Defra

Camellia flower (or petal) blight is a disfiguring disease of camellias caused by the fungus Ciborinia camelliae. It is one of the most serious diseases of camellias in the USA. An outbreak in the UK would be difficult, if not impossible, to eradicate because the fungus produces large resting bodies (sclerotia) which remain viable in the soil for at least three years.

It is indigenous to Japan, but is also found wherever camellias are grown in North America, including Canada. In the last few years it has appeared in New Zealand where it is spreading uncontrollably. There are also unconfirmed reports of suspicious symptoms being seen in some European countries.

The only host is camellia and only its flowers are affected. Symptoms begin as brown specks on expanding petals. A brown rot then spreads up from the base of the flower. The rot continues until the whole flower is dead, leathery and rusty brown.

• The sclerotia, still attached to flower debris, overwinter on the ground or below leaf litter.
  
  
• During warm wet periods between January and April, one to several small stalked structures, up to 100 mm high, arise from each sclerotium. These bear brown saucer-shaped discs (apothecia) 5-18 mm wide.
  
  
• For several weeks millions of spores are discharged forcibly from the top surface of each disc. These spores can be carried at least a mile, and probably further, by wind currents. They infect petals any time after the petal tips emerge from the buds during cool (10-18°C), cloudy and damp weather.
  
  
• Flowers at the top of a bush become as severely infected as those lower down.
  
  
• The fungus can also grow and complete its life cycle on cut blooms. Fortunately, it does not produce any spores on infected flowers and therefore the disease does not spread from flower to flower. However, buried in soil or leaf litter, the sclerotia can continue to produce more spores each spring for up to three years.
  
  

The special requirements mentioned above only apply to camellia plants from outside Europe. As a precaution, and at least until further information is available on the suspected European findings, extra vigilance is required to check all camellia plants for the signs of this very damaging disease. It is good practice to keep imported and other brought in plants, from whatever source, in isolation from own-grown plants and to inspect them regularly until you are confident the plants are free from harmful pests and diseases. Any cut flowers brought in for exhibition purposes should be kept away from growing plants and disposed of safely, preferably by burning, and should not be consigned to the compost heap.