Garden pest control - Gooseberry Sawfly Larva (Description and control instructions)

Scientific Name: Nematus ribesii

As the name suggests these little pests attack the leaves of goosebery bushes; also red and white currants, but not black currants - maybe the strong aroma of the leaves puts them off. The adult female lays its eggs on the underside of the leaves at the centre of the bush close to the ground. When they hatch the first instar of the larval stage is very small and makes tiny holes in the leaf. The next stages are much bigger, up to 20mm long, and they cause the most damage, stripping the bush bare as they move outwards along the branches.

The caterpillar-like larva is light green with black dots and a shiny, black head. If disturbed it clings to the edge of the leaf while bending into a S-shape. All of the leaves can disappear with only the stalks and a few veins remaining. Check any leaves beyond them and the larvae will be there, so they can be rubbed off.

The lack of foliage weakens the bush and it produces a very poor crop the following year.

There can be up to three generations in a season, so the damage can occur anytime between May and September. The best control is to examine the bushes carefully in late April, looking for the eggs or the early larval stage low down in the centre of the bush.

Repeat in early June, July and late August when later generations could be starting. Crush any eggs or larvae, and pick off any leaves showing the small holes made by the first instar larvae as they will probably be still there. It helps to prune the bushes in an open manner or train them as cordons, so that inspection is easy. They survive the winter as cocoons in the soil around the base of the bush, so clearing away debris and mulch in the winter, and disturbing the soil will allow the birds to find them.
When the early signs are spotted remove the affected leaves to ensure all of the eggs and larvae are cleared.