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Attention all UK Veggie-Growers (and Allium growers) - Leek Moth


By Sid


A while ago, I posted a question asking if anyone knew what was eating my leeks. I’ve completely lost my leek crop for the past three years running and this year, my onions were attacked too, although luckily not too much damage was done to them.

Nobody knew what was eating them. I searched the internet, I trawled through my own books and when they didn’t help, I hit the local library. Nothing. Zilch. Naught. Everything I read said that leeks don’t suffer from any pests.

Well, I knew otherwise! So, on a recent visit to the library again, I stumbled upon a reference to Leek Moth. It was described as a pale green caterpillar that tunnelled inside the leaves and then down into the crown of the plant, which usually destroyes them. THAT WAS IT!

A little further research on and I discovered that Leek Moth are yet another European invasion spreading north as a result of global warming. They were first seen in the UK in 2003 [RHS site].

The RHS site does give mention to Leek Moth, saying that they are a major pest on the continent, but don’t usually cause problems in the UK (Oh really?) They occur, according to the RHS, in southern and eastern England. Well, I live in Hereford, about 10 miles from the Welsh border, which is neither south nor east (unless, I suppose, you happen to live in North Wales).

Anyway, the upshot of all this is that if you grow leeks, onions, shallots, garlic or chives you need to be on the watchout for these critters. There seems to be some uncertainty over whether they attack ornamental onions, so it might be worth keeping an eye on those too.

Tunnels appear inside the leaves and eventually, the center of the plant turns into a mushy, slimy mess. The catapillars are about 10 mm (1/3”) long and are pale green.

There is no insecticide available to non-commercial growers that will control Leek Moth or their catapillars. From experience I know this is because the catapillars burrow inside the waxy leaves which repel anything you spray on them. You can pick the catapillars out of the leaves by hand, but once they’ve gone down into the crown of the plant, there’s not much you can do.

The most effective method of control is to use horticultural fleece over the rows which will stop the egg-laying female moths from accessing the plants (each female lays up to 100 eggs).

It’s war. Grrrrrrrr…….

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well done for finding the answer sid. knowing your emeny is half the battle.

20 Oct, 2008


Not another new pest, Sid! It seems never-ending. Congrats on all that research - I hope the fleece works.

It would be a bit difficult to put fleece on my Alliums - the mind boggles! Funny looking flowerbeds I would have, wouldn't I!

20 Oct, 2008


Thank you, Sid, I hope they don't get as far north as here. Perhaps it'll be too cold for them.

20 Oct, 2008


thanks for the imfo sid, just about to plant out garlics , will net with butterfly proof net , hopefully this will keep the moths out!!!..............steve

20 Oct, 2008


I know, Barbara - another one! And if it only reached our shores in 2003, it has spread alarmingly fast - it only took about 3 years to reach me (So watch out David!) Re your ornamental alliums, what I've read seems to suggest they are not effected, but that seems strange to me. I mean, how are they different?

Steve - I think Hampshire is definately in the 'danger zone', but no need to cover them up untill (early) spring, as the moths remain as pupae in leaf little over the winter. Good luck with it :-)

21 Oct, 2008


Will do, Sid, Many Thanks!

22 Oct, 2008


Just one further development - was in the garden today and noticed that a Hemorocallis I have growing right next to the bed where the leeks were this year has got something tunnelling inside the leaves. Don't know if it's the same thing - the leaves are not think enough to actually harbour the catapillers and I couldn't find any on there, but seems a worrying development...

23 Oct, 2008

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