And now one from a bit further away.

As you can see it is really the interior leaves that are more affected than the outside and the tips of the branches

Here is what one of them looked like at the end of June. Between then and now, I did prune of a couple of small lower limbs off of each of them, but it was pretty light pruning and the wounds appear to be healing well.

Cool nights and warm, dry days. The tree "thinks" it's Autumn. I wouldn't worry about it.

They all seem to do that, every year.

Not sure why.

Pretty common for sycamores here to that in August.

Thanks. Just seemed early. If this were 2-3 weeks later I wouldn't have thought twice.

Also. Doesn't seem to be happening in bigger more mature trees in the neighborhood.

It is a wetland tree, isn't it? It might not get enough water to keep all its leves, standing in a lawn. Do wild growing trees also lose leaves now?

Even the wild ones here are doing that. This includes many growing on a riverbank close to me. My London plane still is green though. We have been getting alot of rain lately, about 1 and 1/2 months straight. Having rain at least every 3-4 days. June was our last dry spell, and only 2 weeks in June.

@ poaky1, You had unusually cool nights for July, no?

Anthracnose? http://www.ext.colostate.edu/pubs/garden/02930.html

Several very cool nights in July.

I believe anthracnose is a spring early summer deal. Not the case here I don't think.