The Owosso times. (Owosso, Mich.) 1897-1926, 1921-10-07
Horticultural
Hints
INJURY BY P0WDERY 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 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 fungus
that lives throughout the winter with
in the dormant buds and affects the
new leaves, tender twigs and blossoms
In the spring. Where 1t 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 containing
sulphur, finely divided.
The results of the investigations OF
the United States Department of Agri-
culture have been embodied in Il bull
letin, Control of Apple Powdery Mil
dew" which tells how to prepare and
apply the sprays. 1t also contains a
spraying schedule showing concisely
when and with what to spray. Copies
may be had by addressing the depart
ment at Washington.
The widowed shoots, which should
be pruned, are easily detected during
the dormant season by their gray or
sivcry appearance. Isolated infection
existing IN buds, however, makes II i'm
possible to control the disease by prun
ing alone. In the spring and summer,
particularly the former, the fungus APP
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 foliage
disease and a single infected leaf may
produce enough spores to infect many
trees It is important that every lear
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 tendency for 1t 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
the arsenical solution used at this time
for codling-moth control. This spray
Is very important and should not be
omitted.
A sulphur spray should be given
again about two weeks later. In the
hot interior districts of the Northwest
this constitutes the last time at which
sulphur materials may ordinarily be
used without danger of sulphur SUM-
burn"
The fourth application should follow
within two or three weeks, and at the
time of the second spraying, for cod
ling-moth control. If mildew continues
to be very serious In the orchard, sui
phur msterials must be used for ef-
fective control. They are recommends
ed In any case II the fruit crop is light.
Otherwise, one of the copper sprays
may be used.
Later spraylngs at intervals or TWO
or three weeks until the latter part OF
August Is recommended where the dls-
ease has become established.