Diseases of Potatoes
By H. L. Rees, Plant Pathologist of the State College of Wash
ington.
RHTZOCTONIA ot little potato dis
ease, also known as roaette, is with
the exception of the late blight the
most serious disease of potatoes in
"Western Washington. It is widely dis
tributed in the United States, Europe
and Asia and is of wide interest. It
has been known in Europe sinee 1851
and was first described in America in
1891. It seems to be general on the
Pacific Coast and is eortainly prevelant
in Western Washington, causing losses
last year as high as 50 per cent in some
fields.
Bymptoms There are several char
acteristic symptoms of this disease, some
of which however may be the result of
some other cause. When the plant is
attacked the stem is affected at the
ground, showing as black discolorations
and may girdle the stem for a half to
an inch above the ground. A gray,
moldy growth appears on this area. A
discoloration exactly like this results
from an attack of the black leg disease
but is not accompanied by the gray,
moldy growth. If the attack of the
Bhizoctonia disease is serious the stem
is rotted and the top wilts and dies
early in the season exactly as is the ease
with the black leg and Fusarium dis
ease. However, with the latter the dis
ease is not evident on the stem, the
leaves roll and the plant may or may
jrtot be killed at this time.
When Attack Cornea Later.
If the attack of Bhizoctonia is not
Bevere enough to kill the plants, or the
attack comes on later in the season as
is usually the case in Western Washing
ton, only the outer part of the stem will
fee killed. In this case the discolora
tion and the gray moldy growth appear
but the plant remains alive. The tops
usually develop peculiar twisted leaves
with the leaves crowded together in a
compact rosette-like appearance, not
fonnd associated with any other potato
disease. Aerial tubers small potatoes
on the vines are formed and the pota
toes in the hill are small and very
numerous. This is caused by the gird
fing of the outer part of the stem at the
ground.
The raw ford material from the roots
ascends en the inside of the stem to the
leaves where it is manufactured into
starch. But because the starch can only
deseend on the outside of the stem to
reach the roots and tubers, and sinee this
part is dead at the gronnd and prevents
taedescent of the starch, the starch col
leets on the vines and forms little po
tatoes. Sine little food reaehes the
tubers in the soil those developed there
we small and numerous,
Attacks of Xlack Leg.
Attacks of black leg result in much
the same way except that it kills the
plant early and only a few tubers de
velop either on the vines or in the
ground, and those ia the ground are usu
ally rotted at the stem end. If the plant
is alive late in the season and Ue tubers
ore numerous and not rotted at the stem
end the Bhizoctonia disease has in all
probability caused the trouble.
This disease causes the formation of
a network of fine, hair-like, brown
threads on the surface of the tuber,
which may or may not be large enough
in diameter to be visible to the naked
eye. These can only tie observed, how
ever, as the tubers are maturing and not
after digging. At digging time the dis
ease shows as brown, superficial, elevat
ed irregularly shaped masses, varying in
size from a small dot to a spot as large
as a quarter of an inch wide and half
an inch long. These may be mistaken
at first for soil particles but upon rub
bing they will be found to adhere. If
washed these masses are found to be
dark brown and adhering with a tena
city which necessitates hard scrubbing
or picking to get them off. Either of
these last two symptoms are peculiar to
this disease alone and their presence is a
positive means of identification. This
disease as far as is known does not fur
ther affect the potato except that there
Bre indications that it may spread in
Btorage, and most important its presence
enables rot-inducing organisms to enter
and rot the tubers.
Parasitic Fungus.
Cause This disease is caused by a
parasitic fungus which lives, and may
remain alive, in the soil for years. Pre
viously it has been thought that the
HOME ANT) FARM MAGAZINE SECTION
of healthy plants, lose the bright glint
ening appearance, become dull and roll
up. the roots are found to be partly dead,
are attacked early. Progress oi me un
ease finally turns the leaves yellow or
brown, and the top falls over. Frob
ably this action on the part of the af
fected plant has been the cauBO of not
recognizing the presence of this disease
as it is similiar to that of ripening. But
only manner by which it became present
was by being introduced on diseased
seed, but investigations of Dr. Wollen-
weber of the U. S. Department oi Agn-
, .., .....i.,.,.., ...... ........... ........ ......
DET EOT Showing Appearance of Healthy and Diseased Tops.
culture, in Western Washington indicate
that it is possibly present even in the vir
gin soil. When seed is planted in infec
ted soil, this fungus infects them regard
less of whether the seed have been treat
ed, or not The" potato stems are at
tacked and fungus spores are produced
the ripening is premature and conse
quently Tesults in a reduction of the
vield. If the diseased plants are pulled
up, the roots are found to be partly dead
brittle and frequently bearing a white
or pink mold. If the underground por
tion of the stem is cut across, a pro
DBT EOT Storage Bot Caused by This Fungus.
nounced brown discoloration Is visible
and can usually be found in the branch
es leading to the tubers.
External Evidence Bare.
When the potatoes are dug there is
rarely any external evidence of the dis-
in the gray, moldy growth before noted.
Later the fungus attacks the surface of
the tuber and forms the irregularly shap
ed masses described and known as scle
rotia. These are very resistant to un
favorable conditions and infect the soil
if diseased tubers are planted.
