The disease is first seen as brown spot on the expanding flower petals. In the early stages of disease, veins within the spots appear darker than the surrounding tissue, giving some blooms a distinctive netted appearance.
|Camellia petal blight: Note the distinct netted appearance|
The spots quickly increase in size and often extend into the base of the flower, causing the entire flower to fall to the ground. A ring of white fungal growth may be visible where the blossom was attached to its base.
|Camellia petal blight: Fallen blossoms|
|Camellia petal blight: Note the white ring of fungal growth at the base of the flower (top of image). Later, very large sclerotia are produced at the flower base|
Several weeks after the petals fall to the ground, hard black fungal structures similar in size to a chickpea may be found at the base of the flower (seen above, lower right). These sclerotia can persist in the soil for several years. Under favorable conditions (cool weather followed by warm, wet weather), the sclerotia germinate to produce tiny mushroom-like structures. The “mushrooms” produce airborne spores that land on nearby camellia flowers, starting a new cycle of disease.
|Camellia petal blight: Mushroom-like structures produced from sclerotia germination|
How to Control Petal BlightFungicide sprays can be used to control petal blight, but sanitation is the key to controlling this disease in the landscape. Because sclerotia produced in diseased flowers are the source of future infections, the best way control petal blight disease is to remove all fallen flowers and debris from the ground around camellia plants. The sclerotia are too large and hard to be completely destroyed by composting, so infested debris should be disposed of completely. Remove old mulch each spring and lay a layer of fresh bark or pine straw around the base of each plant. The mulch will interfere with the spread of spores from previous years’ infections.
** Be sure not to add more than 1inch of mulch. Burying the root system by adding 2 or more inches of mulch may kill the plant!