Dennis writes
We do not recommend mixing together two pyrethroids such as Bifen IT and a permethrin product. These products are too similar, and you could create a repellency issue rather than allowing insects to actually contact the treated areas. If you want to add something to Bifen IT for faster intiial knockdown, then we suggest a pyrethrin and/or PBO product such as ExciteR Insecticide.
Answer last updated on: 06/18/2019