Be on the Lookout for Camellia Petal Blight

Petal blight is very common on camellias in the spring. It is caused by the fungus Ciborinia camelliae. Although petal blight can affect both japonica and sasanqua camellias, it is usually seen in early spring when japonica camellias are in bloom. Disease development is favored by frequent rain showers, high humidity, and mild temperatures during bloom.

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

The blighted petals are dry or leathery but do not crumble when handled. Petal blight can be confused with cold injury, but cold injury is usually found on the outer petals, which become dry and crumbly and do not fall from the plant. Flowers from the same plant can have petal blight and cold injury.

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 Blight

Fungicide 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!

A milestone

This morning, Friday 3/11/11, the ten thousandth sample was entered into the PDIC database, which went online in January 2008.