Seen it before sometimes -- it's some kind of late-summer leaf-blight that London planes get & pure Amer sycamores don't.

Would be nice to find a Platanus that is resistant to both diseases.

I have 2 London Plane trees with similar disease. From a distance, tree looks like it's coated with a dull gray/white film - it looks dry. Up close, see photo. The bark also looks dry & dead, and there are small flying insects (new this year). The trees have steadily gotten worse over several years. Everyone I've spoken to locally thinks it's anthracnose, but it doesn't look like any of the photos online. Also new this year, plants below tree are also looking similar. I would love to know how to treat these poor trees!

I think that's powdery mildew, and I think that's part of the problem here, too.

I get the gist that it is nothing life or death? my London plane looks ok. I guess there is no need to spass out yet.

There has been hybrid London Planes that are far superior than the existing species, including American Sycamoures.

Platanus mexicana is very resistant to foliar diseases. They look flawless all year here.

Thanks for the ideas. Powdery mildew photos online don't really look the same, but could just be difference in location, etc. Does anyone have comments on efficacy of standard treatments for powdery mildew?

There's also the lace bug.

Same thing happening this year. I'll post some pics soon.

I think the LP's suffer from a combo of sycamore lace bug and powdery mildew damage.

Leaf:

At least they have attractive bark for the winter or when they are defoliated.

I just can't beliebe after losing ALL their Ash trees the Gateway Arch ground folks decided to plant ALL of one kind of tree again. The planetree in this case.

I do wonder if some of the newer cultivars like 'Exclamation' and 'Columbia' fare any better in this regard. Seems like nobody plants anything but 'Bloodgood' and unnamed seedgrown LP here.

I wonder if it isn't the moisture in the air, the weather etc. My London plane has a few leaves turning burnt orange, but the Sycamores are more affected, getting brown leaves. But this is late summer, if it is just a matter of "ugly leaves" who cares? Next season it may not be a problem. If it is humidity, and is showing up in August especially middle to late August, I could live with it. I am in the country though. There are lots of other trees around, in the city I guess, if you have a specimen tree, and it looks like crap, I might be sqwauking too.

Just bought an Exclamation London Plane acerifolia in Seacoast New Hampshire and its leaves (about 10%) are affected now in late August.

I wouldn't worry much about that. I haven't looked at my regular London Plane lately to see IF I have any discolored leaves. You are likely getting tons of rain now, or had from the 2 hurricanes, so, MAYBE that is why? I'm in SW Pa and we are getting tons of rain now after a pretty dry summer, soon the leaves will be gone anyway, so, why worry?

I don't see any leaves on the ground from my LP yet, I THINK if your LP had a disease the leaves would have been shed, BUT, I am guessing. Now, you haven't let the roots dry out have you? I am guessing you've been getting lottsa rain, so, don't NEED to water it, BUT, IF your area is dry, it WOULD need watered since it is a new planted tree, BUT, you are no dummy, you've planted trees before. Later.