That’s an awfully good question. Since you are new, I will give you a complete rundown on most everything I’m thinking.
If you choose not to follow the advice, that’s ok with me. After all, your tree - your choice.
The short answer is I absolutely don’t know for sure exactly what is bugging your tree. It seems to be affected by a cascade of events over time. Likely only a horticulturist specializing in azaleas, perhaps someone in the industry with specialized equipment could deduce exactly what is wrong with thus azalea.
Yet we do have about 120 medium azaleas and numerous (over 300) 2-3 yoa azaleas I work with most every day. Amazingly, I learn things from them.
This is what I do know.
- The tree Is showing multiple symptoms, including, chlorosis, nutrient deficiency, possible underwatering/over fertilizing, ossifying branches etc.
- The tree hasn’t been through a summer with you and it’s been potted in organic mix, pH unk, kept in full sun/ 70% shade cloth
- Yorba Linda’s water is very hard, mildly alkaline.
- watering regime was every two days
- The weather is hot.
- Someone might of watered your tree too much for five days.
- The tree hasn’t been fertilized for 30 days until yesterday. The 12-4-5 fertilizer used has extra Ca, Mg, Fe
Here’s what I think
1. Likely not root rot, bit just in case should be treated as root rot is present. That’s why H2O2 was recommended as it has successfully used been on a number of trees to solve root issues.
Why not likely? Because as
@Shibui mentions it takes a long time to develop.
See photo of an ongoing root rot experiment presently being done out back on two different cultivar azaleas below.
Azalea on right has been submerged for over 30 days with no signs of root rot. This included two periods of 95F.
Azalea on left was also submerged. It got root rot at 22 days and is now being treated with H2O2 in an attempt to nurse it back to health. Note leave tips on left tree.
View attachment 450671
2. Azaleas who normally live in an acid environment, can produce a neutralizing barrier around their roots to help with high pH to some extent. Yet over time and under stress the tree‘s protection will eventually be overcome. The Fe in the fertilizer likely helped to stave this off and maybe the soil if it’s pH is low, but the hard water, maybe the missed fertilization and continually hot summer temperatures likely eventually stressed the tree over its limit. There is no doubt the roots were damaged in this event. Damage in the leaves shows this to be so.
What do I think should be done?
Just what I posted.
a. Treat for root issues with a short lasting fungicide H2O2. Get tree out of sun in afternoons/evening. Mist.
b. Fix the water issue quickly by using distilled water and add a small dose of acidifying fertilizer with micronutrients
c. Provide a long term solution by adding a good long acting chelating agent to OP’s tap water and continue acifiying fertilizer.
What do I think will happen?
The tree is in the ICU in a deteriorating state. Condition is grave. Prognosis unknown.
Once again, your tree, your choice.
Cheers
DSD sends