The Glenwood post., 1916-04-01
CONTROL Potato scAB
The treatment Of seed potatoes with


The treatment of seed potatoes with
formaldehyde or with corrosive sub
Innate has been recommended for many
years as preventive of scab and other
diseases carried on the tubers.
| Such treatment is, on the whole,
profitable, but has several limitations
| which should be clearly recognized to
prevent disappointment, according to
the specialists of the department. The
object of disinfecting seed potatoes is
to destroy the germs of scab and other
surface parasites which might other
wise be planted with the seed and in
feet the new crop. Only surface infec-
tions are reached by this method. 1t
is only partially effective against deep
pits of common scab. Formaldehyde
is less effective than corrosive subli-
mate against the black sclerotia>or rest
ing bodies of Rhizoctonia, or russet
scab, and against powdery scab. Meth
er chemical, as ordinarily used, will de-
stroy silver scurf. Either one will Kill
surface infections of blackleg, but
neither will reach the internal 1nfec-
tions common in tubers from blackleg
hills. Neither fusarium wilt nor late
blight infection in potato tubers eau
be reached by any seed treatment, nor
can any of the non-parasitic diseases
of potatoes, such as mosaic leaf roll
and curly dwarf, be prevented. See
Farmers Bulletin 544 for descriptions
of these troubles.
Clearly, therefore, the most import
ant precaution against these diseases is
to select clean, disease-free seed pota-
toes from healthy, vigorous plants, as
determined by field inspection during
the growing season and at harvest.
Seed treatment should then be applied
as an additional precaution. 1t will
not be effective, however, if the soil
where the potatoes are to be planted IS
already full of disease.
Soil Conditions and Potato Diseases
Soil conditions have an important re-
lation to potato tuber diseases, ana
many of these are widely spread
throughout the country, perhaps native
to some soils. Common scab IS ia
vored by neutral or slightly alkaline
soil, and seldom gives trouble in aclu
soils. It is therefore increased by lin
ing and by fresh stable manure, wood
ashes, and alkaline fertilizers, such as
nitrate of soda and ground bone, while
acid phosphates and sulphate of am
monia tend to diminish scab.
Rhizoctonia occurs to some extent IN
nearly all soils, but appears to attack
potatoes most when the conditions are
unfavorable to the best development OF
the potato plant. Bring the land to an
ideal state of tilth to minimize loss
from Rhizoctonia.
Powdery scab is worst on cold, weE,
or poorly drained soils. Blackleg, on
the other hand, is carried by infected
seed. No potatoes showing a deep
brown discooration at the stem end
should be planted
Sulphur tends to prevent common
scab. 1t is not substitute for corro-
sive sublimate or formaldehyde, but is
a good drier for cut seed. Applied to
scab-infected soils at the rate of 500
pounds per acre it reduces the scab,
but such heavy applications cannot be
generally recommended as profitable.
Preliminary experimental trials are ad-
vised.
How to Disinfect Seed
The formaldehyde treatment consists
in soaking the potatoes, before cutting,
for two hours in solution made by
adding l pint of formaldehyde to 80
gallons of water. The solution can be
used repeatedly. The gas treatment is
no longer recommended.
Corrosive sublimate is used at the
rate of 1-1,0OO for one and one and
one-half to two hours. Dissolve 2
ounces of the salt in hot water and
dilute to 15 gallons. This is deadly
poison. Use with great care. 1t must
also be kept in wood, porcelain or glass
vessels, as it attacks metal. 1t is more
effective than formaldehyde, particular
ly against Rhizactonia and powdery
scab. Do not uso the same solution
more than three times, as the strength
diminishes with each lot of potatoes
soaked.
To treat large quantities, set several
barrels on slightly elevated platform.
Fit plug in hole in the bottom Of
each barrel, fill with potatoes, cover
with solution, let stand two hours,