212 The Potato 



it has fungicidal properties. Indeed, it has been shown 

 that when sulphur is used in sufficient quantities, it aids in 

 the reduction of powdery and common scab. Gypsum 

 makes a satisfactory material for dusting, but lime in any 

 form should not be used for this purpose as it may induce 

 scab. 



Disease from organisms already in soil 



It must be remembered that seed treatment, while it 

 destroys certain pathogenic organisms on the surface of 

 the tuber, does not insure immunity of the crop from these 

 diseases. Many of these organisms also live in the soil 

 from year to year, and these are as able to attack plants 

 coming from treated as from the untreated seed. The 

 treated seed must be planted in soil that is free from these 

 organisms or where they are much reduced or in an in- 

 active condition. It is impractical to sterilize soil for 

 growing potatoes, although for greenhouse and other 

 valuable crops it is considered to be a good practice. 

 The application of chemicals to the soil that will destroy 

 or retard the growth of these organisms has not given 

 very satisfactory results. Sulphur applied at the rate of 

 450 to 900 pounds to the acre has reduced the amount of 

 scabby tubers to a considerable extent, but it may also 

 reduce the yield. It has been observed that clover will 

 not grow in soil treated in this way. Fertilizers such 

 as lime, which increase the alkalinity of the soil, greatly 

 favor the development of scab, while acid phosphate, sul- 

 phate of ammonia and the like, at least, do not increase 

 scab injuries. 



When potatoes are grown year after year upon the 

 same land, the parasites, especially those that live in the 

 soil, are likely to increase unless one constantly guards 



