84 MAINE) -AGRICULTURAL EXPERIMENT STATION. I907. 



Once the soil is contaminated there are two possible sources 

 of infection of the growing crop ; first from the seed, and sec- 

 ondly from the, soil itself. The amount of scab which may 

 develop on the crop is influenced by a variety of conditions, as 

 well as by the number of scab germs already present in the soil 

 or introduced with the seed. For example scabby seed planted 

 on soil where conditions are unfavorable, for the development 

 of scab may give a comparatively clean crop, while on the other 

 hand relatively clean seed may produce an exceedingly scabby 

 crop, especially the second year, if the soil conditions are favor- 

 able to the. scab fungus. This, of course, is due to the fact that 

 the soil is already contaminated. Infested soil may be expected 

 to produce a more or less scabby crop even though clean seed 

 is planted. 



CONDITIONS FAVORABLE TO SCAB. 



Scab thrives best on an alkaline soil or in the presence of cer- 

 tain fertilizers or chemical substances which tend to promote 

 alkalinity, while acid soils and the presence of certain other 

 chemical salts are unfavorable to its development. Dr. Wheeler 

 of the Rhode Island station has made an extensive study of this 

 subject, and summarizes his conclusions as follows :.* 



"The materials which favor the scab and which are at times 

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

 slacked or caustic lime and carbonates of soda (soda-ash), pot- 

 ash, lime and magnesia." 



"The materials which do not tend to make the scab worse 

 and which may decrease it are : most commercial fertilizers, 

 seaweed, potash salts (excepting potassium carbonate), land 

 plaster, common salt and ammonium sulphate. Sodium nitrate 

 (Chili salt-peter) if used in large quantities may favor scab 

 eventually, but from the amount usually applied no serious 

 results would be expected to follow. In case a soil were badly 

 contaminated and favorable to the disease, superphosphate, 

 ammonium sulphate, kainite, sulphate and muriate of potash are 

 materials which, applied as fertilizers, would tend gradually to 

 alleviate the conditions." 



Heavy moist soils appear to be more favorable to scab than 

 those which are light and dry. It is maintained by some that in 



* R. r. Exp. Sta. Bui 40, p. 95, ( 1 



