New Japanese Maple Struggling

[DeepSouth]

I acquired a couple of mature japanese maples at an auction a couple of months ago. One was, and still is, very healthy. The other not so much. Looking back, I realize I probably should not have purchased it as I noticed it had several issues at the auction, but alas, it does not seem severe enough to not be curable (at least I hope).

It had several decaying/crispy leaves at auction. Over time, it has lost at least 35% of its leaves and the new ones that are growing are are turning black and crisping up. I have kept the tree in a mostly shady area with consistent watering. I have other acer palmatums in my collection that have done well in this particular location of the garden.

The leaf blackening seems to start either at the edges of the leaves or near the petiole, spreading out through the veins. Eventually the entire leaf dies.

I initially thought it was fungal. I have been spraying with daconil regularly and have treated the tree with systemic fungicide (Bonide Infuse granular) to no avail.

I have a few others with similar symptoms, though not to this extreme extent.

This species tends to struggle here in late Summer (I still consider us to be in Summer), but this seems pretty extreme.

New Leaves:



This is what they look like before they fall off:

 

[akillas]

I am also on the border of 8b and 9a, and these last few years have become quite inhospitable for acer palmatum.
I would say you have roots shutting down, either compaction, or overheating.

Tell us about the soil.
Did you acquire it from a northern(more temperate) location?
Did you take it out of the pot to inspect the roots?
Is the pot plastic or clay?
Does the pot sit on a hot surface?

I also lose some new growth in very hot days, even on heat/sun resistant cultivars and under shade cloth, and it looks similar to this-inability of the root to supply enough water to the leaf, either due to rapid water loss from the foliage, or roots shutting down from lack of oxygen/overheating. I would venture the second in your case

The ones that have a coarser inorganic substrate fare way better(almost no foliage loss) because i can water them 2-3 times a day, cooling them down, and roots breathe easier.

 

[DeepSouth]

The soil appears to be mostly or all inorganic. It is fairly coarse, but most grains less than 1/4”, so not as coarse as some of the substrates that I use.

The pot is a mica pot that is beginning to break down. The tree is in mostly shade so should not be getting too hot.

I do plan to repot them in the Spring with fresh soil and a new pot.

It looks pathogenic to me. I too have issues with scorch from heat and Sun, but this is presenting differently. I am also noticing some twig for back as well, which is making me think pseudomonas?

Here is a picture from today.

 

[akillas]

None of my trees ever had this, so i dont know this bacteria pattern. It certainly doesnt look fungal to me, it lacks basic symptoms.

It sounds like the soil is fine (if you lifted it and saw it wasnt compacted)
If it is pseudomonas, its hard to cure..It never really goes away, every time you stress (bonsai train) the tree, it comes back. If the guy sold it to you in a dry period and masked its symptoms, i would return it.

 

[DeepSouth]

Dang. Well, I am going to try treating it with Phyton 27 and streptomycin, removing anything that looks infected, and just leave it alone for the next year of growth.

Pseudomonas appears to be fairly ubiquitous among most plants and targets weak ones. Considering the fact that Acer p. always weakens here from the heat near the end of summer, I suspect that I won't ever fully resolved the problem.

 

[akillas]

You could isolate the tree, cut infected areas, keep it under cover so it gets no overhead rain, and water it only by submersion in water. A local arborist and friend recommends this method, along with something copper based as per product instructions. Never seen a full recovery though, and it can infect easily other trees. I would just get rid of it if you have more vulnerable and valuable trees.