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Rosy apple aphid (Dysaphis plantaginea (Passerini))

Rosy apple aphid: shoot damage

Rosy apple aphid colony

Rosy apple aphid: fruit damage

Rosy leaf curling aphid damage

Rosy apple aphid, also known as ‘blue bug’, is one of the most important and damaging pests of apple. A similar species, the pear bedstraw aphid, attacks pear.  The life cycle involves migration between the two hosts apple and plantain.

All commercially-grown apple varieties are susceptible, but Bramley, Discovery, Egremont Russet, Golden Delicious and Jonagold are highly susceptible.

Apple orchards should be carefully inspected  for the pest and its characteristic damage symptoms (discoloured/distorted/curled outer rosette leaves at the green cluster to pink bud growth stage and again at the end of blossom and during early fruitlet development. The pest can readily be distinguished from the less common rosy leaf curling aphid which causes striking red leaf curling.

Cultural controls such as encouraging natural enemies are useful.  Providing refuges and flowering plants in and around the orchard, tolerating less damaging aphid species such as apple grass aphid and avoiding the use of broad-spectrum insecticides will help foster natural enemy populations in the summer and autumn so reducing populations in the current and following seasons.

Control

A spray of an approved aphicide should be applied as soon as infestation is detected.

  • If only rosy apple aphid is to be controlled, then flonicamid (Mainman) is likely to be a good choice as it is a selective aphicide.
  • The neonicotinoids acetamiprid (Gazelle) and thiacloprid (Calypso) are also effective against rosy apple aphid and will control a range of other pests depending on the material chosen.
  • Acetamiprid (Gazelle) is the most selective of these materials.  Although its activity against other apple pests has not been explored sufficiently widely, it is known to control mussel scale very effectively when applied at the correct time for the pest at 90% crawler emergence.
  • Thiacloprid (Calypso) is active against a wide range of other important apple pests including apple grass aphid, sawfly, capsids, mussel scale and leaf hoppers. However, it has little activity against woolly aphid and is considered to have some adverse effects on earwigs in orchards if it is used later in the season after blossom when earwigs have populated the tree canopy. Earwigs are important natural enemies.
  • An emergency authorisation for Movento Top for control of woolly aphid (which lasts until 29 August, 2017) will provide incidental control of rosy apple aphid.

Note that these materials are largely ineffective against winter and tortrix moth caterpillars.

  • The synthetic pyrethroid insecticide deltamethrin (Decis) is also approved for control of aphids on apple but its use should be avoided as it is harmful to predatory mites and other insects.

It is important to apply the above insecticides in warm weather conditions at the full recommended dose and in a sufficient spray volume to give adequate cover.

It is also important to apply the insecticide early, before large colonies form which are difficult to control once surrounded by distorted mature leaves.

Rosy apple aphid has developed strains resistant to aphicides in central and southern European countries but resistance has not been demonstrated in the UK.

  • The risks of the development of resistance to insecticides should be reduced by only treating when necessary and varying the insecticides used for control.

 

Insecticides approved for control of aphids on apple

Choice of insecticides – efficacy factors

Active ingredient Trade name (examples) Class Selectivity Approved for control of – Safety to Typhs 
acetamiprid Gazelle neonicotinoid broad-spectrum, systemic Aphids safe
deltamethrin Decis etc. pyrethroid broad spectrum Aphids, apple sucker, capsids, codling & tortrix moths, sawfly harmful
dodecyphenol ethoxylate Agri 50E physical acting insecticide broad spectrum Aphids, leafhoppers, mealy bugs, spider mites harmful
fatty acids Savona soap broadspectrum Aphids, leafhoppers, scale insects harmful
flonicamid Mainman neonicotinoid selective Aphids and woolly aphid safe
maltodextrin Majestik polysaccharide broad spectruim Aphids, spider mite harmful
pyrethrins Spruzit extract from pyrethrum broad spectrum Aphids, apple blossom weevil, caterpillars, scale insects, spider mite harmful
spirotetramat (120-day authorisation which lasts until 29/08/17) Movento Top tetramic acid derivative selective Woolly aphid unclassified
thiacloprid Calypso neonicotinoid broad-spectrum, systemic Rosy apple aphid. (Also likely to control capsids and sawfly, though not caterpillars or woolly aphid) safe

Choice of insecticides – Safety factors

  Hazards Harvest interval(days)  Max. no. sprays Buffer zoneWidth (m)
Anticholin-Esterase?  Humans Fish &aquatic life Bees
acetamiprid no u h u 14 2 20
deltamethrin no h, i ed d 7 u 50
dodecylphenol  ethoxylate  no u u u 0 u u
fatty acids no u h u 0 u sm
flonicamid no u h u 21 3 sm
maltodextrin no i d d 0 20 sm
pyrethrins no h, i ed d 0 4 50
spirotetramat no h, i t u 21 2 sm
thiacloprid no h, i h h 14 2 30
h=harmful, i=irritant, d=dangerous, ed=extremely dangerous, t=toxic, c=closed cab required for air assisted sprayers, sm=statutory minimum of 5 m for broadcast airassisted sprayers u=uncategorised/unclassified/unspecified

 

Control in organic orchards

Cultural controls such as encouraging natural enemies are useful but, in addition, early season sprays of fatty acids (Savona) is the preferred spray treatment of organic apple growers in the UK for aphids including rosy apple aphid.

  • The sprays have to be applied early at the green cluster growth stage (after the overwintered eggs have hatched in spring, but before reproduction occurs is best) and in high volumes so that the aphids are thoroughly wetted by the spray.
  • Application is sometimes made during gentle rain.
  • Control is especially important on young trees which can be very severely damaged in the years of establishment.
  • Derris is also permitted for aphid control in organic apple production.
  • In other European countries, an oil extracted from the neem tree is used for control of rosy apple aphid in organic orchards but it is not registered for use in the UK. It is fairly effective but precise timing of application shortly after hatching of eggs in spring is critical.

 

Further reading