308 
Journal of Agricultural Research 
Vol. XXXI, No. 4 
Potato wart has been found in over 800 gardens. These vary in 
size from a few square feet to one-fourth of an acre. Furthermore, 
the gardens are usually irregularly shaped and are likely to be rendered 
more difficult to treat by the presence of walks, outbuildings, trees, 
clothesline posts, ditches, or rock outcroppings. It is practically 
impossible to treat all the soil next the fences and buildings. In 
considering the possibility of exterminating potato wart it must be 
borne in mind that the pathogene is undoubtedly present to a greater 
or less extent in soil surrounding the gardens in which its presence 
has actually been established. Spores are easily carried on the feet 
or on implements from one part of the yard to another and also to 
adj acent streets, alleys, and yards. The disease was often particularly 
severe along rear walks where potato peelings had been thrown from 
the kitchen door. Diseased potatoes were sometimes stored in 
earthen-floored cellars. Besides these practical difficulties in the use 
of steam-pan treatments, it is a rather slow and expensive method. 
Because of the difficulties involved in steam-pan treatments, it seemed 
desirable to restrict further studies on soil disinfection to tests of 
chemicals, including a study of the principles underlying their use. 
DISINFECTION OF SOIL BY VARIOUS CHEMICAL TREATMENTS 
Historical 
The use of chemicals by prior workers for sterilizing soil has, like 
that of steam, been practically limited to the treatment of greenhouse 
benches or to seed beds. In either case control rather than eradica¬ 
tion was the object sought. For seed beds particularly, only surface 
sterilization was necessary, as in many cases the control of damping 
off was the principal objective. Halstead (6) carried out an exten¬ 
sive series of experiments by treating soil with ashes, benzine, Bor¬ 
deaux, calcium carbonate, carbon bisulphide, copper sulphate, 
corrosive sublimate, creolin, cupram, formalin, gas lime, kainit, 
kerosene, lime, manure, oxalic acid, sodium carbonate, sodium 
chloride, sulphate of ammonium, sulphate of potassium, sulphide of 
ammonium, sulphide of potassium, sulphur, and sulphuric acid. 
These experiments showed that sulphur was a valuable preventive 
of potato scab; that it was a preventive of soil rot in sweet potatoes, 
especially when used with kainit; and that air-slaked lime was a 
practical remedy for club root in turnips. The other chemicals 
failed to show promise as soil fungicides. As control, not extermina¬ 
tion, of the diseases was the object of the experiments, the amount 
of chemical used was relatively small in all cases. The maximum 
applications of mercuric chloride, for example, were 1 gram per square 
foot dry, or 1 pint of a 1 to 1,000 solution; of sulphur % ounce; of 
calcium carbonate 1 ounce; and of kerosene ounce per square foot. 
Only surface or partial sterilization was possible with the amounts used. 
For the control of tobacco root rot, formaldehyde drenching was 
found by Gilbert (4) to give reasonably satisfactory results, though less 
effective as well as more expensive than the steam treatments tried. 
Hartley and others (7, 8 , 9) have done considerable work on methods 
of controlling damping off among coniferous seedlings. They 
found that the chemicals which gave the best results depended on 
the character of the soil and the organism or organisms involved. 
Efforts of European investigators to control or eradicate potato 
wart by soil-disinfection methods have failed. Among the chemicals 
