Deseret evening news. [volume] (Great Salt Lake City [Utah]) 1867-1920, 1903-09-08
CAUSE AND PREVENTION
OF PEAR BLIGHT.

ture, written by Nj. -, Ndlie, asblhlunt,
In division OF vegetable physiology and
pathology. II It's suggestions are Wig
orously adopted the fruit-growers of
Utah need have little to fear from
this dreaded aud most contagious dis
ease.
There Is probably no disease OF fruit
trees so thoroughly destructive az pear
blight, or fire blight, which attacks
pears. apples and other pomaceous
fruits. Some diseases may be more
regular in their annual appearance,
and more persistent In their attacks
on the fruits mentioned, but when II
does appear pear blight heads the list
OF disastrous maladies. Again, no dis
ease has so completely baflled all at
tempts 10 find q satisfactory remedy,
and, notwithstanding the great progress
made within the last 10 years In the
treatment of plant diseases by spraying
and otherwise, pear blight, has until
recently continued its depredatio,,s UNI
checked. II Is now known, however
that the disease can be checked by SIM
ply cutting out the affected parts. This
was one Of the first methods trieo In
endeayoring to combat the disease.
The remedy which Is discussed In this
paper Is, In general way, similar TO
the old. In the process now proposed,
however there are three vital improve
ments, namely, the thoroughness and
completeness with which the work Is
carried out. the time when the cut
ting should be done, and u thorough
knowledge of the disease so as to know
how to cut.
The method of holding the blight In
check, Prof. Waite says, was discover
ed through a careful scientific investl-
CATION of the life history of the mi
crobe which causes IT, The lnvestiga-
lions were carried on in the field and
laboratory, and extended over several
years. In the short account which fol-
lows no attempt viii be made to enter
into the details Of the work, nor to in
troduce all the evidence to prove the
various statements, but simply to give
such points as Will enable the readel,
to intelligently carry out the method
advocated.
WHAT is PEAR BLIGHT?
Pear blight may be defined as a
contagious bacterial disease of the
pear and allied fruit trees. 1t attacks
and rapidly kills the blossoms, young
fruits, and new twig growth, and runs
down in the living bark to the larger
limbs and thence to the trunk. While
the bacteria themselves rarely kill the
leaves, at most only occasionally a.-
lacking the stems and midribs of the
youngest ones, all the foliage on the
blighted branches must of course even
tually die. The leaves usually succumb
In from one to two weeks after the
branch on which they grow Is killed,
but remain attached. and are the most
striking and prominent feature Of the
disease.
The most important parts of the tree
killed by the blight are the inner bark
and cambium layer of the limbs and
trunk. OF course, when the bark Of
limb Is killed, the whole limb soon dies,
but where the limb liz simply girdled by
the disease, II may send out leaves
again the next season and then die.
All parts of the tree below the point
reached by the blight are healthy, no
more injury resulting to the unaffected
parts Of the tree than II the blighted
parts had been killed by fire or grid
ling
Blight varies greatly in severity and
In the manner In which II attacks the
tree, Sometimes II attacks only the
blossom clusters or perhaps only the
young tips of the growing twigs; some
times 1t runs down on the main
branches and trunk; and again 1t ex-
tends down only few inches from
the point Of attack The sudden COLI
lapse Of the foliage on blighted
branches and trunk; and again 1t ex-
tends town only "a few inches from
the point of attack. The sudden coll
lapse Of the foliage on blighted branch
es has led many to believe that the
disease progresses more rapidly than
IL really does. 1t rarely extends
further than two or three inches from
the point of attack in one day, but oc-
casionally reaches as much as one
foot.
1t is an easy matter to determine
when the disease has expended itself
on any limb or tree, When II Is still pro-
crossing, the discolored, blighted por-
ton blends of gradually into the nor
mai bankibut when 1t has stopped there
is a sharp line of demarcation between
the diseased and healthy portions.
CAUSE OF THE DISEASE.
Pear blight is caused by very mi
mute microbe Of the class bacteria.
This microbe was discovered by Prof
n, j, Burrill, In 1879 and is known to
science az Bacillus amylovorous. The
following are the principal proofs that
II causes the disease. % The microbes
are found In immense numbers In
freshly blighted twigs; 60 they can be
taken from an affected tree and Guilt
waited In pure cultures, and in this way
can be kept for months at a time. 49,
by inoculating healthy tree with these
cultures the disease ~ produced, "a
In u tree so inoculated the microbes
are again found In abundance.
LIFE HISTORY OF THE MICRoBE,
Blight first appears In spring on the
blossoms. About the time the tree IL
going out Of blossom certain flower
clusters turn black and dry up as II
killed by frost. This blghting of BIOS
SONS, or blossom blight as II Is called,
IL one OF the most serious features Of
pear blight. One OF tho most remarkJ
able things about this disease is the
rapldity with which II spreads through
an orchard at blooming time. This
popularity has thrown much light on
the way the microbes travel about,
which they do quite readily, notwith-
standing the fact that they are sur
rounded and held together and 10 the
tree by sticky and gummy substances.
lUty Hlt dbit W iiNt anu luulilply w
the nectar OF the blossom, whence they
are carried away by bees and other in
scots, which Visit the blossoms In great
numbers for the honey and pollen. II
a few early blossoms are infected, the
insects will scatter the disease from
flower to flower and from tree to tree
until It becomes an epidemic In the or
chard. and the dead and blackened
branches are seen In every direction.
We shall see later how the first bios
SONS are infected. From the blossoms
the disease may extend downward into
the branches or run In from lateral
fruit spurs so as 10 do Il large amount
of damage by girdling the limbs,
Another way In which the blight
gains entrance In through the tips OF
growing shoots. In the nursery, when
trees are not lowering, this Is the us
l. A |. L. La 80.