Daily Kennebec journal. [microfilm reel] (Augusta, Me.) 1870-1975, 1912-12-20
Agricultural Help
Scab Of Potatoes.

The Maine Agricultural Experiment
Station has been studying the question
of potato scab for several years. Some
very interesting results have been OBJ
tanned, a part of which have been pub
lished.
Practically wherever the potato has
been grown it sooner or later is at
tackled by ''scab." A study of tht
European literature on the subject a
once reveals the fact that scab is only
4 name for a type of disease and thai
several similar appearing diseases OF
this type, caused by as many individ'
ral parasites, have been recognized
and described.
|, In America it has been quite gener.
ally accepted for twenty years OF
more that practically all of the
potato scab is of one kind and caused
by plant parasite known as Oospora
scabies. There. is no doubt about this
fact With regard to the form appearing
IN Maine. The plant pathologiSt oil
this Station has isolated this organism
from potatoes from various parts OF
the State, and has grown it in pure
culture for over six years. During this
time young potato tubers have been
several times inoculated with these
pure cultures, under control conditions,
and typical scab spots produced.
In certain of the middle west and
western states some students of the
subject have in recent years expressed
the opinion that this is not the case
there and that fungus known as
Rhzoctonia is capable of producing a
form of potato scab under the climatic
a. H., -t..4s hot,
States. Rhizoctonia is a very common
fungus in the soil of Maine potato
fields. 1t produces in this State little
black and brown. oval, rounded oil
sometimes irregular bodies which
closely adhere to the surface of pota-
to tubers. but apparently do not harm
the latter in any way, not even in
juring the skin beneath. They are
most conspicuous when the potatoes
are beng washed before cooking and
are commonly thought to be hard par
ticles of black soil. In reality these are
not dirt at all but firm masses OF
sterile fungus threads which live over
winter on the potato tuber in semi
dormant state. AS yet we have no evil
dence that this fungus ever causes po-
tato scab in Maine, but this matter
will be thoroughly tested in the green
house this winter using pure cultures
of RhiZoctonia to inoculate potatoes
grown in pots of sterilized soil.
Recently there has come TO the Sta
ton from an adjoining county of Can
ada specimens of an entirely different
form of potato scab. This is the pow
derry or corky scab. 1t should not,
however, be confused with the danger
Gus wart disease or potato canker
sometimes called black scab. This lat
ter disease has not been reported as
being found on the mainland of North
America.
The powdery seab is one of the Eu-
ropean forms and. like the potato can
ker and blackleg disease. was probab-
ly brought TO America With seed pota-
toes. One writer states that THE
disease is rampant in the west of Ire
land, not uncommon in Scotland and
the north of England, but is rare IN
the SOUTH The same author states
that it is not known to attack any
other kind of cultivated plant so rota-
ton of crops is important in its con-
troll
The parasite which causes the pow
derry scab is one of the slime moulds,
somewhat similar to that which causes
the club root of the cabbage and allied
plants. In it's vegetative stage it is a
minute, naked. protoplasmic, amoe'
bold body, capable of independent
movement. and living in the surface
cells of the potato. Later the vegeta-
tive form is converted into mass of
minute. smutty spore-balls which
break forth on the scabbed area. Hence
the name ''powdery seab."
Powdery scab appears first as little
slightly raised pimples with a slight
discoloitation of the surface of the
tuber. These pimples later break open
and form spots which closely resemble
the ordinary type of scab found in
Maine If the spots are very nunler-
GUS and close together the resemblance
is quite marked and the diagnosis can
he made certain only by microscopic
examination. In moist soils. instead
of forming typical scab spots, These
diseased areas may become followed
out to a considerable depth till large
cavities, over an inch in diameter, are
produced
In connection with the studies upoT
poidIO SCdD HbW DtlHS tailtto oii ~
this Station we wish to examine affect
ed tubers from as many different parts
of Maine as we can obtain them. We
wish to determine especially if there
is more than one kind of scah in this
State. The potato growers can assis
materially in this work if those WHIT
read this article will each send MS
few specimens of scabby tubers. Care
should be taken in each case to en-,
close the sender's name and address
If desired shipping tags will be SEN
on request, which will carry the pack
age without payment of postage by the
sender Specimens which differ from
the ordinary type of scab in appear,
ance are especially desired.
Orone, Maine, Dec. II, 1912.
CHAS. d. WOODS,
Director