Camellia Flower Blight


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Camellia Flower Blight has arrived in Europe


photo dr. Luther Baxter

In 1998 some foreign journals made it known that the most important disease of the camellia, called Flower Blight, has also reached Europe.

Knowing his bad habits well, it is to be expected that he will arrive at us as soon as possible. In order not to be unprepared to face it and to limit its activity, as has already been done in many other countries, it is good to disclose as much as possible, news relating to its life cycle, how it spreads, but above all what are the main ways to keep it under control.

The news that the most important and devastating disease of the camellia has managed to overcome all the severe precautionary measures imposed by the various phytosanitary centers of many European countries, came as a surprise.

Discovered since 1919 in Hara in Japan, under the name of Sclerotinia camelliae Hara and, subsequently, in 1979 replaced with Ciborrinia camelliae Kohnit has remained invincible to every control up to the present day and has always proved relentless, devious and tireless, capable of overcoming mountains, deserts and even oceans. In fact, from Japan it first reached California in 1938 and later most of the United States:

For over fifty years, it seemed that this disease had to coexist only with the camelophiles of China, Japan and the USA and that the severe phytosanitary measures of all other countries were able to block its spread. Unfortunately, first New Zealand (1993) and later also Europe (1998) suffered the contagion of this disease.

What is Ciborrinia Camelliae Kohn?

It is the fungus that produces the so-called Flower Blight, specific for the Camellia only and for no other plant, and only for the flower, so no other part of the plant is infected.

The onset of the disease takes place as soon as the petals begin to show their color. The first symptoms appear as small dark brown spots on the petals, which gradually widen more and more starting from the basal part of the petals, and rapidly within a day or two, infect the entire flower.

The infection is produced by the fungus that absorbs the nourishment from the petals causing their fermentation (figure on the side).


photo dr. Luther Baxter

As the tissues change color, the veins of the petals tend to become darker, thus making it more evident that the flower has been infested by the fungus, unlike what is produced by strong wind or rain on the tips of the petals ( figure to the side).


photo dr. T.M. Stewarb

Another feature of the disease is highlighted by the hyphae of the fungi that develop in the basal part of the flower, which in fact form a mouse-gray collar in the shape of cotton wool (photo below left). This feature differs from what can always be seen in the same place, when the camellia was attacked by Botrytis (photo below center).


photo dr. Stewarb


photo dr. Stewarb


photo dr. Luther Baxter

At the end of the infection, the flowers fall to the ground and continue to maintain their shape and solidity for a few days. During this period the fungus continues to perform its task, both in the basal part of the flower still on the tree, and in the fallen flowers, until the formation of hard bodies, dark brown to black, called Sclerotia.

At this point it is good to point out that no spore is produced by the tissue of the flower affected by the fungus and therefore the infection cannot be transferred from one flower to another, as is the case with Botrytis and other diseases. This detail is the only beautiful thing you encounter when examining all the other bad qualities of the mushroom.

How does the fungus spread?

The sclerotia remain dormant (or hibernating) on ​​the ground or inside, or in the mulch material during the summer and the first part of winter. They can remain active in the soil for 1-5 years. They become active and begin to germinate in mid-winter or early spring, depending on the ambient temperature. This means that they are active when the majority of the camellias are in bloom. The sclerotia germinate producing one or more small brown corpuscles supported by a thin stem and having the shape of a saucer: the so-called apothecia 1-2 cm large (photo above).


photo dr. Luther Baxter

It is precisely from the upper part of the apothecia that a very large number of spores are expelled, with some violence, when they reach maturity and the temperature and humidity are favorable, for a duration of about 7-14 days.

The spores can, if carried by the wind, cover distances of several kilometers.

The Ciborrinia fungus develops well when the temperature is between 10-20 ° C and the humidity is high, much less well at lower or higher temperatures and undergoes a significant decline in periods of drought (15-20 days). It is therefore not active in autumn and at the beginning of winter.

Disease control.

At present, a complete and effective remedy against the Ciborrinia Camelliae Konh fungus has not yet been identified, in any case preventive measures have proved highly effective.

