Q.Pieris Japonica Flaming Silver Lost Colour
My Pieris Japonica once looked beautiful (see photo with red foilage) but over the last couple of years it has lost colour. It is still alive and does get new growth, but new leaves often drop off and discolour. I’ve tried various fertilisers, feeds, and iron and sulphur products. I’m wondering if drainage is the issue (root rot maybe?). How can I fix that given that it is in the ground and not potted?
Certified GKH Gardening Expert
Root rot is, certainly, contributing to the issue. I don't think that it started with this, though.
I am noticing signs of spider mite infestation, and bacterial infection. I'm willing to bet that they are related! Spider mites, along with their own set of symptomatic damage, will bring about infections to your plants as well.
Before adding anything else to the soil, I would remove that layer of debris from the entire bed. Any infected foliage that falls will become a vector for contamination, so removing and destroying it will help stop the spread of contamination.
After, you can treat the plants and soil with a fungicide. Wettable sulfur will suffice, though copper fungicides will be stronger.
Spider mites will need repeated pesticide exposure to kill them and their eggs.
Here are some articles that will help: