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Teachers Guide #5.3 – Camellia refers to FACT CARD 5.3 Camellias
Camellias
Significance of Camellias
All of the 267 species recorded within the genus Camellia originated from Asia
except C. lanceolata, which is a native of the Philippines and Indonesia. In China,
Camellias have been used in the last three centuries as ornamental plants, and to
provide food from fermented young leaves, cosmetics, culinary and industrial oils,
high grade charcoal for fuel, and tea. In Japan, green tea made from leaves of
Camellia sinensis that have been steamed, rolling and dried, is an integral
component of the tea ceremony. Besides its cultural significance, Camellias have
been used in Japan in textiles, ceramics, brewing, cooking, household utensils, tools,
printing, crafts, farming, fuel, medicine and foodstuffs and cosmetics. Camellia plants
have also been used as roadside trees and fences. Camellia is the symbolic flower in
more than 30 Japanese communities.
Camellias were introduced into Europe in the 17th century with the beverage tea, and
later became treasured as ornamental flowering plant. They were introduced into the
United States in 1774 to establish tea growing, but this venture failed. Ornamental
Camellias did not became established in the United States until enthusiasts began
seeking perfect blooms around the 1940s, many years after the first flowering cultivar
was imported to New Jersey in 1797. Ornamental Camellias were introduced from
England to Australia in 1826. They were introduced into New Zealand soon after by
missionaries and others from Australia, and from England by British settlers. Some of
the oldest Camellia trees in New Zealand are found in Akaroa, which was established
in 1840 by French colonists.
Use of Camellia
Some species of Camellia are still grown for their economic value. The leaves of C.
sinensis L. var. sinensis and C. sinensis var. assamica are used to make tea.
Crushed seeds of some species such as C. oleifera, C. chekiangoleosa, C. reticulata,
C. grijsii, C. vietnamensis, C. crapnelliana and C. gauchowensis are cultivated for
production of high quality oils. The oil is used in cosmetics and for cooking, while
other Camellia products are used by pharmaceutical and manufacturing industries.
Production of tea oil from C. oleifera is currently under investigation in Georgia, US.
The oil is used in cooking and in the cosmetic industry, with process residues being
considered for livestock feed and insecticide formulations.
Green tea recipe
Camellia sinensis, the tea plant, is used to make the tea we drink. There are many
different processes used to dry the leaves for making the beverage. There are also
many varieties of C. sinensis used to make tea, with villages in China having their
own strain of tea plants with different qualities. There is even a tea variety developed
in China that does not have caffeine.
Try this Chinese recipe for green tea. The tea is reported to be delicious, very
smooth and not bitter.
1. Pick young shoots with 2-3 leaves from C. sinensis.
2. Roll several shoots between your hands until the leaves darken and become
crinkled. Bruising the leaves allows the fermentation process to begin. Do not
break the leaves into pieces.
3. Place thin layers of leaves on a tray in a shady location and allow the
fermentation process to occur over 2-3 days.
4. Dry the leaves in an oven at 106°C (250°F) for 20 minutes. This step is
necessary to remove all the water in the leaves and stop the fermentation
process.
5. Store the tea in an airtight container, or use immediately.
Ornamentals
Most Camellias are now grown for their ornamental value. Camellia flowers have
been selected for centuries to produce a wide range of colours, flower forms (single,
semi-double peony, anemone, rose-form double and formal double), and sizes (1-23
cm) (Figure 1). The most popular ornamental species of Camellia are C. sasanqua,
which flowers in autumn and winter, and C. japonica L. and C. reticulate, which
flower in winter and spring. Inter-specific hybridisation has led to around 5600 hybrids
being registered worldwide.
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Figure 1: Flowers of Camellia japonica cultivars (clockwise from top left) Little Michael,
Nuccio’s Pearl, Wilhelmina and San Dimas.
Fact
There are 32,000 entries of Camellia cultivars in the International Register, but many
of these are invalid names - synonyms, duplications, etc. Many entries represent
extinct cultivars, where the names have been extracted from books produced in
Japan and China hundreds of years ago, as well as in Europe in the 19th century. So
the number of valid entries is possibly around 15,000.
