No Ortho products!
Orthene is not part of an organic program.
As Howard has said many times, you can
treat spider mites with just about anything (orange oil, insecticidal soap, etc.) every three days for nine days and that will kill them off. If you have them in large trees, use the hose end sprayer and point it up as far as you can. Spider mites appear when a plant is already in a weakened condition, so the usual advice applies: look at your trees - can you see the
root flare? If not, they're planted too deep, they can't "breathe" like they should, and this is enough to cause the distress that attracts the mites. Pull back the grass, carefully scrape the dirt away from the base until the flare is well-exposed. This alone will help trees, and yes, if you have to pull so much back that the tree appears to be standing in a shallow dish, that's okay.
Other problems - how much water is the tree getting? Are you watering too much, is the drainage poor, is there too little water? If they are well-established, chances are they get too much rather than too little water.
Avid Spray is
Abemactin, which is acceptable in an organic program. Take a look at the price, see how much you would need, and choose if you want to try the orange oil or other home remedy treatments first or go to the abamectin.