Charlevoix county herald. (East Jordan, Mich.) 189?-1953, 1916-04-08
CONTROL POTATO SCAB

formaldehyde or with corrosive subli-
mate 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 infect
the new crop. Only surface infections
are reached by this method. 1t is only
partially effective against deep pits of
common scab. Formaldehyde is less
effective than corrosive sublimate
against the black sclerotia or resting
bodies of Rhizoctonia, or russell scab,
and against powdery scab. Neither
chemical, as ordinarily used, will
destroy silver scurf. Either one will
kill surface infections of blackleg, but
neither will reach the internal infec-
tions common in tubers from blackleg
hills. Neither fusarium wilt nor late
blight infection in potato tubers can be
reached by any seed treatment, nor can
any of the nonparasitic diseases of po-
tatoes, such as mosaic leaf roll, and
curly dwarf, be prevented. See
Farmers Bulletin 544 for descriptions
of these troubles.
Clearly, therefore, the most important
precaution against these diseases is to
select clean, disease-free seed potatoes
from healthy, vigorous plants, as de-
termined 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, ii the soil where
the potatoes are to be planted is already
full of disease.
SOIL CONDITIONS AND POTATO
DISEASES
Soil conditions have an important
relation to potato tuber diseases, and
many of these are widely spread
throughout the country, perhaps native
to some soils. Common scab is favored
by neutral or slightly alkaline soil,
and seldom gives trouble in acid soils.
It is therefore increased by lining and
by fresh stable manure, wood ashes,
and alkaline fertilizers, such as nitrate
of soda and ground bone, while acid
phosphate and sulphate of ammonia
tend to diminish scab.
Rhizoctonia occurs to some extent in
nearly all soils, but appears to attack
potatoes most when then the conditions
are unfavorable to the best develop
ment of the potato plant. Bring the
land to an ideal state of tilth to minim-
ize loss from Rhizoctonia.
Powdery scab is worst on cold, wet,
or poorly drained soils. Backlog, on
the other hand, is carried by infected
seed. No potatoes showing a deep
brown discoloration at the stem end
Il
should be planted.
Sulphur tends to prevent common
scab. II is not a substitute for cor
rosive 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 can not be
generally recommended as profitable.
Preliminary experimental trials are
advised.
HOW TO DIsINFECT SEED
The formaldehyde treatment consists
in soaking the pototoes, before cutting,
for two hours in solution made by
adding one pint Of formaldehyde to 30
gallons of water. The solution can be
used repeatedly. The gas treatment is
no longer recommended.
Corrosive sublimate is used at the
rate of IL, 900 for one and one-half to
two hours. Dissolve ounces Of the
salt in hot water and dilute to l6