This challenge is found difficult by many. First things first, fully upgrade your machete; maxing out the number of throwing blades and damage over time. As soon as the challenge starts head to the center of the arena where the squirts are spawning and continuously attack. Be sure you kill almost all of the green squirts in this way.
Next, target the squirt dispensers and finish clearing up the rest of the squirts and finally the turrets. After you finish off the turrets throw your machete to kill any squirts left floating over the lack of ground.
Use damage over time to its full effect, attack one turret/dispenser 1 or 2 times then target the next one. This saves many valuable seconds.
Protip: Practice getting a power shot every throw to maximize the chances of hitting a moving target.