What could cause a whole hill of red apple to die? It's been healthy for 15 years with very little care, now within a couple of months the whole hill is brown. Looking up close, the roots and stalks that are still green look fine.

I'll take some to the nursery this weekend and ask. My guess would be some kind of disease, something filtering thru the soil from uphill neighbor, or rats or squirrels eating it.

Any guesses?