What is dangerous mildew on grapes, and how to cure it

One of the most dangerous enemies of the grape is mildew fungal disease. Many gardeners have been trying to fight this ailment for decades, but not everyone succeeds.

Let's look at the causes of the appearance of the disease and find out how to deal with it.

Description and danger of illness

Mildew (or downy mildew) is one of the most dangerous fungal pathologies of European grape varieties. This disease hit the vineyards of England in 1834. They brought it along with new grapes from North America. In a short period of time, mildew spread throughout Europe. The great decline in grape yield at the beginning of the twentieth century is also explained by the appearance of downy powdery mildew.

Clarified spotted areas are observed on infected grape leaves.Young leaves form small round spots of an oily yellow color, while older leaves form angular spots along the veins. When wet and warm weather mildew begins to progress. Over time, on the lower part of the leaf, under the affected areas, appears grayish-white, shiny fluff of the mycelium. All other parts of the plant are affected in a similar way: ridges, antennae, shoot tips, inflorescences and young grapes. Inflorescences affected become yellow and curled. Over time, they darken and dry up. Sick berries, the size of which reaches the size of a pea, begin to grow brown, and then shrivel and die (such berries are called “leathery”, after infection they are no longer suitable for eating or making wine). In most cases, infected leaves fall prematurely, and the affected shoots dry out.

In order to "expel" mildew from the grapes, you need special chemical agents, often used to combat it and on other plants.

Causes of downy powdery mildew

The pathogen mildew belongs to the group of false powdery mildew fungi and is closely related to the blue mold of tobacco, peronospora of hops and late blight of potatoes. At the confluence of the male and female nuclei of hyphae, zoospores are formed, which can overwinter on fallen leaves of grapes without any special problems.

Throughout the summer and early autumn, oospores actively reproduce in the affected leaves. They have a very thick inner wall, so they easily tolerate cold and wet winters. At the beginning of April, when the soil is still quite wet, but the air temperature in the daytime is already at least + 8ºС, zoospores enter the active phase. They create one sprout tube each, at the end of which there is a single sporangia. If with the help of rain, wind or fog this sporangia falls on a grape leaf, it will break the shell and release more than 60 zoospores.

These small lumps of plasma begin to move in drops of liquid with the help of flagella. When they find the stomata, they form a tubule in it that grows inside the tissue and causes a primary infection.

The process of infection of a healthy grape leaf occurs most quickly at a temperature of + 20 ... +27 ºС. In such conditions, sporangia will have time to infect a grape bush within 4-7 hours. At temperatures below + 8 ° C and above + 30 ° C, sporangia cannot germinate, so infection does not occur. With the help of haustoria, hyphae grow quickly and get all the necessary nutrients from the grape cells.

The incubation period lasts from 5 to 18 days, depending on the season and weather conditions. As a result, oil spots are formed on the leaves, which indicates damage to the cells of the vine.

The incubation period lasts from the beginning of the sporangia hitting the grapes until the first signs of the disease appear. After its completion, the fungus is very strongly deposited on the plant and begins the processes of reproduction.In most cases, this occurs at night, when the air humidity is high, and the temperature is not below +12 ºС.

In the future, a shiny white fluff is formed, which is a large cluster of branched, tree-like sporiferous birds. Ovoid sporangia appear at their ends. At the slightest breeze of wind, these sporangia fly everywhere.

When the weather is dry and hot, they quickly die (in about 3 days), but if it rains and the sporangia settle on the leaves of the grapes with drops, they immediately infect the plant. Such a cycle can be repeated 6-8 times in summer. But again, it depends on the weather.

How to deal with grape disease

Many gardeners, who first planted a plant in their area, do not know how to treat mildew grapes, but at the same time there are two main methods of getting rid of this ailment: using chemicals and using traditional remedies.

Drugs

Most often for the treatment of downy mildew use a solution of copper sulphate.For spraying the leaves do a weaker solution, but if you have to spray woody stalks, then use a composition that is more saturated with copper sulphate.

Spray grapes can be such means:

• Burgundian or Bordeaux liquid. These solutions can be sprayed all parts of the vine. For the preparation of a 1 percent Bordeaux mixture, freshly quenched lime (120 g) of copper sulfate (100 grams) and water (10 liters) are used. To prepare a 3 percent solution, you need to take three times more of the vitriol and three times more lime, 10 liters of water. Mixtures of any concentration are also prepared (the amount of ingredients per 10 liters of water is calculated, knowing how many ingredients are needed for a 1% solution). To prepare the composition of the correct concentration, you need to use a nail: if the nail turns red when it is lowered into the prepared liquid, then the solution is highly concentrated, and you need to add some water or lime.To prepare a 2 percent burgundy liquid you will need: blue vitriol (400 grams), soda ash (350 grams) and water (20 liters). To test the solution for proper preparation, you can use red litmus paper. When lowered into the solution, it should remain red.

