Press Backspace (Windows and Linux) or Delete (Mac OS X).
When you delete an emitter, the emitted particle object is not automatically deleted. If this particle object isn’t connected to other items in the scene, you can delete it also. Use the
Outliner to delete it.
Note: Emission begins only at the frame specified by the emitted particle object’s
Start Frame attribute (by default, frame 1). For example, to emit particles at frame number -5, you must set the
Start Frame of the emitted particle object to -5.