The Mobridge news. [volume] (Mobridge, Walworth Co., S.D.) 190?-1917, 1914-05-08
POTATO SCAB
BY n. S. COE,
Consulting Plant Pathologist, South
Dakota Agricultural Experiment
Station, Brookings.

disease of potatoes caused by a fungus
growth. The often repeated state
ment that potato scab is caused by
certain soil conditions, moisture con-
ditions. sod ground, etc. is erroneous
However, it is true that grub worms,
wire worms, or quack grass roots may
mar the surface of potato tubers, yet
these marks ale deep and generally IN
the form Of small holes and have moth
ing to do with potato scab. h spores
or germs are carried over winter IN
the scabby portions OF the infected
tubers; they may also be present IN
the dust clinging to unintected tubers.
These spores serve as one source or
infection for the following year SO it
will be impossible to grow a scab-free
crop Of potatoes from seed which Is
dnfected. The potato sCab disease also
lives from year to year in the soil, II
when soil once becomes infected 1t
will be impossible to grow a crop free
from scab, even though the seed is
created. for at least six years and then
only on condition that other crops,
such as turnips and sugar beetS are
mot grown in the rotation, since the
Scab disease affects these crops and
will have a renewed vigOr after grow
ing on these host plants for a season.
Manure from stock which have been
fed scabbv potatoes should not be car
ried to land where potatoes are used In
the rotation, since the scab organism
will pass through the digestive tract
OF these animals uninjured and thus in
feet the soil. However, it is safe to
feed scabby potatoes If they have been
cooked. for cooking will Kill the organ
ism. Potato scat thrives best in al
kaline soil and is checked by avidity,
@o the application of lime or ashes will
tend to increase the disease. while
the blowing under of green crops will
have a tendency to check it.
II we are going to control potato
scab we must not plant diseased tubers
without treating them with either for
Jmalin or corrosive sublimate. We
must also guard against planting pO-
ltatoes, treated or u~ntreated, on land
which is infected and we should espe-
-cially guard against injecting new
land. Only clean seed should De plant
ed with a clean drill on clean land II
we are going to raise potatoes not in
lfected with scab.
Seed Treatment.
Either formalin or corrosive subli-
innate may be used to treat diseased
rtubers for potato scab. However, since
corrosive sublimate is very poisonous
and is no better and more expensive
than fOrmalin. in the writer's estima-
ton. the formalin method is to be pre-
ferred. In treating potatoes with for
lmalin they should be soaked for two
hours in a solution consisting Of one
pound or pint of 40 per cen formalin
TO 80 gallons of water. The same so
luton can be used ove and over again
without losing it's strength. The pOta-
toes can best be handled by putting
them in gunny sacks oil other contain
,ers and immersing them in barrels or
watts Of the solution for the stated
time. The potatoes should not be left
in the formalin solution for a longer
period, since the terminating qualities
will be lessened. After treatment they
can be planted Immediately or opened
up to dry. Care, however, must DE
taken after treatment 70 see that they
do not come in contact with untreated
bins or seed. All sacks used in hand
ling the potatoes should be dipped in
the solution and the drill should be
thoroughly washed before planting
time.
In disinfecting large quantities OF
potatoes, %fumigation with Tornado
hyde gas has proven efficient. The
,potatoes should be placed in an air.
tight room in crates with Slated bot
toms and sides or in bins not over
six inches in depth. II the potatoes
are are in crates the crates should be
set at least two inches apart so as to
allow a free circulation Of the gas be.
tween them. Calculate the cubic con.
tents of the room and for every 1000
cubic. feet use % ounces OF potassium
,permanganate in a shallow layer in the
bottom OF a tub which has been placed
in the center Of the room and pour the
Iformalin, which has first been diluted
about one-third with water. over the
potassium permanganate. 1t would al
~ Do q good plan 90 sprSnkle the door