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 caught unprepared to face it and to limit its activity, as already 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 quickly 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 with 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.
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 moist and weedy 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 instead of 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.
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 the sclerotia, is one of the most difficult fungi to fight, as indeed all those that leave hibernating organs in the ground with a marked capacity for saprophytic life, such as Botrytis, Sclerotinia, etc. To all this it must be added that each apothecium can spread millions of ascospores that, 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 the operations to eliminate the 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 media 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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The Goto islands are located in the most westerly area of Japan and are surrounded by the ocean, which means that they are blessed with a very mild climate due to the warm Tsushima current. The whole area is covered with naturally grown yabu-tsubaki (Camellia japonica) and plantations are estimated to contain about 10 million camellia trees. For this reason the Goto islands have, for the first time, been designated a special economic district for the development of the camellia industry by the Japanese Government. Historically speaking, camellia trees in the Goto islands have been used as wind breaks to protect agricultural crops not only from violent storms in summer but also from cold northern winds in winter. At the same time camellia seeds have been an important source of high quality vegetable oil in the food industry. Furthermore, a new possibility has emerged in the cosmetic industry following the development of new technology by a major commercial company in Japan.
Thus, it is very important to maintain the constant supply of camellia oil for the sustained development of a new industry. The purpose of this research is to find possible reasons for the irregularity of seed production in yabu-tsubaki in the Goto Islands, which has been revealed by recent statistics, and to establish a technical basis to stabilize the production of camellia seed for the utilization of camellia oil.
Occurrence of flower blight in the Goto Islands and maintenance of street yabu-tsubaki
Flower blight on yabu-tsubaki in the Goto islands is believed to have been endemic for many years. However, accurate estimates of the damage caused are not available due to the lack of systematic disease surveys.
The fungal pathogen (Ciborinia camelliae) specifically infects the petal of camellia following the dissemination of ascospores from apothecia formed from the previous years' sclerotia in the soil. Normally prevailing infection in the field is known to occur from January to March. However, natural occurrence in the field has been observed in a certain area in the Goto islands as early as November. The life cycle of C. camelliae under natural field conditions of the Goto islands is shown in Figure 1.
Img.1 The life cycle of Ciborinia camelliae in the Goto islands.
Yabu-tsubaki has been used as a symbol of Goto City for many years and more than 400 yabu-tsubaki are planted in both sides of city boulevards (Figure 2).
Fig. 2 A street scene of Goto City with Fig. 3 Deep watering through pipes camellias as street trees. for healthy camellia growth.
The trees are regularly pruned and therefore the average number of floral buds per tree is limited to a range of 300-400, though potentially at least 1,000 floral buds could be produced.
Recently a new method has been introduced for water supply to maintain the healthy growth of street camellia trees (Figure 3). This improvement has resulted in the increased production of flowers by providing deep watering around root system of the street camellia trees in the boulevards, which was not available in the past (Figure 10). It is important to point out that the increase in the occurrence of flower blight coincided with the increase of flowers in the absence of effective disease control measures in recent years.
Fruit productivity of the selections of productive yabu-tsubaki in the Goto islands
During the three-year period between 1981 and 1983, extensive surveys to find highly productive yabu-tsubaki trees were conducted throughout the entire Goto islands. The surveys resulted in the selection of the 50 best trees and they were planted in the Ondake Botanic Garden (now a part of the Goto Camellia Forest Park) as a gene bank for the future use (Figure 4).
Fig. 4 Camellias selection of the most productive for camellia oil being cultivated in the Goto Camellia Forest Park.
In 2012, ten yabu-tsubaki trees out of these selections were used for evaluating seed production under field conditions where all trees were exposed equally to natural infections by C. camelliae.
Abundant formation of apothecia and frequent release of the ascospores under the camellia trees in the experimental plots were confirmed (Figures 5 and 6). Flowers were examined for flower blight infection and the number of flowers was recorded for each tree.
Fig. 5 Abundant formation of apothecia Fig. 6 A fallen yabu-tsubaki flower showing flower Ciborinia camelliae blight infection and young apothecia of Cibornia camelliae on the ground.