Among the different strategies proposed to break the life cycle of the fungus and which have given excellent results, we list some suggestions:

  • keep the ground under the camellias free from any type of vegetation, as the sclerotia grow well in humid and weed-covered soils;
  • remove all the flowers that have fallen to the ground as soon as possible and destroy them with heat and deep burial (at least 80 cm) as they can cause new infections;
  • if the flowers denote the presence of the disease, when still on the plant, it is good practice to collect them and put them in boiling water before even letting them fall to the ground;
  • the soil that is under the plants, both in the ground and in pots, must be removed for at least 2-3 cm of depth and replaced with new substrate, or without soil (mulching with various materials). The removed soil must be treated with heat or buried at least 80 cm deep. For potted plants, many growers suggest changing the entire soil (bare rooting camellias).
  • after these operations the ground (for plants in the ground) must be covered with plastic film. This should be put a little before the flowering period and prevents the release of the apothecia and therefore the spread of spores. At the end of flowering the sheet can be removed. This process also facilitates the collection of fallen flowers.
  • a thick layer of pine bark or pine cones can be used to replace the plastic sheet.
  • annual pruning of the plant to allow the air to circulate and the sun to enter and thus reduce the humidity around the flower.
  • need to adhere to the strict rules laid down by the various phytosanitary centers regarding import-export. The cuttings purchased or sold abroad must be free of flowers and roots and must be rooted on new substrates that have been properly sterilized.

Camellia growers now have chemicals available to facilitate their fight against the fungus, including in two categories:

  • those that prevent infection of the flower when affected by the spores;
  • those that prevent the production of the spores themselves.

The phytosanitary service of the Lazio Region can suggest the most suitable type of fungicide on the market, with related directives for the use of the products.

Conclusion

At present, adopting all the suggestions and results achieved so far, the mushroom under consideration is no longer an invincible, sneaky and unstoppable bugbear. In China, Japan, USA and now also in New Zealand, the cultivation of camellia proceeds regularly without trauma or drama; camellia producers continue to sell millions of camellias a year because they have learned to live with the disease and know how to curb it.

Why has this disease continued to survive for over 80 years since its discovery? What are the possible reasons that make it so difficult to completely eradicate?

The cyborrhine fungus, thanks to the great resistance possessed by sclerotia, is one of the most difficult fungi to fight, as indeed all those that leave hibernating organs in the ground with marked saprophytic life capacities, such as Botrytis, Sclerotinia, etc. To all this it must be added that each apothecium can spread millions of ascospores which, carried by the wind, can spread even kilometers away.

Then, when the sclerotia finds excellent living conditions (moist soil, rich in vegetation, and a climate of 10-20 ° C), the apothecia and ascospores develop even more numerous.

If we consider that camellia is a plant that has a wide spread and that ascospores ignore the boundaries of each property, it is very difficult to find ways to defend the flowers from their attack.

Based on my long experience in camellia cultivation (over 30 years) I would like to give some advice to camelophiles.

One of the most important precautions to keep the cyborrhine fungus under control are the care and attention with regular pruning and entry of the air and sun into its foliage to obtain flowers less impregnated with humidity (where the ascospores grow well).

For those who own potted camellias it is good not to wet the flowers but only the ground, placing them in periods of rain in more sheltered places.

As for large crops, I suggest what I have done, that is, importing cuttings from abroad without the flower and roots. In addition, in the greenhouses under the shading nets, suspend the rain watering at the time of flowering and adopt drip irrigation, sending the water to the individual pots, each with its own tube.

A good rule of thumb is to grow camellias both in large pots and in the ground, limiting their height to 2-3 m. It is thus possible to have plants that are always well cared for, well pruned, but above all, operations to eliminate flowers affected by diseases are greatly facilitated.

Large trees, especially if grown against walls or walled up alive in squares covered by concrete, represent only large evergreens, with many leaves and few flowers that are difficult to keep under control and without any value.

It would also be good if the news that is given to combat cyborrhyny were disseminated to a wider range by the means of communication and by the bodies that care about plant health and the protection of the landscape.

As a last tip, it is important to observe the phytosanitary requirements issued by the regional phytosanitary services and in particular the obligation to report to these centers the presence of any plant diseases manifested by the plants being reproduced or marketed.

For those who have only a few plants, the report can be made to the regional manager or directly to the nearest phytosanitary center.

Gen. Ettore Rolando

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