Financial importance
Camellias represent an important part of the nursery trade in New Zealand. The
Camellia industry generates about $2-4 million worth of domestic sales and $0.4
million in export sales annually. Most of the plants are used for amenity or
ornamental purposes.
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Plant care
Choice of location
A garden shaded by deciduous trees provides ideal conditions, including good
sunlight with high humidity, temperatures below 15°C in winter, and shade in
summer.
Soils should be rich in humus, porous, and slightly acidic (pH 5.5).
Camellias also survive well in pots.
Fertilisers
To encourage flowering in potted plants, use a general potting mix consisting of
500 g of 12-14 month release Osmocote Plus (15% N, 3.5% P, 9.1% K, 1.2% Mg,
plus traces of B, Cu, Fe, Mn, Mo and Zn) in 200 L of bark and 50 L of sand. Re-pot
every two years. An alternative soil mix is one-third each of decomposed compost,
garden soil and moss peat.
If the potting mix has no fertiliser in it, add fertiliser weekly to each pot during spring,
immediately before flowering, ceasing application by early summer. Use 2 g of an
ericaceous fertiliser (one suitable for azaleas or rhododendrons) mixed in 1 L water
per plant.
Camellias in the garden will normally thrive without fertiliser. However, they will
respond with improved growth and flower vigour to an ericaceous fertiliser applied
once in early spring prior to flowering. Apply fertiliser to soil under the drip line of
each plant at a rate of half that recommended on the label. Water the fertiliser into
the soil. Avoid using lime, which will increase the pH and create a basic soil.
Watering
Camellias can die in dry soils. Water the soil around Camellias regularly but avoid
creating waterlogged conditions. Soils do not require watering if they feel moist to the
touch.
Pruning
Pruning of 1-3 year-old Camellias encourages earlier and better branching. Cut the
main shoot of 1 year-old bushes back to a length of 10-15 cm to encourage outward
branching.
Prune older bushes to the space available, and the second batch of new shoots
produced by some cultivars, which may cause an undesirable shape in the bush.
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Prune immediately after the new shoots have started forming, after flowering has
finished. Cut the selected branch 2 cm above a set of leaves.
Misshapen bushes can be trimmed to the trunk using a technique descriptively called
‘Hatracking’ (Figure 2). The bush will regenerate and produce flowers in the next
flowering season.
Figure 2: Hatracking of Camellia bushes at the Wellington Botanic Gardens.
Propagation
Camellias can be propagated vegetatively from a single Camellia cultivar, and
generatively from two Camellia cultivars or species, by different methods.
Vegetative propagation
Layering
Seedlings are propagated from a low-hanging downward-pointing branch of a
Camellia bush that is more than two years old. Remove all leaves and shoots of the
branch except for a few leaves at the tip. Cut a small incision near the tip of the
branch, and train the branch down to the ground or into a pot containing standard
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potting compost. Secure the tip in the soil with a peg, heap peaty soil over it and
keep it moist. After two years, roots will have formed from the incision, and the shoot
tip can be separated from the mother bush and transplanted.
Cuttings
With this most successful propagation method, new plants should flower after one
year. Take cuttings in February. From the mother plant, select a top shoot that has at
least two leaves and no buds, and is 15 cm long and olive green (signifying the
optimum level of maturity). Cut the stem diagonally 2 cm below the lowest leaf using
a sharp knife that has been sterilised in alcohol. Dip the cut surface into a rooting
powder. Push the cutting 2 cm deep into sterilised potting mix (heated in a fan oven
at 120°C for 40 minutes) in an 8 cm diameter pot. Cover the pot with a stiff plastic
bag and seal the bag to the pot with string. Incubate under shade at 25°C until roots
form (8-12 weeks). Then remove the bag, and incubate at 16°C for a further four
months when the seedling can be re-potted in Camellia soil.
Root stimulation from stems
During the growth phase (after flowering), remove the leaves on a 30 cm length of
stem on a selected mother plant. Make two incisions 2 cm apart around the
circumference of the stem, and peel off the bark skin. Tie the end of a section of a
transparent cylindrical plastic bag below the scar. Fill the bag with moist moss peat.
