Because I live on a hill with adequate air circulation I never have problems with spider mites outside. Unfortunately, this is not the case with my indoor plants. In the dry, windless interior of my home I place fans near clustered plants to discourage spider mites. Suggestions: With respect to the resistance of mites to insecticides, sometimes things they can't develop resistance to can help - here I use Neem Oil. It kills the mites and they cannot develop a resistance to it. Also 1T. of Murphy's Oil Soap to a gallon of water acts as a sufficant and they cannot develop a resistance to this either. Where do you keep your Junipers? Can you increase air circulation and humidity around them?
Owen NJ Zone 6