Hi Russ,
I had Pear Blister mite surface a few years ago on two 3 year old young Magness Pears (OHxF87 Rootstock). I took the route of hand picking off the leaves at the end of the growing season (1st week of October here at my location in the Siera Foothills of California) and before the first frost. Id say just time it for about 3 weeks before your 1st estimated frost in the fall and you will catch large numbers still living large on those leaves.
I had 90-95% success in this method. Sure it took a little while, but it was no more time consuming than thinning fruit and I didnt need to get the sprayer queued up to do it. Consider it quality time with your good friends (your trees) and your smile will follow.
The following year, I had Pear Blister Mite show up on only a handful of leaves and I picked those off, as I saw the evidence surface. Been blister free on those two trees for two seasons now.
Not full proof, but for young trees, and when there is only a few to deal with . . . This is the method I would recommend.
Then consider dropping the hammer on those microscopic dudes in the dormant season with oil and/or lime sulfer soak.
Good luck!
Gopher Hill ApplesZone 8 in California