Watertown republican. [volume] (Watertown, Wis.) 1860-1906, 1902-07-26
Apple Blight.

Numerous inquiries have been recent
ly received at the Wisconsin Agricultur-
al Experiment Station regarding injury
to apple and pear trees. Affected twigs
have usually been enclosed which were
black and shriveled, the attached leaves
being Drowned as if by fire. The injury
in every case was caused by "blight."
What is blight? The disease known
'blight," 'pear blight" and fire blight, "
is contagious bacterial disease attack
ing. the apple, pear, ounce and allied
fruits. 1t frequently attacks the wild
crab and is occasionally found in the
mountain ash.
What it does: Blight assumes two
different modes of attack known as twig
blight and blossom blight, the cause Of
the two being the same. In the former
the new shoots, growth of the current
season, are affected; in the latter the
blossoms and fruit spurs are destroyed
and commonly portion Of the adjoining
main branches.
The conditions that xfavOr blight: A
wet season favOrs blight; dry season
hlnders it.; very dry season entirely
checks it. The blight microhe soon per-
ishes when exposed to drying conditions.
Unfortunately, conditions that favor
growth of the tree favor blight. Heavy
pruning during the dormant period in
duces strong growth of new wood and
favOrs the development of the blight
germ. Trees heavily manured with
barnyard manure are apt to be more af-
fected than those not SO we'll fed.
Trees that are we'll cultivated often
blight more than those growing in sod.
| How distributed: Blossom blight is
undoubtedly distributed by bees and
other insects that collect honey and pol
len. The blight germs find lodgm ent
in the notary where they multiply rap
idly and are carried from tree to tree at
blossOming time. The blight microbes
are held together by a sticky substance
and are not therefore readily dissemina
ted by the wind. In the case of twig
blight they presumably remain within
the affected tissues until set free by
some agency that ruptures the bark.
The mode of infection in this form of
the disease is not we'll understood but
presumably occurs through the agency
OF insects. Several species of minute
insects inhabit the terminal buds Of
growing shoots.
Remedies: As the blight organism
works wholly in the inner TISSUES of the
plant, it is not possible to control it by
spraying. The only remedy, at present
known. is to remove and destroy, by
| burning, the affected twigs. AS the
blight does not, presumably, live over
winter in the ground, it may be checked
If not eradicated by this method. Usu-
ally. the blight progresses most rapidly
during the period of most rapid growth
of the. trees and generally stops at the
end OF the growing season. At this
| time there is the usually distinct line of
separation between the live and dead
wood. All parts below this line are
healthy and may be preserved. In some
cas- es, however. especially those that ap-
pear late in the season, the line Of de-
maIcatien ia not distinct and the field
| OF injury blends gradually with that of
| the uninjured bark. 1t is essential then
to exercise great care in cutting to re-
move those cases of "hOld-Over" blight.
In removing blighted twigs it is advisa-
BILE to cut far enough back to insure the
removal OF all affected tissues. The re
mOval OF six inches of sound wood below
the line OF separation is not too much
This work is best done in the fall before
the leaves have fallen as the blighted
twigs may then be more readily observed.
The shears or other cutting instruments
should be dipped frequently in an anti
septic solution to guard against trans
! fering the disease to uninfected branch
es. A five per cent. solution of formalin
will answer the purpose. A cloth mois-
ened with this may be carried and used
to wipe the shears. In the case of bloom
blight on old trees nothing of value can
be done as the disease extends through
the fruit spurs to the main branches. 1t
does not follow that such trees will be
killed as the disease may not progress
far enough to girdle the main branches,
only Affecting the portion adjoining the
spurs, in which case recovery may be ex-
pected with no further damage than the
loss Of the ftuit spurs.
f. CRANEFIELD,
Assistant HOrticulturist.
Wisconsin Agricultural Experiment
| Station Madison Wis