What fungi affect plants?: The most harmful fungi

Hello to all agrohuerters! How are you? Today we are going to talk about the most harmful fungi for the garden. Although we have already mentioned it on other occasions, the term plague and disease are not the same. When we talk about our plants having a plague, we mean that a group of arthropods (mites, insects, crustaceans,…), nematodes or other types of animals are causing damage to our crops. However, when we use the term » disease «, we refer to the fact that it is fungi, bacteria or viruses that are affecting our plants.

Spinach downy mildew, one of the pests and diseases of spinach. (Source: agrointegra)

On this occasion, we will focus on fungi, which are a group of microorganisms capable of causing diseases in the orchard or garden.

The most harmful fungi for plants

There are many types of fungi, some can affect the roots (genus Rhizoctonia), the seeds and seedlings (genus Phytium and Phythoptora), the leaves, the fruits, the stem or the vascular vessels.

However, the most harmful and most common fungi to see in our orchards and gardens are the following:

Oidium: ash, bad white or white mold

  • Species affected: Powdery mildew can affect a wide variety of crops, but it is undoubtedly one of the most damaging fungi on vines. It is very common in cucurbits: pumpkin, zucchini, cucumber, melon or watermelon. In addition, it can be found in tomato, potato, chard, spinach or beans.
  • Description and symptoms: It appears in the form of white spots and gradually transforms into a grayish-white powder. Thanks to that white powder, it is one of the easiest mushrooms to spot. It normally develops on the upper surface of the leaves, although it can also spread along the stem or the fruits. Their presence hinders photosynthesis. If we do not control it well, the leaves turn yellow and can dry out.
  • Propagation conditions: Humidity and warm temperatures are the ideal conditions for powdery mildew to appear in our orchard.
Grapes with powdery mildew. (Source: INRA)

For those of you who have a garden, this fungus usually also affects the leaves of rose bushes.

In the following link you can read how to eliminate the hatred of plants.


  • Affected species: Mildew affects a wide group of plants, highlighting the vine and the Solanaceae (tomato, aubergine, pepper or potato). Other crops damaged by this fungus are strawberries, cucumber, melon, beet, spinach or chard.
  • Description and symptoms: It produces greasy-looking spots of different shades on the edges of the leaves or fruits, which later turn brown and wither.
  • Propagation conditions: This fungus takes advantage of plant wounds or leaf stomata to enter. You can infect them through irrigation water. It requires medium temperature (approximately 20ºC) and high humidity (which is why it usually appears after the rains).

Rust on plant leaves

  • Species affected: Rust can affect rose bushes, garlic, onions, leeks, arugula, legumes, asparagus and others.
  • Description and symptoms: Orange bumps appear on the underside of the leaves and small yellow spots on the upper side.
  • Propagation conditions: It needs mild temperatures and very high humidity. It can appear after long periods of heavy rains.
Rust pustules on rosebush.

Botrytis or gray rot

  • Species affected: Botrytis mainly affects strawberries, tomatoes, lettuce, vines, cucumbers and aubergines.
  • Description and symptoms: This fungus causes gray rots and the plant tissue appears rotten. Very common to see if we leave the strawberries for a while in our house.
  • Propagation conditions: The genus Botrytis needs high humidity, little ventilation and mild temperatures to propagate.
Botrytis cinerea in grapes (Source: INRA)

If anyone is curious to see what this fungus looks like under a microscope, here are some photos of a practice I did in the laboratory with a Botrytis -infected strawberry:

Botrytis cinerea under the microscope.

Marssonina or Mancha Negra: one of the most damaging fungi in the rose bush

  • Affected species: mainly affects rose bushes and, occasionally, begonias or geraniums.
  • Description and symptoms: rounded black spots appear on the leaves, which spread and can cause defoliation. The best way to eliminate it is to remove the affected leaves and destroy them.
  • Propagation conditions: It requires mild temperatures and the presence of water. It is spread by rain splashes.
Marssonina, one of the most harmful fungi of the rose bush (Source: Wikipedia)

How to control mushrooms in the garden?

For today, knowing how to identify them is enough. But if you want more information on how to control fungi in the garden, at the following link, Lucía explains how to prevent and treat fungi in the garden in an ecological way.


I hope you liked the article and that, once again, it will help you to keep your orchards and gardens in the best conditions. Tell us about your experiences with these 5 mushrooms in the comments and send us photos so we can help each other.

Have a nice day!

Related posts

Deja una respuesta

Tu dirección de correo electrónico no será publicada. Los campos obligatorios están marcados con *

Botón volver arriba