I have a 75-foot long Photinia x fraseri hedge that is losing leaves. The leaves have dark spots on them. I wonder if it is a mold or fungus. I have not removed trimmings in previous years and air circulation has not been optimum. Some plants have lost almost all their leaves but there is new growth there too. The hedge is about 4 feet tall and is about 20 years old. I was thinking it could use some sort of fertilizer and mulch after I clear out all the old prunings. Any suggestions?
There are a few possible reasons your hedge is dropping leaves. In my own experience with Photinia, they were constantly dropping leaves throughout the year. Some of the leaves had dark spots, but some were just older foliage, reflecting this plant’s tendency to shed older leaves. According to Washington State University’s Landscape Plant Problems (2000), spots on Photinia leaves can be caused by a fungus called Entomosporium mespili, but they can also occur in fall and winter with no disease present. The fungal spots tend to have purple black edges and ash grey centers. Virginia Cooperative Extension has descriptions and images of this fungal disease.
There is another leaf spot of unknown origin, simply called ‘physiological leaf spot,’ described by Washington State University Extension as follows:
“Physiological leaf spot occurs on Photinia in western Washington. The symptoms resemble those of early fungal leaf spot infections. Small red to purple spots appear on the leaves, but do not develop the dark centers characteristic of fungal leaf spot infections. This problem is more common than fungal leaf spot. It causes little damage to plants, although some leaf drop may occur. While the cause of this problem is unknown, leaf spotting appears to be more severe on plants in low-lying or shady areas. Cold temperatures appear to be involved.”
If you want to know for certain what the spots are, you should bring samples to your local county extension agent so that they can identify the cause.
Improving air circulation and removing and disposing of all fallen leaves are always good garden hygiene practices. Avoid getting the leaves wet when you are watering the garden, and avoid summer pruning. The American Horticultural Society book Pruning & Training (DK Publishing, 1996) recommends pruning in spring, though hedges will need to be clipped two or three times a year.
I don’t recommend adding fertilizer, as it could cause your hedge to grow more quickly than you want to prune it. Mulching lightly with compost would probably be beneficial. In general, Photinia is a tough and vigorous plant, and the leaf spots are unlikely to cause its demise.