Why has my gooseberry bush been stripped of its leaves?

The adults lay eggs along the veins on the underside of leaves low in the centre of the bush, which is the last place anyone looks. By the time you notice damage from the outside, there are often hundreds of caterpillars. The bush itself usually survives — a completely defoliated gooseberry generally refoliates and crops the following year — but the current crop is small and the plant is weakened, and it is entirely preventable by looking in the right place at the right time.

Step by step

1. Confirm the pest.Pale green caterpillars up to about 2cm, with black spots and a black head, feeding in groups. They affect gooseberries and red and white currants; blackcurrants are largely left alone.
2. Start checking in late April.Look at the underside of leaves low down in the middle of the bush, which is where the eggs are laid. That single habit prevents almost all the damage.
3. Pick them off by hand.On a garden bush this is entirely practical and immediately effective. Wear gloves against the thorns, work from the centre outwards, and drop them into a bucket of water. Squashing eggs on the leaf undersides works too.
4. Keep checking through the summer.There are commonly two or three generations between April and August. Clearing one lot is not the end of it, and the later generations do the damage to next year's growth.
5. Open the bush up.A properly pruned open goblet on a clear leg makes the interior visible, which is half the battle. A congested bush hides the entire infestation until it is too late.
6. Cultivate lightly under the bush in winter.The pupae overwinter in the top few centimetres of soil beneath the bush. Forking it over lightly exposes them to birds and frost.
7. Let the birds and predators work.Blue tits and other small birds take large numbers of sawfly larvae. Do not net a bush permanently outside the fruiting period — birds are useful the rest of the time.
8. Treat pesticides as a last resort and check the label.A biological or contact product must be approved for edible crops and must reach the caterpillars, which are on the leaf undersides in the middle of the bush. Timing and coverage matter more than the product, and hand picking usually wins on a garden bush.
9. Feed a stripped bush and expect recovery.A defoliated bush refoliates. Water it, mulch it, feed with potash in late winter, and it will crop the following year.

Tips

• The rule of thumb is: check the bush every week from late April to August, starting in the middle, low down. Everything else is optional.
• Damage that appears overnight in June is almost always sawfly. Slugs and birds do not defoliate a whole gooseberry.
• Sawfly caterpillars are not butterfly or moth caterpillars, so products aimed at caterpillars of moths and butterflies do not affect them.
• Cordon-grown gooseberries are much easier to inspect than bushes, which is another argument for the form.

Common mistakes

• Only looking at the outside of the bush — The infestation starts low and central. By the time the outer leaves are damaged you have missed several weeks.
• Assuming a stripped bush is dead — Gooseberries and currants refoliate readily. Feed, water and mulch, and it will be back the following season.
• Netting the bush permanently to keep birds off — Birds are one of the better controls for sawfly. Net for the fruiting period only.

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