Apple Best Practice Guide

Flat scarlet mite (Cenopalpus pulcher (Canestini & Fanzago))

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Adult flat scarlet mite

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Flat scarlet mite damage to leaves

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Flat scarlet mite infestation and damage to fruit

The flat scarlet mite has long been known as a minor pest of apples and occasionally pears in the UK.  The females in particular are easily distinguished  from other mites.

Flat scarlet mite is a relatively sedentary pest which tends to live in groups with a simple life cycle. It overwinters as fertilised females on the bark of apple. They become active in early spring, from April onwards, and invade the foliage and flower/fruit clusters in May.

The first eggs are laid on the wood late in April but subsequently eggs are laid along the midrib, beneath the leaf hairs. Eggs hatch from late June onwards.

Large numbers of mites feeding on foliage and developing fruits have a severe adverse affect on tree health and fruit quality.

Damage to the upper leaf surface starts with yellowing close to the veins which later develops into necrotic patches. Mites also cause bronzing damage to the lower leaf surface in much the same way as fruit tree red spider mite and apple rust mite.

Leaves develop necrotic areas at the base and shrivel and drop prematurely if infestation is severe. Mites feeding around the eye and sometimes the stalk of Cox and other varieties cause severe russet. Damage spreads onto the cheek in severe attacks.

Mating takes place in August and September. The males die and fertilised females migrate to the bark where they overwinter. There is one generation per year.

Populations have been increasing in apple orchards in recent years and damaging populations have developed in some orchards in the fruit growing areas in the UK so monitoring is important.

Control

• A full approval for spirotetramat (Batavia) on apples for the control of sucking insect pests will control flat scarlet mite, but growers may prefer to reserve its use for more difficult to control pests such as woolly aphid or rosy apple aphid. It must be applied after flowering and works best when pests are moving from brown wood to green tissue. It will prevent population build-up but does not offer pest ‘knockdown’.
• The bioinsecticide fatty acids (Flipper) has an EAMU approval for use on apples. It is effective at controlling sucking insect pests such as aphids, whitefly and mites, so may offer incidental control of flat scarlet mite when applied for other pests. It is known to complement the use of Batavia as it provides quick ‘knockdown’. Its safety to beneficial insects such as Typhlodromus pyri or the parasitic wasp Platygaster demades is unknown, but it is generally safe to many other predators and parasitoids, so is considered to be more suitable to IPDM programmes than the synthetic pyrethroids.
• Tebufenpyrad (Masai) is only partially effective giving perhaps about 50% control.  Tebufenpyrad is less harmful to the orchard predatory mite Typhlodromus pyri than some acaricides.
• The efficacy of clofentezine (Apollo) has not been investigated but it is probable that if it has any effect, it will only control eggs and possibly young stages of flat scarlet mite.
• The acaricides acequinocyl (Kanemite) and hexythiazox (Nissorun) are recommended for the control of fruit tree red spider mite. Trials conducted by the manufacturer of these products showed erratic results against other mites. As it has a contact mode of action only, it must contact the mites to be effective. They might offer incidental control of flat scarlet mite when applied for fruit tree red spider mite control. Hexythiazox (Nissorun) works only on the eggs and early motile stages of fruit tree red spider mite and is ineffective against the adults so application timing is critical.
• Resistance of flat scarlet mite to insecticides and acaricides has not been investigated or demonstrated. However, to minimise the risk of resistance, acaricides should be used as little as possible, alternating different products to reduce the risk of development of resistant strains.

Acaricides approved for use on apple which are recommended to control flat scarlet mite, or offer incidental control when applied to control other pests

Control in organic orchards

Emphasis should be placed on natural control by the orchard predatory mite Typhlodromus pyri (see ‘Biological control’).

• Application of foliar sprays of fatty acids which are harmful to the orchard predatory mite, should be avoided unless absolutely necessary.
• Programmes of sprays of sulphur to control scab and mildew can also be harmful to the predatory mite though populations tolerant of the sulphur appear to develop eventually.

Further reading