Good Morning, 

Thank you for contacting the U of M Extension Service. 

First, here is a link to the U of M Extension Yard and Garden website from last year about drought affect on trees: https://extension.umn.edu/natural-resources-news/drought-minnesotas-woodlands  Trees take a long time to react to the drought. If the tree was not watered during the drought years, this could be the result. 

Here is a link about oak wilt: https://extension.umn.edu/plant-diseases/oak-wilt-minnesota

Here is another link that includes information about bur oak blight: https://apps.extension.umn.edu/garden/diagnose/plant/deciduous/oak/leavesbrown.html

Lastly, here is a link to the Plant Disease Clinic if you decide to submit a sample. 

Good Luck!

Thank you for your response for further information. Four links were mentioned but I do not see the link to the Plant Disease Clinic. If that link can be sent, I would appreciate it.

Thank you.

Frank, 

So sorry! Here is a link to the plant disease clinic: https://pdc.umn.edu/ The top line menus have information about submitting a sample and also fees. 

Good Luck!