Then tie the bag around the stem above the incision. Once roots appear inside the
peat-filled bag, separate the shoot with its new roots from the mother bush, and plant
it in an 8 cm diameter pot filled with Camellia soil.
Grafting
This method is suitable for cultivars that do not produce roots readily. Camellia
japonica and C. sasanqua are good stock species. Cut the base of the scion of the
cultivar to be propagated into a wedge, and insert the wedge into a slot cut into the
stock. Secure the scion with grafting tape or cotton wound tightly around the join. The
two pieces will fuse together within eight weeks.
Generative propagation
Raise your own Camellia by crossing cultivars of the same or compatible Camellia
species. Transfer ripe pollen grains from the anther of a flower or number of flowers
of one Camellia bush to a ripe stigma (recognised as receptive by secretion of a
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mucus). Cover the recipient flower with gauze until fertilisation has occurred
(recognised by petal drop) to avoid inadvertent pollination from other genotypes.
Under favourable climatic conditions, a woody seed capsule the size of a walnut will
have formed by autumn. It will open naturally to release up to six blackish-brown
seeds.
Test the resulting seeds for viability by placing them in a bowl of water. Seeds that
sink to the bottom after 10 minutes are viable. Those that float are sterile and
incapable of germination.
Sowing seeds
Press three seeds per pot about 25 mm deep into potting mix contained in a 10 cm
diameter pot. Cover with peat, and water. Place a transparent plastic bag over the
pot and incubate at about 20°C. Remove the bag after the seedling develops two
leaves (3-5 weeks). Prick out each seedling once it has grown a total of four leaves,
into an individual pot containing Camellia soil. Re-pot as necessary. Flowering should
occur 3-5 years after sowing.
Camellia protection
In New Zealand, strongly growing Camellia bushes are generally free from
invertebrate pests and diseases. However, Camellias can be susceptible to a number
of disorders, insect pests and fungal pathogens present in New Zealand.
Disorders
Physiological disorders result from climatic changes, nutritional imbalance or
inadequate drainage, and can usually be rectified by changing the environmental
conditions. Algae and lichen may grow on leaves in shady humid conditions. They
have no effect on the health of the plant but can be controlled with a spray of copper
oxychloride. Camellia cultivars with white or pale pink flowers are more delicate than
cultivars with darker-coloured flowers and may develop brown petals from exposure
to sun or wind. Shading from extremes of weather and careful pruning to prevent
blooms from rubbing against other parts of the plant are recommended. Extreme
frost or changes in temperature can induce buds to drop before flowering.
Transferring the plant to a more sheltered part of the garden could solve this
problem.
Chlorosis of the leaves could be due to natural senescence, a genetic condition, or it
may be caused by extended dry periods resulting in dehydration, or an excess of
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water with poor drainage. Chlorosis caused by alkaline soils, which prevent iron and
other nutrients being available in a soluble form, can be ameliorated by applying acid
fertilisers, compost, and iron chelate or iron sulphate. Yellowing between green veins
in the leaves can indicate lack of iron or magnesium, readily corrected by application
of sulphate of iron or magnesium sulphate. Corky scabs on the undersides of leaves
can result from plants absorbing more water through the roots than the leaves can
transpire (oedema), and can occur through over-watering. It can also occur in
Camellias with a large root mass and little foliage.
Bronze patches on leaves can occur in some cultivars exposed to hot sunny
conditions as a result of sunburn. Shade solves the problem. Potassium deficiency
can result in brown patches on leaves and can be corrected with potassic
superphosphate. An excessive build-up of salts in the soil can result in edges of
leaves turning brown, and is usually corrected by thorough watering to wash the salts
from the immediate root zone.
Insect pests
Sucking insects including scale and aphids, which may affect the vigour of Camellia
plants less than 5 years old, require treatment with insecticides. The scale insect
Pulvinaria floccifera can severely affect young bushes. They can be effectively
controlled by spraying the bushes with Attack® (a mix of permethrin, primiphosmethyl and hydrocarbon liquid) at 1 mL/L water until run-off. Aphids can be controlled
easily with an readily available aphicide from your garden shop. These insects
secrete sugars that black sooty moulds then feed on. Controlling these insects will
also stop new mould growing on the leaves, but the old mould may require wiping off
to remove the unsightly blemish.
