Rhododendron Leaves turning Black

[Brod]

I Noticed today that on My Rhododendron some of the leaves were Starting to turn Black, I wasn't sure what caused it so i figured someone on here might know.
It hasn't flowered this year But has been growing well and has lots of new shoots staring to appear. Some of the new leaves are also starting to go a burgundy colour too, Not sure if this is part of the same thing or Just what happens.

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Any Advise would be greatly appreciated

[Bush bunny]

Where are the black ones? They just look like darker green being the older ones. The lighter leaves appear to be new ones? But in doubt re-pot it, note its drainage. The only suggestion I can make if the leaves are indeed black, it is drowning. I'll enlarge the picture to make sure.

[Bush bunny]

I've enlarged the pics. Maybe more experienced bonsai-ers can make a comment. It could be a nutritional deficiency or have you sprayed it with something? I'm sure that someone will give you an answer, but black usually means to me anyway, I killed an avocado with it, is drainage. Or cold.

[Brod]

I have circled the leaves that are starting to turn black, its not the whole leaf just the end half.

[alpineart]

Hi Brod , mate mine were hit by frosts and have a burn ressembling these pics . My ground growing garden Azalea's are fine its only the bonsai trainers that are effected . I wouldn't be too worried as it certainly looks healthy enough . Time to fert with Azalea or Citrus food and a pinch of chelated iron helps with any yellowing .

Cheers .Alpineart

[Bush bunny]

Maybe just pick that leaf off at its stalk. Quicker remedy, eh?

[treeman]

If it's a sastuki it could be frost. Usually though there are two main reasons for blackening leaf tips. Too much fertilizer or too much water. They are last years/season's leaves so I would not worry too much but if it happens again, I would check out the above 2 possibilities.