272 
Journal of Agricultural Research 
Vol. I, No. 3 
POSSIBLE METHODS OP CONTROL 
The suggestions here given for the control of foot-rot are not based on 
experimental evidence, but on what would seem obvious from a knowl¬ 
edge of the disease and the methods of handling the crop. It has 
already been pointed out (1) that the disease occurs both on the stem and 
roots of sweet-potato plants; and (2) that the pycnospores of the fungus 
can live through the winter and late enough the following spring to 
infect the new crop. With these facts in mind it will be clear that pre¬ 
cautionary and sanitary measures should be employed. One of these 
should consist in the careful selection of healthy potatoes for seed. Se¬ 
lection should be made preferably in the fall at digging time and any 
suspicious potatoes should be discarded. They should be carefully ex¬ 
amined again in the spring when the disease is more easily recognized, 
and all those that show any sign of disease should be rejected. While 
disinfection of the seed in a solution of mercuric chlorid (1:1,000) will 
not destroy the fungus buried beneath the surface of the potato, it will 
kill all adhering spores and clean the potatoes so that diseased spots can 
be more readily detected. After immersing for five minutes in the solu¬ 
tion, the potatoes should be rinsed in water and thoroughly dried. It 
is advisable that disinfection be done on a clear, warm day, just before 
the potatoes are put in the bed. 
Soil that is likely to be infected with the disease should not be used in 
the preparation of the hotbed. If, however, disease-free soil can not be 
obtained, then it should be disinfected by steaming for one hour at a 
temperature of ioo° C. If steam sterilization is not feasible, the soil may 
be soaked in a formaldehyde (40 per cent) solution (1:200). If the latter 
method of disinfection is employed, the soil should be treated at least 
10 days before it is to be used, and it should be occasionally stirred to 
assist in the escape of the gas. 
All decayed, diseased, or discarded potatoes should not be fed raw to 
stock, or thrown on the manure pile to compost, but should be cooked; 
neither should the potatoes be thrown on the ground around the hotbed. 
These practices are too common, and are liable to infect otherwise 
disease-free beds. 
Crop rotation is a good practice, whether for the control of diseases or 
not, and should be practiced by every farmer. It is not yet known how 
long this disease retains its vitality in the soil without sweet potatoes as 
a host, but probably for several years. At least three years should be 
allowed between crops whenever diseases of this type are found, although 
it is doubtful if this length of time will completely eradicate it from the 
soil, but it should reduce it considerably. 
