Plants affected
Gooseberry, red and white currants
Symptoms
Severe defoliation of the bushes and/or the presence of caterpillar-like larvae up to 20mm long. They are pale green with many black spots and they have black heads. Other sawfly species and moth larvae may also occur on these plants.
Cause
The common gooseberry sawfly is the most troublesome pest of gooseberries. It may have three generations a year, with the larvae active in May to June, July and August to September. Female sawflies lay eggs on the underside of leaves low down in the centre of the bush, so the young larvae go unnoticed until they have eaten their way upwards and outwards, devouring the leaves as they go. Defoliated plants are weakened and tend to produce a poor crop the following year.
Control
Regularly check the plants from mid-April onwards for sawflies and pick off the larvae by hand.
Alternatively, spray when young larvae are seen with an insecticide approved for use on gooseberry/currants. Suitable insecticides are thiacloprid (Provado Ultimate Bug Killer Ready To Use) or an organic pesticide such as rotenone* (Bio Liquid Derris Plus*) or pyrethrum (Py Garden Insect Killer, Scotts Bug Clear Gun for Fruit & Veg, Gem Stop Bugs or Doff All in One Bug Spray).
* Rotenone/derris-based pesticides are being withdrawn from sale in September 2008 (date to be confirmed). Gardeners can continue using up rotenone/derris-based products for 12 months after the final selling date.