Really, this late in flower pyrethrum is not an option, you can use it in veg, and while it biodegrades quickly, I wouldn't use it on buds under any circumstance. Control, not eradication, is what you can reasonably achieve. DE will work for control, but you will need to do some serious bud washing after harvest, but you're gonna need to do that anyway to get rid of webs, mites, eggs and poop. As has been said, DE is also messy, since you literally have to throw it under the leaves. Calcined DE (which is what you need) is not good to breath, so wear a mask if you start tossing it around. It works better on thrips, which have a larval stage in the soil, you can just sprinkle it on the surface of the soil and it'll cut the larvae to pieces as they try to emerge from the soil. Mites don't have a "soil stage". I'd look into insecticidal soaps.
To date, there is no definitive link between pyrethum (pyrethins) and cancer, however, I would err on the side of caution, because most studies have to do with ingesting pyrethum(s), not smoking them, heating/burning can radically change the chemical composition of compounds
