Apple grass aphid (Rhopalosiphum insertum (Walker))
Apple grass aphid attended by black ants
Apple grass aphid is the most common aphid species on apple but it only causes minor damage to commonly grown apple varieties. Some apple varieties are more sensitive e.g. Jonathan. The life cycle involves two hosts. Apple, pear and quince are the winter hosts of apple-grass aphid and grasses (especially annual meadow grass) are the summer hosts. The migration to the summer host in May-June is obligate and so infestations do not persist on fruit trees during the summer.
It is widespread and abundant in apple orchards in spring, especially when the previous summer has been wet so favouring the growth of grasses.
The aphid hatches at bud-burst to early green cluster from overwintered eggs on the bark and develops on the rosette leaves and amongst blossom trusses causing minor curling damage of leaves if large populations occur in early spring before or during early blossom. Damage is rarely important unless populations are very high. There is little risk of damage from this pest after mid blossom as winged forms develop which migrate to grass during and after blossom.
Green apple aphid and common green capsid both may be present and causing damage but are readily distinguished.
The severity of infestation by apple grass aphid should be determined in each orchard by monitoring in spring when the usual pre-blossom pest assessment is done.
- At least two blossom trusses should be inspected on at least 25 trees per orchard.
- Presence of the aphids in a particular truss is often indicated by slight leaf distortion and/or the presence of cast skins on the surface of the rosette leaves.
An insecticide treatment for the aphid should be applied before blossom if the economic threshold of 50% of blossom trusses infested with 5 or more aphids is exceeded. Insecticide sprays should only be applied for this pest if strictly necessary as it provides an early food source for natural enemies of other more damaging species.
- Several insecticides are approved for control of aphids on apple but if apple grass aphid is the only pest that needs to be controlled, flonicamid (Mainman) is the preferred choice in conventional orchards as it is selective and partially systemic.
- A full approval for spirotetramat (Batavia) on apples for the control of sucking insect pests will control apple grass aphid, but growers may prefer to reserve its use for more difficult to control species such as woolly 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’.
- A recent EAMU for Flipper has increased the available options should growers wish to reserve other insecticides for control of pests later in the season. It is known to complement the use of Batavia as it provides quick ‘knockdown’.
- The neonicotinoid acetamiprid (Gazelle) is also approved for control of aphids on apple though it can be a little slow acting in cool conditions.
- It is systemic and is highly effective against aphids. It will give excellent control of apple grass aphid and incidental control of several other pests such as capsids and sawfly.
- It has little effect against caterpillars and acetamiprid (Gazelle) is ineffective against woolly aphid.
- Use of synthetic pyrethroids, which are harmful to natural enemies, should be avoided.
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|
|deltamethrin||Decis Forte etc.||pyrethroid||broad spectrum||Aphids, codling & tortrix moths, capsid, sawfly, apple sucker||harmful|
|dodecylphenol ethoxylate||Agri 50E||physical acting insecticide||broad spectrum||Aphids, leafhoppers, mealy bugs, spider mites||harmful|
|fatty acids||Flipper (EAMU 3419/19)||bioinsecticide||broad spectrum||Aphids, blossom weevil, two-spotted spider mite||unspecified but generally safe in IPDM programmes|
|flonicamid||Mainman||neonicotinoid||selective||Aphids and woolly aphid||safe|
|maltodextrin||Majestik||polysaccharide||broad spectrum||Aphids, spider mite||harmful|
|spirotetramat||Batavia||tetramic acid derivative||selective||Sucking insect pests||unclassified|
|Choice of insecticides – Safety factors|
|Hazards||Harvest interval(days)||Max. no. sprays||Buffer zoneWidth (m)|
|Anticholin-esterase?||Humans||Fish & aquatic life||Bees|
|fatty acids||no||h, i||h||u||0||8||20|
|spirotetramat||no||h, i||t||d||Start of ripening||2||10|
|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
Chemical control of apple grass aphid is usually not attempted in organic orchards because the pest only causes minor damage which is tolerated.
- Emphasis should be placed on cultural control measures such as the provision of artificial refuges for earwigs and lacewings and of flowering herbs in and around the orchard to encourage predatory insects.
- High volume sprays of fatty acids could be applied when damaging infestations develop if necessary on more sensitive varieties.
- Pyrethrins (Pyrethrum 5 EC) was previously approved for use in organic orchards but permission had to be sought from certification bodies before use. The approval for use of pyrethrins was revoked on apple and stocks should have been used up by 31 May, 2020.