The Hood River glacier. (Hood River, Or.) 1889-1933, 1915-07-08
BIRKNER DISCUSSES
SCAB PATHOLOGY
From the Mosier Bulletin

himself by a study of national anC
state horticultural bulletins. prsctics
experience. and a thorough course Of
instruction under the Dsvey Tree Ex
pert company, of Illinois, was asked t
give TO the readers of the Bulletin the
pathology and history of apple scsb
Mr.. Birkner, who has charge of the or
chard Of F. A. Shogren. is of an inves.
tigating trend of mind, and is con.
stantly laboring for the control anC
elimination Of all orchard infections
and diseases.
Following is Mr.. Birkner's treatise
on the subject of apple scab:
Apple Scab Ventura inoequalis.)
This fungus disease is one of the
most destructive with which the apple
growers have to contend, owing to its
wide range and almost annual occur
anee. 1t will become injurious every
season if there is sufficient moisture at
the right periods for the spores to
mature and germinate.
unlike the other destructive dis.
eases, the scab may cause its injury
early in the season and even destroy
the crop without the orchardist reaiz-
ing the cause.
The winter stage is passed in the
dead leaves upon the ground. If the
weather is favorable, as the leaves are
developing in the spring, the asco
spores (spores in cases) mature and
are shot into the air to be caught by
the wind and carried to the young fruit
or leaves where they germinate and
start infection. A couple of cold, rainy
days during hte first month or two of
growth is most favorable for this to
happen.
AFTER the leaves and fruit are once
infected from these spores, the scab
spots produced are capable of forming
the summer spores (conidiophores) by
which the disease can be spread, at
any time when the weather conditions
are favorable, even up to the time
when the fruit is nearly ready to pick.
1.-THE greatest damage can be done
during rainy spell just before, during
or after the blossoming period. II the
conditions are favorable at this time,
the greatest injury Is caused by the
stems of the fruit becoming infected.
AS the scab develops, it interferes
with the proper flow of sap at this
point, preventing the fruit from devel-
oping. This injury causes the young
apples to fall just after blossoming or
as the June Drop"
'In this way, the crop is destroyed
so early in the season that the grower
does not realize the full extent of his
loss, or if he does, he generally attrib-
utes it to cold weather, imperfect pol
lenization of the fruit, or to a number
of other imaginary causes. When he
comes to know the real culprit, is usu-
ally the time when he begins to spray
to protect himself against this loss.
"If the fruit is sprayed with fungi
eide in such a manner as to keep it
thoroughly covered, the spores of the
fungus are uanble to germinate and
penetrate the tissue and consequently
cannot produce the scab spots. dry
spring that prevents the ascospores in
the fallen leaves upon the ground from
maturing, or the spores from germi-
mating and penetrating the tissues of
the leaves and young fruit, will accom-
plish the same result. To cause infec-
tion requires rainy spell of from Sc
to 48 hours. A cold drizzling rain
makes the ideal condition for the
spread of the disease.
"Ihe best protection by the fungi
eide is secured by spraying the trees
thoroughly as soon as the blossom buds
separate sufficiently to make it posi-
bic to reach the stems with the solu-
tion, but the work must be started in
time to complete it before the bios
SONS open.
"a second application should be
made just after the petals fall and a
third about three or four weeks later.
In case the trees are infected and the
weather rainy, a fourth application
should be made nine to ten weeks after
the petals fall, to prevent late infec-
tion of the fruit.
Historically, scab is not new dis
ease although of apparently recent oc-
curranee here. 1t is known practically
everywhere the apple grows in Amer
lea, Europe, Australia, New Zealand,
Africa, and elsewhere. 1t is essential
ly cool climate disease and in the
southern states only occurs in the ele-
waited districts.
"Scab was the first apple disease to
receive the attention of Investigators,
and its successful treatment was
worked out as early as 1891. In 1892
the Cornell station came to the reali-
zation of the Importance of early
spraying for scab. In this year the
first application. using Bordeaux mix
ture was made June l3, about one
week after the blossoms had fallen
from the trees. At the time of the
second spray, June %, small portions
affected with scab fungus could occa-
sionally be found upon the apples in
places thickly covered by the Bordeaux
mixture previously applied. These por-
tions were undoubtedly attacked before
the first spray was made" This spray
it will be seen was applied soon after
the petals fell but was too late. That
the first spray should be on before the
blossoms open was made evident by
H. e