88 EXPERIMENT STATION. [Jan. 



Wheeler and Tucker have made many observations on the 

 influence of fertilizers on potato scab. They found that such 

 substances as common salt, oxalic acid, calcium chloride and 

 land plaster (gypsum) did not increase the scab, and in some 

 instances appeared to lessen it. Various fungicides and chemi- 

 cal substances have been tried by Arthur and others, some of 

 v^^hich were applied to the soil and others to the seed tubers. 

 Many of these have been found beneficial in checking the scab, 

 but none appear to be as effective as corrosive sublimate and 

 formaldehyde. 



In our experiments arbitrary substances were taken, some 

 of which under proper conditions were known to have a fungi- 

 cidal action. 



It was thought useless to use fertilizers in excess as a means 

 to the end, as it had been shown that fertilizers as a rule have 

 little or no effect on the increase or decrease of the scab in land, 

 Avith one exception. It was noted repeatedly on experimental 

 plots at the station that where potash was applied in the form of 

 the carbonate the relative amount of scab was always increased.^ 



The experiments described in the following pages were car- 

 ried on in circular, lined tiles with a diameter of 23 inches, 

 with therefore an area of approximately 424 square inches, 

 or a soil area of a little less than 3 square feet. 



In the application of the substances no attempt was made to 

 bring the quantities used to an amount that would make them 

 commercially valuable, and up to the present time this policy 

 has been carried out, as the idea primarily was to find some 

 substance which would be beneficial in the eradication of the 

 scab, and then work the amount down to a commercial scale. 



The potatoes used in all the experiments were free from scab, 

 but were all treated with formalin (1-250) to kill any spores 

 of scab fungus which might be present. After the tubers were 

 dried they were planted in the tiles which contained equal 

 amounts of soil known to be badly infected with the scab fungus. 



In the experiments carried on in 1908 the substances and 

 amounts used are shown in Table I. Where liquids were used, 

 the amount of water in indicated proportions was added. 



> Influence of Various Potash Salts on Potato Scab, 13th Ann. Kept., Mass. Agr. Exp. Station, 

 1907, pp. 39 and 133. 



