What is cherry blackfly?

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.

Symptoms

• 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
• 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

Control

Non-pesticide control

• 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
• Aphids have many natural enemies, including ladybirds, hoverfly larvae, lacewing larvae and several parasitoid wasps. Some of these are available for biological control of aphids in greenhouses (aphid predators). In spring damaging aphid infestations often build before natural enemies are active in sufficient numbers to give good control

Pesticide control

• Treatment is only feasible on trees small enough to be sprayed thoroughly
• In spring once the leaves have become curled the damage is done and it is too late for effective spraying
• Small trees can be sprayed with plant oil winter tree wash (considerd organic e.g. Growing Success Winter Tree Wash) in December to reduce the number of overwintering eggs
• Ornamental and fruiting cherries can be sprayed with organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Organic Pest & Disease Control, Bug Clear for Fruit and Veg). 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. These contact sprays will give poor results once the aphids have caused the leaves to curl
• More persistent insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Pest Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer) and cypermethrin (e.g. Py Bug Killer). As with organic sprays these contact insecticides will give poor results once teh leaves are curled
• Systemic insecticides, such as the neonicotinoid acetamiprid (e.g. Bug Clear Ultra), are also available. These are absorbed into the foliage and may reach concealed aphids when they feed
• The manufacturer's instructions for pesticides must be followed. When applied to fruiting trees, this includes maximum number of applications and harvest interval
• Do not spray the open blossoms due to the danger to bees and other pollinating insects
• Inclusion of a pesticide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

• 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
• Infestations on cherries gradually 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