Biology Reference
In-Depth Information
Begonia
- dead areas in leaves and flowers
rapidly enlarging and turning black in a moist
atmosphere; profuse brownish gray mold.
Calendula
-gray-mold blight.
Camellia
- flower and bud blight, common
after frost.
Carnation
- flower rot or brown spotting,
worse in a cool greenhouse.
Century plant
-gray mold after overwatering
and chilling.
Chrysanthemum
- cosmopolitan on flowers,
buds, leaf tips, and cuttings. Ray blight on flowers
starts as small, water-soaked spots, which rapidly
enlarge with characteristic gray mold.
Dahlia
-bud and flower blight.
Dogwood
- flower and leaf blight. In wet
springs anthers and bracts of aging flowers are
covered with gray mold, and when these rot down
on top of young leaves, there is a striking leaf
blight.
Eupatorium
- stem blight, common in
crowded plantings. A tan area girdles stem near
ground with tops wilting or drying to that point.
Geranium
(
Pelargonium
) - blossom blight
and leaf spot, most common in cool, moist green-
houses where plants are syringed frequently.
Petals are discolored, flowers drop, gray mold
forms on leaves.
Lily
-
Botrytis cinerea
is common on lilies, but
see also
Rose
- bud or flower blight, cane canker.
When half-open buds ball, the cause is often an
infestation of thrips; but if gray mold is present,
Botrytis
is indicated. Canes kept too wet by
a manure mulch, or wet leaves, or injured in
some way, are often moldy.
Snapdragon
- flower spikes wilt; tan cankers
girdle stems.
Sunflower
-bud rot and mold.
Sweet pea
-blossom blight.
Viola
spp. -gray mold and basal rot of violet
and pansy.
Zinnia
-petal blight, head blight, moldy seed.
Botrytis cinerea
may also infect arabis, ciner-
aria, eucharis, euphorbia, fuchsia, gerbera, gyp-
sophila, heliotrope, hydrangea, iris, lilac, lupine,
May-apple, pyrethrum, periwinkle, rose-of-Sha-
ron, stokesia, viburnum, and wallflower.
Control
Sanitation is more important than any-
thing else. Carry around a paper bag as you
inspect the garden; put into it all fading flowers
and blighted foliage; if infection is near the base,
take the whole plant up for burning. Keep green-
house plants widely spaced, with good ventila-
tion; avoid syringing, overhead watering, and too
cool
temperature. Propagate
cuttings
from
healthy plants in a sterilized medium.
Botrytis douglasii
Seedling Blight
of giant
sequoia and redwood, perhaps a form of
B.
cinerea
.
Botrytis elliptica
Lily Botrytis Blight
, general on
lilies, also reported on tuberose and stephanotis in
California. Lily species vary in susceptibility to
the disease, but there are several strains of the
fungus, and few lilies are resistant to all strains.
Madonna lily,
L. candidum
, is particularly sus-
ceptible, with infection starting in autumn on the
rosette of leaves developed at that time.
If the blight strikes early, the entire apical
growth may be killed with no further develop-
ment. More often the disease starts as a leaf spot
when stems are a good height. Spots are orange to
reddish brown, usually oval. In some species
there is a definite red to purple margin around
a light center; in others the dark margin is
replaced by an indefinite water-soaked zone. If
spots are numerous, they grow together to blight
the whole leaf. Infection often starts with the
B. elliptica
.
Marigold
-gray mold prevalent on fading
flowers.
Peony
- late blight, distinguished from early
blight (see
▶
B. paeoniae
)
by the sparse mold,
usually standing far out from affected tissues,
rather than a thick, short velvety mold, and by
much larger, flatter sclerotia formed near base of
the stalk. Late flowers are infected, and when
they drop down onto wet
▶
foliage,
irregular
brown areas are formed in leaves.
Pine
- seedling blight.
Pistachio
- shoot blight.
Poinsettia
- tip blight and stem canker.
Primrose
- crown rot and decay of basal
leaves, with prominent gray mold, very common
in greenhouses where plants are heavily watered.
Rhododendron
- flower, twig, and seedling
blight.
