Q What is pear-leaf blister mite?
A It is a microscopic gall mite (Eriophyes pyri) which afflicts the leaves of pears and some related trees, particularly rowan, whitebeam and wild service tree. It is extremely small, 0.2mm long, and is visible only with the help of a hand lens. However, the blisters are easy to spot. At first, they are about 2-5 mm in diameter, but they soon spread over the leaves.
Caption: If the pear blister mite has only affected a few leaves, simply pick them off
Q Is it common?
A At one time it was controlled by lime sulphur sprays. These are no longer available, so blister mite has become more common. Bush, cordon and wall-grown trees can be affected very badly. The problem often occurs on trees that are suffering stress – particularly lack of water.
Q When should I expect damage?
A Pear-leaf blister mites spend the winter under the outer scales of buds. When the buds swell in spring the adults lay eggs in the bud scales. Both the adults and the newly hatched young move out and feed on the unfurling leaves and flowers. Blistering develops at this time but is less noticeable than later attacks.
A new generation is hatched around petal fall. These get into the leaves through the wounds left by the first generation; they feed inside the blisters. These blacken, and, as the leaf tissue dies, mites move into nearby blisters or shoot tips to feed. There are several generations each summer. By early autumn the mites are on the move again to find winter shelter beneath the scales of fruit buds.
Q What symptoms should I look out for?
A Pink-red blisters occur on young leaves in spring. Later they appear as small, raised bumps on the leaves, clustered around the midrib. They start green, redden, and eventually the whole leaf may blacken and fall.
In severe attacks the fruit stalks and fruits are also distorted and may fall early. Look out for scab-like pustules on the fruits from petal fall onwards.
Q What could I mistake it for?
A Pear rust mites (Epitrimerus piri) can cause browning on the leaf undersides and russeting around the eye of the fruit.
Q How do I control it?
A If an outbreak is limited to a few leaves, pick them off before the blisters redden, and dispose of them. If the problem is widespread, removing the leaves is not only impractical but could do more harm than good. There is no chemical control, but the mites don’t have any serious adverse affect on tree growth or fruiting.
Q Are there any resistant kinds available?
A Most sorts of pear seem to be affected – we don’t know of any resistant varieties.
Q Can it be prevented?
A Not directly, but reducing water stress will help. If planting new trees on well-drained soil, incorporate lots of organic material to improve waterholding. Mulch trees in spring to conserve water, and water in drought conditions.
