Zinfandel late season leaf discoloration

[vtoddw]

This happens every year during ripening around August and I've dug around the internet extensively but I don't seem to be able to identify what exactly causes this, so I'm hoping to get some ideas from other growers who may have seen this issue. The interesting part is that it's only on the top of the leaf, but the bottom looks normal.

Any ideas what discoloration means?

 

[Snafflebit]

That is an odd pattern. Maybe some light sunburn?

 

[vtoddw]

That is an odd pattern. Maybe some light sunburn?

Thanks for the reply. That actually makes the most sense given that it's typically only on the top of the leaves.