Something has attacked a grafted hazelnut tree. The tree is a few decades old but this last year or so limbs have started dying. I had visions years ago of raising nuts and got some grafts from PA but I’ve never harvested a nut. The squirrels always beat me to them. So if the trees die the squirrels will mourn more than me.
Montgomery County Maryland
Your tree certainly has a big declinging/dying limb.
We would guess that you may have Eastern Filbert Blight. We think we can see some cankers on the dead branch to the right.
It makes growing hazelnuts commercially, and having the lovely ornamental contorted filbert difficult.
Here is more information about it: https://hort.uwex.edu/articles/eastern-filbert-blight/
We don't recommend treatment. Prune out dead and dying limbs and enjoy it while you have it.
Break the news gently to the squirrels.