THE EFFICIENCY OF FORMALDEHYDE IN THE 

 TREATMENT OF SEED POTATOES FOR 

 RHIZOCTONIA.* 



W. O. GLOYER. 



SUMMARY. 



The object of this investigation was to determine the relative 

 efficiency of the standard scab treatments in the disinfection of 

 seed potatoes affected with Rhizoctonia. Experiments were made 

 with formaldehyde gas, formaldehyde solution, and corrosive subli- 

 mate solution. 



It was found that neither formaldehyde gas nor formaldehyde 

 solution can be depended upon to kill all of the Rhizoctonia sclerotia. 

 The principal reason for this appears to be the inability of the for- 

 maldehyde to penetrate readily to the center of the larger and 

 more compact sclerotia. Also, the efficiency of the gas treatment 

 depends to a considerable extent upon the quantity of tubers per 

 cubic foot of space in the disinfection chamber. Other things being 

 equal, the smaller the quantity of potatoes the greater the efficiency. 

 Neither temperature nor humidity are factors of much importance. 



The standard corrosive sublimate treatment, on the contrary, is 

 thoroughly efficient. Even with a i-to-2000 solution (half standard 

 strength) all Rhizoctonia sclerotia are killed. 



The conclusion reached is, that when it is desired to treat seed 

 potatoes for Rhizoctonia the corrosive sublimate treatment should 

 be used. 



INTRODUCTION. 



The numerous fumigation experiments made in the course of the 

 investigation reported in Bulletin No. 369 of this Station offered an 

 excellent opportunity for observing the effect of formaldehyde gas 

 on the Rhizoctonia adhering to potato tubers. Potatoes in various 

 quantities and under various conditions of temperature and moisture 

 were subjected to the formaldehyde gas treatment, and the effect on 

 Rhizoctonia noted. In other experiments Rhizoctonia-infested tubers 

 were dipped in solutions of formaldehyde and corrosive sublimate as 



* Reprint of Bulletin No. 370; for Popular Edition, see p. 778. 



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