Although important as a pest on pear (Pyrus spp.), this species is also associated with other rosaceous hosts, including various ornamentals. Pear leaf blister mite (Phytoptus pyri) is a widespread and common pest on pears but can sometimes attack apples too. It is currently a pest in most pear-growing regions across the world.
How to recognise them
Adult mites are very small — about the same size as rust mites — and cannot be seen without a x10 to x20 hand lens. The body is white, long and slender, striated and with a few long hairs. Immature forms resemble adults but are smaller. Eggs are spherical and pearly white.
The adults of both sexes overwinter beneath outer bud scales and then become active in the early spring when the buds start to swell. At this time, they burrow deeper into the buds and start to feed on and lay eggs at the base of the inner scales of the bud.
The adults also feed on other parts of the tree including the young leaves and developing flower buds. Development from egg to adult requires 20-30 days during the spring. Several generations develop within blisters during a growing season. Summer generations require only 10-12 days to develop.
As with most mites, populations can be found on the underside of the leaves, which shelter them from sun and rain. However, as the leaves succumb to attack, some of the cells collapse under the blisters formed as a result of the feeding and they enter through these damaged areas.
Small galls are formed where the mites continue to breed throughout the summer. As new mites emerge, so more blisters are formed that then develop into galls. As the days shorten, the mites then progress to the bud scales again for the duration of the winter.
Blister mites attack both foliage and fruit, producing small galls or blisters. The galls can be seen as early as when the leaves start to unfurl. The galls are like green pimples that can change to yellow as the season progresses. Some produce a red colouring that can be seen on the leaf surface.
Usually the galls are present along the main vein but can spread as populations increase. Mites can be transported easily on the wind and on clothing. Severely infested leaves can turn brown and drop off. Damage to fruit is less serious but scarring can render the fruit unmarketable.
Treatment: cultural control
• Inspect bought-in plant material for signs of leaf blisters.
• Monitor crops to aid control during the vital early part of the season.
• Physical removal and burning of affected leaves by leaving the petiole on the branches can reduce pest pressure.
• Make sure that plants are not water stressed.
• Always carry out work on infested crops at the end of the day and ensure good hygiene measures before entering other crops.
Treatment: biological control
Blister mites are not normally controlled by natural enemies. Management of the naturally occurring beneficials plays a key role in successful control.
The predatory mite Typhlodromus occidentalis, which can control spider mites on apples and pears, will also feed on blister mites when they are exposed. However, it cannot enter into blisters.
Treatment: chemical control
If plants are grown specifically for fruit production, check individual pesticide labels for harvest intervals and spray timing information for each product. For all crops grown as ornamental plants, make sure that fruit is removed before despatch.
When treatment is necessary, choose a pesticide that is compatible with your pest management programme. The best timing is after harvest, when mites migrate from leaf blisters to terminal and fruit buds. There they are exposed until buds swell in spring.
Pre-bloom treatments can prevent fruit damage that occurs just before and during bloom. Summer applications of products that have a vapour action or are systemic can give some control but are too late to prevent fruit damage. To evaluate the efficacy of sprays, check blisters for mite survival.
Active ingredient Chlorpyriphos
IRAC code 1B
Formulations Dursban WG, Equity (Dow)
Action(s) A contact and ingested organophosphorus insecticide. Incompatible with biological controls.
Active ingredient Fatty acids
Formulation Savona (Koppert)
Action(s) Contact acting — destroys insect cuticle. Short-term effect on some biological controls.
Active ingredient Diflubenzuron
IRAC code 15
Formulation Dimilin Flo (Certis)
Action(s) Selective and persistent insecticide. Compatible with biological controls.
Active ingredient Spirodiclofen
Formulation Envidor (Bayer)
IRAC code 23
Action(s) Contact–acting insecticide. Incompatible with biological controls.
Active ingredient Lambda-cyhalothrin
Formulations Various including Hallmark WZT* (Syngenta)
IRAC code 3
Action(s) Fast-acting, persistent, contact and residual insecticide. Incompatible with biological controls.
Active ingredient Pyrethrins
IRAC code 3
Formulation Pyrethrum 5EC (Agropharm), Spruzit (Certis)
Action(s) Contact insecticide with short-term effect on biological controls.
Active ingredient Petroleum oil
Formulation Spraying Oil (Certis)
Action(s) Insecticidal oil that acts by physical means. Incompatible with some biological controls.
Fully updated by Dove Associates.
Use plant protection products safely. Always read the label and product information before use.
* Extension of Authorisation for Minor Use (EAMU) required for use in ornamental plant production outdoors and/or under protection.
Dove Associates shall in no event be liable for the loss or damage to any crops or biological control agents caused by the use of products mentioned.
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