Maple Tree leaves looking sick

I have a tray with three Japanese maples. One of the trees has developed this gray dried up spot on several leaves, maybe a dozen. One leave is completely dried up and looks like this all over.

I looked at the bottom of the leaf and didn't see any obvious insects or other pests. The gray crinkled patch appears to go through the leaf. How the rest of the point stays green is beyond me.

Before anybody asks, they were indoors three years ago and not since. Weather has been pretty hot and pretty dry until yesterday. Hurricane season in the gulf is having its usual sudden cooling drop and rain predictions.

What could be causing this? And, of course, what do I do?

Ivan, it looks like some kind of fungus, perhaps?
Not quite sure..

This looks like powdery mildew to me. Aphids can sometimes transmit this to plants. You should be able to treat it with a fungicide. You should be able to find one that treats this type of mildew at any hardware or lawn and garden center. Just my two cents.

Hard to tell but what are the chances it got sunburn?

leatherback wrote: Hard to tell but what are the chances it got sunburn?

Probably not sun burn.

We spent June to a couple of weeks ago with hard sun most of the day. The last couple of weeks have been mostly cloudy. If it were going to be sunburned I really think it should have shown up before now.

I spend time pulling weeds, etc., several times a week and if it had been there last week I would have seen it, I think.

Clicio wrote: Ivan, it looks like some kind of fungus, perhaps?
Not quite sure..

I'm going with fungicide. The maple right side it is showing some.

Arent you in the end of growing season?

I dont do anything to infections in the end of the growing season. The leaves Will drop anyway.

Tropfrog wrote: Arent you in the end of growing season?

I dont do anything to infections in the end of the growing season. The leaves Will drop anyway.

We had the summer dormanr period and now are a couple of weeks into the second growing period. It usually lasts until end of October when the leaves start to change. The maples have new shoots springing out now. The azaleas have suckers a foot long that started growing a couple of weeeks ago.

Usually the trees don't grow much mid August to mid September because the days are long and hot, 95F to 100F or hotter three or four weeks, 35C to 38C. I used to think the dogwoods out in the yard were dying, but they spring back just fine.