The Wisconsin tobacco reporter. (Edgerton, Wis.) 1877-1950, 1914-10-02
,
! NOTE BOOK SKETCHES i.
SHED BURN OR POLE ROT.

SHED BURN OR POLE ROT.
From Bulletin No 237, University Agricultural
Station, by James Johnson.
The previously mentioned diseases of
tobacco have been maladles affecting
the living plant. Now we come to the
troubles of the grower and packer with
the product after it has been harvested
and is no longer in the living condition.
The parasites which can develop on the
living tissues of any host are necessar-
lily more or less limited. The sapro
phytes or organisms of decay which can
develop upon dead material are much
more numerous because of having US
ually a much wider range of substances
from which they can receive nOurlsh-
ment. Consequently we have num-
Der of organisms capable of growing
upon and decaying the tissues of the
tobacco leaf, during curing, fermenta-
ton and storage, when favorable con-
ditions for the development of these
organisms exist.
Shed burn, or pole rot as it is fire.
quently called, is recognized in mild
cases by the development of small dark
spots upon the curing leaf, and re-
sultant loss of elasticity of the affected
parts which renders it valueless for
wrapping purposes. These spots US
ually appear first near the veins or
midribs, presumably because of more
favorable moisture conditions at these
points; later they may run together
affecting the entire leaf which fire.
quently falls apart almost from its own
weight. In severe cases the entire
contents of the curing house may be
destroyed within two or three days.
Under practical conditions it is known
to be brought about by too close hang
ing and poor ventilation associated with
damp or foggy and warm weather.
These conditions analysed, simply mean
favorable amount of moisture, and a
favorable temperature for decay sur
rounding the Individual leaves. Ordi-
narily the disease does not occur until
some days after the tobacco has been
hung and has begun to change from
greenish yellow to brown, indicating
the death of the leaf tissue. Shed burn
has been shown to be due to the devel-
ment of fungi and possibly bacteria
upon the tissues of the leaf, resulting
in the destruction of the texture of the
leaf tissue These organisms of decay
are very commonly present in the soil,
and upon the leaves when they &c
hung in the curing shed. No pract cal
means for their eradication can be su5-
gested and consequently the only means
Of control lies in preventing their
growth by avoiding conditions favor
able for their development in the cur
ing shed.
and experiments both have shown that
the organisms which cause decay in
curing tobacco can make very little or
no growth at temperature below 90
degrees or a relative humidity below IS
per cent. Since temperature and hu-
midity are the controlling factors, it is
evident that anything which can be
done to regulate these factors without
interfering with the proper curing
processes of the leaf will satisfactorily
tend to check or prevent the disease.
Where natural curing is used, the
process becomes almost wholly depend
ent on weather conditions. Ventilation,
to be sure, with properly constructed
sheds and intelligent management, will
go long way toward preventing dam
age in the shed. If the weather condi-
tions are very unfavorable at the criti-
cal stages of curing, however, no
amount of ventilation can prevent dam
in constructing a tobacco shed to bear
in mind that it should be reasonably
eight so that in damp weather as
much as possible of the moist atmos-
phere can be kept out. On the other
hand, a good system of ventilators
should be present so as to allow rapid
reduction of the humidity of the inter-
ior of the shed when the weather be-
comes relatively dry: The up-to-date
ventilating systems of tobacco sheds
are composed of roof ventilators and
horizontal ventilators between the tiers.
When the roof ventilators and bottom
ventilators are open, under normal con-
ditions current of air circulates from
below upwards through the tobacco,
carrying with it the excess moisture.
This system will not work, however,
during unfavorable weather conditions,
necessitating a closing up of the shed
to exclude the moisture, or resort1ng to
artificial means of driving off the ex-
cess moisture Since tobacco will not
cure properly below so degrees and the
temperature most favorable for curing,
i. e., 80 to 100 degrees, is also favor
able to the development of shed burn,
in is evident that temperature regula-
tion in itself, even though it were prac-
tical, would not be of much value. 1t
is possible, however, to control the rel
ative humidity to a large extent by
controlling the temperature and regu.
lating ventilation. The amount OF
moisture that the air can hold varies
greatly with the temperature. The
ratio of the amount of moisture actual
ly in the atmosphere at any time to the
amount that can exist in the air at that
temperature is known as the relative
humidity. The capacity of the air for
holding moisture is doubled for every
increase of 18 to 20 degrees in temper
ature and the relative humidity is cut
down by one-half Consequently we
find that under normal conditions as the
temperature of the air increases in the
shed in the day time, the relative hu-
midity drops down below 80 per cent
and frequently as low as 30 per cent.
AS the temperature falls at night, how