If you have a draw leading up to your place, and the wind goes down the draw, then you have a pretty nice booby trap.
Problem is that it doesn’t kill like Chlorine does. It takes too long.
In the end, this is why most biological and chemical weapons work gets abandoned. It’s too difficult to handle in the field, doesn’t kill quick enough, and if you invent something that does, there’s a strong possibility it ends up killing your forces rather than the enemy’s first.
‘Forest fire’ biological weapons require a can’t miss vaccine, plus an antidote. Inoculation let’s the cat out of the bag.
If the elites could manage it, they’d invent a disease that drove people to digging giant holes and throwing yourself into them.
Most of these guys are more than happy to drive their D-8’s around covering the holes back up for you.
Not to worry; they'll also have slave labour companies for that detail. And remember: they wouldn't bother, but for the public health problem that large numbers of dead bodies pose.