Advice
RHS Help & Advice
Cherry blackfly (Myzus cerasi)
Plants affected
Fruiting cherries and ornamental forms of Prunus cerasus, P. avium and P. padus.
Symptoms
During late spring and early summer, the undersides of the leaves and the shoot tips are covered with shiny black aphids. The leaves become severely crumpled and curled. Later in the summer the damaged leaves may dry up and turn brown. The foliage becomes sticky with the sugary honeydew that aphids excrete and a black sooty mould may develop on this substance.
Cause
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. The infestation on cherries gradually dies out during July but damaged leaves remain visible for the rest of the summer.
Pest avoidance
Vulnerable types of cherries will survive aphid damage, but they are likely to suffer from curled leaves in most years. Where an ornamental, rather than a fruiting cherry is required, growing the less-susceptible Japanese types of flowering cherries is a way of avoiding the problem.
Control
Treatment is only feasible on trees small enough to be sprayed thoroughly. Such trees can be sprayed with Growing Success Winter Tree Wash in December to control the overwintering eggs.
Ornamental cherries can be sprayed with imidacloprid (Provado Ultimate Bug Killer Concentrate), acetamiprid (Scotts Bug Clear Ultra concentrate) or bifenthrin (Bayer Sprayday Greenfly Killer Plus or Doff All-In-One Garden Pest Killer) in late spring when aphids begin to appear on the foliage. Fruiting cherries can be sprayed with organic pesticides, such as pyrethrum (Py Spray Garden Insect Killer or Scotts Bug Clear Gun for Fruit & Veg) or rotenone* (Bio Liquid Derris Plus*), or a synthetic systemic insecticide, thiacloprid (Provado Ultimate Bug Killer Ready To Use).
Once the leaves have become curled it is too late for effective spraying. Do not spray during the open blossom period in order to protect bees.
* Rotenone/derris-based insecticides are being withdrawn from sale. Gardeners who have this pesticide may continue using it until 10 October 2009. Any unused products after that date should be disposed of safely by handing them to the staff at a local authority manned waste disposal facility.
Disposing of old chemicals