Hi, Paul -

I can't be sure, but from the photo it looks to me like some type of lichen. Around here lichen is fairly common on tree bark and doesn't cause any harm. Since the leaves and bark on twigs looks healthy, it doesn't seem like it's a disease.

Hi, Paul,

I agree with nhbabs. Click on the article below to read about lichens. You can simply wash it off tenderly so as not to hurt the bark and it may not return with cooler weather prevailing in the near future (we hope).

Jane

Here is a link that might be useful: Univ. Delaware Coop Ext., lichens

Thank you so much. I see similar growths on my natural trees around here. I'm in the Catskills near Woodstock. Every year I lose about 5 trees for reasons I don't quite understand. I'm from the city so maybe I just don't get the natural cycle of the forest around here yet.

Anyway, thanks again