Biology Reference
In-Depth Information
abundantly in crevices of broken bark, first pro-
ducing conidia extruded in yellow tendrils from
reddish pycnidia and later ascospores from peri-
thecia embedded in orange stromata. Fans of
buff-colored mycelium are found under affected
bark.
Ascospores can be spread many miles by the
wind, landing in open wounds, but the
sticky conidia are carried by birds and insects.
The fungus can live indefinitely as a saprophyte,
and new sprouts developing from old
stumps may grow for several years before they
are killed.
Control
All eradication and protective
measures have proved futile. Hope for the
future lies in cross-breeding resistant Asiatic
species with the American chestnut (and
there has been some success in this line) or in
substituting Chinese and Japanese chestnuts for
our own.
circular lesion, 1/4 inch or less in diameter, with
the raised black dot of a fruiting body in the
center of each spot. If spots are numerous, there
is extensive defoliation. Fruit spots are red at first,
then black and slightly sunken; the skin is rough-
ened, sometimes cracked. Quince has similar
symptoms.
Twig lesions appear on the current season's
growth about midsummer, indefinite purple or
black areas coalescing to form a canker. Primary
spring infection comes more from conidia
produced in these twig lesions than from asco-
spores shot from fallen leaves on the ground.
Most commercial varieties of pear and quince
are susceptible, although some are moderately
resistant.
Fabraea
maculate,
Entomosporium
maculatum (
Diplocarpon
mespili
,
▶
Entomosporium mespili
).
Pear Leaf Blight
,
Entomosporium Leaf Spot
,
Fruit Spot
, generally
distributed on pear and quince, widespread on
amelanchier, sometimes found on apple, Japa-
nese quince, medler, mountain-ash, Siberian
crab, cotoneaster, loquat, photinia.
Fabraea thuemenii (
Entomosporium
thuemenii
).
Hawthorn Leaf Blight
, wide-spread
on
Crataegus
species. Symptoms are similar to
those of pear leaf blight and for a long time the
pathogen was considered identical. Small dark
brown or reddish brown spots, with raised black
dots, are numerous over leaves, which drop pre-
maturely in August. In wet seasons trees may be
naked by late August.
Control
Because the fungus winters in twig can-
kers as well as in fallen leaves, sanitation has
little effect. Standard recommendation has been
to spray three times with bordeaux mixture,
starting when leaves are half out and repeating
at 2-week intervals. The copper may be some-
what phytotoxic, causing small reddish spots sim-
ilar
▶
Diplocarpon (Fabraea)
Ascomycetes, Helotiales,
Dermateaceae
Apothecia develop on fallen leaves; small,
disclike, leathery when dry, gelatinous when
wet; asci extend above the surface of the disc;
ascospores two-celled, hyaline. The anamorph
stage an
Entomosporium
with distinctive cruciate
four-celled conidia, each cell with an appendage,
formed in acervuli (
Fig. 1
).
Didymascella tsugae
Fabrella tsugae
).
Hemlock Needle Blight
. Needles of Canada hem-
lock turn brown and drop in late summer.
Diplocarpon mespili (
Entomosporium mespili
)
(formerly
Fabraea maculate
, Entomosporium
maculatum).
Pear Leaf Blight
,
Entomosporium
Leaf Spot
,
Fruit Spot
, generally distributed on
pear and quince, widespread on amelanchier,
sometimes found on apple, Japanese quince,
medler, mountain-ash, Siberian crab, cotoneas-
ter, loquat, photinia.
Pears may be affected as seedlings in nurseries
or in bearing orchards. Very small purple spots
appear on leaves, later extending to a brownish
(see
▶
to those of blight, but
it does prevent
defoliation.
Fabrella
tsugae (formerly
Didymascella
tsugae
).
Hemlock Needle Blight
.
Needles of Canada hemlock turn brown and
drop in late summer. Spores are matured in
apothecia on fallen needles with new infection
in spring. The damage is not heavy.
