Allium Leaf Miner Is Now Established In The UK. This Is How to Control Phytomyza gymnostoma On Onion Species in UK Gardens & Allotments.

Allium Leaf Miner (Phytomyza gymnostoma) was first detected in the UK in 2002 and has since spread across a lot of the country. It can quickly devastate crops and there are no pesticides approved for amateur use. However, that’s not to say that we cannot protect our crops as explained below.

Harvested Leeks

What Is Allium Leaf Miner?

This pest is a small fly. But the fly causes fewer problems than the maggot which can devastate allium crops such as leeks, onions, garlic, shallots, chives etc. Having said that the fly does suck sap from the leaves and this leaves a trail of white marks on the leaves.

What Damage Does Allium Leaf Miner Cause?

The fly sucks sap from the leaves and this leaves a telltale row of white marks. The maggot causes much more damage and burrows in to the plant tissue of the leaves and stem. This causes significant damage which is then often the site of secondary fungal infection.

Allium Leaf Miner Life Cycle & Biology

This pest is a small fly that can fly considerable distances to infect crops. They can be carried on the wind to distant crops.

Interestingly there is no mention of this pest on Wikipedia, the image libraries are devoid of free images and I have none of my own. It is that new as a significant pest. If you want to see what it looks like follow this link to see commercial stock images. 

The initial indication that the pest is in the area is often the rows of white puncture marks on leaves, where the 3mm long fly has sucked sap from leaves. If you see this in March or April, assume a problem is likely.

Allium Leaf Miner has two generations each year. The first generation lays eggs on the allium stems and leaves in March and April.

The second generation repeats the process in the autumn, in October and November. Because numbers have normally increased by this time it is the second generation that tends to do the most damage.

In both cases the maggots  (larvae) bore into the leaves and stems of the allium host plants to feed. After a few weeks they then pupate and become a dark brown pupae.

The maggots are small, legless, apparently headless, cylindrical larvae. They tunnel into the leaves and stems of the host plants.

The pupae stay in the plant if possible but can pupate in the soil if the plant has rotted away.

The soil borne pupae can be the source of future problems if a crop is netted as the pupae infect via both the first and second generation whilst within the netted area!

Allium Leaf Miner Symptoms

  • Lines of white dots on leaves
  • maggots tunnelling onto leaves and stems
  • Foliage that is twisted and/or distorted in spring
  • Rotting of plants.

How To Control Allium Leaf Miner

There are both chemical (pesticide) and organic treatment methods for commercial growers. But gardeners are not licensed to use chemical means.

Organic Control Methods For Allium Leaf Miner

Insect proof mesh is the best control method. But take care not to trap overwintered soil borne pupae in the meshed area. The best way to ensure this doesn’t happen is to only grow alliums on beds that didn’t grow any form of allium the previous year. Otherwise you just net the problem inside your mesh! And by the second generation numbers will have built up to significant levels.

Ditto where you grow plants from seed. Ensure it is pupae free before sowing. Sowing in trays inside is a good starting point in this respect. Once germinated they can be transferred outside under mesh.

Thereafter net the areas where they are growing. In spring this will be the seedbeds whilst in October and November it will be the growing beds. There is no need to keep the crop netted all summer. To do so means decreased light levels and less growth.

I rarely suggest the need to rotate crops. And if you’ve never had Allium Leaf Miner I stand by that, leeks  and other alliums can be grown on area year after year. BUT, if you have experienced leaf miner before then there is a need to rotate the crop to a clean area.

Allium Leaf Miner – My Commercial Experience

When I grew leeks commercially .. 90-100, 000 a year .. this pest hadn’t entered the country. So I never experienced it.

We grew leeks on the same land year after year with no disease or pest issue whatsoever.

Today, commercial growers have to use pesticides OR mesh huge areas of land which significantly increases growing costs.

Tags: Allium Leaf Miner

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