"Mosaic is assuming great impor
tance as a potato disease in certain
sections of the country. -It is charac
terized by a mottling in the green of
the leaves, sometimes accompanied
also by a crinkling but not a rolling
of the foliage. The disease should not
be confused with the uneven yellowing
which results from the application of
excessive water In irrigated regions
nor with the somewhat different yel
lowing and rolling associated with ex
cessive alkali content in soils, nor
should it be confused with the con
dition of partial absence of coloring
matter, possibly chimera, seen occa
siomflly in fields, more particularly in
certain sections of the West. The
cause of mosaic has never been deter
mined, but it is known that the dis
ease is reproduced when tubers from
affected plants are used for seed. The
experimental data which have been
secured both in the United States and
ih
M
J,
<
m
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A
%
Uniform and of Good Size.
abroad show that the yield from mo
saic plants is less than that from
healthy plants of the same variety
grown under the same conditions or
in the same field. The average reduc
tion in yield in trials made by the de
partment with various varieties and in
several different sections of the coun
try is approximately 30 per cent.
Roguing out affected plants in the
seed plot affords a practical though
perhaps not complete control of the
trouble.
Rot in Winter.
"The late blight of the potato caused
by Phytophthora Infestans and the rot
of tubers which follows in the winter
are too well known to call for descrip
tion.
however, that the planting of tubers
affected with Phytophthora decay af
It has recently been shown.
