320 
Journal of Agricultural Research 
Vol. XXXI, No. 4 
Copper sulphate_ $1, 742. 40 
8 cents per pound, pound per square foot. 
Formaldehyde_ 24, 441. 44 
$29.60 for 60 kilos. Two gallons of 15 per cent solution per 
square foot. 
Kerosene_ 4, 878. 72 
14 cents per gallon (price paid in 1921), gallon per square 
foot. Results with 1 pint per square foot were very promising, 
so that application could probably be greatly reduced; cost at 1 
pint per square foot would be $762.30. 
Kerosene and crude oil_ 16, 988. 40 
Kerosene 14 cents, crude oil 25 cents per gallon (prices paid in 
1921). One gallon of each per square foot. The “crude oil” 
looked like a good grade of machine oil. Crude oil can sometimes 
be obtained at oil wells at 5 cents per gallon. 
Lime-sulphur_ 726. 00 
Concentrated lime-sulphur solution 20 cents per gallon (esti¬ 
mated) 1 part in 6 parts solution, gallon per square foot. 
Oil, crude_ 10, 890. 00 
25 cents per gallon (price paid in 1921) (see above under 
kerosene and crude oil). 1 gallon per square foot. 
Sodium carbonate_ 1, 411. 34 
1.62 cents per pound, 2 pounds per square foot. 
Sodium fluoride_ 3, 136. 32 
18 cents per pound, % pound per square foot. 
Sulphur_ 217. 80 
4 cents per pound (estimated), 2 ounces per square foot. 
Weed killer_ 6, 534. 00 
Weed killer, $1.50 per gallon (price paid in 1921) 1 gallon of 
10 per cent solution per square foot. 
The cost of materials in the foregoing list is based on the amounts 
actually used. Only a few of these treatments, bichloride of mercury, 
Bordeaux mixture, and copper sulphate, were tried in smaller quan¬ 
tities, but with resulting failure. It seems probable that at least 
some of the quantities used could be markedly reduced without 
prejudice to the results. Sodium fluoride at the rate used, 20 pounds 
per plot of .50 square feet, absolutely prevented growth during all 
three years. It would seem likely that a considerable reduction 
could be made in the rate of application of this chemical. The 
amount of chemical used per square foot could very likely be reduced 
for cleaning solution, crude oil, sodium carbonate, and weed killer. 
Cleaning solution is known to be a strong, rapid killing agent and 
in the amount used made a thin mud of the soil to the depth spaded 
up. Crude oil of the type used penetrates soil very readily, and 
sufficient depth of penetration could probably be obtained in most 
soils with smaller applications. Applications of sodium carbonate 
were very heavy, 2 pounds per square foot, and prevented growth 
during the first two years. Weed killer at the strengths used pre¬ 
vented the growth of potatoes during the first two years. It is 
designed to prevent the growth of green plants, and its action on 
wart sporangia might of course be only a temporary inhibition. 
Kerosene used as a fall treatment at 1 pint per square foot gave 
good results, but needs further testing. 
SUMMARY 
The only way to eradicate potato wart in infected soil quickly 
and effectively is by soil sterilization. 
Soil may be sterilized by heat or by chemicals. 
The inverted steam-pan method is the most approved method of 
heat sterilization of soil. 
