12 



BULLETIN 82, IT. S. DEPARTMENT OF AGRICULTURE. 



the soil under field conditions is much needed in order to understand 

 clearly this disease. Such studies are also necessary before control 

 measures can be intelligently worked out. 



SEED TREATMENT. 



Powdery scab has received little attention from the standpoint of 

 control measures except in Ireland, and the results obtained are not 

 fully convincing. Johnson (1908) states that soaking infected tubers 

 18 to 24 hours in 2 per cent Bordeaux mixture, or 1 per cent corrosive 

 sublimate for 1| hours, or 4 per cent formaldehyde solution for 2 

 hours, is effective in killing the spore balls. It has already been 

 emphasized that very little is known regarding the germination of 

 the spores. 



Pethybridge (1911, p. 443) has also studied to some extent the 

 control of Spongospora. His results are shown in Table I. 



Table I. — Yield of diseased potatoes when seed was untreated and following various 



treatments for powdery scab. 



Xo. of 

 plat. 



Treatment of seed potatoes, if any. 



Yield of 

 diseased 

 tubers. 



Xo treatment; seed only slightly affected 



Xo treatment; seed badly affected 



Soaked in formalin solution (1: 600) for 3 hours 



Soaked in copper-sulphate solution (1 per cent) for 3 hours 



Soaked in copper-sulphate solution followed by rolling in slaked lime 



Soaked in and covered -with precipitate of Burgundy mixture for 3 hours 

 Surface 'wetted and rolled in flowers of sulphur 



Per cent. 



54.1 



67.1 



2.6 







4.4 

 2.9 

 1.03 



Regarding these experiments, Pethybridge says — 



From the table it ■will be seen that in all cases the treatment of the seed, tubers 

 resulted in a most satisfactory checking of the disease. With regard to plats 8, 9, 

 and 10, where copper salts were used, the total yield of tubers was, however, quite 

 considerably reduced. The best yield was given with the formalin treatment, and 

 the next best with sulphur. Of these two, perhaps, the sulphur treatment would be 

 the easier to put in practice. 



The results obtained by Johnson and Pethybridge are very inter- 

 esting, but are of a preliminary nature, requiring further study before 

 they can be recommended for practice. 



SOIL TREATMENT. 



Soil treatment with fungicides for Spongospora scab, as would 

 naturally be expected, has given experimenters but little encourage- 

 ment. This matter has been most extensively studied for the past 

 three years in Ireland by Pethybridge (19136, p. 460), whose most 

 recent results follow. 



