Only the new growth seems to be affected. Something is impeding its ability to thrive. I'm inclined to think it's lack of acidity. Azaleas need acidic soil to thrive. As a quick short-term solution, you can add a cup of white vinegar (acetic acid) to a gallon of water and feed it to your bush. Sprinkle some pine needles around the base of it to continuously acidify the soil. Add fresh pine needles every year. Mulch around it to keep the soil moist - they have a very shallow root system and dry out quickly, especially if newly planted. No prolonged periods of direct sun either, they like dappled sun & bright shade. Early morning sun or evening sun is fine, but not that intense mid afternoon sun. I see evidence of sun scorch but this can also be traced to improper PH. Right now it should be setting flower buds for next spring.

Thanks but the soil is probably acidic. It is among several other azaleas which are thriving and have done for some time. Yet this is the only one with this problem. It is also behind some shrubs and below a rowan tree which do provide shade. So once more I am puzzled by this.

Water it well. Its drought, or dryness at the root, which has meant the newer upper leaves have shown symptoms first. If its under the canopy of a tree, that also means its competing with the tree's roots for water, so I'm afraid you will need to keep it watered ongoing, particularly if there's no real rain and its summer. You say you only planted it this year, and it takes at least 18 months for a plant to put out extensive roots so that it can find its own water, probably in the other direction from the tree itself. You can trim off any badly frazzled leaves if you like, but increasing its water supply till winter should solve the problem. And keep it watered next year during warm dry spells - you may find it doesn't flower next year - if it doesn't flower initiation has been aborted (initiation takes place the year before, so its important to keep it well watered during summer).

Thanks, Bamboo. I can try that but am still not convinced that it is drought. I have just checked the roots ball and it is moist as is the soil around it. We have had a wet summer and during the spell when it was initially planted, it was watered daily.

I have added a picture showing the plant in context with adjacent azaleas - it is the one with the label showing. Right next to it is one planted at the same time which is doing fine, and close by are others that have either been planted this year or are already established. None are suffering.

I don't know, Somhairie. The third one to the right seems to be suffering, also the one two on along the arc.
When you planted them, did you do any soil conditioning? If so, did you mix the compost well with the soil, or did you leave lumps and layers of compost underground? Have you fed them recently, and if so, were you careful to be consistent and conservative with the feed? Is there possibly a dog that may be peeing on them?

When I planted the new ones, I layered the hole with some compost and also mixed compost into the soil that I was backfilling. You are right about some of the ones to the right of the picture. Those are established plants and some of the leaves are a little yellowed now as they come to the end of the summer.

It is interesting that you mention a dog peeing on the plants. To the left of the area I have had to remove dog poo a couple of times recently. So I wonder about that now.

I will treat it as drought tho and water from now to the end of the summer.

That layer compost is probably playing hob with the roots, then, Somhairie. Not much you can do about it, except to encourage the earthworms.