I was speaking to a grow bro the other day about this very topic, I don't know how true this is or if its just "bro science" but he said.
"Spider mites are almost always present everywhere, An infestation happens when you have no moving or stagnant air in tent (Somewhere a fan is not reaching) and it gives them the ability to colonize"
Bullshit or ?
I found that they're more active in the warmer seasons outdoors, the only way you'll get them is by bringing soil indoors or unknowingly bringing them in on yourself or pets.
They can be very selective of which plants they setup their homes on too, geraniums/pelargoniums are almost certainly gonna have some along with others plants,
but with weed I have found that they can definitely gravitate to one strain/plant in particular, but will leave other strains alone.. In the past in one of my smaller tents I had a MAC plant which was entirely infested, the other strains which were literally brushing up against that plant were untouched by them.
So they definitely have different preferences when it comes to weed..
I reckon it had something to do with the terpenes but I have no scientific evidence to back up my claims.
I recall the MAC having a dank, earthy kind of savoury smell to it, perhaps it attracted spider mites. The plants besides it smelled of berries/fruit and they completely ignored them.
I actually decided to keep the infested plant until harvest, to keep the mites from potentially destroying my other plants (I feared if I removed that plant they would have spread to other plants).
At harvest I tried to salvage some bud but after spraying sulphur and tobacco juice and pyrethrum on them I just ended up throwing it out as I figured it would probably taste like shit.
There's treatments you can buy, but none really list the active ingredients (very sketchy), I did some research on it and found that some use heavy duty paint strippers like N-Methyl-2-pyrrolidone.
There's no real quick fix for treating plants, these arachnids are pretty hard to kill as they lay so many eggs and breaking that cycle requires quarantining the plant and spraying every 3 days with soap/alcohol/oil mixed in water, under leaves, on the leaves and around the pots, I've successfully eradicated them by doing this for 2 weeks.. If you find them in flower then just let them go and do a budwash at harvest unless you want to use a hardcore chemical which will more than likely leave residual amounts of whatever mystery chemical used on the plants, which you'll end up smoking..