Aug. 15, 1926 
Soil Disinfection for Potato Wart 
321 
Although effective, steam-pan sterilization is slow, cumbersome, 
and expensive. 
The application of small amounts of formaldehyde or of bichloride 
of mercury solutions just previous to steaming the soil can not be 
depended on to increase the efficiency of the treatment. 
Of the 22 chemicals tried in the dilutions and amounts given, 14 
produced wart-free plots during the season treated and during the 
two following seasons. 
Six of the successful chemicals (bichloride of mercury, chloride of 
lime, copper sulphate, sodium carbonate, sodium fluoride, and 
sulphur) were used dry. Kerosene and crude oil were used undiluted. 
Water was used with seven of the chemicals (bichloride of mercury, 
Bordeaux mixture, cleaning solution, formaldehyde, lime-sulphur, 
sodium chromate, and a commercial weed killer). 
Water is difficult to obtain in the principal region infected by 
potato wart, at Freeland, Pa., and this adds to the cost of applying 
chemicals in solution. The use of chemicals dry or applied as strong 
solutions during the late fall would be desirable if the amount of 
water required could thereby be reduced. Such data as were ob¬ 
tained on this point indicate that such a reduction might be possible. 
Some test plots gave such poor growth of potatoes that conditions 
were not favorable to wart infection, and final conclusions as to the 
effectiveness of the chemicals used on them were therefore not pos¬ 
sible. Sodium fluoride prevented growth all three seasons. Sulphur 
nearly prevented growth all three seasons. The growth in plots 
treated with copper sulphate crystals, lime-sulphur, sodium car¬ 
bonate, sodium chromate and a commercial weed killer was such 
that the test of their efficacy is not considered entirely satisfactory. 
The growth in at least part of the plots treated with bichloride of 
mercury, cleaning solution, kerosene, Bordeaux mixture, and crude 
oil was such as to make it seem almost certain that wart would have 
developed if the treatment had not been effective. 
The approximate cost per acre for the materials used in the success¬ 
ful treatments is given. Some of the more promising treatments 
requiring no water are sulphur, $220 per acre, and kerosene, $765 
per acre. Two promising treatments requiring water are lime- 
sulphur, $726 per acre, and Bordeaux mixture, $315 per acre. 
Bichloride of mercury in various combinations seems undoubtedly 
effective but costs $1,900 per acre for iliaterials. Steam-pan treat¬ 
ments if sufficiently prolonged would be effective where usable but 
would probably cost at least $1,500 per acre. 
PART II.—TEMPERATURE CHANGES OCCURRING IN SOIL UNDER 
A STEAM PAN 
INTRODUCTION 
In connection with the test of steam-pan treatments as a possible 
means of exterminating the potato-wart organism in the United 
States, data were secured as to the temperature changes occurring in 
the soil under the steam pan. If a given amount of steam heat is 
fatal to the potato-wart organism, a knowledge of the conditions 
necessary to insure that amount of heat in each type of soil to be 
treated and to the proper depth is essential to efficiency in using the 
treatment on a large scale. 
