The Laurens advertiser. (Laurens, S.C.) 1885-1973, 1910-04-20
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CLEMSON EXTENSION WORK

1
Vat present is the Black Rot of Sweet
Potato. This disease occurs quite
commonly and oes considerable dam
age on potatoes both in the field and
in storage. The rot is caused by a
parasitic fungus which, under GER
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, discol-
ored areas on the surface of the po-
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 pene-
trate the skin and is apparently do
ing no serious harm. Later the rot
extends into the potato and causes
the affected area to turn black and
to emit the odor which is so charac-
teristic of rotton potatoes. When such
potatoes are stored in warm, moist
places, the rot producing fungus be-
comes especially active and b. means
OF tiny spores, which are produced in
small black pustules on the surface
OF the diseased areas, spreads rapidlv
from one potato to another. Under
such conditions the disease is also
spread by the filaments of the fungus
growing from the rotton potato direct
ly into adjoining healthy potatoes. In
this way the rot might spread to every
potato in 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 dan
ger of spreading the disease from one
field to another comes in bedding such
potatoes. Slightly diseased potatoes
seem to sprout as readily as healthy
ones, and the slips from such pota-
toes are diseased.
The disease transferred with such
slips to the field remains on the plant
and attacks the potatoes when they
develop. The fungus which causes
black rot also lives over 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:
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 1t is we'll to use vines instead 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, sc vines
growI from diseased potatoes, If plant
ed on land which is free from disease,
Will produce sound potatoes.
Nc", rs | have said black rot oc-
ours on the majority of the farms in
this state, and is responsible either
directly or indirectly for the loss of
thousand of dollars worth of potatoes
annually, so it is we'll for every farm
er to look out for it and guard against
its spread. If you have already bedd-
ed your potatoes and are not sure that
they are free from disease, plant as
much Of your crop as you can from
vines and on land not previously plant
ed 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 qualities of each.
Potatoes should not be banked for
two years in succession i'm the same
place, because the fungi which cause
these rots will live over i'm the old
banks and attack the new potatoes as
soon as they are banked. Where po-
tato 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 l per cent. solution of copper sui
phate (Blue stone)
III. w. Barre,
Bontanist S. c. Experiment Station.
Haven't you noticed that the best