Aug. 15 1925 
Soil Disinfection for Potato Wart 
303 
at a temperature of 150°. The second of these plots gave the best 
results, being almost entirely free from disease.” On the basis of his 
experiments Gilbert recommends that soil to be disinfected should 
be spaded up and thoroughly pulverized and steam applied by the 
inverted-pan method. “ The steam should be kept at as high a pres¬ 
sure as possible, 80 to 100 pounds being best, and the treatment should 
continue for one to two hours, depending on the pressure maintained.” 
Numerous investigators have obtained results very similar to those 
of Gilbert, and the use of the steam-pan treatment of seed beds for the 
control of soil-borne diseases has become common practice in many 
places. Formaldehyde drenching has also been a common treatment 
for seed beds. The strength and quantity of formaldehyde solution 
recommended varies considerably. Gilbert recommends “ 1 part of 
commercial formalin to 150 to 200 parts of water, three-fourths to 1 
gallon of this solution being used to the square foot of bed space.” 
Both steam and formaldehyde treatments had been used with such 
success in this country that Kunkel and Broadbent, who in 1919 
experimented with possible methods of exterminating potato wart, 
undertook a retesting of these methods, notwithstanding the reported 
lack of success with them in England. They also tried combinations 
of the two treatments. In 1919, field work on this project was 
carried out by Broadbent 5 in heavily infected soil near Freeland, Pa. 
Broadbent’s data show that his steam treatments varied from 25 
minutes at 85 pounds gauge pressure to 175 minutes at 105 pounds 
pressure. No wart infection appeared in plots treated for 85 minutes 
at 90 pounds pressure, but occurred in a number of plots steamed 70 
minutes. Plots which were sprinkled with 0.41 percent (or stronger) 
formaldehyde at the rate of 0.59 pint per square loot and immediately 
steamed for 30 minutes at 90 pounds pressure were free from. wart. 
The treatments with formaldehyde alone were unsuccessful. 
1920 Steam-Pan Treatments 
Steaming operations were begun at Freeland, Pa., on May 26, 
1920. Thirty-one plots were treated up to and including June 8. 
The remaining seven plots were treated during the period June 25 
to July 2. The garden used for the steam-pan experiments in 1920 
adjoined the one used for similar work in 1919, the latter in turn 
adjoined the garden from which the disease was first reported. 
Freeland is at the southern boundary of the glacial advance and the 
soil contains elements of the Volusia and DeKalb types. Both are 
largely silt loams with a tendency to be acid. The gardens of the 
coal miners of that locality are largely a conglomeration of soil, 
ashes, coal-dust, cinders, and debris of any kind, and the steam- 
treated garden was no exception. 
The source of steam for the experiments of both years was a large 
high-pressure (135 to 140 pounds) main used for pumping, hoisting, 
and other work about the mines. Steam was conducted nearly 200 
feet from the main through a ^£-inch pipe, a 20-foot length of steam 
hose serving to connect this pipe with the steam-pans. The steam- 
pans were those used in 1919, one covering 5 by 9 feet and the other 
6 by 9 feet. These are merely shallow open boxes; the sides are 
made of 2 by 6 inch material from the lower edge of which an iron 
6 Unpublished report of field work in soil disinfection to exterminate potato wart, 1919. 
