318 
Journal of Agricultural Research 
Vol. XXXI, No. 4 
that if the wart spores were not killed, any inhibitory action of the 
chemicals should have been overcome and the disease produced in at 
least some of the pots. 
SUN AND AIR TREATMENTS 
In planning soil treatments with a view to the extermination of 
the potato wart it is necessary to know something of the rate and 
methods of spread of the pathogen in order to know how far beyond 
the known limits of the infected area soil treatment will be necessary. 
It seems certain that wart spores are present in wind-borne soil, 
but the slowness with which the wart disease seems to spread in 
infected gardens indicates that comparatively few infections result 
from wind-borne soil. It was thought that relatively short exposure 
of spores to air and sun might be sufficient to kill them. An experi¬ 
ment to test this was carried out in the greenhouse during the winter 
of 1920-21. Wart-infected soil was spread in thin layers, 34 and 
34 inch deep, on wart-free soil in pots in the greenhouse and exposed 
to air and sunlight for from 2 to 12 days. The wart-infected soil was 
used as it came from the garden except that where necessary lumps 
were broken and stones and debris removed in order that the total 
thickness of the layers of soil should not exceed the specified 34 or 
34 inch. At the end of the exposure periods the pots were planted 
to potatoes by pressing a single tuber partly into the soil in each 
pot and covering it with wart-free soil. Of the 48 tubers planted in 
pots containing J4 inch of this wart-infected soil, 44 produced wart- 
mfected plants. Of the 48 tubers planted in pots containing 34 inch 
of wart-infected soil, 36 produced wart-infected plants. Of the 20 
tubers planted in pots containing J4 or 34 inch of the same lot of 
wart-infected soil and not exposed to air and sun, 8 produced wart- 
infected plants. These results seem to indicate that wart spores 
near the surface of freshly cultivated soil retain their vitality for 
some time, long enough for the soil to dry out and be blown about. 
In another experiment 60 tubers were wet, rolled in wart-infected 
soil from the same source and exposed to air and sunlight for from 
2 to 25 days. Only 3 of these tubers, exposed 2, 9, and 12 days, 
developed wart when planted. The fact that nearly all of the soil 
had fallen from these tubers before they were planted may account 
at least in part for the low percentage oi infection obtained. 
COST OF TREATMENTS 
The cost of many of these treatments is much too high to warrant 
their use except under special circumstances. 
Cost of Steam-Pan Treatments 
With a minimum of overlapping a 6 by 12 foot steam pan would 
treat 65 square feet of soil at a time, making 670 pan areas per acre. 
Steaming 1 pan area every 134 hours would accomplish the treat¬ 
ment of 5 pan areas each 8-hour day. The cost would approximate 
$15 per day divided as follows: Engineer $5, 2 laborers at $4, one- 
third ton of coal at $6 per ton; or $2,010 per acre. In addition there 
would be the cost of water, which would have to be hauled or pumped ; 
dray age on coal; transportation of men; rental or depreciation of 
outfit; probability of nigher labor costs, especially for engineers; 
