Hi, this is Steve and thank you for your Ask Extension question regarding your locust tree. It’s difficult to diagnose a problem based on your pictures. However, two of the most common issues with locust are canker and collar rot. I’ll send a link to a CSU fact sheet and perhaps you can do some diagnosis based on the information contained. The other issue to think about would be if there has been any work around the roots (digging/construction/applications of herbicides/etc) which could cause a sudden decline in the tree.

Here is the link to the fact sheet: https://static.colostate.edu/client-files/csfs/pdfs/honeylocust.pdf
If you would like to submit further pictures, please send a picture of the entire tree in the landscape, the trunk where it goes into the soil, and any other pictures of damage to the trunk or limbs.

Again, thank you for your question.

  After reading your fact sheet, I think I have canker in my tree. Your thoughts?

3 photos added.

    Thank you. 

           Gary

Gary, I would think that is correct. As the fact sheet points out, either issue is generally fatal to the tree and your locust appears to be in late stages. You could reach out to a Certified Arborist to confirm if there is any rescue treatment. Arborist can be found at treesaregood.com and there is a search feature based on miles from your zip code which will list Arborists. Thank you for reaching back with the pictures and don't hesitate to contact us with any further questions.