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Pest and Diseases : Leek Moth

Written by Vicky Standing

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Posted on 15 February 2021

What is Leek Moth?

Originally a problem restricted to growers in the south of the UK, Leek Moth has spread its wings (literally!) and is now a potential issue wherever you are in the country. Acrolepiopsis assectella is a small grey-brown moth, 8-9mm long and similar to many other similar small and innocent moths. The caterpillars however, can do a great deal of damage, especially during hot summers in which many pest thrive.

What damage do they cause?

The young Leek Moth caterpillars burrow within the leaf, leaving brownish-white patches on the outer parts of the leek. As they get bigger, they invade deeper into the core of the leek, causing more significant damage and causing rotting which leads to slimy yellow leaves and the collapse of the plant. There tends to be two hatchings in the UK – the first at the end of the winter when the most likely damage is to the leaves and the second, more substantial threat, during the summer when the caterpillars invade the shaft of the leek and cause it to rot, either in the ground or during storage.

What do the caterpillars look like?

The caterpillars 1mm when newly hatched and grow to around 10mm at pupa stage. Creamy yellow in colour they have a dark head and small raised spots across the body. In spite of the name, the Leek Moth is a threat to all Alliums so look out for it on onions, shallots and chives too.

How do I prevent Leek Moth?

The most effective way to keep your leeks protected is is to cover them. Giant Easy Fleece Tunnels are ideal during cooler weather but in summer this be a little too warm so MicroMesh would work well later in the season. Rotate your crops to eliminate the danger of overwintering pests and start your leeks and onions off undercover in Rootrainers to protect them from early attacks will help. Clear away any plant debris and don't compost any material which may have been affected or contain any lingering caterpillars or moths. If you've not managed to cover your crop, look out for brownish-white patches caused by early activity and remove any caterpillars you might spot . The good news is that if you cut back any badly damaged foliage Leeks can often recover and go on to crop well - onions are often not so lucky, but by being vigilant covering your crop, the Leek Moth is a fairly easy pest to defeat.

 

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