The watchman and southron. [volume] (Sumter, S.C.) 1881-1930, 1910-04-16
BLACK ROT OR SWEET POTATO.
Clemson Extension WOrk-Article III.

most destructive diseases in this State
at present is the Black Rot of sweet
potato This disease occurs quite
commonly and does considerable
damage on potatoes both in the field
and in storage. The rot is caused by
parasitic fungus which, under cer-
tain 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 mottled, discolor-
ed areas on the surface of the pota-
toes. Quite frequently these discolored
areas are observed in potatoes when
they are dug, but at this stage the
disease only seems to penetrate the
skin and Is apparently doing no Sc
rious harm. Later the rot extends
into the potato and causes the af-
fected area to turn black and to emit
the odor which is so characteristic of
rotten potatoes. When such potatoes
are stored In warm. moist places, the
rot producing fungus becomes espe-
cially 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 filaments of the fungus grow
ing from the rotten pc cato directly in
to adjoining healthy potatoes. In
this way the rot might spread to ev-
cry potato in a bank.
If slightly diseased potatoes are
stored in place where conditions are
unfavorable for the development of
the rot, they frequently remain part
ly rotted until spring. The real dang
er Of spreading the disease from one
field to another comes in bedding
such potatoes. Slightly diseased po-
tatoes seem to sprout as readily as
healthy ones, and the slips from such
potatoes are diseased. The disease
transferred with such slips to the field
remains on the plant and attacks the
potatoes when they dvelop. The fun
gus which causes black rot also lives
over in the soil from year to year
and where potatoes are planted ev-
cry year on the same land, the dis
ease constantly gets worse.
To prevent black rot then we must
First secure disease free seed for
planting.
Second, avoid planting potatoes on
the same land for two years in sue
cession.
Quite frequently it is impossible to
secure potatoes for bedding which
are entirely free from disease. In
such case it is we'll to use vines in
stead Of slips, for the fungus which
causes the disease remains in the
vicinity of the roots of the plants. 1t
does not live in the vines and leaves,
so vines grown from diseased po-
tatoes. II planted on land which Is
free from disease, will produce sound
potatoes.
Now. as I have said, black rot oc-
ours on the majority Of the farms in
this state and is responsible either di-
rectly 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 it 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 crop as
you can from vines and on land
not previously planted in potatoes.
When you gather these potatoes,
bank separately the ones grown from
the vines and the ones grown from
the slips and note the keeping quail
tiles 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 them out thoroughly and then
spraying the walls and floor with a
per cent. solution Of formaline or a