Name the pest...

[Bonsai Nut]

What insect pest causes this damage on red leaf Japanese maples? It only happened in a short window a couple of weeks ago... no damage before or since. Almost looked as if there was an insect hatch or swarm... and that whatever caused the damage is now gone.

 

[penumbra]

Have you eliminated mechanical or chemical causes? I don't believe this is insect damage but it might be fungal. A closer look might reveal a leaf skeletonizer, but their damage is usually more distinct and while the edges would be sharp, the patches are generally larger.

 

[KateM]

I don't know of the pests that would up and go...
To me it looks more like burn damage from some spray.

 

[SeanS]

Agreed I think chemical damage

 

[Dav4]

Rain drops!!!!

 

[Bonsai Nut]

Very strange... this damage is only seen on five trees - all of the same cultivar. Four are in landscape, one is in a bonsai flat. They were from two different vendors (though it's possible they could be from the same wholesaler). This is the first spring I have had these five trees. I have many other Japanese maples - none of which show any damage. None of the other tree species in my garden show any damage.

 

[rockm]

I believe This is most likely a fungal thing. I’ve seen it happen on some maples every so often. It happens when leaves stay wet and conditions are right.

Thinner leaves cultivars seem to be more susceptible

 

[Dav4]

I'd bet fungal as well

 

[bwaynef]

I saw it on one of mine recently. While my initial suspicion was it was fungal, it did only show up after I'd trimmed outer foliage.