As super cool said, don't drop tornadoes on green, but you also have to be careful of dropping the green on the webs/near them of the tornadoes that patrol them will shoot it at your group.
The green shit during quils only appears if tornados hit the green puddles left by your raiders. Try to clean up as many of those as possible and the green stuff should stop spawning.
Something we found out is that poodles near the bridges will also spew shit everywhere. Because tornados also spawn in all the bridges so watch out for that. You can also have tornados people die. On our first kill both tornado dudes died while clearing so no tornados spawned