Oxford Democrat. [volume] (Paris, Me.) 1833-1933, 1920-09-14
Rot Following Potato Blight.


The Maine Agricultural Experiment Sta
tion is frequently asked whether II Il
best to dig the crop at once, whore th'
foliage Is blighting badly, or to della!
harvesting till some time after the top
are entirely dead. This question hal
been answered by experimental worl
done both by this and the Vermont Sta
tiou.
In Maine In 1908 an equal area on 9
field planted with four early and foul
late varieties, both sprayed and nm
sprayed, was dug on September Z and
October 8 respectively. The potatoes
were placed In bags and at once stored ir
a cool, dry cellar. About January ]
both lots OF each variety were carefully
sorted to determine the total weights OF
the decsyed and sound tubers in each.
In every case, whether the variety was
early or late and whether the plots on
which they grew were unsprayed or par
TALLY protected from blight by the use
of bordeaux mixture, the loss was de-
cidedly greater In the case of the early
dug and stored potatoes. The differ
enoes were, of course, more striking
where no spray had been applied.
Greater losses were also obtained In the
case of the early varieties.
The record on January l Of the per
centages of loss from rot was made on
the basis of the total yield obtained for
each variety on each different date of
digging. The practical farmer is only
interested In how far early or delayed
digging influences the total amount of
merchantsble tubers which may be ex.
pected after all the rotting has appeared
in storage. Therefore only these figures
will be given here. On January about
81 per cent of mercbantable tubers of
early varieties, so per cent of the late or
42 per cent merohantable of all varieties
were obtained where the crop was dug
and stored on September Z, as compared
with October 8. In other words, on the
average, more than twice as much mer
charitable potatoes were obtained by de-
laying harvesting till after the plants
were entirely dead, than was the case
when the crop was dug while blight was
still active on the foliage and the spores
of the fungus which causes the rot were
being produced in large numbers.
The Vermont experiments were made
in 1902 and 1908. The first year the re-
suits were obtained from six fields on
four different farms near the station.
Equal portions of each field were dug on
four different dates, from August Is to
September 80. At least five varieties of
potatoes were represented, some early,
but most late. The soil on the differen.
fields varied from sandy loan to heavy
clay. All the fields showed blight and
some were badly affected on August Is.
On the date of the second digging, Sep
tember 6, the leaves on the plants on ali
the fields but one had been killed, and
here they were badly affected. On Sep
tember 1S the entire plants on all of the
fields were dead.
The total average per cents Of decay
for each date of digging, including the
rot which appeared In the storage OF the
first three lots up to September 30, were
as follows: Aug. 25, 35 per cent; Sept. 8,
20 per cent; Sept. 1s, 8 per cent; Sept.
80, 8 per cent. The amount OF loss from
decay varied with the character of the
soil where the potatoes were growing,
but the general trend was-the same. On
a light, well-drained, sandy soil about 10
per cent decay was obtained when the
crop was dug and stored on August 25,
and none occurred in the last two lots
dug. On the other hand potatoes, grown
on a heavy clay soil dug and stored Au-
gust rs, showed loss Of nearly 75 per
cent from decay up to September 80,
while those which remained In the
ground till this date showed only about
S5 per cent decay.
The second years work at Vermont
ground, slightly moist and sandy. On
the first date Of harvesting the foliage
was from one-third to one-hslf killed by
late blight; on the second date the leaves
were all dead, but the stalks green; on
the third the stalks were practically
dead; and on the fourth the tops were
entirely dead. The per cents of total rot
resulting from the harvesting and storing
at different dates were: Aug. 81, IS per
cent; Sept. ., 20 per cent; Sept. IA, 18
per cent; Sept. 81, II per cent; Sept. 2S,
7 per cent.
While the storage period In the Yer
mont experiments was much shorter
than in Maine 1t will be seen that the re-
suits obtained there are in entire agree
ment with those secured here. 1t is in
teresting to note that In 1908 in Yer
mont, as In Maine, the yield of sound
tubers was doubled as the result of delay
ing harvesting till some days after the
blighting tops were entirely dead.
It may, therefore, be stated quite con-
fldently that whore potato tops are
blighting it is best to delay harvesting, If
possible, till a week or ten days after the
plants are entirely dead and that longer
delay does no harm.
CHAs. D. WOODS, Director.