Sorry about your sweet taters.I have read up on Voles. I don't don't how they found the sweet potato ridge as much as I kept the adjacent areas tilled up that would have destroyed their tunnels. The are here according to what the State of AL has on file on them. They are down right out nasty mean destructive garden predators. There reproduction rate is phenomenal. I may have to go to a protected raised bed method of raising a few hills of sweet potatoes if we are to have any to preserve.
Last spring I had a 4x8 bed of carrots. I just broadcast the seed and let them grow. I start thinning when they get to baby carrot size. When I started pulling there was nothing but the greens. Those voles took over half my carrots.
They did not touch the onions or garlic on either side. I will plant carrots again as the weather cools. I'm thinking about planting them with garlic around all sides.
Yes, voles are nasty pests!