Pest infestations

[Vickie Cave]

We live out in the country and used to have a cat that "took care" of any rodent problem that a "country liver" may have. However, when our cat was no longer with us and our property was not lived in for a while, we aquired some RATS! Yuck! We quickly bought rat poison and took care of the problem. Can we require in the lease, that the tenants continue to buy rodent poison or is that something we would have to do as the landlords? We would be living out of state...how would this work if we needed to provide for this?
Also, our area is prone to fleas. When we lived there, we treated our home living space every six months. Could we require our tenants to maintain and pay for this treatment in order to avoid any further pest infestations? Yucky subject, huh?
Thank-you.