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.