Bonanza - Season 1 Episode 29 -

Len Keith, a miner, wants to purchase some land adjacent to the Ponderosa from rancher Andy McKaren. Andy's son, Tod, is anxious to sell. Keith has offered him a partnership,and more importantly, he is in love with Keith's daughter. When Ben warns Andy that a mine on the property would foul up Ponderosa water, Andy agrees not to sell the land. Len Keith, determined to get that land, plants tick infested cattle in a Ponderosa herd to turn Andy against the Cartwrights.