On the north east end of the farm, there is a section with some Overloaded Harvest Golems. They look dead but are shooting lighting at each other. Target one and use the Harvest Watcher Heart you have to be able to drive one.
Once inside, you will get a special action bar with the abilities [ 1 ] Reaping Blows and [ 2 ] Rocket Boost. Head just south to the field filled with Energized Harvest Reapers. Once there, keep #2 on cooldown, running around the fields spamming button #1 .