16 
Bulletin 91. 
results. The ground ought to be thoroughly pulverized before 
planting. After the seed is planted great care should be exercised 
to prevent the soil from forming a crust. The potato plant does 
best in a well aerated soil. The crust not only tends to weaken 
the plant by cutting off its air supply, but it also frequently de¬ 
lays the shoots in reaching the surface of the ground; and if such 
plants are infected with this disease they suffer severely and are 
frequently killed before they reach the surface of the ground. 
(See Bulletin 70, p. 6). Even after the plants are up and well- 
established the formation of crust on the soil ought to be carefully 
guarded against, since it seems to furnish better conditions for the 
O O 7 
development of this disease. Observations indicate that fields 
which are sparingly watered and thoroughly cultivated suffer less 
from this fungus and the tubers are much freer from scabs. 
The Runs .—Deep runs are better than shallow ones, since 
they give better circulation of air at the base of the plants, and 
they also enable the grower to supply the roots with an abundance 
of moisture, while the soil near the surface, where the tubers form, 
can be kept comparatively dry and thus avoid conditions which 
favor the rapid development of this fungus. 
Late Planting .—Late planting frequently gives better results 
than early planting. This may possibly be due to the wet weather 
early in the spring which makes the conditions favorable for the 
growth of the fungus. Later the weather becomes settled and the 
ground can be kept well cultivated and the moisture of the soil 
is more easily controlled. A loose, open soil favors the growth of 
the potato plant and seems to check the rapid development of this 
disease. 
Old Stems .—Infected potato and weed stems are often left 
scattered about in the field after harvest, and these are blown 
about by the wind and many of them are lodged in irrigating 
ditches, where they usually remain until the following summer, 
and as soon as the fields are irrigated, many of the stems are car¬ 
ried by the water into new fields and thus may become the prin¬ 
cipal means of infection. The burning of all vines and weeds 
after harvest is an excellent practice. 
The Seed Potato .—A careful study of seed potatoes shows that 
it is almost impossible to find a lot of seed of which at least a few 
are not more or less infected with this disease. Observations in¬ 
dicate that seed tubers are usually the principal means of spread¬ 
ing this disease. (See Bulletin 70, p. 9). Too much care cannot 
be given to seed selection. 
Tubers keep best in a dry, well ventilated dugo-ut which is 
kept at about 40° F. Seed tubers ought to be stored in compara- 
