Gardening Tips for Camellias

Camellias are large plants that do not need direct light. These hard, wooded plants are often grown in pots. Plants should be repotted after the dormant season before they begin to grow again.

Camellias can be repotted as often as needed and should be watered abundantly as they start to grow. Camellias should also have an occasional showering or washing to remove dust from their leaves.

Liquid manure is one of the best fertilizers to use for camellias, though it should only be applied when they are dormant or growing but not during the blossoming season. Otherwise the buds may be over stimulated and will be turned into leaves instead of flowers.

During the winter, camellias can handle a considerable amount of cold, even below freezing temperatures, for very short time periods. Once the plant has begun to grow and then to blossoms, it needs a great deal of heat.

Camellias generally blossom very fully, then rest a few days or even a week. On

Camellia flowers are now opening, providing colour in the grey winter days. This is also the time when the flower blight fungus (Ciborinia camelliae) awakens from its dormancy in the soil, and starts to produce infective spores. It is a time to be aware! A description of the disease symptoms appeared in the last two issues of the NZ Camellia Bulletin. This article focusses on the life cycle and possible control options for camellia flower blight.

Life cycle. The fungus spends the summer and autumn (i.e. the non- flowering period) in the top layer of the soil, underneath camellia bushes that were infected in the previous season. The organism survives as sclerotia. These are hard black structures, which appear very much like small irregular pebbles. Even if seen, they are not easily recognised as being of fungal origin. Most will be buried 1 or 2 centimetres under the leaf litter. Exactly when the fungus activates itself is unknown in New Zealand, but if it behaves the same way it does overseas, then it synchronises well with the flowering period of C. japonica. Upon activation, sclerotia germinate to produce a stipe (i.e. a stalk) which grows upwards until it reaches the soil surface. It then expands to produce a saucer-shaped structure called an apothecium, These are usually a tan colour, and can range up to a centimetre or more in diameter. These structures are far more obvious than sclerotia, and may be spotted by a gardener on the lookout for them (Photos 1 and 2). However, small apothecia may go unnoticed.

These apothecia produce spores, which they forcefully eject into the air. Typically, just a few apothecia can release millions of microscopic spores over several days. As the old apothecia expend themselves, new ones form to replace them. Therefore an infested area may go on being a source of spores for months. The fact that the fungus can produce so many spores may seem alarming. However, there are many environmental factors that render them non-viable and so restrict the spread of most to a few hundred meters. Nevertheless viable spores may travel up to 2 km.

Once a viable spore lands on an open flower, it usually germinates to form a microscopic fungal thread. This penetrates the tissue then expands and grows in it. The result is the characteristic "blight" symptom. Only the flower tissue is attacked. Leaves and stems are unaffected. Interestingly, no spores are produced from the flower tissue itself! This is unusual for a fungal plant pathogen and helps to distinguish the disease from Botrytis, which will sporulate under conditions of very high humidity. The period from first infection to total blossom death can be as short as 5 days. Once invasion of the lower part of the plant occurs, a grey ring of fungal tissue forms around the base of the blossom, where it was attached to the plant. After 2-3 weeks, this area hardens and develops into a hard black sclerotium.

By this time of course, the blossom has fallen from the bush. The newly formed sclerotia lie in the leaf litter to be covered by falling petals and other organic material. They do not produce apothecia in the season of formation. A period of maturity is required which means they do not produce spores until the following season, whereby the cycle repeats itself. If therefore, apothecia are found under a camellia bush it means the disease must have attacked the flowers last year. Not all sclerotia will necessarily germinate the season after they are formed. Some remain viable for many years and may germinate and produce apothecia (hence spores) several years after their creation.

Control. No control program yet devised has been 100% effective on this fungus. It is crucial therefore, that preventive measures be taken to stop it ever establishing in the garden (or region). The control section is divided into two parts. One part deals with preventing the establishment of the disease, the other deals with managing it, once it has gained entry to the garden.

 Prevention. Do not move flowering camellia plants from known infected regions (e.g. Wellington) to non-infected regions. Be careful, even in the non-flowering season (or if the plants have been disbudded so there is no flower tissue). The following recommendations apply.

1. The plants should be small. Infected blossoms can lodge in the branches of large, bushy plants and sclerotia can form there unnoticed. These can then fall to the soil if the plant is moved.

2. The plants should be bare rooted, or at least growing in a sterile growth media that was not present in the previous season.

3. Nursery Managers in infected regions should take care. B1ossoms can fall into other plants or pots surrounding an infected camellia, thus providing a source of infection for someone's camellias at home.

4. Destroy all flowers at Camellia flower shows. As the fungus does not form secondary spores, showing flowers from infected regions is not as large a risk as it initially may seem. However, shattering varieties can drop infected petals without being noticed. Certainly, leaving the spent blooms there after the show is over, is very dangerous as these may be a source of spores in the following year.

5. Dipping cut blooms into a suspension of Bayleton fungicide will stop the disease, even if infection has occurred. If blooms must be sent out of an infected region (for shows and the like), then consider this procedure. 6. Watch your own camellias very carefully. If there is any sign of the disease, pull off the infected blossoms and burn them. Do not put them in the compost heap as this does not kill the sclerotia. .

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