How To Make A Tool Break Multiple Blocks

I am making a farming mod, and one of the ideas I have is to make a scythe tool, which breaks multiple crops in an area, like a 3x3. Kind of like hammers in certain mods, where they break a 3x3 area, but instead I want the scythe to break only crops in a 3x3 area, I also want to be able to change that area, like for a wooden scythe, it breaks a 3x3, but an iron scythe breaks a 5x5, something like that. Anyone know how to do this?