Biology Reference
In-Depth Information
Briosia azaleae (see
Pycnosystanus azalea
)
(
Pycnostysanus azaleae
).
Bud and Twig Blight
of azalea and rhododendron, widespread but
occasional.
Pycnosystanus azalea (formerly
Briosia
azaleae
)
Pycnostysanus azaleae
).
Bud and
Twig Blight
of azalea and rhododendron, wide-
spread but occasional. The disease was reported
from New York in 1874 and, as a rhododendron
bud rot, from California in 1920. It was particu-
larly serious on Massachusetts azaleas in 1931
and 1939. Flower buds are dwarfed, turn brown
and dry; scales are silvery gray. Twigs die when
lateral leaf buds are infected. Successive crops of
coremia are produced on old dead buds for as
long as three years, the first crop appearing the
spring after summer infection. The coremia heads
are dark, and the buds look as if stuck with tiny,
round-headed pins. Prune out and burn infected
buds and twigs in late autumn and early spring.
Spraying with bordeaux mixture before
blossoming and at monthly intervals after bloom
may be wise in severe cases.
Infection starts near a terminal bud in late
summer and progresses down a twig into
a node, sometimes beyond into 2-year wood.
The needles redden and die; they are conspicuous
in spring but drop in late summer. Then brown to
black apothecia with a greenish surface to the cup
appear on twigs. Cut off and destroy infected
twigs.
▶
Cercospora
Deuteromycetes, Hyphomycetes
Conidia hyaline to pale to medium green or
brown; long, usually with more than three cross
walls; straight or curved, with the base obconate
or truncate, tip acute to obtuse; thin-walled; not
formed in a fruiting body but successively on
slender conidiophores, which emerge in fascicles
or groups from stomata and usually show joints or
scars where conidia have fallen off successively.
The conidiophores are always colored, oliva-
ceous to brown, pale to very dark (
Fig. 1
).
This is the largest group of the Dematiaceae,
with about 400 species, all parasitic, causing leaf
spots or blights. The teleomorph state, when
known, is
Mycosphaerella
.
Cercospora apii
Early Blight
of celery, general
on celery and celeriac, first noted in Missouri in
1884 and since found in varying abundance wher-
ever celery is grown. The disease is most severe
from New Jersey southward. The name is some-
what misleading; in Florida early blight rarely
appears before the Septoria disease known as
late blight. Foliage spots appear when plants are
about 6 weeks old. Minute yellow areas change to
large, irregular, ash gray lesions, covered in moist
weather with velvety groups of conidiophores
and spores on both sides of leaves. Sunken, tan,
elongated spots appear on stalks just before har-
vest. The disease spreads rapidly in warm, moist
weather, the spores being splashed by rain, car-
ried with manure or cultivators, or blown by
wind. The life cycle is completed in 2 weeks.
Control
Seed more than 2 years old is probably
free from viable spores; other seed should be
treated with hot water, 30 min at 118
to 120
F.
Calonectria
Cylindrocladium under Blights.
Calonectria
▶
colhounii
Blight
on
Leucospermum.
Cenangium
Ascomycetes, Helotiales
Apothecia small, brown to black, sessile or
substipitate on bark; spores hyaline, elliptical,
one-celled; paraphyses filiform.
Cenangium ferruginosum
Pine Twig Blight
,
Pruning Disease
;
Cenangium Dieback
of fir
and pine. The fungus is ordinarily saprophytic
on native pines but may become parasitic
when their vigor is reduced by drought. The
disease is considered beneficial to ponderosa
pine in the Southwest because it prunes off the
lower branches; on exotic pines it can be
damaging.
