The Western news. [volume] (Libby, Mont.) 1933-current, 1940-07-18

ms Dllgnt IS caused by bacterial
organism, a parasite quite unlike
insects, and fungi 1t attacks prin-
cipally the apple, pear, and ounce.
A very light infection that soon dies
out may occasionally be found on
stone fruits, and on service berry,
hawthorn. and some other pomace-
Gus shrubs. It never attacks will
lows, poplars, and other wild plants
that are not related to the apple.
The blight germs gain entrance to
the trees in several ways. ID
Through wounds made by pruning
tools, cultivators, etc., co through
bites of insects. particularly the
green aphis; CD through the open
flower. to which it is carried by
bees, ants, and other insects. and,
as has recently been shown, by the
wind. When once the germ gains
entrance it multiplies rapidly and
works downward through the bark
but may not cause any visible eff
feet until weeks after the infection
has taken place, so that the grower
is badly deceived as to just when the
disease was acquired.
The following symptoms are very
characteristic. If the infection be-
gins in flower cluster or in the
end of shoot, as it usually does,
the leaves first wilt and droop, then
turn brown in the apple and nearly
black in the pear. Soon they be-
come dry, hard, and brittle. The
bark of the affected twig likewise
becomes slightly darkened in the
apple and nearly black in the pear.
The line between the diseased and
the healthy bark is not sharp and
distinct during the growing season,
SO that it is often difficult to de-
termine just how far the disease
has progressed. and it is usually
farther than an inexperienced per
son would suppose. On cutting in
TO the diseased bark one finds the
inside at first pinkish in color in
stead of healthy green, but when
it has been diseased for a few weeks
it becomes darkened through to the
wood, which remains nearly white
and normal. This is essentially
bark disease and will continue. in
varieties, to run down
the limbs and trunk into the roots.
sometimes killing the tree outright
in a single season It practically
ceases to spread downward at the
end of the growing season and be-
comes dormant during the winter,
but with the opening of spring ac-
hvlty is renewed and another
stretch of bark is killed. This con-
tinues until the tree is completely
overcome. Sometimes the attack be-
gins in the Water-sprouts at the base
of the tree. Under these circum-
stances it reaches the roots in
few weeks, where it can not we'll be
treated, and the case becomes prac-
tically hopeless.
There is general impression
that plants or animals that are very
vigorous resist diesase better than
those that are generally unhealthy
and stunted This certainly is not
the case with apple and pear blight.
In slow growing trees the disease
makes but moderate progress down
ward through the bark and gener-
ally dies out without reaching the
larger limbs, while in very rapidly
growing, vigorous trees it progress
es rapidly, sometimes running
through the bark from the tips to
the roots in a single season.
Often there may be seen on the
blighted leaves and branches. and
especially on the blighted fruits.
yellow exudate in tiny droplets. or
even in larger quantities running
down the tree. This contains enor
nous numbers of the germs of the
disease and is freely visited and
eaten by ants, wasps, bees, and
probably other insects, that carry
It to other trees, especially to the
flowers, where fresh attack be-
gins. A single bee may thus infect
several hundred flowers during the
season, and swarm of bees could
infect many thousands. This ac-
counts IN most cases for the very
extensive and sudden attacks that
many orchards have suffered.
When the healthy leaves have
fallen in the autumn, those on the
diseased twigs and branches still
cling to the trees, where they are
very conspicuous. At this time also
the diseased bark has turned quite
dark, especially in the pear. and
the line between it and the healthy
bark is more sharp and distinct
than during the summer season.
Here, In the deeper layers of the
bark, in the line between the di-
seased and the sound tissues. the
bacteria that caused the blight live
over the winter. On the assump-
ton that they do not live over in
the ground or anywhere else ex-
cepting the region just indicated
the following treatment is advocated
BY the United States Department of
Agriculture and by many of the ex-
pertinent stations, and is extensive
ly practiced by orchardists with
some measure Of success.
Treatment OF the Blight
In a single sentence we can saw
that the only known method of
curing blighted tree is to cut out
and burn all affected parts. This
seems simple enough, but there are
important details that determine be-
tween success and failure. AS a mat |
.er of fact, very few inexperienced
men are successful, largely because
they will not pay close enough at
,entlon to these important details
VI, E.