760 ANNUAL REPORT OF THE Off. Doc. 



plaster (gypsuiiij was used. Calcium clilorid had a marked poison 

 ous effect upon the potato plants and nearly destroyed them. Land 

 l)laster appeared not to have increased, and it may have lessened, 

 (he \ield sli^htlv. \Miere calcium at the same rate as in the cal- 

 cium chlorid and land plaster was applied to the form of wood 

 ashes, air-slacked lime, calcium carbonate, calcium oxalate and cal- 

 cium acetate, the vigor of the plants and the yield of tubers were 

 wonderfully increased, but the crop was so badly scabbed as to be 

 worthless. 



''3. Where the fertilizer was used without any lime compounds no 

 scab resulted, showing that the acid soil must have rendered dor- 

 mant or destroyed the scab fungus introduced on the scabbed seed 

 tubers of the two previous years. 



''i. The treatment of the seed tubers with a 1 to 1,000 solution of 

 corrosive sublimate for one and one-half hours was utterly useless 

 where the soil was favorable to the disease and where it was already 

 badly contaminated by two preceding lots of scabbed seed tubers and 

 scabbed crops. In other experiments by us heretofore where the 

 soil was favorable to the disease, but where little or no contamina- 

 tion already existed, Bolley's corrosive sublimate treatment proved 

 highly effective. It is probable that some germs escape even thid 

 treatment, but fewer, of course, where the seed tubers are not scab- 

 bed, so that there is danger if potatoes and root crops are grown fre- 

 quently that serious contamination may nevertheless result event- 

 ually. The necessity, on land intended for potato growing, of avoid- 

 ing the frequent use of fertilizers which tend to make the soil more 

 favorable to the development of the scab fungus is therefore obvious. 



''o. The materials which favor the scab and which are at times 

 applied to land are: Stable manure of all kinds, wood ashes, air-slack- 

 ed or caustic lime and carbonate of soda (soda ash), potash, lime 

 and magnesia. 



"6. The materials which do not tend to make the scab and whicli 

 may decrease it, are most commercial fertilizers, seaweed, potash 

 salts (excepting potassium carbonate), land plaster, common salt 

 and ammonium sulfate. Sodium nitrate (Chili saltpeter), if used in 

 large quantities, may favor the scab eventually, but from the 

 amounts usually applied no serious results would be expected to fol- 

 low. In case a soil were badly contaminated and favorable to the 

 disease, super-phosphate, ammonium sulfate, kaiuit, sulfate and mu- 

 riate of potash are materials which, applied as fertilizers, would 

 tend gradually to alleviate the conditions. 



"7. Sulfur when mixed thoroughly with the upper seven to eight 

 inches of a badly contaminated soil favorable to the disease, though 

 checking the scab somewhat, was practically useless. 



