Question:
What makes potatoes
scabby? What
can be done?
Lynelle
Minnesota
Answer:
Common scab is most
prevalent and severe
in neutral (pH 7) or
slightly alkaline
soils. The optimum
pH for scab
development is from
pH 6.0 to 7.5. In
general, scab is not
a serious problem in
soils with a pH of
5.5 or lower. The
scab organism is
very sensitive to
soil moisture, pH,
and temperature. The
incidence of the
disease is generally
greater in sandy or
gravelly soils than
in heavier soils.
The amount of soil
moisture at the time
of tuber development
is very important.
Several practices
can limit the
severity of scab.
1. Planting
resistant varieties
is the most feasible
and practical
control. Varieties
showing some level
of scab tolerance
include: Norchip,
Norgold Russet,
Reliance, Russet
Burbank, Shurchip,
Norland, Hi-Plains,
Pungo, Redskin,
Russet Sebago,
Shoshoni, and
Superior.
2. Avoid
planting seed
exhibiting scab
lesions.
3. Crop
rotation in which
potatoes will be
planted in the same
area only once every
3 or 4 years. Avoid
rotating with root
crops; instead plant
grains, grasses, or
legumes.
4. Maintain
good moisture levels
in the soil while
tubers are
developing.
5. Avoid the
use of fresh manure
just preceding the
potato crop.
6. Chemically
treating seed pieces
before planting with
the fungicide Captan
will effectively
reduce seedborne
scab inoculum. You
may want to avoid
the problem
altogether by
planting your
potatoes above
ground. You can
purchase
"potato
barrels", or
simply create your
own. Use a piece of
chicken wire or
hardware cloth to
create cylinders
about 3 feet tall
and 2 feet in
diameter. Loosen the
soil underneath for
good drainage, and
set the cylinder in
place. Place a layer
of hay in the bottom
of the cylinder, and
add a few inches of
soil. Then plant
your seed potatoes,
about 4 per
cylinder. Cover with
another few inches
of soil. Once the
potato stalks have
grown 4-6", add
a layer of hay, then
more soil.
