Ask Mr. Smarty Plants

First, the good news. It's perfectly normal for bark to peel off a Platanus occidentalis (American sycamore).

On the other hand, this tree has several liabilities. Some of those that might apply in this case are:

Canker stain: First, see this Texas A&M website on Trees, scroll down to "Sycamore," reading especially the paragraphs on anthracnose and cankers. This Pennsylvania State University College of Agricultural Sciences site has more diagnostic information. Finally, take a look at these pictures of canker stain, and compare them with the symptoms on your trees.

American plum borers: A description of this pest of fruit and ornamental trees is found in this Cornell University Integrated Pest Management site on the American Plum Borer. And, again, pictures of the beastie.

Sycamore lacewings: This Ohio State University Extension website on Lace Bugs details their appearance and treatment, but says they are seldom a serious threat. Again, the symptoms of this would show up more in the leaves than the bark of the sycamore.

Okay, more bad news than good news, sorry. Because we are more experienced in the care and propagation of native plants than we are in pests and diseases, we suggest you contact the Hays County Extension Office for information and perhaps a better diagnosis of how serious the problem is. The contact information is at the bottom of the webpage.