How to process and how to deal with mildew on grapes?
During the development of American open spaces, not only new types of cultivated plants were brought to Europe, but also pathogens unknown until then. One of these diseases, which caused a great decline in European winemaking at the end of the 19th century, is a grape disease called mildew. About her and will be discussed in the article.
What is mildew
This infectious disease, also called downy mildew, is one of the most common and dangerous diseases of grapes. It is caused by mushroom-like organisms (oomycetes) and affects all green parts of the vine, as well as inflorescences and berries.
Outwardly, mildew looks like a little transparent oily spots of a yellowish color on the foliage, covered with a white coating (actually a fungus) during rain and damp.
Did you know? The name of the disease is the transcribed English word mildew ("mold"), which, in turn, comes from a combination of the words mil (Old English mele, which means "honey") and dew ("dew"). Long before the appearance of harmful fungi from America in the Old World, this word denoted a sticky trace left by aphids on plants. And the full name of the disease in question in the English version sounds like downy mildew ("fluffy rot").
The disease reduces the effectiveness of photosynthesis, leading to significant (up to 70%) crop losses, and also affects the quality of grapes (reduces the sugar content of berries and increases acidity).
If you touch a leaf stricken with real powdery mildew, brown marks will appear on it.
Reasons for the appearance and stage of development
The causative agent of the infection - the Plasmopara viticola fungus - parasitizes exclusively on the vine.
It will also be useful for you to find out what to do if the grapes rots, dries and turns yellow.
The spores of the fungus form in the fall, survive the cold in the fallen leaves, and in the spring they germinate in conditions of significant humidity and are carried by the wind. After this, the spores enter the plant tissue, disrupting the vital functions of the cells and destroying the green pigment - chlorophyll.
It is humid weather that plays into the hands of infection, leading to the development of the disease as an epiphytotia (epidemic). Especially often, such a massive spread of the disease can be found in vineyards in floodplains and grape schools (nurseries for seedlings) due to frequent, plentiful watering.
In addition, the causes contributing to infection are:
- excess nitrogen and lack of potassium fertilizers;
- individual susceptibility of the variety;
- early pruning of the bush;
- untimely garter.
The ideal environment for spores is a temperature of +20 ... + 27 ° C and high humidity, in such a condition infection occurs in a matter of hours. In dry and hot weather, spores die, but the plant can be infected again, especially in conditions of temperature difference and rainy summers.
Signs of mildew on grapes
You can suspect infection by lightening certain sections of foliage. At first, the spots can be light green, not too contrasty, and then turn yellow. The spots are rounded in shape, without clear boundaries, their size is most often about 2-3 cm, but can reach 5 cm.
On the older foliage, the spots are angular and located along the veins (the so-called "autumn mosaic").
During the development of the disease, necrosis appears on the spot (tissue death), the foliage can become reddish and begin to fall off. Inflorescences also turn yellow and curl, the shoots dry out. The berries are wrinkled and turn brown, becoming unfit for human consumption.
Important! A characteristic feature of mildew is the islands of the white gun on the underside of the leaf. It is important to differentiate the plaque that occurs during mildew, with a fluff from infection with a felt tick (itching). In the latter case, the fluff cannot be simply erased by touch. And also, over time, the plaque from the tick will change color, while the fluff mildew remains white.
How to treat the disease
Ignoring measures to combat the causative agent of the disease or improperly selected processing dates can lead to the loss of almost the entire crop. Every grower must know how to save the vine with the help of chemical and folk remedies.
The general treatment rules are as follows:
- Lead time . You can get rid of mildew if the bush is already sick, thanks to the latest treating fungicides. Most likely, it will not be possible to cure neglected forms of the disease, but in any case, after uprooting the bush on the ground, it will be necessary to use antifungal drugs.
- Dates are determined based on the duration of the incubation period of the disease (from 3 to 13 days). Its duration depends on the air temperature and is calculated by the so-called Muller curve. Often, to determine the duration of the first treatment, the “three dozen” rule is used, which states: after setting the air temperature to at least 10 ° C and the intensity of precipitation more than 10 mm, the incubation period is 10 days. At the end of this period, the first therapeutic measures are carried out.
- The number of sprayings and their timing are determined by the number of sporulation cycles (usually 6–8 per season) and the incubation period. The longest latent period is in May, and the shortest in August. Be sure to spray the bushes before flowering and during fruiting, before and after harvest. During flowering, preparations are used only in case of extremely adverse weather conditions (high humidity).
- For highly resistant varieties, procedures are performed twice a season: in spring and after harvest.
Preparations and chemicals
For a long time, copper-based preparations, including Bordeaux fluid, were considered the only remedy effective against mildew. The disadvantages of copper-containing preparations are the suppression of the growth of bushes and burns of shoots. In addition, some varieties categorically do not tolerate copper and begin to crumble.
