Biology Reference
In-Depth Information
numerous fruiting bodies on exposed wood and
callus layer. Killing of successive callus layers
results in a canker similar to European apple
canker. The disease is not common enough to
be serious.
Nectria coccinea var. faginata
Nectria Beech
Bark Canker
on beech in the Northeast. The dis-
ease occurs solely in connection with the woolly
beech scale insects (
Cryptococcus fagi
and
C.
fagisuga
), but it has caused high mortality in
Canada, killing 50 % of beech stands; it is epi-
demic in Maine on American beech and is now
present in much of New England and New York.
The scale nymphs, covered with a woolly
white down, cluster thickly around cracks and
wounds in bark, often making trunk and branches
appear to be coated with snow. The small yellow
larvae establish themselves on the bark in
autumn, each inserting its sucking organ, stylet,
into the living bark, which shrinks and cracks.
Nectria
enters through these cracks and kills sur-
rounding tissue in bark and cambium. When the
cells are dead, the insects can no longer obtain
food; therefore, they disappear.
White pustules of sporodochia are pushed out
through dead bark, bearing elongate, three-to
nine-celled, slightly curved macroconidia. Red
perithecia, slightly lemon-shaped, appear in clus-
ters on the bark, often so abundant that the bark
appears red. After ascospores are discharged, the
upper half of the perithecium collapses and sinks
into the lower. The eventual canker is a deeply
depressed cavity surrounded by callus. After the
cambium dies,
Nectria
Ascomycetes, Hypocreales,
Nectriaceae
Perithecia bright, more or less soft and fleshy, in
groups, basal portion seated on a stroma; spores
two-celled, hyaline or subhyaline (see
Fig. 1
).
Nectria cinnabarina
Dieback
,
Twig Canker
,
Coral Spot
, cosmopolitan on hardwoods, most
common on maples but also found on ailanthus,
amelanchier, apple, crabapple, apricot, ash,
blackberry, chokecherry, beech, birch, elm, hick-
ory, horsechestnut, mimosa, linden, paper mul-
berry, pear, peach, sophora, locust, and honey
locust. It may also appear in stem cankers on
vines and shrubs-ampelopsis, barberry, box-
wood, callicarpa, cotoneaster, currant, goose-
berry, fig, honeysuckle, kerria, California laurel,
rose, and syringa. The fungus is widespread as
a saprophyte. On ornamental trees and shrubs it is
weakly parasitic, producing cankers around
wounds and at base of dead branches or causing
a dieback of twigs and branches.
On maple, the fungus is more pathogenic,
killing twigs, small branches, young trees, and
girdling larger branches. It is more frequent on
Norway maple and boxelder; it may also invade
red, sycamore, Japanese, and other maples. First
symptoms are small, depressed, dead areas in
bark near wounds or branch stubs. Conspicuous
flesh-colored or coral pink sporodochia, formed
in dead bark, bear conidia. Later the pustules turn
chocolate brown and form pockets, in which
perithecia are produced. The canker is most
common in severely wounded or recently
pruned trees. Sapwood has a greenish discolor-
ation. Open cankers are eventually formed with
successive rolls of callus. Remove diseased wood
and
the leaves wilt;
the twigs,
branches, and roots finally die.
Control
Ornamental trees can be sprayed or
scrubbed to kill the insects. A dormant lime sulfur
spray is very effective. Oil sprays will kill the
scale but may injure beech. Late summer
spraying for crawlers can supplement the dor-
mant spray.
Nectria desmazierii (
Fusarium buxicola
,
Anamorph).
Canker
and
Dieback
of boxwood
(see
Fig. 4
).
Nectria ditissima Sometimes reported but not
confirmed in the United States; reports probably
refer to
Nectria galligena
.
Nectria fuckeliana
Canker
on fir.
Nectria galligena (
Cylindrosporium mali
,
Anamorph).
European Nectria Canker
,
Trunk
Canker
, widespread on apple, pear, quince,
aspen, beech, birch, maple, hickory, Pacific dog-
wood, and various other hardwoods. This is one
bark,
cutting
beyond
the
greenish
discoloration.
