Cherry blackfly is an aphid that sucks sap from the foliage of fruiting cherries and ornamental forms of Prunus cerasus, P. avium and P. padus during late spring and early summer, causing tight leaf curling.

• During late spring and early summer, the undersides of the leaves and the shoot tips are covered with shiny black aphids
• Leaves become severely crumpled and curled
• Later in summer the damaged leaves may dry up and turn brown, but the aphid leaves the plant
• Foliage becomes sticky with the sugary honeydew that aphids excrete, and a black sooty mould may develop
• Susceptible types of cherry will survive aphid damage, but they can suffer from curled leaves in most years
• The damage seems to have little effect on the trees long term health and affected trees often put on a good crop
• Predators will often wipe out populations of these aphids by late spring

Aphids form the basis of many food chains in the garden and it is not unusual to have some of these animals in a healthy balanced garden ecosystem.  Check cherries frequently from spring onwards so action can be taken before a damaging population has developed. On established trees aphids can usually be considered part of the biodiversity they support, natural enemies will normally reduce numbers during summer. 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
• Where an ornamental, rather than a fruiting cherry is required, the problem can be avoided by growing the less-susceptible Japanese types of flowering cherries
• 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

Pesticide control

• The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.

   

• 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 and shrubs. 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)
• A systemic containing the active ingredient Flupyradifurone (Provanto Smart Bug Killer) is available for use on ornamentals and selected edibles
• The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available

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Pesticides for gardeners (pdf document)

• Cherry blackfly overwinters on the tree as eggs, from which wingless aphids hatch in spring as the foliage develops
• Winged forms appear in June-July, and these migrate to wild flowers known as bedstraws, Galium species
• Populations on cherries gradually are eaten by natural enemies and die out during July, but damaged leaves remain visible for the rest of the summer
• There is a return migration from bedstraws in the autumn, when the winter eggs are laid