Beetles of grass grub Costelytra zealandica and bronze beetle Eucolaspis brunnea,
and larvae of case moth Liothula omnivorous, chew the leaves of Camellia plants,
but they rarely affect the vigour of mature Camellia plants and have no effect on the
flowers.
Diseases
Viruses
Viruses can infect Camellias, but their effect is usually minor and aesthetic. Viruses
can cause irregular blotches of white on coloured flowers, and irregular blotches of
yellow or pale colour on the foliage. A virus causes ringspot, identified by faint green
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rings in young leaves that turn bright green with dark edges within yellowing leaves
as they mature. Viruses can be introduced by grafting on to infected stock, and by
using scions from infected plants as cuttings. Some breeders do this on purpose to
create a variegated leaf in a new line of Camellias.
Fungi
Fungal diseases of Camellia plants are more serious. Dieback caused by the fungus
Glomerella cingulata can be lethal to Camellias. Symptoms include sudden death
and wilting of young shoots, followed by the dead leaves holding on to the shoot, and
dying of tissue and growth of a canker, which continues to enlarge, extracting water
and nutrients causing yellowing of leaves, loss of foliage and dieback of twigs and
branches. The wind-borne fungus Exobasidium spp. affects young leaves at the ends
of branches, causing them to become light green to white, or deep pink to red.
Phytophthora cinnamomi is the main fungi of several species that cause root rot.
Root rot disease is common in waterlogged non-aerobic soils. Symptoms are
expressed in summer, when leaves become yellow and die, and branches wilt and
die back from the tip until the whole plant dies. Roots of an affected plant will be dark
brown and brittle, and contain few white fibrous roots essential for a healthy plant.
Two fungal diseases of flowers are of concern because of the importance of
Camellias for their flowers. Botrytis cinerea causes botrytis flower blight or grey
mould, characterised by water-soaked brown spots on the petals. The spots spread
fast to form tan to grey-brown blotches associated with the blighting and decay of
blooms. Colours on diseased flower petals quickly fade as the flower withers into a
brown-grey wrinkled mass. The disease is prevalent when relative humidity exceeds
the threshold of 93% for when botrytis spores infect the petals. Consequently, the
disease can be a problem in glasshouse-grown Camellias. The other flower disease
is Camellia flower blight, otherwise known as Camellia petal blight.
Camellia flower blight
Since Camellias are most commonly grown for their attractive flowers, the most
important disease affecting Camellias is Camellia flower blight, as the premature
browning and fall of infected flowers detract from their aesthetic value and can make
blooms unfit for showing (Figure 3). Camellia flower blight is caused by the sclerotialforming fungus Ciborinia Camelliae, and is specific to flowers of most species of
Camellias. The pathogen does not affect Camellia bushes themselves.
Camellia blight was first identified in Japan in 1919 and first found in the United
States in California in 1939, spreading to most states where Camellias are grown
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within the next 50 years. In New Zealand, the disease was first reported in Wellington
in 1993. It is present throughout New Zealand in most regions north of Ashburton.
Figure 3: Symptoms of Camellia blight, comparing healthy and blighted flowers on Camellia
japonica.
While the symptoms of flower blight are similar to those of Botrytis infection, with
browning and premature dropping of flowers, the diseases are easily distinguishable
from one another. With flower blight, the entire and intact whorl of petals (corolla)
separates easily from the receptacle, leaving a characteristic grey ring of fungal
hyphae at the point of separation (Figure 4). With Botrytis, the petals come away
separately, with no sign of grey fungal growth on the broken surfaces.
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Figure 4: Early C. Camelliae infection in a Camellia flower (left), and advanced flower
infection (right) showing growth of mycelium at the base, which eventually will develop into
sclerotia.
The pathogen has a simple life cycle (Figure 5). Wind-borne spores arising in late
winter and spring from the apothecia of soil-borne sclerotia infect the flowers of
Camellias, and develop within the fallen flower to form new sclerotia. These produce
apothecia in subsequent years.
Figure 5: Lifecycle of Ciborinia camelliae.
