A serious pest of Pear, Apple and Sorbus trees - both in the USA and UK - Europe.
Pear leaf Blister Mite can either cause fruit spot damage, or spotting - blistering of the leaves - normally on the undersides. In the UK, is is more of a problem of Pear Trees grown against walls and fences.
The damage first appears on pear leaves with typical small green pimples which soon turn to red, and then brown.
The coloring on apples is different to that on Pears in that the pimples rarely ever turn brown. A small magnifying glass will reveal the minute midges - just a millimetre or so in length.
Severe attacks of Pear Leaf Blister Mite can ruin the leaves and impair the ability of the leaf to fulfil its function.
The mites feed on young fruit and cause small russet areas which in turn lead to deformed fruits.
Adult mites enter the bud scales in late autumn to overwinter, then emerge in early spring just as the new tender foliage is bursting. They then burrow below the skin - epidermis - of the leaf causing an irritation which results in the small galls on le leaf. Eggs are laid the following autumn - fall - and the young remain in the blister to feed until maturity. they then leave the blister galls and start life afresh on new unaffected foliage. The cycle continues.
Spraying with Provado - a systemic insecticide - has given promising results. Otherwise remove affected leaves and burn. Winter oil wash is also an option. Insecticides should be applied pre-bud bust and thereafter cropping.
Underside of affected Pear leaf - clearly showing the galls - blisters
of the pear leaf Blister mite.