Leek pests and diseases: Complete guide with photos

Hello to all agrohuerters! In today’s article we will learn how to identify leek pests and diseases. Here we go!

As we saw in another article, the leek is a classic among the classics in our garden. It is a very versatile vegetable and therefore used in many stews in our day to day. The scientific name of the leek is Allium porrum, belonging to the families of liliaceae such as onion. It is a plant native to regions between Europe and Asia. One of its advantages as a crop is the few demands it requires and the little space it needs. Of the 3 parts of the plant, only the stem and the bulb are consumed.

orchard leeks

Because they belong to the same genus, leek pests and diseases are very similar to those of onions.

1. Leek pests and diseases: the most important pests

Onion moth (Acrolepia assectella)

This insect can cause damage to our leeks due to the larvae that penetrate inside. The females lay eggs at the end of May. The main symptoms are a yellowing of the leaves, stop in the development of the plant and it can reach its complete deterioration.

Below you can see a photo of this moth:

Onion moth. Onion moth. Leek pests and diseases. (Source:

And on the other hand, here we have Acrolepiopsis assectella causing damage:

Acrolepiopsis assectella. (Source:

leek thrips

Brownish marks can be seen on leeks that are affected by these small insects, thrips. They can even dry up the leaves. Adult thrips are black and nymphs, on the other hand, are pale yellow. This species is very harmful especially in hot and dry summers.

Control: Surveillance and chromatic traps.

Thrips in the leek. (Source:

nematodes in leek

Nematodes, as we have seen on other occasions, are a kind of worms that live in water and soil. They are usually transmitted by irrigation water, contaminated substrates, or by tools that have previously been in contact with affected areas. The larvae enter the plants through the parts that are in contact with the soil (absorbent root hairs).

They parasitize the roots of plants, preventing the normal absorption of water and nutrients.This results in a decrease in growth, wilting and yellowing of the leaves.The clearest symptom is nodules on the roots.

The leek is susceptible to nematode attack during any phase of its development, although the youngest plants are the most likely to be attacked. In some cases the bulb softens.

For more information about this plague and how to prevent and eliminate it, you can consult the post: Nematodes: what they are and what to do if they cause diseases.

onion fly

Whitefly larvae penetrate the interior of the plant and grow within it. They feed from the inside, and this causes wounds, which can end in bacterial rot, the plant can die. Special care must be taken in seedbeds and seedlings, since very little time passes from when these symptoms are appreciated until the small plant dies. The damage it causes in these cases is irreversible.

2. Leek diseases

Among the most important diseases are:


One of the fungi that can affect leeks is mildew. This fungus also affects other types of crops such as tomatoes, melons, broccoli, radishes, turnips… It can be damaged by the fungus at any stage of growth. However, due to the conditions that require cold and humidity to develop, it usually appears as a seedling and in mature plants. It produces greasy-looking spots of different shades on the leaves, which then turn brown and wither.

To control this disease we must prevent transplanted plants from being infected and it is recommended to choose varieties resistant to this disease. In addition, it is important to keep the soil clean of weeds or weeds and be careful with excess irrigation water.

Rotten leek: Botrytis

Botrytis is another fungal disease and our leeks are not immune to it. This disease favors a warm and humid climate, which is why it is one of the most important diseases in greenhouses. The most characteristic symptom is bud and fruit rot (known as gray rot). It can also affect some leaves but is usually rarer.


This is all for today, I hope you have become a little more familiar with leek pests and diseases and see you in the next article.

Have a nice day!

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