I never advise poisoning voles since you are also going to poison anything that may feed on the dead vole. This would include cats, dogs, owls, hawks, ravens and other carnivores.
I’d suggest using a repellent like Bonide Mole-Max to drive them from the area. It works quickly.
You can also bait regular mouse traps with peanut butter and place them in the vole pathways and kill them that way.