Daily Kennebec journal. [microfilm reel] (Augusta, Me.) 1870-1975, 1918-09-12
LATE BLIGHT
OF POTATOES
How Does It Live Over the
Winter and How Does 1t
Spread?

Orono. Me, Sept. 1.-THE follow
ing was issued today from the Maine
Agricultural Experiment station
Charles D. Woods director:
Letters addressed to the Maine
Agricultural Experiment Station in
dictate that there is need OF wider
publicity relative to what has been
learned in Maine and elsewhere re-
sarding the above questions. re-
cent inquiry indicated that the
writer thought the disease lives over
winter in the soil. This is natural
inference since the organisms that
cause certain other diseases Of pota-
toes not only are carried by the seeu
tubers but persist in the SOIL Tor
varying periods after they are once
introduced. Since at the present
writing late blight can be found to
some extent in all but the most
thoroughly sprayed fields over con-
siderable area of the potato growing
sections Of the State. a discussion of
the manner in which the disease
spreads and the agencies concerned
therein is timely.
AS is well known late blight, often
incorrectly called rust" is caused by
q fungus which not only destroys the
foliage but causes destructive rot
of the tuber as we'll. Frequently the
greatest loss comes from tuber de-
cav. Typically this is dry rot,
causing a rustybrown discoloratlon
Of the outer portions of the tuber.
In severe outbreaks, occurring in the
field at harvest time and soon there
after, the disease on the tuber
progresses with great rapidity and
the entrance Of secondary organisms
produces a soft, mushy, sinking de-
cav which is too familiar to the ex-
perienced potato grower to require
description.
Fungi as a rule reproduce them
selves by means of relatively simple
bodies called spores which serve
similar purpose to that OF the seeds
| of higher plant%. The late blight
| fungus belongs to a class of which
several representatives produce a re-
productive body capable Of living
over winter out of doors. The re-
suits of certain investigations have
| indicated a tendency on the part OF
the late blight fungus to do this but
| there Is no conclusive evidence that
these bodies ever develop sufficiently
| to function in this way.
f0k a
blight lives over winter is by means
of tubers affected with dry rot. Re-
peated observations show that par
TALLY decayed seed pieces from such
tubers, when planted, are stimulated
! to early termination. The fungus
attacks the young sprouts and later
| spreads to the parts above ground
! 1t then throws out branches on the
surface upon which are produced
| large numbers of delicate, thin
walled spores. The spores fall or
nearby leaves of healthy plants
| terminate and send a fungous thread
into the tissues. Here the fungus
| branches and Families through the
| leaf, killing the tissues and eventual
| ~ producing the characteristic
brownish blotches on the leaf. The
under sides Of the outer portions OF
| these diseased areas. more especially
| in the morning or on rainy or cloudy
days, show a delicate frosty covering
made up of hundreds of fungus
branches, each carrying numerous
spores. All of the above takes place
before the owner of the field is aware
lower leaves of the healthy pants are
thoroughly coated with bordeaux
mixture early in the season and
spraying is followed up to protect
new growth the disease cannot get
beyond the first stage mentioned
above, for the protective spray Is on
the leaf in advance of the spore OF
the fungus.
The spores of the late blight
fungus are also readily killed by dry
ing. Hence hot sunshiny weather
checks the spread of the disease
while moderately COOL cloudy or
rainy weather favors it. The spores
have no means of getting from pant
to plant of themselves but they are
light and are very likely readily car
ried by the wind. Once the upper
leaves are diseased it is evident that
those below may be infected as the
result of spores falling on them. Rain
fall both by washing and scattering
is undoubtedly an important factor.
moreover If temperatures are right
the spores Of the fungus. instead OF
terminating directly. may each pro-
duce several free. swimming bodies
which move about in films Of rain or
dew ON the leaf. After they come to
rest they also throw out germ tubes