Berberis sawfly
A sawfly whose pale grey-green larvae, spotted and blotched in black and yellow, strip deciduous berberis and mahonia to the midribs. They feed in groups and they are startlingly fast — a plant can go from untouched to bare in under a week, which is why the damage is so often blamed on something the grower did.
Caused by: Arge berberidis
What brings it on
Arrived in Britain in 2000 and now widespread in England. There are two or three generations a year, so a plant cleared in June is routinely stripped again in August by the next brood.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Berberis sawfly
Checked 2026-08-13
Usually seen: May, June, July, August, September
Preventing it
Ordered by how much difference each measure actually makes, not by how often it is repeated.
- Check the interior of the plant rather than the outside from late May. The larvae start on shoots deep in the bush and are usually only noticed once they reach the outer growth, by which point most of the feeding has already happened.
source
Horticultural consensusmoderate confidence
- Royal Horticultural Society: Berberis sawfly — control
Checked 2026-08-13
Dealing with it once it is there
- Pick the larvae off by hand where the plant is small enough to reach into. Deciduous berberis recovers well from complete defoliation provided it does not happen year after year.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Berberis sawfly — control
Checked 2026-08-13
What it affects
On sprays and treatments
GrowingHQ does not tell anyone what to apply, at what rate, or how often. Pesticide approvals differ by country, change without notice, and the product label is legally binding — it is also the document you are holding. What is described here is cultural and physical control, which is what a home grower can act on without a label in front of them.