Middlebury register. (Middlebury, Vt.) 1886-1937, 1890-06-06
Sarm Copies.
THE POTATO ROT AND APPLE
SCAR


SCAB.
bulletin of the State Experiment Station.
The Potato Rot and Blight.-Judging
from the census report the annual potato
crop of Vermont is between four or FIVE
millions of bushels. How much greater
it would be were it not for bug, scab,
blight and rot, we will not attempt to
say. 1t is probably an underestimate to
say that one-half of the crop in this State
was lost last year from the blighting of
the vines and the rotting of the tubers in
the field and cellar.
The weather of last summer was pecu-
liarly favorable for the development
of diseases of this nature, but unless
preventive measures are taken much
loss may be expected again this season
because of the large amount of infected
seed planted this spring.
Cause The blight of the stops" and
the dry rot of the tubers are both caused
by the same thing, minute fungus.
The wet rot of the tubers follows the dry
rot as soon as the tubers are weakened or
killed by this fungus. The fungi which
cause the various rots, mildews, rusts
and smuts of our plants are themselves
plants of a low order which live within
the tissues or upon the surface of higher
plants and feed upon the juices or sap
of their hosts. If numerous, they serious
ly injure or even kill the plant they live
upon.
If the brown tissue of a potato affected
with the rot be examined under micro
scope of high power the minute thread
like branches or tilaments of the fungus
that causes the rot and blight will be
found running through it III every drec-
ton. If such pOtatoibe planted, the
thread-like filaments of the fungus grow
up in the tissues of the young sprout,
and enter the leaves as they are develop
ed. In midsummer the fungus produces
its spores, microscopic bodies which cor
respond to the seeds of higher plants.
These are borne upon minute branches
which are thrust out through the pores
of the potato-leaf, chiefly on the under
side. These spores are produced in i'm
mense numbers and are so very small,
about one-thousandth of an inch in diam
ter, that they are scattered by every
breath of wind. If the conditions of
moisture and temperature are favorable,
they germinate as soon as they fall upon
a potato-leaf, and thus the infection
spreads with marvellous rapidity. 1t is
often only few days, in some fields OBJ
served last summer only few hours
from the time the first indications of the
blight are seen until all the plants of the
field are blackened, decayng mass. 1t
is possible that the blight may spread
from a single diseased plant over the
whole of the largest pOtato-field in the
State. We will leave a discussion of the
passage of the rot from the tops to the
tubers for future bulletin, and now
speak of treatment to save the tops from
being killed.
Remedies Nothing can be done to kill
the fungus in the plant. but we have
great reason to hope that it is possible to
kill the spores, and thus prevent the
spread of the disease from the infected to
the healthy plants. This can be done by
spraying with a mixture of copper sui
phate (blue vitrioD and lime, known as
the Bordeaux mixture. 1t was tried here
ana at several of the other experiment
stations last summer and in all cases
proved beneficial.
The potato field at the experiment
farm was about three-quarters of an acre
in extent. The blight first appeared in
one corner of it. and had spread in a
diagonal direction across the field. follow
ing the direction of the wind, before any
steps could be taken to check it. The
field was then sprayed with the Bordeaux
mixture. The work was begun at one
side of the field and the rows were spray
ed for some distance beyond the middle,
The next time the work was begun at the
other side of the field and again con-
tinued some way beyond the middle
The applications were made one week
apart. A number Of rows In the middle
of the field were thus sprayed twice.
Nearly all of the plants at the ends of
the field rotted, while two-thirds of those
in the middle of the field, and which were
sprayed twice, were saved.
Ii is necessary to consider in this con-
nection that the fungus had spread to a
considerable extent before any spraying
was done; and further that even where
sprayed twice the application was a
mild one, since only two-thirds the
amount of copper sulphate given in the
directions below were used, and twenty
two gallons made to extend over nearly
three-quarters OF an acre. Judging from
this experiment and those of others
made last year, we believe that by APP
plying the Bordeaux mixture in time