Fruit and vegetables

Downy mildew of the vine

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What is the downy mildew of the vine

This is a disease caused by the fungus plasmora viticola, originating in North America and widespread in Europe since the 19th century. The microorganism belongs to the category of oomycetes, which generate spores that form during the vegetative cycle of the plant. The germination of these spores remains dormant during the winter period and then completes as soon as the climatic conditions permit. Once their development is completed, the oospores emit the zoospores which are responsible for the actual infestation of the vines. As fungi, zoospores proliferate in climatic conditions of humid heat or at least when heavy rains persist. The shoots must be at least 10 centimeters long to allow their movement on the veil of water through a pair of flagella. If the shoots are smaller they do not have the necessary space to reach the stomatic openings of the plant where they generally nest. Through the emission of a tube, the pathogen sucks the lifeblood of the plant which it uses as nourishment causing its death.


Symptoms attack late blight on the leaves of the vine

The first symptoms of the development of this type of pathology are evident in the upper part of the leaf. These in fact have spots, three centimeters in diameter, with irregular contours. They are located on the edges of the leaf and have a yellowish color, hence the name oil spots. These discolored parts tend to turn black because necrosis begins, unless the environment is particularly humid. In this case, in fact, the spots will be whitish in color, a condition that highlights the formation of the reproductive structures of the fungus. If the climatic condition is optimal, both necrosis and whitish efflorescence can occur, without the formation of oil spots, which means the very advanced state of the disease. In this case the leaves fall early, unless they are old leaves or plants particularly resistant to pathogenic attacks. The branches instead undergo attacks on the nodes, becoming a purple color. At this point there are openings from which the whitish efflorescence emerges, and the branches take an unusual S shape.

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