Biology Reference
In-Depth Information
stays wet, small black sclerotia are formed in the
petals in another 2 or 3 days. Infected blooms
seldom drop normally but remain hanging on
the bushes in an unsightly condition for weeks
and months, some even to the next season. Many
of the sclerotia, however, drop out and remain in
the litter on the ground ready to send up apothecia
the next winter.
Both Indian and Kurume varieties are
attacked, the peak of infection coming with
mid-season varieties such as Pride of Mobile or
Formosa. In some seasons dry weather during
early spring allows a good showing of azaleas;
in other years blight starts early and there is little
color unless azaleas are sprayed. On Belgian aza-
leas in greenhouses blight may start in December.
Control
Some mulches and soil treatments will
inhibit apothecial production. Secondary infec-
tion is bound to come from some untreated azalea
in the neighborhood. Spraying gives very effec-
tive, even spectacular, control if started on time,
when early varieties are in bloom and midseason
azaleas are showing color. Sprays must be
repeated three times a week as long as petal
surface is expanding, about 3 or 4 weeks. After
that, weekly spraying is sufficient. Spraying is
mandatory now for the big azalea gardens, and
the admission fees from the lengthened season
pay for the program many times over.
The original successful formula was: Dithane
D-14 (nabam) 1 1/3 quarts to 100 gallons water,
plus 1 pound 25 % zinc sulfate, 1/2 pound
hydrated lime, and 1 ounce of spreader Triton
B 1956. Later work showed that the lime could
be omitted, Dithane reduced to 1 quart, and zinc
sulfate to 2/3 pound to prevent injury in periods of
drought. The spray should be a fine mist, applied
from several directions to get adequate coverage.
Commercial growers should beware of order-
ing azaleas from the South unless they are bare-
rooted and all flower buds showing color
removed. As a matter of fact, any potted or balled
and burlapped plant grown in a nursery near
azaleas could very easily bring along some of
the tiny sclerotia in the soil, and they might
remain viable more than 1 year. All traces of
soil should be washed off roots, and the plants
wrapped in polyethylene for shipping.
Pellicularia
Basidiomycetes, Aphyllophorales
Includes some species formerly assigned to
Corticium, Hypochnus
, and
Peniophora
. Hyphae
stout, very short-celled; mycelium branching at
right angles; basidia very stout, formed on
a resupinate, cottony or membranous layer of
mycelium. Anamorph state a
Rhizoctonia
, with
sclerotia made up of brown, thin-walled, rather
angular cells, or
Sclerotium
, with sclerotia having
a definite brown rind and light interior.
Athelia rolfsii (formerly
Pellicularia rolfsii
(Anamorph,
Sclerotium rolfsii
).
Southern Blight
,
Crown Rot
. The disease has been known, in its
sclerotium stage, for many years on hundreds of
plants. The connection with
Pellicularia
is recent,
and the name does not have universal agreement.
One strain of the fungus has been called
Sclero-
tium delphinii
in the North, where the disease is
usually designated crown rot. This is, however,
a variable fungus with single spore cultures from
the
Pellicularia
stage producing sclerotia typical
of
Sclerotium delphinii
and of
S. rolfsii
, with inter-
mediate forms. Sclerotia of the southern blight
strain are very small, round, tan, about the size,
shape, and color of mustard seed, the pathogen
being frequently called the mustard-seed fungus.
Southern blight affects almost all plants
except field crops like wheat, oats, corn, and
sorghum. Fruits and vegetables include Jerusa-
lem artichoke, avocado, bean, beet, carrot, cab-
bage, cucumber, eggplant, endive, lettuce, melon,
okra, onion, garlic and shallot, pea, peanut, pep-
per, potato, rhubarb, strawberry, sweet potato,
tomato, turnip, and watermelon. Ornamentals,
too numerous to list in entirety, include ajuga,
ageratum, amaryllis, azalea, caladium, calendula,
campanula, canna, carnation, cosmos, China
aster, chrysanthemum, dahlia, delphinium,
daphne, duranta, gladiolus, hollyhock, hydran-
gea, iris, jasmine, lemon verbena, lily, lupine,
marigold, morning-glory, myrtle, narcissus,
orchids, phlox, pittosporum, rose, rose-mallow,
rudbeckia, scabiosa, sedum, sweet pea, star-of-
bethlehem, tulip, violet, and zinnia.