Modern antifungal agents (organic fungicides) are divided into protective and treating by the nature of their action, and by contact and systemic ones according to the degree of penetration into the plant and the area of action. The advantage of systemic fungicides is that they penetrate further from the place of application into the tissues of the entire plant and are not washed off by rain.
Using other drugs, it is better to add adjuvant (adhesive) in the form of an oil emulsion to the solution.
Contact fungicides should be applied evenly over the entire vine, including shoots and fruits. They are applied to the foliage from the underside, while preventing liquid from draining.
- The first treatment and preventive measures are carried out with the help of protective drugs ("Alette", "Pencoceb", "Ridomil", "Champion").
- Further, during the growing season, if the first signs of the disease were noticed, then as soon as possible, systemic (“Quadris”, “Folpan”, “Mancozeb”) or combined (“Thanos”, “Healer”) medications are used in high concentration.
- After harvesting, strong systemic drugs and urea, which also has antifungal properties, are usually used.
Modern microbiology is developing new, environmentally friendly drugs with an antifungal effect. One of the most popular biological products for fighting mildew is Fitosporin-M. This product is exclusively of natural origin, created on the basis of the bacterial culture of Bacillus subtilis.
Therefore, chemical fungicides cannot be completely replaced by a biological product; they must be combined with each other.
Important! Bacillus subtilis does not tolerate bright sunlight, therefore it is necessary to apply Fitosporin-M only in cloudy weather or at the end of the day when the sun has already set.
For many years of struggle with mildew, various folk remedies were invented, including:
- ash solution (pour 1 kg of wood ash into 10 liters of water and keep in a dark place for 1 week, then strain);
- potassium permanganate solution (1 teaspoon per 1 bucket of water);
- a kind of home-made analogue of biological products based on hay sticks - infusion of fresh hay (pour 1 bucket of hay with water and infuse for 4-6 days, then dilute with water in a ratio of 1: 3);
- soda solution (baking soda in the amount of 1 tablespoon mixed with 1 cup of liquid soap and 1 tablespoon of vegetable oil, dilute the mixture with 1 bucket of water).
Folk remedies are safe and natural, but their effectiveness, unfortunately, is inferior to chemical drugs, so you can not count on a positive result from using only home methods.
Mildew prevention is a key issue in viticulture.
- The vineyard should be placed in a well-ventilated place to avoid the accumulation of moist air. For the same purpose, it is necessary to carry out stepsoning and stamping of vines.
- Vertical drainage for irrigation, due to which less excess moisture remains in the surface soil.
- Cancellation of night watering and foliar feeding in the rainy season.
- Autumn fallen leaves need to be burned.
- In spring, it is recommended to cover the soil with a film or a layer of straw or ash.
- Timely pruning.
- Regular weeding.
- Planting dill around the bushes.
- Balanced mineral nutrition (with emphasis on magnesium, potassium and phosphorus).
- Selection of varieties having a disease resistance gene.
Did you know? In Japan, technology for the prevention of mildew and other fungal infections using electrolyzed water (E-water) has been used for many years. This solution is pH neutral and is not harmful to grape crops and people. In 2018, the United States announced the start of using NaOClean technology.
Grape varieties resistant to mildew
Unfortunately, despite all the efforts of breeders, the most delicious and beautiful European varieties are most prone to illness. American varieties are almost not susceptible to disease. As for the hybrids of American and European varieties, their degree of resistance is different and varies depending on the climate, type of soil, growing conditions. Actively growing bushes are generally more susceptible to mildew than old ones.
- Gift of Magarach;
- Saperavi North;
- Original White.
Absolute resistance is not possessed by any variety, therefore, treatment and prophylactic measures should be an integral part of the care of the vine.
Is it possible to consume wine from mildew-infected grapes
Mildew wine made from sick clusters is unstable, has a characteristic mold tone related to wine defects, and is also more prone to the development of diseases such as turn and puss (due to the high content of nitrogenous substances).
Turn and pousse are manifested by a change in the color and taste of the drink, the appearance of a dense black precipitate at the bottom of the vessel and can lead to the absolute unsuitability of the wine for consumption.
- lighting or sulphonation of sludge;
- fermentation on pure yeast cultures;
- fermentation of wort on a clean healthy pulp;
- transfusion immediately after the stage of silent fermentation, without waiting for clarification;
Mildew is a formidable disease that can negate all the efforts and expenses of winegrowers, leading to a significant decrease in yield and product quality. The development of the disease can be lightning fast, therefore the main role in the fight against this ailment is played by the preventive measures (including the mandatory use of special chemicals), discussed in the article.