Gooseberry sawfly (Nematus ribesii)
A serious pest of gooseberries and its relatives, red and white currants, which can strip all of a bush's leaves down to the veins in a matter of days in serious cases. While this won't necessarily kill the plant, it will seriously affect yields and encourages disease.
The adult emerges in April and lays its eggs, often along the veins on the underside of the lower leaves in the centre of the plant - just where it is hardest to spot them. The eggs hatch and the larvae, which eventually reach 2cm long, emerge. They look very much like caterpillars - pale green with black spots and a shiny black head - but have more back 'legs' than butterly and moth caterpillars. They feed first low down, at the centre of the plant, before spreading outwards and upwards. Within a month they will have grown to full size. They then drop to the soil and form a cocoon from where the next generation emerges - there may be three or four of these a year.
- Very pale green, 1mm long eggs laid on the undersides of leaves near the bottom of the plant
- Tiny holes in leaves near where the eggs have hatched
- Larger holes further up and towards the ouside of the plant follow
- In severe cases, complete defoliation
Prevention & control
- Check plants regularly from the April onwards.
- Pick off caterpillars and any leaves with eggs on them
- Remove mulch and turn over the soil at the base of plants in autumn/winter to expose overwintering cocoons.
- The nematode, Steinernema carpcapse (e.g. Nemasys Gooseberry Sawfly control) can be sprayed directly onto the larvae (it infects them with a bacterial disease) but you need to spot them early and order it quickly
- Pyrethrum sprays are probably more cost-effective but, again, you need to spot and treat while the larvae are young.