New York Agricultural Experiment Station. 221 



showed 87, 45, and 48 per ct. of the tubers attacked by it. Though 

 no comment was made on these results it appears that a longer 

 immersion than two hours is more effective in killing the fungus. 

 Giissow 14 conducted field experiments in which lots of seed tubers 

 attacked by Rhizoctonia were immersed for 3 hours in a solution of 

 one part mercury bichloride to 2000 parts of water (equal to 1 ounce 

 to 15 gallons of water), and, also in a bath of formalin made up of 

 one half pint to 15 gallons of water. At the harvest it was found 

 that the tubers treated with formalin were almost as badly covered 

 with Rhizoctonia as were the original potatoes, while those immersed 

 in mercury bichloride solution were practically free. 



PRESENT TESTS. 



METHODS. 



To ascertain the efficiency of the formaldehyde gas, three or more 

 Rhizoctonia-infected potatoes were placed in the fumigator along 

 with the various quantities of tubers that were used in the experi- 

 ments made for the determination of factors involved in tuber 

 injury. The chemicals used, the fumigator, the quantity of tubers, 

 and the conditions of moisture and temperature under which these 

 experiments were conducted are described in Bulletin No. 369. 



For comparison with the results obtained by the gas method of 

 treating seed potatoes, experiments were also conducted in which 

 the standard immersion or dip methods were employed. Rhizoctonia- 

 diseased tubers were immersed in solutions of formaldehyde and 

 mercury bichloride for 2 and 1? hours respectively. The standard 

 strength of formalin was used unless otherwise noted, namely, one 

 pint of formalin (a 37 per ct. solution of formaldehyde) to 30 gallons 

 of water. Of mercury bichloride, two different strengths were used, 

 namely, one part of the salt to 1000 and 2000 parts of water. The 

 latter strength is one-half that usually employed in practical dis- 

 infection. After immersion in these solutions the potatoes were 

 permitted to drain and dry under sterile conditions. 



Before and after each experiment cultures were made of the un- 

 treated and treated sclerotia to determine the efficiency of the 

 treatment. In making these cultures the usual precautions were 

 used to maintain sterile conditions in handling instruments, petri 



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



