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

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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…….

• 20 Oct, 2008
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