The gazette-times. [volume] (Heppner, Or.) 1912-1925, 1916-03-16
NOW IS TIME TO Pre-.
PARE FOR CAMPAIGN
AGAINST POTATO PESTS
Diseases May Be Introduced on Seed
and Care Should BE Exercised
i'm observation-disclosures
Outlined.
By M. B. MCKAY
Assistant Plant Pathologist
n n

Particularly at this time of year il
is very appropriate to remind all po
tato growers of the diseases that may
be introduced on the seed, and tt
outline the methods of treatment
that have proven most effective in
their control. With this end in view
the following suggestions are offered
The diseases which are most apt to
be introduced with the seed are late
blight, common scab, Rhizoctonia
(Black Scurf), and wilt.
Late Blight: The fungus produc-
ing late blight on the potato vines
grows within the potato tubers caus-
ing a rotting principally in Storage.
Infection by this fungus may be dis
tinguished by darkened slightly
S unken patches on the surface of the
tubers varying in size from a quarter
of an inch in diameter to include the
whole potato depending ON the Sc
verify of infection and the storage
conditions. On cutting into the tub
ers, the tissue underneath the sunk
en- areas will be found darkened.
Such infected tubers when planted
may produce weak diseased plants
which may serve as centers for the
spread of the disease to the surround
ing plants. Because the fungus grows
deep within the potato tissues, no
method of seed treatment is effective
in killing the fungus. Consequently
the only way to avoid bringing in this
disease is to plant only potatoes that
are free from this fungus. However
all seed potatoes should be treated,
preferably by the method outlined
under common scab, to kill any or
ganisms that may be on the surface
of the tubers.
Common Scab: 1t has been dem
onstrated that seed treatment with
Mercuric chloride corrosive sublim-
ate) using one part to one thousand
parts of water is effective in controll-
ing common scab. In making this
up for use the amount to be used
should be carefully weighed out and
dissolved in small quantity of hot
water in clean wooden or porcelain
container, but never in metal con-
tainers as the solution reacts with the
metal and rapidly deteriorates. AT
ter dissolving it may be diluted to the
required amount in similar contain
ers and is ready for use. The pota-
toes should remain in this solution
from V to hours. This solution
should not be used more than three
times as dirt and trash carried into
it cause it to lose it's fungicidal pow
er. A convenient way to make up
this solution is to have the druggist
or other person from whom the mer
curic chloride is purchased, weigh it
out in small amounts to be dissolved
in given amount of water for the
required dilution. Four ounces of
mercuric chloride in thirty gallons
of water gives the required strength
and may be a convenient amount of
solution to use. 1t should be borne
in mind that this substance is very
poisonous, so should be kept away
from small children or stock.
Care should be taken not to rein
feet the potatoes by placing them
back in the same bags or storage
place unless they, too, are disinfect-
ed. All potatoes whether they show
evidences of scab or not, should be
treated before planting as they may
have been selected from badly dis
eased lots and are apt to contain
spores which might infect the new
crop if left untreated.
Rhizoctonia (Black Scurf) The
seed treatment recommended above
for the control of common scab also
kills any portions of Rhizoctonia that
may be attached to the tubers, and
should be used as a precautionary
measure on all potatoes used for
seed.
Wilt: At present the best known
method of control for this disease
is to plant disease free seed on rotat-
ed land. If the seed potatoes are
once infected, no method of seed
treatment is effective in killing the
fungi as they grow inside of the po-
tato tubers. Detailed inspection of
seed stock by cutting across the stem
end of the potatoes to determine
whether or not sign of strand discol-
oration extending down into the po-
tatoes occurs is highly desirable. If
very many tubers show such discol-
Grafton the whole lot should be dis
carded as seed to avoid introducing
this disease into the fields. 1t is high
ly important that the soil be kept as
free as possible from destructive par
asites.