The trouble with berberis

by Richard Jones

The branches are bare of leaves and several of the bushes are completely defoliated. The culprits are not hard to spot: small speckled greyish sawfly caterpillars.

Picture-winged fly - Rhagoletis meigeniiA few weeks ago I mentioned that I had seen my first berberis sawfly, Arge berberidis, fluttering around a bush of Berberis thunbergii. I made light of it since the bush is fairly thuggish and nothing else much eats it. My interest was purely academic. Having heard about this invader, which probably arrived about 10 years ago in imported horticultural material, this was the first time I had seen it in south-east London.

My interest in this bush was first roused a few years ago when I found a small picture-winged fly, Rhagoletis meigenii (pictured above), in London's Battersea Park in June 2000. At the time this pretty little insect was thought to feed on the native Berberis vulgaris, but was believed to be extinct in Britain, having been last recorded in 1897. I went back the next month and found it on the B. thunbergii bushes (the purple-leaved cultivar) in the ornamental gardens. Despite close attention to the many hedgerow bushes in East Dulwich and elsewhere, I've not seen it again. A colleague found it a couple of years later on the same garden shrub in Essex, but as far as I know this is the sum total of its known occurrences here. Curiously this was almost exactly the same time that the now widespread berberis sawfly arrived in Britain.

Unlike the sawfly, which feeds on the leaves, the grubs of the picture-wing fly develop in the small berberry fruits. Having seen bushes weighed down with berries in autumn, I've often wondered why the fly has not been more widely seen. A very similar species, Rhagoletis cerasi, is a major pest of cherries on the European mainland and I'll bet UK cherry growers are keen to know whether it is spreading.

Berberis hedge defoliated by the berberis sawflyI walked past the same bushes at the weekend and my observations now take on a different tone. The branches are bare of leaves and several of the bushes are completely defoliated. The culprits are not hard to spot: small speckled greyish sawfly caterpillars. If they keep on like this B. thunbergii is doomed.

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Gardeners' World Web User 21/07/2008 at 16:40

I too am having the same problem and have never had it before. I have 7 Berberis in both my front and back gardens and they have all been attacked, but I have yet to see the culprit as I didn't look too closely - just thought "I wonder what's been eating them?"! I live in north west Kent

Gardeners' World Web User 28/07/2008 at 20:59

We have a Berberis thunbergii that is the main screen for the front of our house (or was) - we only noticed a few days ago that we could see through it quite drastically and upon inspecting it yesterday, noticed nearly all of the leaves decimated. We have shook off many caterpillars - and sprayed it. Just hope it comes back. This has never happened before in the 6 years we have lived here. We live in North Manchester and not heard of anyone else locally that has suffered with this pest?

Gardeners' World Web User 30/07/2008 at 11:55

I have had the same problem on my Berberis for the last 2/3 years with just the leaves right at the end of the branches left, this weekend I saw many flies, almost certainly the same as above flitting around the bush. This is in the Harrow side of London

Gardeners' World Web User 06/08/2008 at 18:09

I have them on my berberis too, I'm in sunbury, right at the end of the M3. How do i get rid of them?

Gardeners' World Web User 06/08/2008 at 23:03

I have this too. First time ever and it's made a mess of my mature barberry. I noticed the flies first in early July, but I couldn't identify them in any of my books (obviously my books are too old for this one). Now I've identified it, I shall be spraying!

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