Aug. 15, 1925 
Soil Disinfection for Potato Wart 
307 
Table I .—Presence of wart in 1921 following steam and combination treatments 
in 1920 a 
TV art absent 
Wart present 
Formaldehyde 
Steam 
Formaldehyde 
Mercuric chloride 
Steam 
Amt. 
Plots 
Amt. 
Amt. 
Plots 
Strength 
per 
Pressure 
Time 
Strength 
per 
Strength 
per 
Pressure 
Time 
sq. ft. 
sq. ft. 
sq. ft. 
Num- 
Num- 
Per cent 
Pints 
Pounds 
Minutes 
her 
Per cent 
Pints 
Per cent 
C.c. 
Pounds 
Minutes 
her 
90 to 95 
85 
3 
90 to 95 
115 
1 
90 to 95 
75 
1 
90 to 95 
100 
1 
2 
y 2 
90 to 95 
40 
1 
90 to 95 
85 
1 
l H 
52 
90 to 95 
40 
1 
90 to 95 
70 
1 
140 
25 
1 
140 
12 
1 
ly 
V2 
90 to 95 
40 
4 
i 
V2 
90 to 95 
40 
2 
y 2 
Y2 
90 to 95 
40 
1 
2 
V2 
90 to 95 
30 
1 
1 
y 2 
90 to 95 
30 
1 
3 
y 2 
90 to 95 
25 
1 
2 
y 2 
90 to 95 
25 
1 
i y 2 
X /2 
90 to 95 
25 
4 
1 
X 
90 to 95 
25 
3 
1 to 400 
160 
90 to 95 
25 
1 
1 to 500 
80 
90 to 95 
25 
1 
1 to 1,000 
80 
90 to 95 
25 
1 
1 to 1,333 
80 
90 to 95 
25 
1 
1 to 2,000 
80 
90 to 95 
25 
1 
1 to 4,000 
80 
90 to 95 
25 
1 
1 to 20,000 
80 
90 to 95 
25 
1 
° Commercial formaldehyde considered as 100 per cent. One plot was destroyed during winter 1920-21. 
English weights and measures were used when metric apparatus was not available or whenever more con¬ 
venient for any reason. 
(135 to 140 pounds) carried by the mains was tried. Steam at this 
pressure heats the soil very rapidly but the treatment is too difficult 
to carry out. The 12-minute steaming period was due to the bursting 
of the hose. An ordinary boiler can not maintain such high pressure. 
The combination of formaldehyde with short periods of steaming did 
not prove effective. Formaldehyde applied at the rate of one-half pint 
per square foot does not penetrate the soil more than about an inch. 
Steaming for 40 minutes at 90 pounds pressure can not be depended 
on to sterilize deeper than 3 to 4 inches. As noted before, this 
treatment might result in a clean crop the first year, before the deeper- 
lying spores are brought to the surface by cultivation. As will be 
noted in Table I every plot treated with both steam and mercuric 
chloride was found to have warted plants. The quantity of mercuric 
chloride solution applied penetrated only a fraction of an inch and 
the steam treatment added would not be effective to a depth greater 
than 2 to 3 inches. 
The results of the 1920 steam-pan experiments seem to eliminate 
the steam-formaldehyde and the steam-mercuric chloride treatments, 
inasmuch as they were too expensive to use unless they insured 
absolute eradication. The results also cast grave doubts on the de¬ 
pendability of steaming alone for 85 minutes at 90 pounds pressure. 
The steam-pan treatments as carried out were not effective. The 
failure of the longer treatments was probably due to the fact that the 
method of controlling the amount of steam supplied was not accurate, 
as determined later. However, much of the ground could not be 
readily treated by the steam-pan method. 
