Photinia is about 4 years old, in a semi-sunny semi-protected position, has thrived till about 2 weeks ago when I started to notice that the leaves were not as perky as usual (seem to be half drooping), and around 70% of them have gone quite a deep red colour. There is new growth/flower coming through at the ends of many of the stems (looks like mini purple flower heads). I thought it may be dry, so watered it 10 days ago, but seems to have had no effect. Any ideas please.
Red Tipped Photinia 90% Red With Droopy Leaves
Certified GKH Gardening Expert
It sounds like a root rot, but there are a few that it could be, such as cotton root rot, phytophthora root rot or root rot stemming from poor drainage.
Check the roots and base of the plant for damage. You can try drenching the soil with a fungicide which will work on some forms of root rot. But some of the root rots are fatal once the plant is infected.
Keep a close eye on nearby plants. If they start to fail in the same way, than it is an incurable form of root rot and the plant must be removed ASAP or it will continue to spread.