Aug. 15, 1925 
Soil Disinfection for Potato Wart 
311 
failure of water solutions of chemicals in such amounts was therefore 
not cause for surprise. Like the plots in the steam-pan treatments, 
most of the chemical plots were planted to an immune variety in 1920 
because of a mixture of seed, so that the results of the treatments 
were not obtained until 1921. These spring treatments in 1920, all 
of which failed to eliminate wart, included: Formaldehyde, applied so 
as to furnish all possible combinations of 1 and 2 per cent solutions, 
used hot and cold, at the rate of 1 and 2 quarts per square foot; 
bichloride of, mercury, from 3^ pint per square foot of 1 to 32,000 to 
2 quarts of 1 to 250; chloride of lime, % pint per square foot of solu¬ 
tions made by dissolving 12 ounces or 24 ounces in 43^ gallons of 
water; a commercial “potato powder 77 (compounded from white 
arsenic, lime, and copper sulphate), 1 pound to 3 gallons of water and 
2 pounds to 3 gallons, % pint per square foot; and Bordeaux mixture, 
8-8-50 and 16-16-50, % pint per square foot. 
Chemical Treatments, Fall of 1920 
Notwithstanding the fact that the penetration tests indicated that 
applications of 2 quarts per square foot would immediately penetrate 
only 4 to 5 inches, treatments made in the fall of 1920 were confined 
to applications of 1 pint or less per square foot or to dry chemicals. 
This was done because of the difficulty that would undoubtedly be 
experienced in obtaining sufficient water if heavy applications were 
attempted on a large scale. Part of these treatments were made 
during rain and snow storms with the hope that the rains would 
carry the chemicals into the soil to a sufficient depth to insure com¬ 
plete sterilization. While rainfall can undoubtedly take the place of 
some of the water that would otherwise be required, it has not been 
determined to what extent this is possible. Where rainfall is reason¬ 
ably heavy it is a potential source of most of the water required, as 
1 inch of rain is approximately equal to 5 pints per square foot. 
The plots treated with chemicals in the fall of 1920 were spaded 
up and planted to wart-susceptible potatoes in the spring of 1921. 
The results are tabulated in Table II. As shown in this table, two 
plots were treated with a lime-sulphur solution at the rate of 1 pint 
per square foot, consisting of one part of commercial solution, testing 
33° Baum6, to two parts of water, and permitted very little growth. 
The few stunted plants that appeared bore no tubers and showed no 
sign of wart. No wart occurred in plots treated vrith crude carbolic 
acid, or with denatured alcohol at the rate of ^ gallon per square 
foot. A plot treated with kerosene at the rate of 1 pint per square 
foot gave striking results. The odor of kerosene was quite evident 
when this plot was dug nearly a year after treatment, and the tubers 
were absolutely free from wart, scab, and black scurf. The plot 
adjoining it on the upper side had 47 per cent of wart and the tubers 
in nearly all plots were more or less severely infected with scab and 
scurf. While the plot was evidently at the edge of the infected area 
and may have contained relatively few wart spores, the results were 
such as to warrant further tests of kerosene. The plants in plots 
treated with creosote, potassium permanganate, sugar, and sulphur 
were free from wart at harvest, but the soil in them was probably 
only lightly, if at all, infected. Plots treated with bichloride of 
mercury and salt (both dry and in solution), with Bordeaux, and with 
chloride of lime, showed a large percentage of wart except for one 
Bordeaux plot in lightly infected soil. This garden was said to have 
