Dieback: Dieback is a serious disease of both C.
japonica and C. sasanqua caused by the fungus Glorerella
cingulata. This fungus usually requires a wound to enter
the plant. Leaf scars, hail injury and wounds created from lawn
mowers, pruning cuts, falling branches and insects are points
of entry for the fungus. The fungus may be spread by insects
that walk across wounds or by splashing rain or water. Spread
of the disease is usually during the spring and early summer
months.
The disease is characterized by sudden wilting of new growth,
particularly in early summer. The leaves characteristically cling
to the branches for a considerable length of time after they
die. Cankers can sometimes be seen at the infection point, and
these may ooze pink masses of fungal spores during extended periods
of wet weather.
The best control of dieback is sanitation. The fungus lives
inside the plant and cannot be completely controlled by spray.
Diseased branches should be removed about 6 inches below the
lowest visible symptom of disease. Pruning tools should be dipped
in a solution of fungicide or bleach and water between each cut
if infection is suspected. All wounds should be sprayed with
this solution. This diseased twigs should be burned or physically
removed. Spraying of plants with a fungicidal solution in the
spring during the normal leaf-fall period will help to prevent
the spread of the fungus.
Root rot: Camellia root rot is caused by a fungus (Phytophthora
cinnamomi) which occurs in the soil. This pathogen may be
found occurring naturally in the soil or it may be brought in
on the roots of camellias, rhododendrons, and other woody ornamentals.
Most Camellia japonica varieties are susceptible to root
rot, while Camellia sasanqua and Camellia oleifera are not as susceptible.
Root rot is usually associated with poorly aerated or poorly
drained soils. Symptoms may appear at any time, but they often
show up during periods of hot, dry weather. The first sign of
this disease is the stopping of growth either with or without
yellowing. In more advanced stages the leaves on one or more
branches become gray-green, wilt, and finally die. Plants infected
with root rot are unable to take up water and will eventually
die from lack of water. If the roots are examined they are brown
with rot.
Three approaches to control exist: 1) use C. sasanqua and C. oleifera as understock for grafting. This gives some
protection; 2) use vigorous fast-growing varieties; 3) use a
fungicide as a soil treatment. This is expensive and may not
completely rid the soil of the fungus. Most important, however,
is to do whatever is necessary to improve drainage of the soil.
Camellia flower blight: This disease of camellia caused
by the fungus Ciborinia camelliae occurs only on the flower
and does not affect the rest of the plant in any way. Since camellias
are enjoyed mainly for their flower, this can be a very devastating
disease.
Flower blight is not usually a problem early in the season.
It generally appears in late winter to early spring when the
temperatures are on the rise. However, it may be seen earlier
if conditions are proper for the fungus. Warm, humid weather
following a cold spell will cause sporulation of the fungus and
subsequent infection. This disease is characterized by brown
spots on the petals. These usually enlarge until the entire blossom
is blighted. Infected flower tissue feels "slimy" to
the touch.
Infected flowers fall to the ground and the fungus produces
hard, resting bodies called sclerotia. These sclerotia may remain
under the bush or in the soil or debris for several years. Under
proper weather conditions (temperatures from 45 - 70° F,
wet) these sclerotia germinate and develop saucer-shaped mushrooms
(apothecia) about 1/2 inch in diameter that release spores. These
spores are carried by the wind and cause infection when they
land on a flower.
Control measures involve the removal and destruction of all
fallen blossoms. If all flowers could be picked up every year
this would disrupt the life cycle of the fungus. However, this
is only effective if you do not live close to other camellia
growers as the fungal spores may easily blow from yard to yard.
If flower blight has not been found in an area, it is important
not to bring flowers or infected soil on plants into this area.
Protective fungicidal spray have only provided limited protection.
At this point, eradication is not truly possible although investigation
of various control methods continues. Some fungicidal sprays,
such as Bayleton, applied weekly will reduce disease incidence
but not eliminate it.
Other diseases: Other diseases of
camellia include leaf gall, sooty mold, lichens, nematodes, and
virus variegation. None of these are usually life threatening.
For more information contact
the ACS horticulturist.
ACS publishes Camellia Diseases,
a leaflet of more information that is illustrated with color
photographs. Please email the gift shop for ordering information
for Camellia Diseases, item 4206/Diseases.
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