Dig them up and look at the roots. I suspect that they will show that there
was not any new root development. This can a result of several factors the
first being rain and saturated soil, another is that the root stock was
damaged by handling and transportation from the grower.

Dr. Huey is a very hardy root stock, if you dig them and find that the root
system is healthy, the grafts were probably damaged and they existing canes
simply used their store of food and then died. Again this is usually a
result of poor handling.

Examining the root system will most likely give you the best indication of
what caused the canes to die.

Tim