The Yakima herald. [volume] (North Yakima, W.T. [Wash.]) 1889-1914, 1906-09-19

of the pear blight precede the general
pruning A special set of skilled helI
should do this work. Then the ordinary
primers can follow Even in ordinary
pruning. il is safe plan to disinfeci
when leaving each tree, in order to avoid
carrying the disease in case the prunei
has cut into an overlooked case Of the
blight.
There is question in regard to the
blight running down on the bodies of the
trees. Where the disease occurs on the
limbs. it can readily he sawed off, as the
removal of even the greater portion oi
the branches of the pear tree by nc
means destroys the value of the tree
II will push its new top vigorously and
in two or three years be in full bearing
again. Where the blight has run past
the main forks, however. a serious ques-
ton is involved. Where inefficient, I'M
skilled labor has to be used. and where
there is but little blight to work out.
we advise pulling out all trees where il
has run down on to the bodies, unless
some especially skilled hand can do the
work. A strip of cloth may be used to
wash such trees. Many growers, when
the matter is explained to them, con.
denim such trees and root them out, and
blight germs disappear and die very
shortly after they are exuded or wash
ed out by the rains from the twigs. 1t
also dies when the blighted bark dries
up It can only live along the advanc.
ing margin of the disease or in the thick
heshy bark which has been invaded by
he bacteria. and which does not have
time to dry out till the cool weather ap.
proaches. The thick bark on large limbs
and branches remains moist during a
long period, especially in the winter. BY
this method, the Importance of which
we shall show later, the germs are able
to carry over from one season to anoth.
err The germs are killed by high TEN.
peratures. They are wholly destroyed
when subjected to a temperature of IS
degrees centigrade for ten minutes. They
are wholly uniniured, however, by any
degree of cold likely to occur. Temper
atures of 40 degrees below zero have no
effect whatever. They may even be
frozen in this temperature but thaw
out Immediately when plunged into
warm water. proceeding with their ac-
tivities miniured. Cold retards their
development, but prolongs their life.
"The blight virus, being always a
sticky material, and usually requiring a
considerable mass, speaking from a mi
croscopic standpoint, to produce infec-
ton, is not blown by the wind. OF
course. the negative of such a PROPOSE
ton is hard to prove conclusively. but
careful experiments have been made to
test this matter by covering blossoms
with mosquito netting, alongside arti-
fcially infected flowers, and it was read
lily found that the uncovered flowers Wis
tied by insects contracted the blight.
while those covered by bags, mosquito
netting, or other material, which kept
out insects. remained free from the dis
ease. Occasionally humming- bird Wis
its the infected blossoms, as we have
observed in a number of instances
Doubtless birds, getting the g,,mmy
blight long distances. We look upon
insect distribution as by far the most
important means of infection, especially
on blossoms. in carrying the blight from
flower to flower tree to tree. and or
chard to orchard, although doubtless, oc-
ca Sionally long-distance distribution is
accomplished by birds or other agencies,
including man himself After the BIOS
soming period is over. or even before it
is entirely finished, blight may be found
attacking the tender tips Of growing
twigs. Our common insects have been
! found to be active agents not only in the
distribution of the disease, but in pune
turing the germs into the tissues While
it is easy to prove that insects causel
some of the infections of the twigs. it is
not absolutely certain that they do all
the inoculating Twigs are found with
starting in the axis of the leaves OF in
the tender bark where no puncture can
be found on careful examination 1t is
possible that the germs may enter in
damp weather through growth cracks
where the cuticle is ruptured. exposing
tender tissues. However. in the numcr-
Gus experiments / have made. atomizing
the germs from the tissues has result
ed in most cases, except where pune
turc through the euticle has been made
by pin point or where. by the breaking
of the leaf stem or some slight abrasion,
the skin has been ruptured, allowing
the germs to enter. We have, therefore,
two main methods of entry of the germ:
~ the blossom clusters. and (2) the
tender tips OF growing twigs. Blight oc-
casionally enters by third method d.
rectly into the tender growing feshy
bark, although, as a general rule, this
method OF entry is comparatively rare.
Sometimes the agency is plainly evident.
Sap suckers become infected by punctur-
ing cases Of hold-over blight and start
the disease in healthy trees. We have
several observations along this line, and
doubtless many more occur in nature
The presence of some skin puncturing
insect may doubtless cause a large num-
her of infections in certain orchard.
1t is even possible for the whiffietree or
implements used in cultivation TO trans
fer the infection, and the pruning tools
are certainly very frequent cause of
transmitting the disease.
The first factor is the presence of the
bacillus. The pear blight germ must be
present in the orchard or must be car
ried in there during the season in order
TO have the blight. No matter how un-