I have found lots of holes in my leeks, on investigation, I found a caterpillar.

Can you tell me what type it is and how I can prevent this happening again?

You have found the larvae of the Leek moth, which can also attack onions, shallots and garlic.

There can be as many as three generations each year, so action needs to be taken as soon as any signs are visible.

On affected plants; destroy the worst ones, as the caterpillars may have already pupated in them.

Spray/drench the leek foliage with a suitable insecticide a couple of times, and this might help.

Good hygiene is imperative, remove and destroy all old plant remains.

My leek leaves were full of holes as soon as they opened out and many of the plants rotted and died.

< style="font-weight: bold; font-style: italic;">What was the cause of this and what should I do to prevent the same thing happening again?

It is likely that Leek moth caterpillars would have caused the damage.

Eggs are laid in April / May and the young caterpillars eat through the folded leaves then penetrate to the growing points of the leeks.

When the affected leaves unfold, the holes are then visible, if the growing tip has been affected then the plant is likely to die.

Normally there are three generations of caterpillar per season.

Pupae can over winter on fallen debris, so keep the area clear of debris to reduce this risk, and destroy any unhealthy old plants, by burning them.

The same pest can also attack onions, shallots and garlic.