I found leaves showing red blisters caused by Pearleaf Blister Mite on an Asian Pear tree in the Fort Langley area a few days ago. This mite attacks pears and some varieties of apples in BC (Gala, Newtown, Rome Beauty, sometimes McIntosh and Spartan) as well as several ornamental trees and shrubs. The Blister Mite is very common across the Coastal; area of BC and in most pear growing areas around the world. It is very easy to control with the right timing,however, it is too late for this year.
This tiny (less than .2 mm long), wedge-shaped mite (not a spider mite) is too small to see with the naked eye or with anything less than a 20X hand lens. This mite over winters as mature females at the base of buds or under bud scales. As the buds start to swell in the spring the females penetrate into the buds laying eggs. Feeding injury causes the red blisters that become visible after 20 to 30 days.
An early dormant spray in October or early November produces the best control. If you miss this date, you can get fairly good control with an early February application. The organic spray combination that works is lime sulfur and dormant oil.
For identification and controls in BC home gardens and home orchards see: Home & Garden Pest Management Guide For British Columbia – Pests of Fruit Trees
For identification and controls in BC commercial orchard see: Rust Mites and Pearleaf Blister Mites