198 THE POTATO 



RHIZOCTONIA 



This disease of the potato is sometimes known to 

 growers as "Little Potatoes," "Stem Rot," and 

 "Rosette." 



Considerable research work in regard to rhizoc- 

 tonia was done by Prof. F. M. Rolfs when he was 

 at the Colorado Agricultural College. Prof. A. 

 Nelson also presents some interesting facts in "Bul- 

 letin 71 " of the Wyoming Experiment Station. 

 In the information which follows these two sources 

 have been consulted freely. 



This rhizoctonia fungus attacks the underground 

 portions of the plant. It is a true parasite, living 

 either in the internal tissues or upon the external 

 parts. It attacks the stem at or just below the 

 surface of the ground, destroying the bark in whole 

 or in part. If the attack be a severe one it may 

 result in the death of the plant, but if less severe 

 it may induce a wet rot and thus result in the death 

 of the plant, but if still less severe it may simply 

 girdle the stem, the plant continuing to live and 

 often producing as a result of the girdling an en- 

 larged and apparently vigorous top. Owing to the 

 fact that the girdling will prevent the return of the 

 elaborated sap on the underground portions, there 

 can be no tubers formed, or if formed they will be 

 few and small. In many instances when the plant 

 is thus prevented from forming the underground 

 tubers it will throw out from the stem at points 

 above the injury many short tuber-forming 

 stems. These tubers are small and green, and of 

 no value. 



The tubers are also attacked by the fungus, and 

 on the surface of these small, hard knots of myce- 

 lium, known as sclerotia, are produced. These 



