Final works best, for me. I’ve tried Contrac, and it works, but the blocks are waxier, and have less grain than the Contrac. They “take” to the Final better/more quickly.
Google “brodifacoum”, and “Rat Island”. The Feds used the stuff to eliminate rats on an entire island.
https://www.iwla.org/publications/o...Issue-2/chemotherapy-for-island-wildlife
