Rosy apple aphid is a small (2.5mm) dull pinkish or purple-grey sap-sucking insect that feeds on apple foliage and

An immature fruit, usually small.

Dense colonies of slate and pinkish-grey aphids develop on the underside of the foliage in spring and early summer. Affected leaves at the shoot tips become curled and yellowish. Where the aphids have been sucking sap from the fruitlets, they prevent the fruits' normal development. These fruits often remain small with a pinched appearance around the eye end. In late summer, some branches may have normal fruits while others have only damaged fruits, reflecting the distribution of aphids on the tree earlier in the growing season.

Heavily affected shoots show stunted growth with distorted leaves that start to turn brown during the summer. The main damage is to the developing fruits, which can be severely undersized and malformed.

In home gardens not all fruit are usually affected and so some aphids can be tolerated. Aphids form the basis of many food chains and it is not unusual to have some of these animals in a healthy balanced garden ecosystem. Check apples frequently from spring onwards so action can be taken before a damaging population has developed. On tall trees aphids can be considered part of the biodiversity they support, natural enemies will normally reduce numbers by late summer. In addition artificial treatments are only likely to be successful if the entire plant can be reached. When choosing management options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section and avoiding pesticides. Within pesticides the shorter persistence products (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached.
 

Non-pesticide control

• Where possible tolerate populations of aphids, they form an important part of many food chains and can be part of a healthy garden ecosystem
• Use finger and thumb to squash aphid colonies where practical
• Encourage aphid predators in the garden, such as ladybirds, ground beetles, hoverflies, parasitoid wasps and earwigs. Be aware that in spring aphid populations often build up before natural enemies are active in sufficient numbers and then give good control
• Some natural enemies can be purchased for use as biological control of aphids in greenhouses, including hoverfly larvae, lacewing larvae and several parasitoid wasps. More information about these can be found on the ‘aphid predators’ page.

Pesticide control

Little can be done to deal with aphids on tall trees as treatment is only likely to be successful if the entire plant is sprayed. Once leaf curling has occurred pesticidal control methods are unlikely to be effective.

• Little can be done to deal with aphids on tall trees as treatment is only likely to be successful if the entire plant is sprayed
• On fruit trees overwintering aphid eggs can be destroyed by using a plant oil winter wash (organic e.g. Growing Success Winter Tree Wash). This can be used when the buds are fully dormant in November-early February on a dry frost-free day. Plant oil winter washes are less likely to be detrimental to natural enemies and can mean that spring sprays are unnecessary 
• Organic sprays, such as natural pyrethrum (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear Fruit & Veg, Vitax Rose Guard) can give good control of aphids. These pesticides have a very short persistence and so may require reapplication to keep aphid numbers in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults
• Plant invigorators combine nutrients to stimulate plant growth with surfactants or fatty acids that have a physical mode of action against aphids (e.g. Ecofective Bug Control, Growing Success Bug Stop, Rose Clear 3 in 1 Action SB Plant Invigorator and Westland Resolva Natural Power Bug & Mildew). These products contain some synthetic ingredients and so are not considered organic
• More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer)

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Pesticides for gardeners (pdf document)

Rosy apple aphid overwinters on apple trees as eggs that are laid in autumn in bark crevices and around the buds on the shoots. These eggs hatch in spring as the leaves begin to emerge from the buds. While sucking sap, the aphids secrete chemicals into the foliage and fruitlets, which cause the distorted growth.

Several generations of wingless aphids develop between bud burst and early summer. During June-July, winged forms of the aphid develop that migrate away to wild flowers known as plantains, Plantago species, where they spend the rest of the summer. Populations on apple die out during the summer but there is a return migration from plantains in autumn when overwintering eggs are produced.