An ultrasonic instrument includes a body, an actuation assembly, a shaft assembly, and an end effector. The actuation assembly includes an activation member that is operable to move in a first direction to select a mode of operation. The shaft assembly extends distally from the body and includes an acoustic waveguide. The end effector includes an ultrasonic blade that is in acoustic communication with the acoustic waveguide. The activation member is operable to move in a second direction to activate the end effector in a mode of operation selected by movement of the activation member in the first direction.