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

Adult flat scarlet mite

Flat scarlet mite damage to leaves

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

  • For chemical control of flat scarlet mite, of the acaricides approved for use on apple in the UK, the EAMU for abamectin (Agrimec) offers good control.
  • Of the other acaricides fenpyroxmate (Sequel) appears the most effective giving >95% control of flat scarlet mite after about 6 weeks. A spray should be applied as soon as damaging infestations develop.
  • Tebufenpyrad (Masai) is less effective giving perhaps about 50% control. Both fenpyroximate and tebufenpyrad are much less harmful to the orchard predatory mite Typhlodromus pyri.
  • 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.
  • 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

Choice of products – efficacy factors

Active ingredient Trade name (examples) Class Selectivity Approved for control of Safety to Typhs 
abamectin Agrimec acaricide selective Flat scarlet mite unknown
clofentezine Apollo acaricide, ovicidal selective Winter eggs of fruit tree red spider mite on apple safe
fenpyroximate Sequel METI acaricide selective Fruit tree red spider mite in apple safe
pyrethrins Spruzit extract from pyrethrum broad spectrum Aphids, blossom weevil, caterpillars, spider mites harmful
tebufenpyrad Masai METI acaricide and aphicide selective Fruit tree red spider mite, rust mite us

Choice of insecticides – Safety factors

Read the label before applying any sprays

Hazards Harvest interval(days)

 

Max. no. sprays or dose Buffer zoneWidth (m)
Anticholin-esterase?  Humans Fish & aquatic life Bees
abamectin no h t ed u 2 40
clofentezine no u u s 35 1 u
fenpyroximate no h,i,e ed u 14 1 40
pyrethrins no h,i ed d 0 4 50
tebufenpyrad* no u ed d 7 u 18
Keys: d=dangerous, e=risk of serious damage to eyes, ed=extremely dangerous, h=harmful, ir=irritant,  t=toxic u=unspecified or unclassifiedMETI = mitochondrial electron transport inhibitor

* not recommended for use with hand-held sprayers

 

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 (potassium soap) (Savona) or pyrethrum (various products), 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