My early Red Norland potatoes have always died back before my later maturing Kennebec but this year that did not happen. The Kennebec died back first and the Red Norland kept on growing. I think the combination of a few days of 100 degree temperature followed by 10 inches of rain is the cause. I've been growing these varieties for 35 years and this has never happened before. I started digging them anyway and the potatoes look fine even though the vines are still quite green.
Here are the Kennebec potatoes! Dead!
And here is a box of some of the larger Red Norland.