Table 1. The percentage of camellia fruits to flowers from the 1981-83 selections of yabu-tsubaki
|Flower no. *||258||185||94||172||78||65||127||87||106||118|
|Fruit no. **||31||68||58||34||20||30||42||34||52||13|
* Counting date: February 18, 2013
** Counting date: August 16, 2013
How to deal with camellia, azalea and rhododendron flower blights
For several years, I have been dealing with a common problem that specifically affects camellias called camellia flower blight and caused by the fungus Ciborinia camelliae.
In the spring when the flowers appear, small, brown, irregularly-shaped blotches develop on the petals. These blotches grow larger and eventually the flower turns brown and dies. Infected petals develop prominent dark brown veins, which gives them a netted appearance. Affected flowers often fall off the plant prematurely, often as intact flowers. The disease only affects the flower, so it occurs solely while the plant is in flower.
Camellias infected with Ciborinia camelliae develop dark, hard, irregularly-shaped black nesting structures called sclerotia within the base of the decaying petals. These survive after the flower dies and remain dormant in the soil during the winter.
The sclerotia germinate as the plant comes into flower the following year. They produce small, brown cup-shaped reproductive structures called apothecia, which sometimes can be found on the soil surface below an affected plant. These apothecia release huge numbers of spores, some of which are carried upwards in air currents to the flowers of the plant.
Spores have been known to lie dormant in the soil for several years and travel on the wind up to 12 miles. To infect the flower, the petals need to be wet, so infections are more common in mild (59 to 70 degrees), wet weather.
Azaleas and rhododendrons are also plant species that are highly susceptible to another fungal flower blight called Ovulinia petal blight. Ovulina azaleae infects flowers of both native and introduced azaleas and rhododendron as well as mountain laurel, especially where there are heavy morning fogs. The fungi cause disease, which results in the premature death of blossoms. Drooping, wet flower petals remain attached or tumble onto nearby leaves.
The Ovulinia fungi infect wet blossoms when temperatures are mild, 50 to 70 degrees. Similar to camellia petal blight, this fungus infects only the petals of blossoms, causing white to brownish spots that can enlarge rapidly. This fungus produces sclerotia, that are black, flattened, irregularly shaped and approximately 1 / 8th- to 2 / 5ths-inch long.
As with camellias, the resultant apothecia forcibly discharge large numbers of spores that are carried by the wind onto emerging blooms where they germinate. The spores are also spread by insects, especially bumblebees. This makes it possible for the fungus to spread between many blossoms within several days of an initial infection.
Using sanitary practices in the garden is the best way to control this disease:
• Remove and dispose of fallen, old and infected flowers.
• Do not add camellia, azalea or rhododendron petals or leaves to composting piles or mulch, as it’s almost impossible to heat the compost pile to 140 degrees, the temperature required to kill the petal blight fungi.
• Remove the top layer of potting soil when new azalea, camellia or rhododendron are purchased and replace it with pathogen-free soil.
• Plant in a well-ventilated location.
• Avoid overhead irrigation. Use drip or micro-sprinkler irrigation instead.
If cultural methods fail to provide adequate control, consider applying an appropriate fungicide such as chlorothalonil, thiphanate methyl or triforine one month prior to bud break or before any rainy weather to help reduce the chance of infection. Reapplication may be warranted every 10 to 14 days while foggy or rainy conditions continue.
If petal blight is persistent, gradually replace susceptible plants with resistant plants. Best results ensue when good sanitation and cultural practices are followed.
The best prevention for any fungi or pest infestation is a healthy plant. For the best performance, plant camellia, azalea or rhododendron plants properly to maintain good health. Space plants well and prune them to provide good air circulation.
Each year after blossoms are spent, apply a fresh layer of uncontaminated organic mulch between host plants. Maintain a 4-inch mulch layer to help suppress Ovulinia and Ciboroinia camelliae petal blights in the soil. Keep mulch several inches away from the trunks of the plants.
Initially just spots, the camellia flower blight infection, Ciborinia camelliae, spreads over the petals turning the entire flower brown.
There is currently no effective way of controlling camellia flower blight. However, some cultural techniques and protective fungicide can help reduce the likelihood of infection.
- Collect and destroy all diseased blooms on and beneath the plant.
- Each spring, remove the old mulch, and then lay a layer of 2-3 cm of fresh bark or pine straw mulch around the base of each camellia. The mulch will interfere with the spread of spores to the flower buds.
Notes: Be sure not to over-mulch camellia burying the root system under 4 cm of mulch may harm the plant.
