Keowee courier. [volume] (Pickens Court House, S.C.) 1849-current, 1910-04-20
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. CLEMSON EXTENSION WORK J.
Article IL.
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Black Rot Of Sweet Potato.

One Of the most widespread and
most destructive diseases in this
state at present Is the black rot Of
sweet potato. This disease occurs
quite commonly and does considera-
bic damage on potatoes both in the
heldp and In storage. The rot is
caused by a parasitic fungus which,
under certain conditions, Is able to
pass from one plant to another and
thus spread the disease.
The trouble first appears as brown
or black patches or mottlcd, discol-
ored areas on the surface of the no.
tatoes. Quite frequently these dis
colored areas are observed in pota-
toes when they are dug, but at this
stage the disease only seems to pen
citrate the skin and Is apparently do
Ing no serious harm. Later the rot
extends into the potato and causes
the affected area 10 turn black and
to emit the odor which Is so charac-
teristic Of rotten potatoes. When
such potatoes are stored in warm,
moist places, the reproducing fun
gus becomes especially active, and
by means Of tiny spores, which are
produced in small black pustules on
the surface Of the diseased areas,
spreads rapidly from one potato to
another. Under such conditions the
disease is also spread by the fila
ments Of the fungus growing from
the rotten potato directly into ad-
joining healthy potatoes. In this way
the rot might spread to every potato
in a bank.
If slightly diseased potatoes are
stored IN a place where conditions
are unfavorable for the development
OF the rot, they frequently remain
partly rotted until spring. The real
danger Of spreading the disease from
one field to another comes in bed
ding such potatoes. Slightly diseas-
ed potatoes seem to sprout as readily
as healthy ones, and the slips from
such potatoes are diseased The dis
ease transferred with such slips to
the field remains on the plant ana
attacks the potatoes when they de-
velop. The fungus which causes
black rot also lives in the soil from
year to year and where potatoes are
planted every year on the same land,
the disease constantly gets worse.
TO prevent black rot, then, we
must (firsD secure disease-free seed
for planting; (second) avoid plant
ing potatoes on the same land for
two years in succession.
Quite frequently 1t is impossible to
secure potatoes for bedding which
are entirely free from disease. In
such case ii Is we'll to use vines in
stead of slips, for the fungus which
causes the disease remains in the vi
cinity Of the roots Of the plants. 1t
does not live In the vines and leaves,
so vines grown from diseased. pota-
toes, If planted on land which Is free
from disease, will produce sound DO
tatoes.
Now, as l have said, black rot oc-
ours OH the majority Of the farms in
this State, and Is responsible, either
directly or indirectly, for the loss Of
thousands OF dollars worth Of pota-
toes annually, so it Is we'll for every
farmer to look out for 1t and guard
against its spread. If you have al
ready bedded your potatoes and are
not sure that they are free from dis
ease, plant as much OF your corp as
you can from vines and on land not
previously planted in potatoes. When
you gather these potatoes, bank sep
arately the ones grown from the
vines and the ones grown from the
slips and note the keeping qualities;
Of each.
Potatoes should not be banked for
two years in succession in the same
place, because the fungi which cause
these rots will live over in the old
banks and attack the new potatoes
as soon as they are banked. Where
potato houses or cellars are used for
storing, they should be cleaned out
and disinfected before the new crop
is put in. This can be done by clean
ing then. out thoroughly and then
spraying the walls and floor with a
per cent solution Of formaline or a
per cent solution Of copper sui
phate (bluestone.)
III. w. Barre, ROtaniSt,
S. G. Experiment Station.