Once I marveled at what a wonderful "fence" with majestic blooms our new pampas grass hedge created from septic line water ... no, the roots do not invade the pipes & clog them up. They evaporate more water, so the lines & grass over them don't work so hard.
THEN the ground nesting yellow jackets (that we call Africanized hornets due to their aggressive attacks, even away from the nest) found last year's brown leaves the perfect thatch hut for nests. UGH. Once inside, nothing can get them, then they breed like crazy (1 queen = 5000 workers per year) and in summer, nest begin popping up everywhere like never before.

One was so big, I had no solutions but to burn it and WOW - you'll need the fire department standing ready - like burning a haystack!!! Had regrets later that the pampas fence was gone.

I have spent hundreds of dollars fighting wasp wars since, you name it, I've done it. Best solutions:
1. Spring: Get those queens! Rescue Yellow jacket disposable traps @$5usd employed every 100', best hung from cedar trees, near pampas, materials used to build nests
2. Summer: Traps designed to use fish scraps + drown wasps in soapy water. No garbage nor water (including day sprinklers) to make wasp think this is a good place to nest, easy pickings.
3. Fall: back to disposable traps or make your own apple juice ones

Nest found:
a) if in hole in ground? fill with ammonia or wasp killer at night (red light flashlight they can't see + they all bed down at night except for the sentries) ... country boys pee in these holes day/night
b) on wall, in shrubs? any wasp killer will do - best to buy one that kills your type of wasp, has looong spray, wear light colors, run like hell while shooting down pursuers ... up to 50 yards in daylight
c) pampas? UGH THE WORST Are you lucky? Then they are going in a hole at the top & any full can of killer will wipe them out. Not lucky? Then they are going in under the thatch and maybe a skunk will find the livers you threw in there, maybe not. Other than fire - this is the ONLY thing that works: Raid Concentrated Deep Reach Fogger