How to recognise it
This fungal infection only affects the flowers of camellias and is initially noticed by brown flecks appearing on the petals. The flecks rapidly expand across the petals and the petal veins will darken, until the flower dies and falls.
A ring of white/greyish mycelium followed by small, hard, black sclerotia (fungal spores) can sometimes be seen at the base of affected petals. These new spores do not spread from flower to flower, however once the flower has fallen they germinate into reproductive structures called ‘apothecia’ which release spores the following year to reinfect the plant. The apothecia can sometimes be seen on the ground; they are small structures, similar to mushrooms with cup-like tops.
This disease is sometimes confused with grey mould or frost damage, however it can be distinguished by the brown areas occuring at any point on the petal (frost damage generally starts at the petal edges) and by the white or greyish ring of fungal mycelium or black sclerotia around the base of the petals (you will need to remove the calyx to see this) which are not present with either grey mould or frost damage.
Why it’s a problem
Affected flowers are discoloured and will fall prematurely.
Where you are likely to find it
On all species of camellia. Since it is only affects the flowers you will only notice it while the camellia is flowering.
Infections tend to occur in wet weather since the spores require the petals to be wet in order to infect them.
How to prevent it
When purchasing camellias, buy them bare rooted with no flowers on the plant. This will ensure that you do not introduce camellia flower blight spores into your garden from the flowers or compost debris of new plants.
Good hygiene standards in terms of your equipment and clothing (spores can spread on boots or gloves) can prevent this spreading between camellias.
Ensure good air flow between plants to reduce moisture levels (which this disease requires to spread). Water plants from the base to avoid wetting the flowers.
How to get rid of it
Clear any fallen flowers and dispose of them (not on your garden compost, where the spores will continue to develop) to reduce the number of spores overwintering on the ground to infect the plant the following year. You may find it easier to completely remove all flowers and flower buds as soon as you spot the disease – you’ll miss out on that season’s display but you’ll have a better chance of eradicating the fungus. A deep mulch (over 10cm) can also help bury the spores, however this depth of mulch may not be practical.
Currently there are no specific fungicides available for use against this disease on a domestic scale in the UK. If permitted in your local area, dipping the flowers in, or spraying them with, a fungicide containing triadimefon, triadimenol or terbuconazole applied every 2 weeks can be effective in killing the fungus developing on that flower. A preventative fungicide containing pentachloronitrobenzene can be sprayed on the ground around the plant as soon as the flower buds start to open to suppress the growth of the apothecia.
You should also try to identify the source of the infection (likely to be a plant within 200 metres of your infected camellia) so that action can be taken to rid that plant of the disease.
Is it good for anything?!
Other useful information
This disease was first identified in Japan in 1919. It has since spread to the USA, New Zealand and Europe.
Some national authorities require any cases of camellia flower blight to be reported, so if you suspect you have a case in your garden please check with the relevant authorities.