red tip photinia leaf drop
Leaves suddenly start turning pale green to pale/medium brown and dropping off of the branches. This happens quickly. These are healthy, dark green plants.
I would treat for a Leaf Spot fungus.
Apply a recommended fungicide at the first sign of disease or when new growth starts, and repeat application every 7 to 14 days. Be sure to follow the directions on the label. However, the use of fungicides for management of Entomosporium leaf spot is most effective when initiated early at new leaf emergence, and continued regularly until leaves become mature in early June. Then, applications should be made when conditions favor disease development (immediately following rainy periods). Fungicides do not be applied during hot, dry periods.