Powdery mildew

Powdery mildew

The White Sick that afflicts plants

This pathology is commonly identified with the name of Mal Bianco. The species of fungi that induce powdery mildew are different and for this reason it is one of the most widespread dysfunctions. Plants affected by White Sickness are easily recognizable and, as can be deduced from the name used for the pathology, have white spots almost as if they were in dust on the entire surface of the leaves, on the roots and on the stems. Typically, the low leaves of the plant or tree are most affected, despite the fact that the fungus can be found on any living part of the plant. As the disease progresses, the number of spores increases throughout the plant, infecting it entirely in both length and width and causing the resulting increase in spots and white dust. But the powdery mildew not only infects the leaves, in fact in the plants and trees for agricultural production, it also creeps on the fruits leading to the formation of white spots on them. The main cause of the proliferation of this pathology is the presence of a high degree of humidity in the environment, especially in areas with poor ventilation, and is therefore widely diffused in plants found in northern latitudes. The pathogen can spread even in drier climatic conditions if it is helped by some details, for example the irrigation carried out to give water to the fields. The sudden cure of this fungus is necessary because with the progress of the infection the yield of the crop plants becomes poor and unprofitable.

Reproduction of the fungus and symptoms

The reproduction of Ascomycetes, that is the type of fungus that infects the plant, occurs both asexually and sexually. Thanks to this ability, Ascomycetes can take different forms from each other in relation to the type of plant or tree they attack. Asexual reproduction is, however, the most common procedure as the fungi of the Erysiphal family produce oidiospores which consequently spread powdery mildew. After the formation of the famous whitish spots, the spread of the disease occurs through the spores that reside on them and which are, in turn, helped to spread by the winds. Over time, the young spores mature and are ready to initiate a new infection in a different region of the plant. The persistence of the fungus is very strong, in fact the pathogen is able to survive even during the winter thanks to the formation of particular defense structures on dead or dry areas of the plant. As for the symptoms and the external conditions of the plant, powdery mildew is one of the easiest pathologies to understand. First of all it is characterized by the characteristic white spots that appear on the surface of leaves, grass, shoots, stamens and branches. The spots almost have the appearance of white powder or tiny cotton balls and, in the case of leaves and shoots, they can appear both on the upper and lower surfaces of the affected area. As the disease progresses, the color of the spots changes from white to a diffuse light brown. Symptoms of the disease are present only on living areas of the plant. After the formation of the spots and their color change, the infected plant and fruit undergo further damage: cracks and detachments begin to appear due to the necrosis caused within the cellular tissue of the area. The final stage of the disease involves the total death of the plant which is damaged even inside the roots.

Symptoms of the disease in various plant species

Many plants are subject to powdery mildew and depending on the class to which they belong they are vulnerable to particular types of fungi that all fall under the name of Oidium, but contain the adjective related to the plant, flower or tree they attack. These fungi attack various types of fruit trees including vines, apple trees, hazelnuts, peaches and others. As for flowering plants, powdery mildew attacks rose, begonia, dahlia, chrysanthemum, etc. In the vine, the fungus tends to violently attack the berries and buds, easily managing to infect all the cellular tissue and one of the consequent symptoms is the sudden fall of the leaves.

Defense and care of plants from Oidium

To fight the infection and free the plant from the pathogen, we proceed by using sulfur-based substances and fertilizers and decreasing the presence of vegetation in the plant. It must be said that this type of treatment must be carried out to prevent the onset of the disease, since it can do nothing against infections already in progress. Sulfur is used because it is capable of interfering at the cell membrane level and blocking the growth of the fungus. In case of ongoing infections, one can try to contain the reproduction of powdery mildew, but it cannot be completely eliminated. The infection is contained by detaching the dead and dry parts away from the plants, subsequently the infected parts must be kept away from plants or crops and burned. In the case of garden or indoor plants, the air circulation must also be kept under control; while as regards the fields, to avoid the proliferation of the fungus it is good to keep under control the use of fertilizers and irrigation.

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