230 Repokt of the Department of Botany of the 



on the treatment of the potato scab, Morse 20 states that a tem- 

 perature of 60-65 degrees Fahr. is more effective than a lower one, 

 and that in moist air the gas is more efficient. Later 21 he states 

 that a temperature above 80 degrees is most effective. However, 

 under ordinary farm conditions, unless specially equipped, it is almost 

 impossible to obtain a temperature of 80 degrees when it is most 

 desirable to treat tubers. In the preceding bulletin, No. 369, tem- 

 perature does not prove a factor in determining the cause of the 

 injury to the tubers, but humidity shows some evidence of being 

 a causal agent. The data in Table I of the present bulletin, however, 

 indicate that temperature and humidity are less important in the 

 treatment for Rhizoctonia than is usually believed, for under almost 

 similar conditions widely variable results were obtained. One of 

 the most important factors concerned in the inefficiency is the 

 quantity of tubers in the fumigator. Where several experiments 

 were conducted with the same quantity of tubers the averages 

 show least efficiency where potatoes at the rate of 16 pounds (equal 

 to 167 bushels per 1000 cubic feet) per cubic foot were used. In 

 Bulletin No. 369 it is shown that the factor of adsorption is depend- 

 ent upon the quantity of tubers in the fumigator. The writer 

 believes that if a sufficient number of experiments were conducted 

 the data would show that there is a gradual decrease in the efficiency 

 of the gas as the quantity of tubers is increased. 



The conclusion drawn from laboratory experiments that the 

 formaldehyde gas and liquid treatments are inefficient in killing 

 the Rhizoctonia is partially substantiated by other writers. Rolfs 22 

 and Giissow 23 conclude, from the results of field experiments, that 

 the mercury bichloride gives better results than the formaldehyde 

 solution. Selby 24 came to an opposite conclusion, namely, that the 

 formalin dip method was better than the corrosive sublimate treat- 

 ment. However, so far as the control of Rhizoctonia is concerned 

 this conclusion appears unwarranted. The plats in his experiments 

 were very small, mostly on infected soil and the yields irregular. 

 Moreover, the causal relation of Rhizoctonia to rosette is uncertain. 



"Morse, W. J. Potato Diseases in 1907. Me. Sta. Bui. 149:316. 1907. 

 "Morse, W. J. Blackleg: A Bacterial Disease of Irish Potato. Me. Sta. Bui. 



174:325. 1909. 

 ^Rolfs, F. M. Colo. Sta. Buls. 70 and 91. 

 ^Giissow, H. T. Canada Expt. Farms Rpts. 1912:200. 

 24 Selby, A. D. Ohio Sta. Buls. 139 and 145. 1903. 



