Montgomery County sentinel. [volume] (Rockville, Md.) 1855-1974, 1901-05-10
Aqrifultnral.
BLACK KNOT.
has o. Townsend, State Pathologist

Chas. o. Townsend, State Pathologist.
Black Knot is fungus disease Affect
ing both wild and cultivated varieties Of
plums and cherries 1t is an American
disease that has been known for more
than one hundred years, and so far as
can be determined had its origin in the
eastern part of the United States. For
long time the knots we're supposed to be
due to stings Of insects, but careful ex-
animation has shown that they are due
to distinct and we'll known fungus,
(Plowrightia morbosa,) To appearance
the knots are at first light brown in
color, but gradually deepen with age
until they become perfectly black. The
first indication that knot is forming is
a slight swelling under the bark, the
swelling increases until the bark splits
and the brown surface Of the knot ap-
pears. These abnormal growths may
form on any part Of the tree, i. e., either
upon the branches or upon the trunk.
Il is not uncommon for large number
of knots to appear upon the same tree at
the same time. The knots vary in size
and in shape from small, more or less
irregular, out-growths that are scarcely
visible, to ugly knots that are larger
than q mans head. Sometimes the knots
extend for Sc ,eral inches along the sur
face Of the branches upon which they
appear without at once destroying the
life of the affected branch However if
several Of the knots appear upon the
same tree it is only question of time
when the life of the tree will be des-
troyed.
The fungus that produces the Black
Knot forms two sets Of spores. one set
known as summer spores is produced
early in the spring, usually 10 May the
other set, called winter spores, is formed
10 the late fall or early winter, usually
in December. The summer spores are
capable of terminating just as soon as
conditions are favorable, hence if they
chance to lodge in suitable place upon
the tree they will form new knots The
winter spores do not germiuate immedi
ately, but retain their vitality until the
warm, moist days of spring come. when
they terminate and produce new knots
similar to those produced by the summer
spores. The fact that this fungus forms
two SETS of spores accounts for its rapid
spread and for its very destructive nature.
The spores seem to be able to cling to
almost any part of the tree, especially
where the bark is rough, hence we find
the knots forming most frequently in the
crotches of the branches The fungi
produced from these spores arc able to
penetrate the bark at all points even on
the trunks After the fungus has pen
etrated the bark and produced knot it
grows along between the bark and the
wood for several inches beyond the vis
BILE knot, so that the removal Of the knot
alone does not remove all Of the fungu4.
With these facts in mind the remedy
for the trouble readily suggests itself
In the first place the knots themselves
should be cut off and burned II they
are growing upon twigs or branches,
the affected parts should be cut off sew
eral inches below the knots in order to
remove all of the knot-producing fungus.
If the knots are growing upon the trunk
or upon large limbs they should b. cut
oli aud the bark for several inches in all
directions should be removed and burn
ed with the knots aud the surface should
be washed with fungicide Oron Sui
phate, one pound in twenty gallons of
water) If the trees are very seriously
infested they should be cut down and
burned completely and promptly. Hav-
ing removed and burned all the knots
the next step consists in spraying the
trees thoroughly with some fungicide in
order to destroy any spores that may be
lodging upon the branches. Probably
the most satisfactory fungicide is B1r-
deaux mixture which should be applied
Just as soon as the trees can be freed
from knots. The spraying should not
be confined to the diseased trees, but all
plum and cherry trees in the same vi
cinity should be sprayed in order to
destroy any spores that may be lodging
upon them. This treatment should be
repeated several times through April.
May aud June In spraying after the
foliage appears it must be remembered
that full strength Bordeaux mixture is
liable to injure the leaves of japan
plums, hence a mixture containing a
small amount Of bluestone (two pounds
in forty gallans Of water) and large
excess of lime should be used at that
time The earlier the knots can be cut
out in the winter the better and they
should by no means be left until the
foliage appears, as they are then OBJ
secured ard sometimes bard to find,
especially when they are small 1t is
therefore a safe rule to cut out the knots
whenever they are found. especially in
the winter and spring. When work
carefully done is followed by thorough
spraying it is entirely possible to con.
troll the Black Knot. Since the spores
Of this fungus may be carried long dis
iances by the wind or by insects it is
necessary that oil infested trees in any
plum or cherry growing section be prop
erly treated. 1t is therefore desirable
that all premises upon which Black
Knot is present be reported TO the State
Pathologist, who will see that the in
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