- In dormancy, and up to the buds showing color, apply Organic Super Sulfur or PLANThealth Buxus Blight Buster.
How to Get Rid of Bugs & Fungus on Camellias
Camellias (Camellia spp.) Are an important feature in an all-season garden. The sasanqua species blooms in fall and the japonica blooms during the winter when few other plants are in bloom. With heavy, broadleaf evergreen foliage and flowers of various colors ranging from white to shades of pink and red, camellias thrive in U.S. Department of Agriculture plant hardiness zones 7 to 10 in well-drained, acidic soil. Camellias can be worth the effort with a prolific, long-lasting flower show, but they do require special attention due to the potential of attack from bugs and fungus.
Observe good cultural practices. Healthy shrubs are less likely to develop insect and disease problems, although proper watering, fertilizing and mulching are not a guarantee against these pests. Fertilize lightly with a balanced blend, such as 8-8-8 or 10-10-10 fertilizer, in March and July. Apply 1 tablespoon of fertilizer per foot of plant height, spreading the fertilizer evenly just outside the dripline. Irrigate just enough to moisten soil, but do not over-water. Weekly watering during warm weather with no rain is recommended if soil tends to dry out. Spread a 2- to 3-inch layer of organic mulch around the base of bushes, but do not touch the trunk with mulch.
Identify insect pests on your camellias. Scale insects, aphids, mites and mealybugs are sucking insects that take juices out of the undersides of leaves and young stems. Beetles and weevils chew on foliage and buds, causing a ragged look and distorted buds. Mealybugs are identified by cottony little masses at leaf junctures and along stems. Aphids are soft-bodied, pear-shaped insects that feed in colonies, exuding a sweet substance called honeydew, which often grows a black sooty mold. Scale are the most serious insect pests of camellias. Appearing as little humps, often in colonies on undersides of leaves and stems, scale causes yellowing of leaves and leaf drop. Mites also colonize on the undersides of leaves, causing leaves to have a dusty appearance, often accompanied by webbing.
Control mealybugs or aphids, which usually disappear by the warmest part of summer, with a strong spray of water. When water is not sufficient, insecticidal soap or narrow-range oil can be used to control these pests, as well as scale and mite insects. Apply oil sprays in spring or fall, as application during times of extreme temperatures can cause injury to plants. For especially difficult-to-control infestations of sucking or chewing insects, an insecticidal spray - such as Malathion or Sevin - or systemic insecticide - such as Cygon or Orthene - can be used. Follow manufacturer's instructions for all insect control products.
Install one or more sumps to improve soil drainage. Fungi can attack roots or flowers of camellia. Poor drainage is generally the cause of root problems, resulting in root rot. When roots are damaged by fungus, the plant can be stunted or killed. Drill with an auger to make holes 1 to 4 inches in diameter just outside the plant dripline. Fill the sump holes with pea gravel or sandy loam. Flower blight results in brown streaks and rotten blossoms. Remove affected flowers and discard in the trash. Do not compost. Apply fresh mulch around bushes. Cool, wet weather during the blooming period creates susceptibility to this disease.
Leaf gall is another fungal disease that appears in spring. New growth has an abnormal appearance - thickened leaves and shoots - with discoloration that is green, then white or pink. As the disease runs its course, leaves turn brown and become crunchy. Remove infected leaves and shoots at the first sign of the disease, rake the bed of debris and avoid overhead watering. If the camellia comes down with the disease one year, prevent it the following season by spraying it with a fungicide containing mancozeb at budbreak. Reapply every one to two weeks, according to label instructions.
Camellia Pests and Diseases
Camellias' reputation for being hardy and sustainable garden shrubs is well deserved. However from time to time some seasonal condition or insect event may cause concern in the home garden. Before reaching for the most lethal or toxic chemical to eliminate the problem, consider which solution will have the smallest impact on you and your beneficial friends in the garden. Most insecticides cause a blanket kill effect (non selective) on all the insects, spiders and mites wiping out both good and target bugs. This is now known as a vacuum effect that is unfortunately recolonised by the bad bugs first. Camellias Victoria recommends 'integrated pest management' practices be employed rather than a "ground zero" approach to pest control, i.e. tolerate minor infestations for the sake of friendly predators such as lady birds, praying mantis, native birds, etc.
