Martha has a few suggestions about what to do about crayfish in the lawn:
Crayfish are mini-lobsters, so I'd put out live traps & have a feast.
Or I'd cover the affected area with the kind of mesh that's used to protect fruit trees from birds.
Cut the grass as short as possible, apply the mesh, use those u-shaped garden staples every few feet to hold it down, then fill in the holes with sand.
If you absolutely MUST use poison