where are you.. can we see the whole tree ... ken

Hi Ken, we are in Essex near Chelmsford. I attach a couple of additional photos.

"Essex near Chelmsford" is most likely in the United Kingdom, England. What has your weather there been like? Wet? Dry? Warmer than normal? Colder than normal?

This might be a fungal disease or an environmental condition. Difficult to know without a lot more information.

Ok. Sounds like you are in US. Thanks for the advice but I need a local expert

Hi there, I live in the US and my walnut tree looks exactly like yours. Did you figure out what was causing this damage? It would be really helpful for me right now. :) -Amy

Draught, most likely. August 2020 was very dry over here, and the smaller of the two young trees was losing whole branches with leaves gradually turning black beginning from tips and edges. I will increase watering of the smaller tree and hope it saves the tree.