Blackened and rolled leaves on a maple – what causes this?

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Question by: Hardy G

I greatly enjoy reading your garden tips, which in my view as a qualified gardener, and in contrast to those countless so-called experts, are without exception highly competent. Now I would like to ask a question which has troubled me for many years. The problem is an Acer palmatum dissectum atropurpureum (60 cm high, 180 cm wide). This wonderful tree, positioned on the edge of a sunny pond, produces its leaves anew without problems every year – but in June/July the majority of the feathery leaf tips roll up and turn black, yet remain on the tree and do not drop off. A relocation and spraying it with Orthocide fungicide 50, 0.2%, or Dithane Ultra, 0.1% have unfortunately only proven partially successful. This year, I noticed at the beginning of May a stripe, approximately 12 cm in width, running diagonally across the entire plant in a relatively sharp delineation, along which the feathery leaf tips half roll up and discolour to dark grey. This is surely the starting point for the disease. Dear colleague, do you know this problem? If so, I would be delighted if you could provide me with some competent tips.

The GARDENA gardening expert

Dear colleague, many thanks for your kind words – I humbly thank you for them, not without quiet pride.

Dear Mr. G.: On the matter of the Japanese maple itself: When you say “withering” and “Acer palmatum”, I naturally first think of Verticillium alboatrum / V. dahliae. Yet obviously the branch sections do not die off completely and are fully healthy again the following year – until June and July! I wonder whether we should be thinking of leaf margin drought due the high summer conditions and the “sunny” pond edge you mentioned? In my experience, the interaction of soil, sun and wind leads repeatedly to this variety of Japanese maple, which prefers half-shade and is sensitive to water, being unable to suck the transpiration right into the tips of the leaves, because the force is already consumed half-way up the leaf.

However, you say that the problem is occurring at present. Due to something which I have just experienced: Could it be that, as opposed to the other years, the current damage pattern, due to its sharp delineation, has been caused by a severe night frost?

These three possibilities have now arisen from a remote diagnosis, without being able to view the damage. I suggest the following: Should you have found no approach to a solution, please email me with a few explanatory pictures. Perhaps in this way we can resolve the issue.