Overwintering leeks are susceptible to damage from the Allium Leaf Miner, and with the milder weather this year, they seem a little more active than usual.
What are they & when are they active?
The allium leaf miner is a fly that lays its eggs on leeks, onions and other alliums. When the maggots hatch they eat little tunnels from the leaves, leaving a trail behind them.
There are two main hatchings each year, in early spring, and in late autumn. It is this late autumn hatching that causes most damage to leeks that are overwintering (the spring hatching is usually too early, before leeks reach maturity)
What does damage look like?
Initially, you may see a line of white dots in the leaves. This is the first sign, and comes from the adult flies feeding on the plants before they lay eggs.
The next sign you may see some of the leaves beginning to be ‘shredded’ – the work of the maggots.
After that, you may see the small brown/red pupae tucked into holes in the leeks, and there may be visible leaf curling.
Finally, the damaged parts of the leeks will begin to rot, so if you haven’t worked out why your leek leaves/stems are rotting, this may well be why!
What can I do?
The best thing to do is cover your crops with fine mesh netting if Allium Leaf Miner is a problem in your garden. Get the nets on from late August onwards and be sure they are well secured.
It’s a sensible idea to rotate crops next season so that you don’t grow them in the same spot twice.