Lincoln County leader. [volume] (Toledo, Lincoln County, Or.) 1893-1987, 1910-07-01
FIRE BLIeHTIlN APPLE TREES
A Brief Description o, the Disease
and Its Cure.
By H. s. Jackson. Oregon Agricultural College.
Corvallis.

Fire blight is the most serious of all
the diseases which attack the pear and
apple. 1t is contagious disease of
bacterial originI which, Eunder proper
conditions, may attack. k.any part of the
tree. Besides the..pear and apple, the
ounce, wild crab apple, hawthorns,
mountain ash, serviceberry and some
other pomaceous. trees are subject to
attacks of this disease.
Myriads of germs are present in all
freshly blighted portions of the tree
and in the sticky ooze exuding from
cankers. The germs live almost en-
tirely in the sappy portion of the bark,
though in some vigorous growing vari-
eties of pears the germs have been
known to invade the sap wood to
limited extent. Fire blight occurs in
more or less severity in nearly all
parts of the United States where
pears and apples are grown.
In Oregon fire blight has appeared
in two general localities - one in the
Southwestern part of the state, includ-
ing the Rogue River valley, the other
in the Northeastern part.
Beginning in the spring the first ap-
parent damage produced by the disease
in an infected orchard is the blighting
of the blossoms. Infection is brought
about by insects, principally bees,
which have visited case of hold-over
blight and become covered with the
organisms contained in the sticky ex-
udation, inoculating the flowers in
their search for nectar. The organ
isms divide and multiply in the nectar
and are able to enter the living tissues
through the unprotected hectares.
Having entered the tissues they quick
ly blight the blossoms, pass down the
blossom-stem and into the fruit spur,
killing the tissues and cutting off the
leaves from water supply, causing
them to shrivel and dry, thus produc-
ing "fruit spur blight" The latter
occurs several weeks after blossom in
fection. In very serious cases nearly
all the fruit spurs may be blighted in
this way and the trees set no fruit.
Usually the germs die out and do not
grow into the twig or branch on which
the spur occurs, but occasionally the
germs may continue into the bark of
the branch at the base of the fruit spur
and form typical canker. Fruit spurs
on the larger branches are a fruitful
source of body infection and many
cases of blight canker originate in
this way.
The name "fire blight" is given to
this disease because of the characteris-
tic appearance of pear foliage on twigs
or branches which have been killed by
the organisms. The leaves turn black
as though scorched by fire and fire.
quently remain on the tree during the
following winter. 1t should be noted
that this color of the foliage is charac-
teristic of the pear when it has been
killed during the growing season. If a
grower not familiar with the pear
blight desires to known how the "twig
blight" looks let him girdle twig in
midsummer and watch the results.
The cankers are also quite character
istic, but are very variable in appear
ance. The disease progresses most
rapidly in the fleshy outer layer of the
bark and at first produces watery
appearance in the affected area. Later
the tissues of the bark are more or less
broken down and the cankers become
dark in color.
One of the most fruitful sources of
infection has been by the pruning
shears or saw. In pruning, if an
active canker is cut into, the tools be-
come infected and serve as inoculating
instruments to spread the disease.
The only method known of control
ling fire blight is to cut out all cases
of cankers wherever they appear.
Spraying with fungicides is of only
supplementary value and the various
blight cures are worse than useless.
Experience has shown that it is of
little permanent value to attempt to
cut out the fruit spur and twig blight
as they appear. Unless these forms
of the disease extend into the branches
on which they occur and canker is
formed the disease usually becomes
naturally limited and the germs gradu-
ally die.
The efforts of the grower should be
directed to cutting out all cases of
blight canker and body canker during
the fall, winter and early spring, when
the cankers have become more or less
limited in their growth and are not
actively spreading.
Summer cutting is intelligently ap-
piled is frequently of great value,
where there is only little
blight. In the autumn before the
leaves fall is a good time to do the cut
ting, as all cases of twig blight are
easily observed.
The trees should be particularly ex-
amined for cases of the collar rot. 1t
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