MOST COMMON INSECTS
These small and easily recognized insects are usually associated with new growth. They can be green, black or brown in color and may occur on flower buds during autumn and even winter and new growth in spring. Aphids are sucking insects whose damage weakens the host camellia and are often associated with the spread of more serious diseases. Squashing them between your fingers can attain control of small infestations. Some people recommend squirting with a strong spray of water, be cautious, this may only be spreading the problem further around the garden. For chemical control, you should ask for a modern low toxic and, most important, selective insecticide eg. 'Confidor'.
This pest invades our gardens in spring and early summer, they use favorable wind currents to cover large distances to spread through our gardens. Control, same as for aphids.
Two types are found in quantities which may require more than an occasional walk past squeezing the rolled up growth tips. They are the cabbage white and the light brown apple moth larvae. For a major outbreak requiring spraying, use a chewing insect spray, eg 'Carbryl'. A biological spray 'Dipel' may be applied, this has proven effective in orchards and vineyards. Whilst it is not 100% effective once the microbes are active a high level of caterpillar control is achieved.
May be found on camellias where plant vigor is not strong, also large containers, heavy shade and over dry conditions seem to promote scale. Scales are small roundish insects that may be found on the underside of the foliage or on the stems. They can be white, brown or black and are often found in conjunction with ants. The ants offer protection to the scales and also aphids in exchange for excess sap that they exude that the ants use for food. Control of the scale will also make the ants move on. Use “Pest Oil” or “Malascale” as recommended and use a follow up spray to kill off any secondary hatchings.
European garden weevil damage is easily identified by tell-tale scalloped chew marks around the outside of the leaf. The damage is unsightly but usually localized to a small area of thegarden. Weevils are nocturnal so identification can be tricky as catching one isn’t easy. The traditional method is by far the easiest using trap boards. Weevils only move ader cover of darkness so a plank (50cm x 15cm) strategically placed near the affected plant flat on the ground gives this villain a hiding spot. You will find your weevil waiting for you in the morning. Chemical control would be a residual chewing insecticide, eg. "Carbryl".
Two-spotted mite (also known as red spider mite) may choose camellias as a host over the hotter months. This seems more common in garden situations where dry, still conditions are constant particularly along fences and in shade houses where over-crowding occurs. Chemical control of mite has become nearly useless due to chemical resistance of the mite. Changing the host environment is beneficial, more direct watering of the foliage, pruning overhead branches to reduce shading is also effective.
They are so small and difficult to see without some magnifying device that they often go undetected. They are wormlike and range in length from 0.1 to 0.3 mm. They also have considerable reduction in body structure the two pairs of hind legs and most body setae have been lost and the front legs are reduced. The symptoms they produce include odd color patches on leaf surfaces, leaf margins that roll inward or downward, swollen and distorted leaves, galls, russetting, and “witches brooms”. The symptoms are often confused with the symptoms of growth regulator or herbicide damage.
Biological Control: Predatory mites are voracious eaters will devour the imbalance and then establish their own balance in your garden. Notes: predatory mite are very susceptible to many chemical sprays, use with caution. Predatory mites can be bought by mail order and sourcing through the internet is a good way to access them.
This unsightly black sticky substance is actually growing on the residue products secreted by aphids and scale. Identification and elimination of the pest as previously discussed will correct this situation, followed by an application of white oil or pest oil to eliminate the sooty mold spores.
Botrytis (Gray Mold)
This is one of the most common airborne fungal diseases affecting camellias. It causes premature aging of blooms and brown spots especially in the centre of flowers. To confirm the presence of botrytis turn the affected flower over and look for grey hairlike growths around the base of the flower. Botrytis may also result in pink circles on the front of the flower as in roses. Botrytis is a seasonal event commencing around late April with sasanqua flowering and continuing throughout the entire season. Cool, moist and very still conditions favour botrytis and, infrequently, these are constant enough to make this disease a big problem for home gardeners. Keeping potted plants spaced and maintaining affected bushes trimmed to allow better air circulation make it unlikely problems will occur. If chemical control is required most rose fungicides such as Triforine or Mancozeb contain agents to combat Botrytis.
Camellia Dieback and Canker: (Glomerella cingulata.)
This is one of the most serious of all camellia diseases and is caused by the fungus Glomerella cingulata. Leaves on affected branches suddenly turn yellow and wilt. Branch tips usually die. Gray blotches appear on the bark and stem, and then sunken areas (cankers) develop, eventually girdling the stem. Parts of the plant above the stem canker lose vigor, wilt and die. Damaged plants show more symptoms during hot, dry weather.
