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Cause Physiological leaf spot is a problem on photinia in western Washington and Oregon. The cause is unknown. About 25% of the leaf spots samples that have come into the OSU Plant Clinic are of an abiotic nature. Leaf spotting appears to be more severe on plants in low-lying or shady areas. Cold temperatures also appear to be involved.
Symptoms Symptoms resemble those of early fungal leaf spot infections. Small red to purple spots appear on leaves but do not develop the dark centers characteristic of fungal leaf spot infections. It causes little damage to plants, although some leaves may drop.
Cultural control
- Do not plant in low-lying areas where cold air settles.
- Plant in full sun.
- Provide proper culture for plants. Healthy plants are less likely to be affected and can recover from injury more quickly.
- Space plantings and prune to provide good air circulation in the canopy.