Spider mite is best controlled early in the year - around May, before the mites have even started "webbing" the foliage. After the vines have been pruned, excess cut away and disposed of, and strung, spray the vines with a 2% pyrethrum spray. Pyrethrum (a distillate of a particular kind of marigold - French Marigold) is a natural substance and can be found in organic formulations with soaps as a spreader and wetting agent. It's pretty easy to apply with a backpack sprayer. It's a good idea to spray the poles too, as mites may be lurking on them too.
Later in the season, at the burr stage, it's better to use lime sulphur, in a 1% solution. Again, commonly available, but be sure not to get the fruit tree sprays with dormant oil. Lime sulphur will not hurt the plant, and may need to be repeated in a week or so from the first spraying.
One additional note: if you have been using sprays which are also designed for mildew control, you have likely been propagating spider mites, because these mixes tend to kill the natural predators of the mite.
I understand that the major predator of spider mites is the Anthrocorid Bug, which I have never actually sourced or identified in my hops.
If you possibly can, increase the prevention tactics next year: clean up around the vines (will help with all kinds of diseases), add lots of compost (your soil and plants need all the micronutrients), and drip irrigate plentifully. It's an amazing thing, but healthy plants will withstand both diseases and pests. Oh, and plant other crops around your hops to encourage beneficial insects!
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