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Current control options
Current control strategies are aimed at interrupting the lifecycle of the pathogen by
preventing formation of sclerotia or apothecia, thereby preventing the release of
ascospores, or by preventing infection of flowers on Camellia bushes.
Limiting its spread
The spread of the disease from an endemic area, and its introduction into new
locations could be restricted by only transporting Camellia plants that are free of
flowers, and as bare-rooted cuttings or scions. These measures aim to prevent old
sclerotia in the soil or potential sclerotia in infected flowers from being transported
along with the plant. It would be extremely effective if adopted, but home gardeners
and many nurserymen often do not recognise that the pathogen is present when
purchasing or transferring cuttings. Home gardeners who select their plants on the
appearance of the flowers are also unlikely to purchase bare-root cuttings that are
too young to flower. Once the disease is established in a region, a number of cultural
and chemical methods can be used to prevent its development.
Cultural control
The disease may be avoided by growing autumn-flowering species such as C.
sasanqua, or cultivars that flower early in the season before apothecia are produced
by the soil-borne sclerotia (mid-late July in New Zealand). While this approach might
be effective, most growers of Camellias prefer to have Camellias flowering during the
winter-spring period, when apothecial production is at its peak.
The fallen infected Camellia flowers may be raked up and burned to kill the
developing sclerotia. A plastic sheet laid underneath flowering bushes makes
collection of fallen flowers easier, and prevents apothecial development from
sclerotia underneath. This approach would be highly effective if adopted universally,
but is practised by only a few Camellia growers. Further, home gardeners do not
usually burn the flowers, instead adopting the easier approach of discarding the
flower debris in compost. As sclerotia may survive composting, council or private
green-waste composting schemes can contribute to the spread of the disease.
Moisture levels on the ground where the sclerotia fall can be reduced, thereby
depriving the sclerotia of moist conditions for subsequent development. This can be
achieved by trimming the lower Camellia branches to about 0.5 m above ground,
raking off loose-leaf litter and weeds to expose bare soil, or by covering the exposed
ground with either black polythene or 75-100 mm thick pine needles. Adding ground
cover could also be effective in smothering the soil-borne sclerotia and suppressing
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apothecial production from sclerotia underneath. However, these methods would
have limited control of apothecia produced by sclerotia developing in flowers that fall
after the ground cover has been applied. The apothecia could still form in wet
seasons or after periods of rain.
Fungicide application
Fungicides can be applied to soil under Camellia bushes to prevent production of
apothecia by sclerotia, or they can be sprayed on to the bushes during flowering to
protect blooms from infection by ascospores. Alternatively, cut blooms can be dipped
into fungicide solutions prior to display at flower shows.
Application of fungicides to soil immediately prior to apothecial production has
generally given effective control of apothecia. Alto® 100SL (100 g/L cyproconazole)
or Shirlan® 500SC (500 g/L fluazinam) sprayed on to infested soil at 4 L/ha in 1000 L
water/ha in early August, and reapplied 3-4 weeks later, can be effective in
preventing production of apothecia during August to November. No fungicides are
registered in New Zealand for use against C. camelliae, so the risk in controlling the
pathogen is borne by the user.
Many foliar-applied fungicide sprays have been evaluated for protection of flowers
against infection by ascospores, but generally they have not been successful in
controlling the disease. For any degree of effective protection, the fungicides needed
to be applied repeatedly during flowering. Bayleton® 5 DF (50 g/kg triadimefon),
applied at 1 g/L water to Camellia bushes weekly during flowering, only reduced
numbers of blighted flowers by 31-77% in every season over six years in the United
States. In New Zealand, Camellia bushes sprayed fortnightly until run-off with either
Alto® 100SL at 0.15 mL/L or Shirlan® at 1.0 mL/L water, both containing a surfactant
to help spread the fungicides during the 8 weeks of flowering, had disease levels
similar to that of the untreated control (17%).
Dipping Camellia blooms into fungicide solutions has been shown to be effective in
preventing infection of cut flowers. Healthy Camellia blooms dipped into a solution
containing Cereous 250EC (250 g/L triadimenol) at 2.0 mL/L water, or Bayleton 5DF
(50 g/kg triadimefon) at 4.0 mL/L water plus a few drops of washing up detergent, for
5 min 1-7 days prior to showing, can effectively delay the onset of the disease.