Control and Prevention There are
three points connected with this disease
which make the problem of control not
an easy one for solution, i. e., 1) the
possibility of the fungus being present
in the virgin soil, (Z) tne possiDinty
that the fungus may remain alive in the
soil for several years even when other
crops, if possible avoiding root crops and
the present methods of seed disrarection
used will not kill the fnngus as it exists
in the sclerotia. But the following ree
o.nmendations if carefully followed out,
have been found to be valuable in elim
inating and preventing this disease,
Rotation of Crops
If the soil is badly infected rotate
for three years at least, with some other
crops, if possible avoidng root crops and
using cereals or grass. In any case at
ways rotate crops, select the lignter typ
es of soil for potatoes, avoiding heavy,
noorlv drained soils, and maintain
eood physical condition or tne son Dy
deep preparation and culture. Keep
down the weeds. Do not plant affected
seed whether treated or not. Burn the
diseased refuse potato ctop material,
Clean culture methods are very import
ant and highly valuable in the control
of this disease.
Potato Wilt or Dry Rot.
Potato . wilt or dry rot, otherwise
known as the Fusarium disease, is not
equal in importance with the Bhizoc
tonia disease in Western Wasnington, ai
though the fact that it is present neces
sitates a warning, This disease seems
to be rather generally distributed over
the United States and appeared in West
ern Washington last year in widely sep
arated regions. In the whole country
the loss amounts to millions of dollars
annually, but the loss in Western Wash
ington is as yet unknown since many
growers are not aware of the presence
of the disease,
Symptoms If the Infection is severe
the disease first becomos noticeable
when the plants are about a foot high,
or if not, a little later. The leaves as
sume a lighter green color thaa those
ease. Occasionally the stem end may be
rotted similiar to the rot caused by
black leg, but when placed in storage
and left the disease UBuaiiy dccoium
apparent Beginning at the stem end
the tuber shrivels, the inside becoming
brown and rotted. The rot is not parti
cularly soft nor does it possess a mater
ially objectionable odor. But the pres
ence of this fungus makes the entrance
of rot inducing bacteria easy ana u
these enter they will cause a wet rot
accompanied by a very disagreeable
odor. Affected tubers may be detected
by slicing them, beginning at the stem
end. If there is a brown discoloration
underneath the skin and more or less
parallel to the surface tins disease
probably present. This discoloration
may be in shape of a continuous ring
or it may be discontinuous (See illustra
tion!. The distance to wnicn me -
coloration extends from the stom end
depends entirely on the length ot time
since infection occurred and the environ
mental conditions.
Cause This disease is caused by a
... I J- AVa
parasitic fungus wnicn iivra .u
soil, Low long is unknown. The fungus
enters the plants tnrougn me
roots and works upward in the vessels
which conduct the sap. These vessels
become filled and plugged with the
fungus itself and the flow of sap is pre
vented. This results in tho wilting and
premature death of the plants.
Rotate With Other Crops
Control and Prevention After the
soil becomes infected rotate with other
. .... .. nnt
crops for totiT or iivo yra".
use manure, on which diseased tubers or
vines have been thrown, for the potato
land. This disease apparently aoes no
oxist in the virgin soil and can only oe
introduced by planting diseased seeo.
Keep the disease out of the fields by
planting only clean seed. This may be
insured by using potatoes for seed
which do not show a discoloration at tne
stem end when eut. Treat as lor scbd
s that all spores on the surface may do
destroyed. Probably the best Method of
control is to plant only white varieties
of potatoes since in Western wasning
ton the red varieties seem to be parti
cularly susceptible while the white var
ieties are either not susceptible or only
slightly so.
Tho lTniti Blalu 1m T exported ill
vulucd at tl,735,099.
Now Bonth Walot in 11 iPrte4
and beere valued t S9S1.491.
.11 .vi ir T min it. I want
Tint's the money y ""'"S" . -h beller. In
$60.00 A WEEK AND EXPENSES
County Bales """S",, , TJ,," -irehip with me. No
the tqao deal, "gX, h. taken the country
WO.ll roll, handy as n ""'." "t 0U to h.odl.
BiTi. Iiou " (1;'nish''aemon.traUni( tub on liberal plan,
your county. I J'" Jr.",0a an let kif f r money in
I'm poeltWe absolutely - '-- Doath De(ore
a ween m '
I KMOW ITI
TWO SALES A -
1300 A MONTH
I. r
--j3sj ass
""y i - Taira nrnpri ritai
.11 ma neoin. . - it. n
hftine.
tie to
,1.v You ehould nn aa wen. -----SfKoo
.5n a MONTH. The work it ery
eaey, eleant, permanent,
meaoi a buaineat at your own.
Quick
Ohio, sot
r ?
s J
fateinatuiK.
It
H. 8. SOBIKSOH
President
913 Factories Bldg., Toledo, 0.
DEMON
BTRATIHO TUB
FTJBMI8HED
Little capital
needed. I grant cre
dit Help you out
Back you up Don't doubt
Don't hesitate Won't hold back-
Yon oannot lose. My other .men are
building honici, bank aocounie, so oan you.
Act then quick. BEND NO MONET just name on
penny post card (or tree tub offer. Hustle I
Pleasures at Bungalow City fojfa
Bayoeean are many hunting, trout sod deep-sea ""?Y Q W
fiahing, surl bathing, swimming in bay, artificial "
,urf Natatorium. and clam-baking are enly a few. MKtyT .
Bummer bungalows completely furnished, including V Jntfc&L it
water, electric lights, fuel, Janitor serviw-very "ijjfSJ I
moderate rates. BAT OCEAN y jsjS5Sg I