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Powdery mildew, also known as ash or white mold, is a fungus that is part of the Erisiphaceae family (Erysiphaceae) and contains many different species (more than 900) that affect various species of plants and trees worldwide.

 

Symptoms

Symptoms for Powdery Mildew shown on plant - dying plant

Powdery mildew is characteristic as it forms a kind of white cottony powder. This dust is a mass of spores that the fungus itself has produced in its development and affects all the aerial parts of the plant. Although it mainly affects the leaves, especially the younger ones, it can be found both on the underside and on the plate’s upper side.

 

Activity

Ascospores 3d illustration

It is a fungus (Ascomycete) whose vegetative cycle generates mycelium and schistocytes (a reproductive structure where the spores are enclosed) during the winter, and mycelium developed in addition to a series of chained conidia during the summer. As of spring and during the summer, the spread of ascospores (spores) occurs, giving way to the infection’s spread. This infection can stay until the fall. Therefore, the fungal infection will appear in the epidermal cells, but we will find the spores on the plant’s surface.

 

The plant will provide the fungus with everything it needs to live. They usually do not cause the plant’s death but weaken it, causing damage by necrosis in the leaves and immaturity of the fruit.

 

Humidity is an essential variable for the fungus’ growth since a high degree of humidity is a critical requirement in the fungus’ development and survival. The growth of spontaneous plants, high nitrogen content, or poor ventilation within the crop is also favorable for this infection.

 

Powdery Mildew and How It Affects Foliage

Gooseberry berries on palm with Powdery mildew fungi plant disease.

The spores cover the leaf surface, causing a slight blockage; consequently, they produce a loss of the plant’s photosynthetic capacity. This causes the plant to darken, turning to darker green and brown tones, causing the leaf’s death. The plant has difficulties breathing through its stomata since the spores collapse them in white powder. It also produces losses in the crop since many fruits do not develop fully.

 

  • Powdery Mildew on Vine: The species of fungus that infects is Erysiphe necator. Produces a reduction in size in the branches. The leaves darken and die. The powdery vine mildew necrotizes the fruits, even cracking if they have not reached their final size. Marijuana powdery mildew: Cannabis (Cannabis sativa) is affected by powdery mildew. The fungus is present on both parts of the leaf. The leaves curl up, and their fall occurs. It may have purple or reddish spots. The flowers show a decrease in pollen, and the fungus can cause their death. The infected fruits lose their shine and have a bad taste; the unripe ones do not ripen. It occurs both in indoor and outdoor crops. 
  • Powdery mildew on rosebush: The species of fungus that infests the rose bush is Podosphaera pannosa. This fungus usually appears on the underside of the leaves of the rose bush, although we can also find it on the top of these. It seems especially in the new shoots; even so, it can infect leaves and flowers. A white powder is produced on the plate and, if it appears on young leaves, it can even deform them as they grow. It usually acts in summer, although it spends the winter dormant in buds.
  • Powdery mildew in Appletree: The species of fungus that infects it is Podosphaera leucotricha. It infects the leaves, flowers, shoots, and especially the buds of the tree.
  • Peach powdery mildew: The species of fungus that infects them is Podosphaera pannosa. It infects leaves, young shoots, and fruits. This spice also affects the apricot and almond trees.
  • Mango powdery mildew: the species Oídium mangiferae infects mango. Depending on the variety of mango that is grown, the degree of infection varies. The fungus develops in young tissues. The leaves are deformed, producing possible defoliation. The fruit falls prematurely and appears entirely covered by the fungus.
  • Powdery mildew of cereals: wheat, oats, barley, rye. The species of fungus that infects them is Blumeria graminis. It is usually present in the upper part of the lower leaves, although it can be present in all of them. The grain may appear empty.

 

Treatment

Treating powdery mildew on a zucchini plant.

Here we look at 9 ways to treat Powdery Mildew:

  1. Use of resistant species: There are varieties of species on the market that show resistance to powdery mildew, usual hybrids of several plants from different countries within the same species. However, not all species have this option, such as watermelon, among others.
  2. Destruction of spontaneous plants and stubble: Elimination of plants through different mechanisms. If we maintain a high crop density, we promote poor ventilation conditions, which favor the pest’s appearance.
  3. Eliminate affected plant parts: All affected plant parts are cut and collected and burned or thrown away. It is important not to mix with the compost because they can spread through the humus.
  4. Late sowings: Delaying our crop sowing to avoid meeting the ideal conditions for the fungus, that is, mild temperatures and high humidity.
  5. Limit the supply of nitrogen: Control exogenously added soil nitrogen levels; besides, nitrogen is linked to all parts of the plant and is one of the primary sources. Nitrogen favors the appearance of this pest.
  6. Sulfur application: The application of sulfur is a widespread practice; it is a fungicidal mechanism of action, lethal for powdery mildew. Its use must be controlled and the treatment times must be well respected since if we use it in excess, we can damage the rest of the microorganisms present in the soil.
  7. Use of mycorrhizae: Mycorrhizae are filamentous structures generated by fungi. It is a symbiosis between the fungus and the plant since they favor the plant to absorb nutrients and other substances necessary for its growth. Furthermore, this treatment is incompatible with fungicides since these would eliminate both species of fungi.
  8. Natural or homemade fungicides: Treatment with propolis, a substance generated by bees from the plants’ resin and shrubs pollinate. Milk is also used as a homemade fungicide made from skimmed milk and sodium bicarbonate; in this case, it’s the lactic acid that will act as a fungicide itself.
  9. Chemical control of the disease: Use of chemical products with fungicidal action. We must bear in mind that one of these products main purpose is to eliminate all types of fungi, including those that can benefit the crop and also affect the soil and, consequently, the microorganisms that inhabit it.

 

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