Abstract: A mowing machine of the offset rotary type wherein an assembly of rotary blades is carried by a frame movable along a surface bearing grass or foliage and including an additional rotary mower blade carried by a swinging arm at one end of the machine frame. The swing arm is held in a forward position by biasing springs, and it is moved to a rearward position to direct the additional blade around obstacles such as tree trunks and fence posts by retraction of an hydraulic cylinder, the rod end of which is coupled through a slack coupling to the swing arm. Operation of the hydraulic cylinder can be under manual control by the person driving the mowing machine, and it can be automatic in response to operation of a sensing element carried by the machine frame forwardly of the swing arm for detecting obstacles by contact.