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

What should I do?
Here are our top tips to your most common questions on managing cherry blackfly
 Should you remove cherry blackfly? Tolerate these aphids. It is usual to have some in a healthy, balanced garden. They are a vital food source for a wide range of wildlife in the garden.
Do cherry trees with cherry blackfly still produce cherries? Yes. Cherry trees with cherry blackfly will still produce fruit. There are other reasons that cherry trees may have reduced fruit production, see our page on reasons for unproductive fruit trees; cherry fruit drop can also be a problem. Cherry blackfly aphids will not kill cherry trees.
Do I have to control cherry blackfly? You don’t have to kill or control them. They are part of the biodiversity of gardens and a vital food source for other wildlife in your garden. If you do decide to control aphids, these are the ways you can cause least harm to the environment and avoid pesticides.
 

• Check plant frequently from spring onwards so you can act before the damage has developed
• Where possible tolerate populations of aphids they form an important part of many food chains and can be part of a healthy garden ecosystem
• On established trees aphids can usually be considered part of the biodiversity they support, natural enemies will normally reduce numbers during summer
• 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.  In spring, aphid populations increase before the natural enemies are active in sufficient numbers – so if you wait a while, they’ll often give the control

Pesticides

The RHS recommends that you don’t use pesticides.

Pesticides (including organic types) can have negative side effects such as:

• Reduced biodiversity, including natural enemies that could keep the aphid populations in check
• Impacts on soil health and wider adverse environmental effects
• Harm to pollinating insects such as bees

Where you cannot tolerate aphids, manage them using the information above as your first course of action. The pesticides listed below are legally available in the UK, but this information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife. Always follow the instructions on the products very carefully. For edible plants, make sure the specific plant is listed on the label.

Plants in flower should not be sprayed due to the danger to bees and other pollinating insects

• 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 
• 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 that combine nutrients to stimulate plant growth with surfactants or fatty acids also have a physical mode of action against aphids (e.g. Spot-On Bug Control, Growing Success Bug Stop, SB Plant Invigorator and Doff Universal Bug Control). These products contain some synthetic ingredients and so are not considered organic
• On fruit trees and shrubs: Winter wash is a plant oil application to the bark of fruit trees and shrubs targeting overwintering aphid eggs (organic e.g. Growing Success Winter Tree Wash). This may be used when the buds are fully dormant in November-early February on a dry frost-free day

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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