Botrytis in onion: What is it and how to fight it

Botrytis is a common fungal disease on onions

Today, one of the most used production systems are greenhouses. These promote very high humidity conditions, which considerably facilitate the proliferation of some pathogens, especially fungi. Diseases and pathologies can severely limit production and affect the quality of vegetables. A disease that gives many problems to farmers is Botrytis in onions.

If you have problems with this fungus, I recommend that you continue reading. In this article we will explain what is Botrytis in onion, how to combat it and how to prevent it.

What is Botrytis in onion?

Botrytis in onion can cause great damage to crops

Botrytis in onion can cause extensive damage to crops

When we speak of Botrytis, also known as gray rot, we refer to a fungal disease whose culprit is Botrytis cinerea. This fungus can attack new shoots, leaves, stems, fruits and flowers of vegetables, thus causing immense damage to the crop, and consequently significant losses to the producer.

This fungus usually remains on dead plant tissues and plant debris. Once the environmental conditions are adequate, they favor its development. But what are these conditions? so that the Botrytis cinerea start to proliferate, a great help is diffuse light. Also the strong temperature changes favor their development. Of course, it does not withstand temperatures well above 35 degrees or close to 0 degrees. The optimum temperature for this fungus ranges between 15 and 25 degrees. What’s more, condensation formation it also helps this fungus to develop. This can be caused by dew, rain or high humidity that is created inside the greenhouse.

Generally, the points where a major infection occurs are usually the wounds caused by insects, the pruning cuts and the petals of the flowers that have been aborted. In those organs that have been affectedthe fungus penetrates them and promotes a grayish type of sporulation. This sporulation lasts if the humidity is high.


If we want to carry out a good control of this fungus and combat it, it is essential to understand how the life cycle of the fungus works. Botrytis cinerea and what is its behavior. Usually, from the time of inoculation until the development of the first symptoms, less than 24 hours. In the event that environmental conditions are not favorable for the development of the fungus, it can quietly overwinter in plant debris and living plants. In general, the infection cycle is made up of the following phases:

  1. Adhesion and germination: The spores adhere to the host surface and eventually germinate.
  2. Penetration into the affected plant tissue: They are introduced through natural openings or wounds. An enzymatic action of the fungus can also occur on the crop.
  3. Establishment of the fungus: The pathogen establishes itself in the penetration zone. Sometimes affected plants activate their own defense mechanism in order to control the pathogen.
  4. Spread in plant tissue: Dissemination into plant tissue begins. This determines both colonization and destruction of infected tissue. The time period of this phase is very short.
  5. New cycle of infection.

How to cure onions?

It is best to prevent Botrytis in onion

The best thing is to prevent Botrytis in onion

Now that we know what this fungus is and how it works, let’s find out how to combat Botrytis in onions. Of course all infected parts must be removed and destroyed sooner. So as soon as we detect the symptoms of this disease, we must take the appropriate measures.

Once the problem has become more serious, we will have no choice but to use curative fungicides that have excellent activity against the fungus Botrytis cinerea. These usually inhibit the growth of its germinative tube on the plant and also in the first phases of colonization of the leaf.

Prevention of Botrytis in onion

Although there are possibilities to eliminate Botrytis in onion, It is always best to prevent than to cure. Therefore, it is recommended that you follow these tips to prevent this fungus from affecting your harvest:

  • Improve cultural practices: Avoid lack of lighting and high densities when planting.
  • Facilitate better ventilation as possible.
  • Keep them low humidity levels.
  • Regulate the temperaturein the case of a greenhouse. It is of great help to avoid that the temperature is optimal for the development of the fungus Botrytis cinerea.
  • Apply products that help wound healing. This must be done via foliar.
  • Also via foliar, carry out preventive treatments with products of natural origin. These can be based on Bacillus subtilisspecifically the QST 713 strain.

I hope that this information has been useful for you to cure your onion crop and take preventive measures to prevent them from being affected by Botrytis.

Botrytis in onion: What is it and how to fight it

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