• Chloroxide copper. Specialized stores sell 90 percent wettable powder (40-50 grams are diluted with 10 liters of water and sprayed with grapes).
• Copper silicate. To prepare this solution, you need to purchase copper sulphate (2 percent) and a solution of silicate glue (4 percent). Glue needs to be poured into the vitriol and mixed (but not vice versa, otherwise an unstable suspension will turn out). In the end, you have a dark green liquid. The test for concentration is carried out by means of a piece of paper with a purgen. When lowered into the solution, it should remain slightly pink.
• Almost all the preparations based on copper are excellent help from mildew, in particular, and with the defeat of grapes. Many solutions are sold immediately divorced: "Tsiram", "Zineb", "Kaptan", "Kuprozan", etc.
• Preparations based on lime and sulfur: "Planriz", "Alirin-b".

Very often it is necessary to perform spraying 5 or more times over the summer. This is due to the fact that under certain weather conditions the mildew fungus actively reproduces. One of the most vulnerable grape varieties is Kishmish. Some agronomists have to spray this grape variety every 2 weeks throughout the growing season.

Folk remedies

Treat powdery powdery mildew can folk remedies. You do not need to buy various chemicals, make strict solutions and test them for concentration. Here are some ways to treat traditional methods:

• Tincture of wood ash. For its preparation you will need: 1 kg of wood ash and 10 liters of water. The tincture is kept in a dark place for 7 days. After that, you can spray the leaves of grapes on both sides. Processing is carried out at the first signs of illness. This solution can strengthen the root of a plant by pouring soil around the grapes on it.

• Manganese solution.On a bucket of water add a teaspoon of potassium permanganate and spray the resulting solution with the leaves on the reverse side. While they are wet, they can be powdered with "powder" from wood ash.
• Dill can also be planted around the grapes. It helps in the fight against mildew, and in the case of infection - reduces the number of necessary treatments.

It should be understood that when mildew affects grapes, treatment with folk methods is not always effective. In difficult situations it is better to immediately turn to chemicals.

Preventive action

One of the main preventive measures in the fight against mildew is pruning old remnants of the vine. It is burned together with leaves fallen in autumn. This can significantly reduce the risk of a new relapse in the spring. After that, it is necessary to carry out chemical treatment of the grape bushes and the adjacent soil, using a solution of ferrous or copper sulfate.

Preventive actions include several stages of processing grapes from mildew during the growing season,and spraying is best done in dry weather. Usually engaged in the processing in the early to mid-summer. The main stages of spraying:

1. The best time will be a period when the inflorescences are a little loose. For spraying use Bordeaux liquid 1.5% or 2%;
2. The second spraying is carried out after the flowering of the grapes. Use the same solution Bordeaux fluid, only less concentrated (1 percent);
3. The third spraying is carried out after the size of the grapes reaches the size of small peas. Use the same solution as in the second spraying;
4. The last spraying for the purpose of prevention is carried out 10-12 days after the third treatment. To do this, use a solution of copper oxychloride (0.4 percent). To prepare such a liquid, you must buy a package with copper oxychloride powder (40 grams). The entire contents of the bag is diluted in 10 liters of water and mixed thoroughly, after which you can start spraying.

Such prevention will be effective only when the grapes are properly rejuvenated and trimmed.In this case, when spraying the solution will fall on each leaf, and destroy all pathogenic fungal sporangia.

Mildew: the most resistant grape varieties

For a vivid example of the resistance of grapes to various fungal diseases, including mildew, a five-point scale was introduced:

• 0 points - full 100% protection against all diseases. At the moment, such varieties do not exist, but Dutch breeders have reported that they are working on this, almost impossible task.
• 1 point - the plant has a high immunity and is almost not affected by downy mildew. In most cases, these plants do not require prophylactic treatments. This category belongs to "Vitis Riparia" - a very fruitful grape variety. But it grows small clusters with small blue berries, so it is practically not used for dining purposes.
• 2 points - resistant varieties that can be affected only in very wet weather for a long time. After several treatments, mildew disappears without a trace. This category includes the following grape varieties: "Clairette Bulbasa", "December", "Arch".Some agronomists put "Arochnu" 1.5 points (from the list of the most delicious table grades, it is the most protected from downy powdery mildew).

• 3 points - varieties of medium resistance need 2-3 single sprays throughout the growing season. Three grades received the following varieties: Bianca, Moldova, Victoria, Augustine, Timur, Arcadia, Talisman, Lora, Danko, Rusmol, Viorica, "Murom", "Riesling Magaracha" and others.
• 4 points - susceptible varieties that need special protection from the fungus. Spray need 4-5 times per season. With improper care dies from 25 to 50% of the crop. This category includes such varieties: "Rkatsiteli", "Aligote", "Cabernet".
• 5 points - varieties that without timely chemical protection can lose from 50 to 100% of the crop. In this case, the plant may die. These varieties need to be sprayed every 1.5 - 2 weeks throughout the growing season. The five-point grades received the following varieties: “Kishmish Khishrau”, “Cardinal”, “Rizamat”.

Currently, most entrepreneurs are trying to use grape varieties with 2 or 3 points. Otherwise, there is a risk of large crop losses. At the same time, breeders continue to try to bring out the “ideal” grape variety, which will receive zero points, but it will not lose its table quality.