Pear leaf blister mite is a microscopic insect pest which lives inside the tissue of pear tree leaves. Affected leaves have a characteristic mottled blistered appearance. Starting in spring the affected areas take on a light green or pale orange colour compared to the rest of the leaf. These areas eventually turn black over the summer.
A full infestation can look very dramatic, but the effect on fruit production is less serious than it appears.
There are no sprays available to combat this pest over the spring or summer, and they have few natural enemies.
The initial infestation is best controlled by removing the affected leaves. This only works in the early stages as removing too many leaves will simply weaken the tree, but it is effective because it disrupts the life cycle of the mites.
The best approach to managing an infected tree over the summer is to make sure it is well cared for, in other words keep it watered as necessary and keep on top of any other pests which might also weaken it.
Sprays or oil washes applied during late autumn or early spring may be helpful in killing the mites, as they over-winter on the tree near the leaf buds. They are invisible to the naked eye, but you may be able to see them with a strong magnifying glass.
Blister mites spread between trees on the wind, particularly between late autumn and early spring when they are not protected inside the leaf tissues.