Black / yellow dots on the edge of Korean hornbeam leaves (Carpinus turczaninovii)

[Unagi]

Hi everyone, I am just back from a 3 weeks holiday and I noticed something unusual on my korean hornbeam leaves. It has small black and yellow dots on the edge of its leaves. Not on all of the leaves, but most of it. The last picture is from one that doesnt have it.

Context:
- My plants were watered by my neighbors, likely over than underwatered
- 3 weeks ago (before I left) the weater was extremely dry with very stong sun. It might got burned at that time?
- In the past 3 weeks, however, was very wet. Almost constant rain and 15-20 C. The plants are on my balcony, so they didnt get water from the rain, but it might be fungal infection because the wet weater?
- I didnt see similar symphyoms on the trees close to this one (chenese elms and ficus microcarpa)

I have this tree since january, maybe it is normal, I dont know.

Is there anything I should treat the tree as a cure or prevention?

Thank you!

 

[Unagi]

Sorry for the ping, but I don't know if I should remove the leaves, spray them with something, quaranteen the tree, or just leave it alone. I am sharing a few closer pictures and one from the back of the leaves (didnt see anything strange). Any opinions?

 

[Unagi]

With the hope that it can help you to help me, I made some pictures about a leaf under my microscope. The last few pics are from the back of the leafs. I would say there are no bugs (like spiders or such) on the leafs, it must be either environmental (sunburn? unlikely?) or fungus/bacteria?

 

[KateM]

It's hard to tell...
Be on the lookout for hornbeam rust, though it does not look like it from your pics.
My opinion, which is hardly worth anything, that it could be heat stress to leaves with some opportunistic fungal infection during following high wetness/humidity...
Hornbeams are understory trees.
I would spray with untifungal and hope for the best.

https://purduelandscapereport.org/article/hornbeam-rust-an-emerging-rust-disease-in-the-us/

 

[Unagi]

Be on the lookout for hornbeam rust

That sounds/looks horrible to be honest... I hope my case will be something innocent. I don't have antifungal spray, but I will visit a shop tomorrow. Thank you for helping!

 

[KateM]

I would cut off the most affected leaves and spray.

 

[SFDrake]

Is it getting enough light on the balcony? Also how humid is it there? I would monitor the watering and spray it down like KateM advised. Good luck!