What is cherry blackfly?
Cherry blackfly, Myzus cerasi, is a black aphid that can cause damage to the leaves of cherry trees. Eggs are laid in cherry tree bark crevices on in autumn, and in April the aphids hatch, congregating on the under-surface of leaves at shoot tips. They are small, dark-brown or black, and shiny. They suck the sap from the leaves, and excrete sticky honeydew onto the leaves. This may cause the development of black sooty mould which reduces the leave’s photosynthesis activity. The aphids’ feeding causes the affected leaves to curl up. The physiological damage that they cause to the tree is usually minimal and doesn’t affect crops. They are usually attended by ants, as for other types of aphid. In late spring the winged form of the black cherry aphid migrates to other plants, bedstraw (Galium), eyebright (Euphrasia) and speedwell (Veronica), and they return to the cherry trees to lay their eggs in autumn.
How to treat cherry blackfly
As with all aphid problems, the most environment-friendly solution is encouraging natural predators such as ladybirds, lacewings and hoverflies. If you have a smallish tree in your garden, you can remove the aphids by hand, or by squirting water from a hosepipe, or by spraying a dilute soap solution (a few drops of washing up liquid in a litre of water) onto the underside of the leaves every 2-3 days for a couple of weeks. Keeping ants away from cherry trees by means of grease bands reduces the size and number of cherry blackfly colonies, and prevents the ants from deterring the action of the natural predators. A winter wash can reduce the number of eggs.
If cherry blackfly become a problem recurring year after year, we recommend expert help.