Prevention and Treatment: Keep camellias as healthy as possible. Plant in a well-drained acidic soil, avoid wounding and fertilize properly. Remove diseased twigs by pruning several inches below the cankered areas. Disinfect pruning tools between all cuts, using a solution of one part household bleach to nine parts water. There are fungicides available to treat the affected areas which can be applied during wet periods and normal leaf drop periods to protect fresh leaf scars from infection. Apply all chemicals according to directions on the label.
Leaf Gall: (Exobasidium camelliae)
This disease is more common on sasanqua varieties of camellia (Camellia sasanqua) than on Camellia japonica. It is caused by the fungus Exobasidium camelliae. Leaf galls are most often observed during the spring flush of growth. New shoots and leaves become enlarged, thickened and fleshy, and appear abnormal. The color of the affected areas turns from light green to nearly white or pink. The galls later rupture on the undersides of the leaves revealing a whitish mass of spores. The galls eventually harden and become brown. Plants are seldom severely damaged.
Prevention and Treatment: Remove and destroy young galls before the lower leaf surfaces turn white and spores are released, or the disease will be worse the next year. Rake up and remove fallen leaves. Avoid wetting the leaves when watering. Humid, moist, shady conditions favor gall formation.
Phytopthora and Pythium
Young cuttings and seedlings are especially prone to these root rot diseases particularly when in potting mixes rather than the garden. The use of “Fongarid” as a protective drench is a worthwhile practice for all propagators to make routine, even if only a few cuttings are attempted a year. Propagation trays or pots should be washed down in household bleach at recommended rates for floor cleaning.
In larger plants root rots are more likely to occur as secondary issues taking hold only if there are pH issues or micro nutrient problems. Regular re-potting even if no increase in size is required (say every second year), fertilizing regularly especially in pots in spring and autumn with a complete fertilizer, and maintaining a soil pH at a range of 5.5—6.5 will keep healthy camellias.
Camellia Petal Blight
Just the mention of this disease leaves Australian camellia growers in a cold sweat! At present camellia petal blight is not in Australia, however our friends in New Zealand and the UK are the most recent additions to the list of infected countries, which includes China, Japan, USA and most of Western Europe. This fungus disease uses air currents to spread, its spore landing on camellia blooms, turning them brown and to mush in as little as a day. The devastated bloom falls to the ground where the full cycle of the fungus is completed and ready for repetition next season.
Chemical control has to date been almost useless as chemicals are only in the developmental stage or very expensive. Even cleaning up the spent blooms will only help a little as wind spread has been found to be a massive 300 kilometres a season. The greatest risk to Australia is an illegal imported plant being brought in outside our stringent quarantine services. Soil contaminated shoes are also a major threat so declare your shoes to the Quarantine officer at the airport for inspection. They are happy to assist you with this.
Camellia flower buds may drop off of the plant before opening or the tips of the young buds turn brown.
Prevention and Treatment: Bud drop can be caused by several different factors. One of the most common causes is large fluctuations in temperature or moisture. Camellias perform best planted in areas with uniform moisture that are not too wet or too dry. Freezing temperatures can cause buds to drop before opening. Hot weather during the autumn or spring may encourage shoot growth and cause the plant to drop its flower buds. Avoid planting varieties that bloom late in the spring and plant in a shadier, cooler location to help prevent this problem. Other plant stresses due to a lack of nutrients, poor soils or drainage can cause flower buds to drop. Excessive use of nitrogeneous fertilisers such as, Blood & Bone and Nitrosol can also push new foliage growth at the expense of flowers. These fertilisers are best applied just after the flowering cycle to maximise the regrowth spurt. Camellia bud mites cause buds to develop slowly and either open late or fall off before opening. Camellias that drop their buds year after year may have a varietal problem or a problem of location that can be solved by transplanting.
Camellias planted in full sun or against a north or westfacing wall often get sunscald. Leaves will develop scorched or bronzed/yellow areas on the side of the plant directly exposed to the sun. Leaf-spotting fungi may infect the damaged leaves. Sunscald is a particular problem on camellias transplanted from shaded to sunny locations.
