Oomycetes: Symptoms and treatment


It is common to confuse Oomycetes with true fungi, because the symptoms and damage they cause are almost the same. In addition, the treatment that is applied for some may also be used for others.

Still, I think it is very important to know the Oomycetes, organisms that affect numerous plant species throughout the world.


  • What are Oomycetes?
    • 1.1 What are its characteristics?
  • Why are Oomycetes not fungi?
  • types of Oomycetes
    • 3.1 Schimmel
    • 3.2 Phytium
    • 3.3 Phytophthora
  • What are the symptoms and damage they cause?
  • How are they treated?
  • Can Oomycetes be prevented?

What are Oomycetes?

The oomycetes They are pseudo-fungi (false fungi) that belong to the group of Protestants Omikota (or Omisetes). The species are classified according to the way they eat. On this one, we have saprophytes, which are those that feed decomposing organic matter and parasites.

The latter have a special interest in agriculture and horticulture, because they can end the life of plants if the measures are not taken in time.

What are its characteristics?

It is a series of organisms that have a cell wall composed of cellulose. What is more, during the alternative life deployed phases, in which cells present two positions of homologous chromosomes in their cell nuclei, with haploid phases in which cells have a single set of chromosomes.

The haploid phase, in these organisms, is the reproduction phase. This is sex when it produces gametangia; This is Antheria and Ogonia. In them, meiotic division occurs, which will cause a deployed oospore that will have thick cell walls. This will be released and will finish producing hyphae from which the sporangium will develop.

On the other hand, the asexual phase is the one that occurs when motile asexual spores, called zoospores, have a flagellum that is directed forward, and another to the rear. These are found in environments where the humidity remains high , like the substrate of a plant.

Why are Oomycetes not fungi?

For a long time it was believed that they were. In fact, they are classified in the Fungi Kingdom. However, today, Oomycetes and fungi have few but important differences:

  • The cell wall of the Oomycetes is cellulose. Fungi have it from chitin.
  • They are usually not septate organisms. The cells of fungi, on the other hand, are divided by their internal walls.
  • As they grow up, our protagonists have deployed nuclei , and not haploid like mushrooms.

With all this, they are now in the brand Heterokonta or estramenopilos, which they share with diatoms for example.

Types of Oomycetes

It is estimated that there are about 700 types of Oomycetes, among which we distinguish the following:


El mildew is a very, very common disease in plants causing the leaves to be covered with a kind of white dust. Depending on the variety, we find some that seem to have a predilection for a specific type of plant species.

For example, the Plasmopara viticola mainly affects the vine, hence it is known as vine mildew.


The phytium are a group of Oomycetes that affect an even larger number of plants. To young plants, such as seedlings, can cause irreversible damage and even death . But when they are adults, and if they are healthy, it is difficult for them to cause serious problems, after some mild symptoms, such as some brown spots on the leaves.

Likewise, it is interesting to say that the P. oligandrum species parasitizes other Oomycetes, which is why it is used as a biological control agent.


It is a genus of Oomycetes that attacks many, many species of plants. They are quite specific for the species they attack; I mean, that species of phytophthora they have a preference for a certain type of plant.

For example, P. ramorum especially affects oak trees, causing death; And pee infestation is common in plants such as tomatoes.

What are the symptoms and damage they cause?

It will depend a lot on the species of Oomycetes that attacks the plants. In general, the symptoms and damage we will see the following:

  • On the sheets: yellowish or brown spots, whitish powder, premature fall.
  • In this race: Chances, cracks. Early death of branches.
  • In the fruits: brown or blackish spots, rotting of the fruits. Often, the stem that connects them to the branches is black, as in the tomato.

How are they treated?

Although they are not fungi, they can be treated with the same products; That is with fungicides. But to the result is the expected, it is important to first identify the disease and seek a treatment that is designed to treat the particular disease.

One of the most recommended is copper. Kupric fungicides act by contact, and depending on the composition, it may be natural and therefore suitable for organic farming. It is especially useful as a preventive in seedlings and young plants, but it is also quite effective as a curative.

El Fosetil-El It is a systemic fungicide. The leaves absorb it, and from there it is distributed throughout the plant. It is widely used to fight mildew and phytophthora. The best known product with this composition is Aliette, from Bayer, recommended especially for browning conifers. You can buy it here.

Can Oomycetes be prevented?

As always when talking about pathogenic organisms, it can not be 100% prevented. What is happening is to take a series of measures that will help minimize risks. They are as follows:

  • Buy healthy plants. If they have brown spots, black stems or finally bad appearance, they should not be taken home.
  • Water only when necessary. Excess moisture in the roots weakens the vast majority of plants, except those that are water.
  • Make sure the soil drainage is good, and install systems to improve it in case puddles form an hour or days to absorb. More information.
  • Separate diseased plants as well as possible. The ideal is to have a space-enabled where they have them, in which they will be isolated until they improve.
  • For the pots: Use suitable substrates for plants and new ones. In addition, the pots must be clean and disinfected.

We hope this was of interesting to you.

Abbas Jahangir

I am a researcher and writer with a background in food and nutritional science. I am the founder of Foodstrend.com, our reputable online platform offering scientifically-backed articles on health, food, nutrition, kitchen tips, recipes, diet, and fitness. With a commitment to providing accurate and reliable information, we strive to empower our readers to make informed decisions about their health and lifestyle choices. Join us on Foodstrend.com's journey toward a healthier and happier lifestyle.

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