Shoshone journal. [volume] (Shoshone, Idaho) 1884-1931, 1921-01-14
Horticultural
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INJURY BY PoWDERY MILDEW
Specialists Advise Pruning and Spray
ing to Control Disease Attacking
Various Trees.

Removal of widowed twigs in win
ter pruning to eliminate sources of
holdover infection in dormant buds,
and repeated spraying during the
growing season are the important steps
In proper control of apple pOwdery
mildew, according TO specialists of the
United States Department of Agricul-
ture who have been investigating this
menace to apples and other fruits in
the Pacific Northwest.
This disease has occasionally done
severe damage to Eastern orchards
also, and is recognized as a cause of
damage to nursery stock. While it at
tacks apple trees chiefly, it also occurs
on pear, ounce, plum, cherry and june
berry trees. Some varieties of apples,
notably the White Pearmain and the
Winesap, are more resistant to this
malady than other varieties, though
none are wholly immune.
The disease is caused by a fungus
that lives throughout the winter with
in the dormant buds and affects the
new leaves, tender twigs and blossoms
in the spring. Where it is necessary
to spray for apple scab, and where
lime sulphur or other sprays are used
for this purpose, the treatment usually
suffices for mildew control. In regions
outside the range of apple scab, espe-
cially in arid districts, mildew must
be treated independently, the most eff
fective sprays being diluted lime-sul-
phur solutions and those co" tanning
sulphur, finely divided.
The results of the investigations Of
the United States Department of Agri-
culture have been embodied in bull
letin, Control of Apple POwdery Mil
dew" which tells how to prepare and
apply the sprays. 1t also contains
spraying schedule showing concisely
when and with what to spray. Copies
may be had by addressing the depart
ment at Washington.
The mildewed shoots, which should
be pruned, are easily detected during
the dormant season by their gray or
silvery appearance. Isolated infection
existing in buds, however, makes it i'm
possible to control the disease by prun
ing alone. In the spring and summer,
particularly the former, the fungus ap-
pears on the leaves, tender twigs and
fruit, and sends down tiny suckers
that penetrate the cells of the growth
beneath. These extract the sap of the
tree for the sustenance of the fungus.
Since this mildew is largely a foliage
disease and a single infected leaf may
produce enough spores TO infect many
trees it is important that every leaf
be covered by the spray. If the leaves
are thoroughly sprayed, twigs and fruit
will be covered at the same time. Lime |
sulphur possesses the best wetting !
power of any of the sprays ordinarily |
used, but there is a tendency for it to
form in drops, leaving unprotected !
areas. The use of such "spreaders"
as caseine and saponin with any of the
sprays is advised.
The first application should be made !
when the cluster buds have separated,
but before full bloom. 1t protects the
early foliage and blossoms and hard
ems tender varieties against subsequent
injuries from spraying.
The second application, or calyx
spray, should be applied as soon as
most of the petals have fallen. Lime
sulphur solution may be combined with
-he arsenical solution used at this time
or codling-moth control. This spray
s very important and should not be
omitted.
A sulphur spray should be given
gain about two weeks later. In the
lot interior districts of the Northwest
his constitutes the last time at which
ulphur materials may ordinarily be
Ised without danger of sulphur sun
urn"
The fourth application should follow
within two or three weeks, and at the
ime of the second spraying for cod
ng-moth control. If mildew continues
o be very serious in the orchard, sui
hur materials must be used for eff
ective control. They are recommend
d in any case If the fruit crop is light.
otherwise. one of the copper sprays
lay be used.
Later sprayings at intervals of two
r three weeks until the latter part OF
ugust is recommended where the dis
ase has become established.