Firstly you would need to have to establish that it is not an antibiotic producing fungi, lytic bacteriophage or that the plant species itself does not make antibacterial compounds (eg. tannins). Ideally you want to get a pure culture of this leaf derived bacteria. You will want to take the piece of leaf off the plate and vortex it in saline to dislodge the bacteria and then perform serial dilutions which you then plate until you get single colonies. Once you have a pure culture then you can then take the supernatant of a mixed culture (incase your lawn bacteria is needed to induce antimicrobial compound production), filter sterilize and then apply it to a lawn and look for inhibition. Similarly with the remainder of the leaf derived solution you can filter sterilize and then apply to a lawn and look for phages causing the clearance.

As I mentioned in my previous post you can filter sterilize a culture and use the resulting solution (may want to concentrate it using a rotary evaporator) to look if there is inhibition on the lawns when you add a volume to a well punched into the agar.