758 ANNUAL REPORT OF THE Off. Doc. 



the first crop takeu off the rye sod was mcrchautabk', though some 

 what scabby. The uext year the potatoes were more nearly clear of 

 the disease, aud in the third year the appearance of the tubers was 

 excellent. iSome traces of disease remained, but the extent of its 

 presence was immaterial fiom the standpoint of a grower. 1 em 

 phasize the fact, however, that 1 used varieties most resistant of 

 scab. 



This rye -was plowed down each spring in the first hot days when 

 the growth was about one foot high, and acid was produced by its 

 deca}'. Experiments at the Rhode Island Station were showing 

 clearly that the scab fungus delighted in an alkaline soil, or one 

 treated with lime, and that it made little development in an acid soil. 

 The natural inference was made that a growth of rye plowed down 

 in warm weather would cause the formation of sufficient acid to pre- 

 vent the growth of scab, and this remains true for some soils, but 

 not for all. Some land) is neutral or slightly acid, as shown by the 

 litmus paper test, and any body of green vegetation rotting in it 

 would produce a decidedly acid condition, unfavorable to the scab 

 fungus. In the case of such soil it appears feasible to destroy the 

 fungus by producing acidity in it by green manuring. 



Other land is alkaline, and, if it is so in marked degree, a green 

 crop rotting in it would not produce any excess of acid. Farmers 

 are aware that some land may be "soured" to the point of unpro- 

 ductiveness by green manuring in inidsummer while other land will 

 not become "sour" through the practice. Likewise may land in 

 tested by the scab fungus be made sufficiently acid through the 

 plowing down of a coat of green stuff" in the spring to prevent much 

 development of the fungus, while other land, strongly alkaline, 

 would not be rendered acid and unfriendly to the fungus in this way. 



Lime corrects soil acidity and thus promotes development of this 

 disease. It is unwise to use lime on land immediately preceding a 

 potato crop, provided there are any scab germs in the soil or on the 

 seed, and the same is true of fresh stable manure. 



Sulphur for Scab. — The New Jersey Station obtained some strik- 

 ing results from the use of sulphur on the land at the rate of 300 

 pounds per acre in the row, the seed being treated with it also. A 

 series of experiments indicated that a sovereign remedy had been 

 found, but tests elsewhere brought out the fact that soil conditions 

 are a prominent factor, and that while the sulphur, like a green 

 crop ])lowed diown, would check the fungus in some soils, it was only 

 slightly effective in other soils. 



Some Station Conclusions. — From special Bulletin ''S" of the New 

 Jersey Station I take the following: 



''In soil known to be thoroughly infested with the germs ca^islng 



