With cooler damper weather comes the potential for disease in the garden. Are you seeing spots or brown soggy patches on petals of your favorite camellia blooms? It may be camellia petal blight, a fungal disease that affects all cultivars of Camellia japonica.
Infection initially causes small, brown, irregularly shaped blotches in petals that enlarge rapidly until the entire flower is brown and dead. Except when wet, blighted petals are dry or leathery but do not crumble when handled. Blossoms drop prematurely to the ground, often as intact flowers. Prominent dark brown veins give infected petals a netted appearance. Symptoms that distinguish camellia petal blight from other diseases include petal veins darker than the surrounding tissue, infections beginning near the central part of the flower (not appearing first near petal margins), and symptoms that occur only on petals.
Outbreaks can occur when new plants are planted in soil infested with the reproductive portions of the fungi. Once established the pathogen cannot be eradicated. Wet or humid weather and mild temperatures (about 59° to 70°F) during bloom are optimal conditions for this disease.
Prevention is the best control. Remove the top layer of potting soil when new plants are purchased and replace it with pathogen-free soil. Plant camellias in a well-ventilated location and avoid overhead irrigation. Pull off infected flowers as they appear and collect fallen blossoms and dispose of them – don’t add them to compost bin.
Each year, when blossoms are no longer present, apply a fresh layer of pathogen-free organic mulch and maintain a 4-inch layer of organic mulch beneath and somewhat beyond plants to suppress pathogen production. Remove fallen petals and other camellia debris before applying fresh mulch, but otherwise avoid moving or disturbing existing mulch where fungi may be present. Keep mulch thin near the trunk or several inches away from the trunk.