12 BULLETIN 82, U. 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 (190S) 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 poivdery scab. 
Xo. of 
plat. 
Treatment of seed potatoes, if any. 
Yield of 
diseased 
tubers. 
i Per cent. 
Xo treatment: seed onlv slightly affected 54. 1 
No 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 
67.1 
2.6 

4.4 
2.9 
1.03 
Kegarding these experiments, Pethybridge says — 
From the table it will be seen that in alt 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 (19135, p, 460), whose most 
recent results follow. 
