Thank you for your question. At this time I am unable to give you a positive answer to the growth. At first I was thinking a fungus of sorts perhaps a bark canker but am unable to confirm this. It well me a type of fungus though. You may want to consider contacting a licensed arborist to check out the growth. Was there any vine growth on the tree? Perhaps this is some roots of it left behind. I have turned your question over to an OSU agent who hopefully will get in touch with you or me. In the meantime I have listed links below that may be of some help. Also consider getting in touch with your county OSU Extension Service. I have listed their information also.

Thank you for allowing us to help you with your gardening questions. Here are some other helpful websites:
BYGL Newsletter: http://bygl.osu.edu/
OSUE FactSheets: http://ohioline.osu.edu
State Master Gardener Volunteer website - http://mastergardener.osu.edu

Licking County OSU Extension Office

771 E Main St, Suite 103

Newark, Ohio 43055

Phone:<personal data hidden>

Fax:

4<personal data hidden>

Link:

Visit the Licking County Office website

https://plantvillage.psu.edu/topics/walnut/infos

https://s3.wp.wsu.edu/uploads/sites/2071/2013/12/Disease-Problems-in-Walnuts.pdf

http://fruitandnuteducation.ucdavis.edu/fruitnutproduction/Walnut/Walnut_DeficienciesPests/Walnut_Diseases_Disorders/

https://www2.ipm.ucanr.edu/agriculture/walnut/Shallow-Bark-Canker/

Hi Amanda;

Your question and concern for your English Walnut trees has been forwarded to the Licking County Extension Service for their review. Hoping they respond soon with beneficial information.

Thanks again for allowing us to be of assistance to you. Have a Great day.