Biology Reference
In-Depth Information
after leaf fall in autumn with bordeaux mixture to
prevent infection through leaf scars.
Nectria magnoliae
Nectria Canker
, similar to
the preceding but
found on magnolia and
tuliptree.
Neofabraea
Anthracnose
.
Neofabraea
▶
perennans (
Gloeosporium
perennans
) (see
Pezicula malicorticis
).
Peren-
nial Canker
of apple, also bull's-eye rot of fruit.
Pezicula malicorticis (formerly
Neofabraea
perennans
(
Gloeosporium perennans
)).
Peren-
nial Canker
of apple, also bull's-eye rot of fruit.
The disease is much like northwestern anthrac-
nose. It often follows after winter injury or starts
at pruning cuts where aphids congregate, or may
appear after an application of wound dressing.
Fig. 4
Volutella Blight or “Nectria” Canker on Boxwood
▶
of the more important diseases of apple and pear
in Europe but is less serious in this country. In
eastern United States it is primarily an apple
disease; on the Pacific Coast it is more common
on pear.
Young cankers are small, depressed or flat-
tened areas of bark near small wounds or at base
of dead twigs or branches, darker than the rest of
the bark and water-soaked. Older cankers are
conspicuous and somewhat like a target, with
bark sloughed off to expose concentric rings of
callus. Cankers on elm, sugar maple and birch are
usually circular; those on oak irregular; on bass-
wood elongate, pointed at ends. If the canker is
nearly covered with a callus roll, it indicates that
the infection is being overcome.
Small red perithecia are formed singly or in
clusters on bark or on wood at margin of cankers.
Ascospores discharged during moist weather are
disseminated by wind and rain. Creamy-white
sporodochia protruding through recently killed
bark of young cankers produce cylindrical
macroconidia and ellipsoidal microconidia. Inva-
sion is through bark cracks or other wounds in
living or dying, but not dead, wood. Infection is
slow, with annual callus formation; only the
smallest branches are likely to be girdled. Youn-
ger, more vigorous apple trees receiving nitroge-
nous fertilizer appear to be more susceptible.
Control
Remove and destroy small branches
with cankers. Clean out trunk cankers and cut
back to sound bark; treat with bordeaux paste.
On theWest Coast spray pome fruits immediately
Nummularia
Ascomycetes, Xylariales
Stroma superficial, composed entirely of fungus
elements, covered with a conidial layer when
young. Perithecia flask-shaped, embedded in
stroma; spores one-celled, dark.
Biscogniauxia marginata (formerly
Nummularia discreta
).
Blister Canker
of apple,
crabapple, pear, mountain ash; also reported on
serviceberry, birch, elm, magnolia, and honey
locust. This is a major apple disease east of the
Rocky Mountains, especially in Upper Missis-
sippi and Lower Missouri River valleys, where
millions of apple trees have been killed. Large
and small limbs are affected. Cankers are dead
areas, up to 3 feet long, mottled with living wood
and dotted with numerous round cushions of stro-
mata, looking like nailheads. Perithecia, with
dark ascospores, are buried in the stromata;
hyphae bearing small, light-colored conidia
grow over the surface. The fungus enters through
branch stubs, bark injuries, and other wounds.
Control
Avoid especially susceptible varieties
like Ben Davis. Shape trees early to prevent
