1- Vine powdery mildew (Uncinula necátor Burr.) What is vine powdery mildew?
The powdery mildew of the vine is a disease caused by a fungus that winters in the buds, the shoots, the leaves and the bark of the vines.
Powdery mildew is also known by other names depending on the geographic region; Other names by which this vine fungus is known are:
2- Symptoms and Damages of powdery mildew:
Powdery mildew can attack any green part of the vine.
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:
- When the clusters become visible (phenological stage F), most of the shoots have between 5 and 10 cm.
- At the beginning of flowering (beginning of phenological stage I).
- With pea- chickpea size grains .
- 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.
7- ✅ Active materials, fungicides to treat powdery mildew.
- AMPELOMICES QUISQUALIS
- POTASSIUM HYDROGEN CARBONATE
- METIL TIOFANATO
- PROPICONAZOLE 1
- PROQUINAZID 1
8- The powdery mildew of the vineyard seriously influences the quality of the wine .
The vinification of vintages with powdery mildew is much more delicate and more complex and does not allow correcting all the defects observed.
The powdery mildew of the vineyard has a negative effect on the quality of the wines from 8% of the berries attacked .
The biggest risk is to obtain wines with phenolic tastes and unwanted mushroom aromas . There are also unwanted fermentation problems that need to be addressed.
The powdery mildew of the vineyard has an impact on the ripening of the grapes and a delay in phenolic maturity, delayed berry growth, fragility of the pulp….
Between 9-13% of berry attack , the sulfur aromas increase decreasing the fruity aromas.
9- How to minimize the impact of powdery mildew in winemaking?
When the harvest is approaching and the attack of powdery mildew is persistent, we can only consider two solutions to be able to minimize the impact :
- The first is to remove severely affected bunches manually, which is excessively expensive and possibly unprofitable for many farms.
- The second is to differentiate the most affected plots and harvest and vinify them independently. It is essential to differentiate the most attacked musts, to avoid contamination.
Oenological treatments can be carried out on the most affected musts, but in attacks between 10-15% the correction is very difficult.
In the end, despite the selection of the grapes and a more controlled and delicate vinification, not all the effects produced by powdery mildew can be masked .
Vine powdery mildew is a disease that can have a serious impact on the quality of the final product .
- From 8% powdery mildew , the organoleptic effects are perceptible, although they can be corrected in winemaking.
- From 15% powdery mildew it is practically impossible to obtain a quality wine.
10- Effects of powdery mildew on the quality of wine.
Some of the effects of vine powdery mildew on the quality of the wine are the following:
- 5% powdery mildew in berry (mild effects, they can be even beneficial): in wine it produces an increase in the concentration of sugars and polyphenols and improves acidity.
- 8% berry powdery mildew (perceptible defects in wine): Moldy aromas appear, fruit aromas decrease and the acid sensation decreases.
- 15-25% berry powdery mildew (very harmful effects in wine): unwanted menthol, metallic and herbaceous aromas appear. Very aggressive tannic intensity. Very pronounced bitterness at the end of the palate. Very marked acidity.
11- Sensitivity of some vine varieties to vine powdery mildew.
The vine (vitis vinifera) is a species sensitive to powdery mildew. The sensitivity to the disease varies according to the varieties.
Varieties Not Sensitive to Powdery Mildew:
- Ugni Blanc
- Petit Verdot
- Alicante Bouschet or Tintorera.
Varieties with medium sensitivity to powdery mildew:
- Garnacha Blanca
- Garnacha Tinta
- Muscat of Alexandria
- Sauvignon Blanc
Varieties very sensitive to vine powdery mildew:
- Pedro Ximenez
- Cabernet Sauvignon
- Pinot Noir