92 



10. Where the tertiHser was used without any lime compounds no 

 scab resulted, showing that the acid soil must have rendered dormant, 

 or destroyed the scab fungus introduced on the scabbed seed tubers of 

 the two previous years. 



11. 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 favourable 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 

 favourable to the di>' ise, but where little or no contamination already 

 existed, BoUey's corrosive sublimate treatment proved highly effective. 

 It is probable that some germs escape even this treatment, but fewer, of 

 course, where the seed tubers are not scabbed, so that there is danger if 

 potatoes and root crops are grown frequently that serious contaminacion 

 may nevertheless result eventually. The necessity, on land intenaed 

 for po:a:o growing, of avoiding the frequent use of fertilisers which 

 tend to make the soil more favourable to the development of the scab 

 fungus is therefore obvious. 



12. The materials which favour the scab and which are at times 

 applied to land are ; stable manure of ail kinds, wood ashes, air- slacked 

 or caustic lime and carbonates of soda (soda ash), potash, lime and 

 magnesiii. 



13. The materials which do not tend to make the scab worse and 

 which may decrease it, are most comrnerciil fertilisers, sea-weed potash 

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

 ammonium sulphate. Sodium nitrate (Chili salt-petre) if used in large 

 quantities may favour the scab eventually, but from the amounts usually 

 applied no serious results would be expected to follow. In case a soil 

 were badly contaminated and favourable to the disease, superphosphate, 

 ammonium sulphate, kainit, sulphate and nuriate of potash are mater- 

 ials which, applied as fertilisers would tend gradually to alleviate the 

 conditions. 



14. Sulphur (the remedy proposed by Halsted) when mixed 

 thoroughly with the upper seven to eight inches of a badly contaminated 

 soil favourable to the disease, though checking the scab somewhat, was 

 practically useless. 



15. The treatment of seed tubers by rolling in sulphur and sprink- 

 ling • he balance in the row at the rate of 300 pounds per acre is claimed 

 by Halsted to be quite effective. The use of the very poisonous cor- 

 rosive sublimate solution would be thereby avoided, yet the additional ex- 

 pense of the sulphur over the corrosive sublimate treatme;it for this pur- 

 pose militates against its use in that way where potatoes are grown at 

 the present low prices. 



16. The marked acidity (sourness) of soils, or the absence of car- 

 bonates in them seems to indicate their ability to produce a scabless pro- 

 duct even when untreated seed tubers are used. 



