Plants affected
Red, white and blackcurrants
Symptoms
Leaves appear puckered or blistered. The distorted foliage takes on a reddish or yellowish green discoloration.
Cause
Currant blister aphids are pale yellow and live on the underside
of the leaves where they feed by sucking sap. They also secrete
chemicals into the foliage and this causes the puckering and
distortion. Other species of aphid occur on currants but they
do not produce this characteristic blistering symptom.
Blister aphids are active on currants from bud burst until July. In midsummer, winged aphids develop and migrate to the wild flower known as hedge woundwort, (Stachys sylvatica). Infestations on currants come to an end at that time, although damaged foliage remains visible until leaf fall. The aphids return to currants in the autumn when overwintering eggs are laid.
Control
Currants affected by blister aphid still make growth and produce a crop, so treatment is not essential. If desired, plants can be treated with Growing Success Winter Tree Wash in December to control the overwintering eggs.
The only insecticides approved for spraying on currants against newly hatched aphids in the spring are the systemic insecticide thiacloprid (Provado Ultimate Bug Killer Ready To Use) or organic sprays such as rotenone* (Bio Liquid Derris Plus*) or pyrethrum (Py Spray Garden Insect Killer, Doff All in One Insecticide Spray or Scotts Bug Clear Gun for Fruit & Veg). There is no point in spraying once the foliage has become distorted.
* Rotenone/derris-based insecticides are being withdrawn from sale.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