Let me break this down quick since hordes need careful planning. Get yourself to high ground first, somewhere you can see the whole area and have room to move. Attractors are your best friend here, and combining them with explosives is going to be your winning strategy. Throw an attractor to bunch them up, then hit them with a proximity bomb (be careful as it may detonate prematurely) or napalm molotov for maximum damage. Setting up traps in bottlenecks is crucial, especially near explosive barrels or narrow paths where they'll get funneled through.

Remote bombs are perfect for when you've got a huge cluster gathered up, but save them since they're harder to come by. A good tip is to break line of sight after tossing an attractor, this forces them to follow predictable paths right into your traps. Keep an eye out for alarm clocks while exploring, you'll need them to craft more attractors and those are absolutely essential for this strategy. If you spot any fuel trucks or explosive barrels in the area, definitely work those into your plan, since one well-placed shot can take out dozens of freakers at once.