The quest this begins allows you access to the item Master Plow on your farm.
It will appear on the side of your farm with the shovel, watering can and bug sprayer for you to pick up and use. If you trash it when you are finished, it will reappear in that area just like the other items; you do not need to keep it in your inventory all the time.
The Master Plow will till an entire line of four plots with each use, and there is no cooldown so you can use it on every row. It's a little finicky about the direct you're facing, so make sure you're facing the row head-on or you will zig all over your farm.
It will not till Occupied Soil until after you have removed the vermin from within.