Onion diseases

Onions are one of the most popular garden crops – not only are they easy to grow, but they are also one of those that will be used more in the kitchen later. But unfortunately, these plants can also have serious problems with fungi and bacteria that live in the soil.

So that you can have an excellent harvest I’m going to tell you what are onion diseases and how can you treat them.

Table of Contents

  • 1 Alternaria
  • 2 Botrytis
  • 3 White tip
  • 4 Variegated onion
  • 5 Onion charcoal
  • 6 White rot
  • 7 Roya
  • 8 Mildew


Alternaria alternata leaf damage

It is a fungus whose scientific name is Alternaria porryIt initially appears as white lesions on the leaves that quickly turn brown. When sporulation occurs, the wounds turn purple.

It can be controlled with chlortanil 15% + copper oxychloride 30% 0,25-0,45% wettable powder.


It is a fungus whose scientific name is Botrytis squamosa, what causes yellowish-white spots on leaves. In severe cases, these leaves become necrotic.

It can be controlled with diclofluanide 3% 20-30% powder for dusting.

White tip

It is a fungus whose scientific name is Phytophthora porri which causes white spots on the tips of the leaves. Basal leaves that are infected rot, and the plant stops growing.

The way to avoid / control it is by doing long rotations, since it usually appears when the land has been infected for more than three years. You have more information about crop rotation here!.

Variegated onion

It is a viral disease, that is, caused by a virus. The leaves turn pale green, and long yellow streaks appear. This weakens them so much that they are vulnerable to yeast infections.

There is no cure, that is why the soil must be disinfected before planting, for example by means of solarization.

Onion charcoal

It is a fungus whose scientific name is Tuburcinia cepulare which causes the appearance of silver-gray streaks that become black, and the death of the seedlings.

It is avoided by disinfecting the soil.

White rot

It is a fungus whose scientific name is Sclerotium cepivorum which attacks the bulbs, causing the leaves to appear yellow which turns brown fast.

It is controlled by doing long rotations, and avoiding planting in very humid soils and / or with a high content of little decomposed manure. It can also be treated with methyl thiophanate 70% MW, at 100 g / Hl.


La roya is a fungus whose scientific name is Puccinia sp. Causes reddish-brown spots that later turn purplish. The leaves dry quickly.

It is controlled with mancozeb 80% PM, at 200 g / Hl.


Mildew on onions

Image – http://www.greenlife.co.ke

It is a fungus whose scientific name is Peronospora destructor or schleideni that makes elongated spots covered by a purplish felt appear on new leaves. The bulbs do not mature.

It can be controlled by avoiding wild grasses, waterlogging, and planting in tight, poorly drained soils. In case of having diseased crops, treat with zineb 10% 20 kg / ha in powder for dusting.

I hope it has been useful to you.

Onion diseases

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