Prevention and Treatment: Prevent sunscald by planting in a shadier location or providing more shade to their present location. Once the leaves have turned brown, they will not recover. Investigation of the sun hardiness of individual camellia classes and cultivars should also be investigated. By way of example and generally speaking, Sasanquas, Reticulatas, Hybrids and many darker flower coloured Japonicas can endure more exposure. This is also predicated upon the presumption that, they live in good soil, receive adequate water and are mulched during warmer months.
Frost is more likely to damage the flowers resulting in browning off and shrivelling. Although rainfall can also cause this affect, frost damage can be more pronouced. Lighter coloured cultivars are particularly suseptible to frost and weather damage and should be sited in a more easterly aspect and not facing towards prevailing, wet or frosty weather directions.
Drought: Severe drought conditions and all the stresses related to them such as, inadequate watering, heat stress can result in the underperformance of your camellias. This can equate to some levels of defoliation and poor flower-set or qualtity. However, established camellias have proved themselves to be extremely drought tolerant.
This disorder appears as numerous small bumps on the lower side of leaves or on stems. The “bumps” are tiny clusters of cells that divide, expand and break out of the normal leaf surface. At first, they form tiny greenish-white swellings or galls. Later, the exposed surface of the swellings becomes rustcolored with a corky texture. Oedema is a condition promoted by abundant soil water taken up by the plant in warm weather. Under these conditions roots absorb water faster than it is lost through the leaves, especially when a sudden cool weather change occurs. This excess water accumulates in the leaves and then is expelled by bursting leaf cells.
Prevention and Treatment: This problem is not caused by disease or insects. Oedema can be caused by overwatering, especially during cloudy, humid weather. Water less frequently and avoid overcrowding plants to increase air movement.
It is advised that correct protective clothing be worn while engaged in remedial spraying, e.g. full body covering clothing, gloves, glasses and face mask. As a further suggestion, if children or pets are an issue, make this the last job of the day so that they are retiring from the garden as you are applying sprays. Never exceed the manufacturer’s recommended application mix rates. Do not apply sprays in climatic temperatures over 25°C. Remember that an environmentally friendly outcome is a safe and sustainable outcome.
Andrew Raper is the owner of Rhodoglen Wholesale Nursery, at The Patch, which is located in the picturesque Dandenong Ranges finging the north of Melbourne. This nursery is at the cutting edge of camellia and other plant material propagation.
Camellia Petal Blight
Camellias are the most enjoyable plant I can think of. They bloom in the fall and winter when the rest of the garden is fast asleep. The gardens become ablaze with color and it is impossible to sit in your comfy chair inside by the fire. You feel the need to get outside and enjoy them despite the weather. So you grab a basket, head out to the garden to pick that perfect bloom only to find that there are these brown blotches all over your blooms? WHAT is this you say as you frantically search for a bloom that is fresh with no spots.
This condition is called Petal Blight. It occurs when cooler temperatures are followed by warmer, humid weather. The culprit, the fungus Ciborinia camelliae Kohn, affects only the flowers of Camellia. It starts as small spots or flecks but quickly spreads throughout the entire flower blossom. When the flowers fall to the ground and decompose, the fungus enters the soil and usually lies dormant until the next year. As the weather begins to show a slight change from cold to warm, the fungal spores are released from the ground, float up in the air and land on opening flowers where they penetrate the petals and the process begins again. Depending on the climate, it can occur as early as December and as late as March or April.
The use of topical fungicide has been largely unsuccessful due to the nature of camellias opening periodically over a period of time. Systemic fungicides that are taken up into the plant have also been unsuccessful. Picking up all of your spent flowers before they decompose is an option but an unrealistic one in most cases. Spores can travel for short distances so even if you are removing all of your blooms, if your neighbor is not, then it's not much help.
We have found that a fresh layer of mulch applied in late fall offers some help to make it more difficult for spores to get into the air. It's not a cure, but it does slow it down.
Here are some suggestions if you want to get the most out of Camellias without Petal Blight.
- Choose fall-blooming Camellias. Petal Blight rarely occurs before the end of December.
- Use Gibberellic Acid to apply to camellia blossoms to encourage early blooming to avoid Petal Blight. This is done per flower and not for the entire bush.
- For enjoying blooms indoors, pick your flowers as soon after opening as you can to lessen the chance of fungal spores.
- Rake up or remove as many blossoms as possible. Destroy blooms by burning if possible. Don't use them in the compost bin.
- Apply a fresh layer of mulch in the fall.