However, none of these strategies are sufficiently effective or practical for ready
adoption by Camellia growers.
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Potential for biological control.
A strategy for integrated biocontrol of Camellia flower blight was developed in a PhD
project at Lincoln University. Two approaches were examined. One approach was to
protect Camellia flowers against wind-borne spores arising from the sexual fruiting
bodies by either stimulating the plant’s natural defence systems or spraying naturally
occurring microbes on to the flowers, but this approach was only partially successful.
Although isolates of naturally occurring leaf-surface microbes such as Bacillus,
Pseudomonas, Aureobasidium and Cladosporium spp. provided almost complete
protection against Camellia blight in petal assays (Figure 6), they did not prevent
symptoms on whole flowers on Camellia bushes, even after repeated applications
with or without additives that were added to the formulation to aid spread of the
antagonists over the flowers. It appears that the microbes were not able to colonise
the burgeoning blooms in competition with other microbes in sufficient numbers to
provide protection against infection.
Figure 6: Results of a petal assay, which evaluated protection by antagonists from C.
Camelliae ascospore infection. Untreated petals (far left column) compared with petals
treated with the pathogen only (middle left), and those treated with the pathogen after
inoculation with an isolate of Pseudomonas, without an additive (middle right) and with an
additive (far right column).
The other approach was to attack the soil-borne sclerotia with naturally occurring
microbes and soil amendments, and thereby prevent apothecial production. Screens
of 400 candidate microorganisms isolated from sclerotial baits and decaying sclerotia
(Figure 7), two isolates of Trichoderma and an isolate of Fusarium lateritium reduced
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the number of viable sclerotia by 38-50%. This indicated that moderately parasitic
micro-antagonists were present in soil under Camellia bushes.
A
B
C
D
Figure 7: Ciborinia camelliae mycelium growing from healthy sclerotia (A), and species of
Trichoderma (B) and other fungi (C and D) growing from parasitised sclerotia.
A range of soil treatments was also investigated in field trials in an attempt to reduce
the viability and germination potential of over-wintering sclerotia. Nitrogenous
fertilisers that contain cations have been shown by other researchers to stimulate
microbial degradation of sclerotia of other pathogen species. Urea applied to soil at
10 g urea/m² (46 kg N/ha) in February and again in June reduced field populations of
C. camelliae sclerotia by 64% in the following November. We think this reduction was
due to stimulation of parasitic microbes.
The direct toxic effect of selected fertilisers on apothecial production was also tested.
A single application of the fertiliser calcium cyanamide at 500-1000 kg/ha to soil
under Camellia bushes immediately before flowering (July-August), was found to give
complete suppression of apothecial production. This treatment could be used for
short-term control of the disease. Calcium cyanamide decomposes naturally in the
soil to urea, and so this may also aid in the reduction of sclerotia. Potassium
bicarbonate and ammonium bicarbonate gave partial suppression (76-87%) of
apothecia at the 300 kg/ha rate tested in the trial, and presumably could be more
effective at higher rates.
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Tree mulches can also stimulate parasitic microbes in the soil. Covering soil under
Camellia bushes with 100 mm thick mulches from trees such as pine, gum, and
manuka, for 9 months resulted in total suppression of apothecia and a 77% reduction
in the population density of soil-borne sclerotia, compared to bare soil. The different
species of tree mulches had a similar effect on reducing numbers of sclerotia.
However, the tree mulches had no effect on the new generation of C. camelliae
sclerotia developing in fallen flowers, which would produce fruiting bodies in
subsequent years.
The successful control strategies developed in this study could be integrated into a
programme for effective control of Camellia blight. Urea applied at 20 g/m² (200
kg/ha) to soil beneath Camellia bushes followed by a 100 mm thick layer of tree
mulch should result in significant suppression of apothecia, thereby preventing
infection of flowers, and resulting in a gradual decline in numbers of soil-borne
sclerotia.
Acknowledgement
Thanks to Dr Vince Neall, President of the New Zealand Camellia Society, for
critiquing this manuscript.
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