Green punk, perhaps the overuse and/or misuse of the products has also contributed to resistance, rather like as is the case with many antibiotics.
Are you certain that all
pyrethrins are illegal in California? I'm using a simple operator's permit on my organic operation (not registered or certified at this point) and I'm allowed to use products like
Pyganic. Sittin' here looking at it on my CalAgPermits page. The CDC says
pyrethrins and pyrethroids are not classifiable in terms of how likely they are to cause cancer, so I'm not sure where or how the state of California might be making that determination.
I personally won't use such products during the daytime, when there is any wind whatsoever, in other words I won't use them if I cannot control
drift, which is really the main issue for me. It does make sense that putting oils into the rhizosphere could or would cause problems, but that's just thinking about it, not actually scoping it.