The Hood River glacier. (Hood River, Or.) 1889-1933, 1912-09-26
BLISTER MITE FORMS
CALLS In LEAVES

The pear leaf blister is a mite
spinder that does not exceed l-l0c
inches in length and oftentimes is
barely one half this length. Being SC
short and also very slender they are
only visible under good magnifying
glass. The work Of this pest is well
known, however, by the greenish.
pimple like elevations induced in the
young leaves. which, on enlarging be-
come red. brown and finally almost
black. When abundant and close to-
gether these malformations which are
commonly termed gals, may coalesce.
forming corky and more or less brittle
patches which if located near the mar
gins of the leaf may split open. Badly
infested leaves loose their functions
and drop. II is not uncommon to find
trees with portions of the young
growth partially defoliated. The mite
also attacks the young fruit but only
temporary and slight injury is done
usually around the blossom end.
The blister mite hybernates IN the
buds during the winter. AS the bud
scales and buds begin to grow the
mites feed at the base of the scales
until the blade Of the young leaf un-
folds, at which time they migrate to
the leaf into which they dig small
round holes, thus gaining an entrance
into the leaf where they feed upon the
tissues. The irritation causes the gals
which are the summer quarters of this
pest. The entrance to the summer
quarters may be seen by examining
the gals on the under side OF the leaf
with good pocket lens.
As soon as the mites are mature,
eggs are laid within the gals. The
eggs hatch in about one week. As the
family increases in size.some of them
leave their old feeding ground, crawl
upward on the stem until they come in
contact with tender leaf, then dig in
to the blade, forming new gall II
conditions are favorable reproduction
and migration takes place at such a
rate that all the new. leaf growth dur
ing the season becomes filled with the
gals. With the close of the season
the leaves begin to drop off and all the
mites leave their quarters, passing
down to the buds into which they force
an entrance. and in which location
they hibernate during the winter.
Since the mites migrate from the
buds to the leaves during the spring
and from the leaves to the buds during
the fall they are exposed for time
during each of the migratory periods.
The exposure is greatest during the
fall. In case of serious infestation
spraying should be done both fall and
spring. In case only one application is
made the work should be done in au-
tumn about the time one half to three
fourths the foliage has dropped. AT
this time the mites are working among
the hairs on the stems and buds at
tempting to find THEN way into winter
quarters. Spraying is effective if done
at the time the bud scales have opened
enough so that the young leaves are
just beginning to show their tips. 1t
is very evident that it is more difficult
to reach the pest at this time since
they are more or less protected. In
making the application all infested
branches should be thoroughly
drenched. The remainder of the tree
need not be sprayed. Lime-sulphur of
winter strength or black leaf 40 o.
l000) with two pounds of soap to each
so gallons of the tobacco solution may
be used. 1t must be borne in mind
that these spiders are extremely mi
mute and that they are more or less
protected, making it necessary to spray
with high pressure so that the spray is
driven in all crevices and comes in
contact with the spider since the spray
only kills by coming in contact with
the pest. w. II. Lawrence.
Pathologist.