Ask Monty

QFor two years small yellow caterpillars have devastated my berberis bush.

The bush is very prickly so squashing them or shaking them off hasn’t worked. Can you help? Peter Waring, Tewkesbury

AYou have berberis sawfly which only appeared in the UK 15 years ago. They attack berberis and mahonia – and can munch their way through the entire foliage of either plant. Other than picking the larvae off by hand there isn’t much you can do except replace the plant with another species.

QI have a camellia which is about 8ft tall.

I’d like to reduce its size – how much can I prune it back safely? Arthur Oldham, Cheadle

ACamellias respond well to hard pruning so you can cut it down to a stub and it will regrow strongly. The best time is immediately after flowering in April or May.

QAMy garden is overrun by woodlice. Do they eat vegetation or cause any significant plant damage? Woodlice feed off rotting wood. They may nibble at seedlings in a greenhouse where the warm damp attracts them but much prefer decaying wood and leaves. Keep the greenhouse tidy and move plants around regularly. Woodlice are an important cog in the eco-machine that recycles vegetation so they’re a gardener’s friend.

Write to Monty Don at Weekend, Daily Mail, 2 Derry Street, London W8 5TT or email monty.don@dailymail.co.uk. Please include your full name and address. We regret Monty can’t reply to letters personally.