Aug. 15, 1925 
Soil Disinfection for Potato Wart 
309 
tried were formaldehyde, lime, bichloride of mercury, and sulphur. 
Malthouse (. 12 , 13, Ilf) and others in England, and Schaffnit and 
Voss (19) in Germany tried a wide range of fungicides in seed and 
soil treatments without finding any method that gave consistent 
control. Malthouse, for example, found that copper sulphate used 
as a summer dressing almost eradicated the disease in 1909, but failed 
to check it the following year. Eriksson (3) reported successful 
control of potato wart with 1 per cent formaldehyde used at the 
rate of 1 liter per square meter. Experiments in England (1) based 
on the results of Eriksson, but on a larger scale, failed to show any 
control where 1 per cent formaldehyde was used at the rate of 2 
gallons per square yard. Every hill, in both treated and untreated 
soil, showed wart. 
In 1919 Kunkel and Broadbent 6 tested formaldehyde on 5 by 17 
feet plots, all applications being made at the rate of 1.08 pints of 
solution per square foot, the strength of solution varying from 0.41 
to 3.28 per cent of commercial formaldehyde. One-half of the plots 
were treated with cold solutions to compare with duplicate plots 
treated with hot (97° C.) solutions. All the plots were planted to 
wart-susceptible potatoes. Wart was found in each of these plots at 
digging time. In addition, tests were made with 10-inch earthenware 
pots. In these experiments the following treatments were effective in 
eliminating wart: Autoclaving pots filled with infected soil for 15 
minutes at 15 pounds pressure; bichloride of mercury, 1 to 20,000 or 
stronger, applied at the rate of 40 c. c. per pot (% cubic foot of soil). 
The following treatments failed to eliminate wart: Copper sulphate, 
1 to 1,000 or weaker, applied at the rate of 40 c. c. per pot; sulphuric 
acid (concentrated commercial) 1 to 300, at the rate ox 625 c. c. per 
pot; copper sulphate crystals, unweighed amounts (some pots re¬ 
ceived four uncrushed crystals of copper sulphate, averaging nearly 
0.5 inch in diameter and others an approximately equal amount of 
crushed crystals). 
Chemical Treatments, Spring of 1920 
In the spring of 1920, experiments were planned to test further the 
results of Kunkel and Broadbent as well as to try a number of new 
treatments. Because of the scarcity of water in much of the wart- 
infected area, this factor must be taken into account in chemical 
treatments which require an extensive use of water solutions. The 
liquid treatments in the spring of 1920 were therefore planned with 
2 quarts per square foot as a maximum application. The plots were 
6 by 12 feet in size and located in the garden in which wart was first 
reported and in nearby wart-infected gardens. The plots were pro¬ 
tected from contamination by trenching and boarding up as in the 
steam-pan garden, but no cages were put over the individual plots. 
A wire-netting fence surrounded the entire group of plots in each 
case (pi. 1, C). 
During the summer a special study of the penetration of chemicals 
into the soil was begun. Chemical tests of the soil from various 
depths in the treated areas indicated that although an application of 
two quarts of formaldehyde solution per square foot might in some 
instances penetrate the soil to a depth of 8 inches it could not be 
depended upon to reach a depth of more than 4 or 5 inches. The 
• From unpublished manuscript and data. 
61911—25t-2 
