What seems odd to me is that the damage is in the middle of the leaves, rather than the tips which is more usual. Hence my suggestion.
Given your history with fungal issues on maples, I would 100% recommend dormant treatments (spray or dip) with lime sulphur, diluted about 20:1, next winter and spring (before the buds open). Strict hygiene, keep foliage dry, ensure good air circulation, make sure your substrate doesn't stay too wet. There does seem to be something going on in your garden, you shouldn't be seeing all these problems.
I thought about the dormant spray last year after always hearing plenty about it but didn’t go for it. I will in future or now, as Bobby suggests. I will allow this maple to dry a bit more than others, I have been watering more frequently recently as I think I don’t water enough, as a general rule.
In terms of my practice, Tom and
@River's Edge i have been actually trying with this.
So, I am not watering foliage mass, only root system (especially with maples), haven’t done so this year at all. I was going to relax that rule once leaves harden off.
I water very thoroughly with every tree, so it runs through.
They are all kept on my bench which is in basically full sun all day. It’s been terrible wind lately so they’ve moved about a bit but I’m aiming for full sun, all my trees should be fine it.
Since bud break, I’ve been following a system treatment rotation. I’ve 2 different fungicides and 3 different pesticides. I spray every 3-4 weeks, ensuring I keep rotating. I’m aiming for prevention over cure, but also ensuring trees don’t get used to the same treatment and become immune.
Most trees are in a complete inorganic mix, molar clay/cat litter. Some have small bit of bark. Others are in a more organic/inorganic mix from Kaizen. A few recently bought are in akadama, this maple is one of them.
Two steps I would take. One fact I would check out regarding lime sulphur.
One allow tree to dry out slightly between waterings, do not water foliage. Wet, high humidity conditions must be avoided. Do not keep the soil wet.
Two, if available apply systemic broad based fungicide ( thiophonate-methyl based fungicide) to be absorbed by the roots. Apply to soil.
Note: Lime sulphur is more effective as a preventative than active treatment. It is normally only applied when the trees are bare of leaves and in a vegetative state.
You may wish to rethink your substrate mix. If you live in a damp climate with wetter winters than perhaps adapt to a less retentive soil mix. I live on Vancouver Island and lengthy periods of rain in the winter and higher humidity is part of my climate. For that reason the majority of my trees are kept in inorganic mix with a maximum of 20% Akadama. When I use straight Akadama or Kanuma for specific situations they are hand watered and far less frequently than the rest of the trees. They are also sheltered from rain during winter.
There is a great explanation of Maple health concerns contained in Andrea Merriggioli's new book " Bonsai Maples"
The focus is that the majority of our issues are husbandry issues, plants suffering additional stress due to the conditions they are kept in. Also that some cultivars are very susceptible to certain fungal issues. Preventative measures are definitely required for them.
They primary culprit is soil mix and watering practices, followed by poor placement and environmental stress!
Thanks for your post, great info. I do ensure to keep foliage dry. I’ll try to keep this tree soil a bit drier, atm I’ve been watering more frequently.. so it’s not necessarily dried out before next watering. I’ve removed all the bad foliage and sprayed now. I have actually ended up spraying with same fungicide twice now in the past month, but it’s a very good one so will hope. Any other advice or am I doing the best I can with this at the moment?
we are in a fairly windy, sunny climate currently. Not raining often at all. Very windy.
The tree has also been moved to opposite side of the garden now, all alone.. about 15-20ft from others.