Powdery mildew: Vine diseases. Protection strategy.

Leaves: Symptoms can appear both on the upper side and on the underside, in both cases an ashy white powder is usually observed, which can be limited to some areas, or occupy the entire surface of the leaf.

Shoots and shoots: the symptoms are manifested by diffuse dark green spots that grow and turn darker as the vegetation advances and even blackish as the lignification of the vine increases.

Clusters: at the beginning they appear as a certain dust that covers the whole grain in a short time.

The most important damage caused by powdery mildew is located in the bunches, since the powdery mildew fungus stops the growth of the grain skin, which is why it frequently cracks, causing direct damage to the quantity and quality of the harvest.

Strong attacks also cause a bad withering of the vine with the consequent decrease in the accumulation of reserves in the buds.

3- Development stages and annual cycle of powdery mildew:

The fungus winters inside the buds and on the shoots. When sprouting begins, environmental conditions usually exist for the fungus to come out of its lethargy and begin its development.

When it reaches maturity, asexual reproduction begins with the formation of a large number of conidia , which, carried by the wind, spread the disease to any green part of the plant.

From this primary focus it can have various contaminations , if the climatic conditions are favorable, throughout the vegetative development of the vine.

At the end of the vegetation, the development of the fungus also stops, preparing to spend the winter in the form of mycelium (asexual phase) inside the buds or in the form of peritheca (sexual phase) in the shoots.

4- Favorable climates for vine powdery mildew:

Temperature, humidity and lighting are the factors that condition the development of this fungus. Temperature is the factor that most influences the development of the disease:

• From 15ºC: its development begins.
• Between 25 and 28ºC: it is the optimal range of temperatures for its development.
• From 35ºC: it stops its development
• From 40ºC: these high temperatures are lethal for powdery mildew.

Environmental humidity is also very important and influences the development of the disease. With high relative humidity the conidia germinate.

Unlike mildew, abundant rains slow its development.

5- Ecological or preventive treatment.

• Carry out the vine plantations in the direction of the prevailing wind.
• Carry out the pruning of the vine stock, the stripping and stripping, to facilitate the circulation of air and sun or light, avoiding a microclimate favorable to the development of powdery mildew.
• Fertilize correctly avoiding excess nitrogen that favors the development of powdery mildew.
• It can be treated with sulfur spray or dusting.

6- Treatment against powdery mildew:

The most opportune moments to carry out phytosanitary treatments are:

1. When the clusters become visible (phenological stage F), most of the shoots have between 5 and 10 cm.
2. At the beginning of flowering (beginning of phenological stage I).
3. With pea- chickpea size grains .
4. At the beginning of veraison (5-10% of the beans changing color).

In sensitive varieties and in favorable areas or years, additional treatments may be necessary.

In less sensitive varieties and less favorable years, fewer treatments than indicated may be necessary.

The only effective protection method for powdery mildew currently is chemical.