he discovered a similar disease on lucern. In 1851 the 

 Tulasne brothers classified all the then known rhizoctonias as R. violacea but 

 Kuhn in 1858 described a species on potato which he named R. solani. Webber 

 (1890) first reported the fungus in America and in 1901 Duggar and Stewart 

 (Bull. 186, X. Y.j gave a list of hosts attacked by Rhizoctonia. It is now known 

 to occur generally in the United States and Canada and is reported from the 

 West Indies, India, Australia and South America. The perfect stage was found 

 by Rolfs in 1903 on potato stems and described as Corticium vagum B. & C. var 

 solani bv Burt. 



Other Hosts 



The complete list of other hosts would be too long to include here but men- 

 tion maj' be made of tomato, bean, lettuce, carrot, cabbage, pea, pumpkin, 

 beet, carnation and pansy. 



Symptoms 



These vary considerably with climatic conditions, age of the plant at infec- 

 tion, and the soil type. The sclerotial stage is very common on tubers where 

 many black sclerotia of varjing shape and .size (but usually small) are found on 

 the surface. They do not cause any apparent injury since they are .superficial. 



