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

down on the bark of the twigs and
branches.
Son microscopic examination of the
diseased tissues, they are found to be
completely filled with countless millions
OF the pear blight germs. These germs
are mixed with a gummy, sticky mater
ial formed by the sap of the tree mixed
with gummy matter, produced by the
decomposition of the tissues.
The Microbe and Its Life History.
"The germ causing this disease is
named by bOtanists Bacillus amylovorus.
For our purposes of discussion, we may
call it the pear blight bacillus, or the
pear blight germ or pear blight microbe.
These germs, as you doubtless know,
are among the most minute of all living
things. The bacteria are plants, and are
the smallest living objects known. They
are SO low down on the scale that they
consist of single elliptical or rodlike
cell. They multiply by frightening a
little and then split in two. This pro-
cess can take place within half hour,
as have proved by observation, in a
hanging drop culture under the micro
scope. They are, nevertheless, capable
of being measured with the best mi.
croscopical apparatus. Our standard of
inca surement for these minute objects
is a micro millimeter, which is the
thousandth part of millimeter, and a
millimeter is about the one twenty.
fifth part of an inch. The pear blight
germ is from two thirds to three fourths
of micro millimeter vide, and from
LII
when it has reached its mature stage.
Curiously enough the young germs are
longer than the older ones, as when they
are growing rapidly their development
in length goes faster than their division.
This germ forms no spores, is very SEN
sitive to drying, and, in fact, is very
short-lived organism. 1t dies rapidly
in the blighting tissues as soon as they
have become fully killed by the germs.
tt can not Withstand drying, usually dy.
ing within two weeks to a month. 1t is
killed by exposure to direct sunshine in
a very few minutes, usually in less than
ten minutes, unless protected in the
bark or twigs. It rapidly dies when
washed into the soil. In fact, the pear
this, of course, simplifies the matter.
On the other hand, it is possible to
cut out the blight by carefully removing
the bark and even the discolored wood
entirely beyond the limits of the disease.
An inch or so at he side in the winter
and three to six inches at he bottom
may be regarded as safe, although such
cutting in the spring or early summer
invariably results in missing many
cases. AS a general principle, we believe
in drawing the line on those cases where
the blight has reached the ground. Even
here, however, it is possible to dig away
the soil and follow up the blight on the
roots. Some remarkable cases of this
sort have been attempted in the orch
ards of Mr.. Brink and Mr.. Thurber near
vacaville, Cal. From our standpoint, if
the pear blight is completely removed,
under disinfection methods, the job is
satisfactory. 1t remains, therefore, with
the grower to decide how much labor he
is going to undertake to save the trees.
Experience in other states has been that
where much work of this sort has been
attempted on the bodies, numerous fail
ures have resulted. There is also more
or less danger in such cases of the blight
in the sap wood. While the germs al
most wholly live in the bark, in the
rich sap wood of the Bartlett pear
and other tender varieties they have oc-
casionally spread out into the vessels.
1t is desirable, therefore, to leave all
such eradication work on the bodies 20
they can dry out, and after a month
or so, paint over the wound with white
paint, which would enable any slight
reddish discoloration from blight gum.
ming to be detected.
I believe that great deal of blight
eradication work in California could be
done to best advantage in the early
autumn, say in September and October,
or perhaps better results could be OBJ
tanned before the fall rains began, for
the drying influences help to finish up
and complete the eradication by the
knife; the work can be done, however,
at any time up to the opening of the
very first blossom.
Gas rule, spraying is of little use
in combating the pear blight, as I have
tried repeatedly, by using Bordeaux mix.
ture and other copper compounds. In
the blooming season new blossoms are
opening every hour of the day, and new
shoots are pushing forth subject to in