Aphids

Key Points

• Aphid species can infest many commonly grown fruit crops
• Foliar distortion is caused by many species
• Reduction in fruit size and quality is caused by some species
• Secretion of honeydew encourages infection by sooty moulds
• Applications of Lorsban WG can control aphids and many other fruit pests

Introduction

Aphids, of one species or another, are capable of causing significant damage to a number of different fruit crops grown in the UK, including apples, pears, plums, strawberries, raspberries, currants and gooseberries. Some of the most commonly occurring and damaging species are Rosy Apple aphid (Dysaphis plantaginea), Rosy Leaf-curling aphid (Dysaphis devecta), Damson Hop aphid (Phorodon humuli), Blackcurrant aphid (Cryptomyzus galeopsidis) and Gooseberry aphid (Aphis grossulariae).

Biology

Rosy Apple aphid (Dysaphis plantaginea)

Eggs are normally found laid in crevices in any areas of rough bark. Winged aphids appear during June and July when they migrate to other host plants, namely plantains. However, if new growth is available colonies will continue to breed through August. Any migrated aphids will return to apple trees in early autumn.

Infestation by Rosy Apple aphid can cause severe damage by curling and distorting affected leaves. In the worst cases damaged leaves become brown and fall from the tree. Young shoots remain short and twisted and fruit produced by infested trusses is small and distorted, ripening prematurely.

Rosy Leaf-curling aphid (Dysaphis devecta)

Eggs of the Rosy Leaf-curling aphid are normally well protected as they are laid deep within crevices or under flakes of bark. Egg laying takes place from mid-June to mid-July with the life cycle being completed relatively early in the season. Colonies are not normally present in significant numbers after the end of July.

Infestation occurs on the same trees year on year, especially older specimens with areas of rough bark. Damage is similar to that caused by the Rosy Apple aphid and is normally very conspicuous. Symptoms are distinguished by the appearance of bright red areas on the upper surface of infested leaves and the lack of distortion or reduction in size of fruit.

Damson Hop aphid (Phorodon humuli)

Eggs are laid in autumn on plum, damson and blackthorn but do not hatch until the following April. The first two adult generations only produce wingless aphids. Subsequent generations are winged and migrate to hops from May to August, causing severe reduction in growth and yield if left uncontrolled. Successive generations of wingless aphids infest hops between June and September, before winged aphids appear once again to lay eggs on plum, damson and blackthorn.

Symptoms of infestation, slight curling of affected leaves, are not always obvious during early stages of colonisation and, consequently, the presence of Damson Hop aphid can often go unnoticed until the glistening of secreted honeydew is seen on leaf surfaces. Where shoots are heavily infested extension growth ceases and fruit size is reduced. Fruit quality is also adversely affected by the growth of sooty moulds on the honeydew.

Blackcurrant aphid (Cryptomyzus galeopsidis)

Eggs are laid at the base of buds or along shoots of currant and gooseberry bushes. After a few days eggs appear shiny black in colour. Hatching begins as buds break and is complete before any blossom has been formed. Wingless aphids are produced during the first two generations, and then winged aphids in subsequent generations. Winged aphids can migrate to other host plants during summer. When they return to currant and gooseberry bushes in early autumn, overwintering eggs are laid, hibernating until the following spring.

There are three forms of Blackcurrant aphid. One migrates from blackcurrant to hemp-nettle in early summer, another remains on blackcurrant throughout the summer, and the third lives entirely on redcurrants and whitecurrants. They colonise the underside of leaves but do not cause any deformation. Dense populations will cause fruit and foliage to become contaminated with honeydew.

Gooseberry aphid (Aphis grossulariae)

Eggs are laid at the base of buds or along shoots of currant and gooseberry bushes. After a few days eggs appear shiny black in colour. Hatching begins as buds break and is complete before any blossom has been formed. Wingless aphids are produced during the first two generations, and then winged aphids in subsequent generations. Winged aphids can migrate to other host plants during summer. When they return to currant and gooseberry bushes in early autumn, overwintering eggs are laid, hibernating until the following spring.

Gooseberry aphids live on currant and gooseberry bushes throughout the growing season and can sometimes be found on willowherb plants during summer. From May onwards infestation causes slight curling of leaves and dense colonies can easily be found on affected shoots.

Product Choice

Aphids infestations in crops of apples, pears, plums, strawberries, raspberries, currants and gooseberries grown in the UK can be controlled successfully using Lorsban* WG (active ingredient chlorpyrifos). Applications can be made to apples, pears and plums at pre-blossom or post-blossom timings. Do not apply to crops in flower or to those in which bees are actively foraging. Do not make applications when flowering weeds are present.

Strains of some aphid species are resistant to many aphicides. Where aphids resistant to products containing chlorpyrifos occur, Lorsban WG is unlikely to give satisfactory control. Repeat treatments of the same product are unlikely to improve efficacy.