Why is grape powdery and how to treat it?

Oidium appears on grapes at different times of the growing season. This disease, also called powdery mildew, poses a great threat to vineyards and can lead to a complete loss of crops.

Oidium and mildew infecting grapes are considered the most harmful crop diseases. Correct care and preventive treatments of the vine during the season will help prevent them.

To combat powdery mildew, chemical and biological preparations are used that are more effective in the early stages of the disease.

Causes of the disease

Oidium of grapes is caused by a fungus. The parasitic mycelium feeds on the living tissue of the plant and spreads rapidly throughout the vine. There is no fungal infection on dead and dried areas. With an outbreak of the disease, the mycelium soon spreads to the inflorescences, depriving them of the opportunity to develop and set berries. And if the ovary has already formed, it falls off during the ongoing infection. As a result, fruiting does not occur.

Spores hibernate in the buds and bark. In spring, when the temperature rises, the fungus is activated and begins to multiply rapidly.

The following factors favor the development of the disease:

• the air temperature is above + 25 ° С;
• humidity from 80%;
• thickened plantings.

Under such conditions, the disease progresses rapidly, moving from one bush to another. Pruning not done on time also increases the risk of powdery mildew.

Symptoms and manifestations

The incubation period of the disease takes 1–2 weeks. Then the oidium begins to manifest itself with various symptoms:

1. First of all, a whitish-gray bloom appears on the leaves.
2. Young shoots of grapes stop developing.
3. Leaves on diseased branches grow with signs of curliness, traces of mycelium are also visible on them.
4. At the next stage of the development of the disease, plaque covers the foliage from both sides.
5. Inflorescences and clusters that have set become, as it were, powdered with flour or ash.
6. Infected flowers dry up and fall off. The same thing happens with berries.

Mildew (downy mildew) has slightly different symptoms. The disease manifests itself by the appearance of yellowish spots on the upper side of the leaves, and after this a brown bloom forms on the lower side of the leaf plates, which soon dries up.

Since both diseases are fungal in nature, preventive treatments can be used to protect grapes immediately from powdery mildew and mildew. The treatment regimen for both diseases can also be of the same type. Today, combined drugs are produced that cope with mildew and powdery mildew at the same time.

Prevention

To protect your vineyard from the development of powdery and downy mildew, you need to take time to carry out preventive measures.

The following steps will help protect the vine from fungal diseases:

• timely removal of stepchildren, garter and chasing of vines in order to prevent thickening of the bush;
• regular cleaning of the trunk circle, destruction of fallen leaves;
• from time to time, inspection and pruning of shoots with signs of disease.

In the spring, before flowering, it is recommended to treat the grapes for preventive purposes with the drug "Azophos" (1 glass per 10 liters of water). Spraying is carried out in the morning in dry weather. Over the summer, the bushes are treated 6-7 times with a 1% solution of Bordeaux liquid (spraying is stopped 3 weeks before the berries ripen).Before wintering, one more treatment is carried out, this time with a 3% solution of copper or iron sulfate.

When buying a seedling, you should choose a variety that is resistant to powdery mildew. Of the popular varieties, the following varieties are almost not affected by powdery mildew:

• "Aligote",
• "White miracle"
• "Harold",
• "Vera",
• "Chardonnay"
• "Kishmish",
• "Merlot",
• "Charlie",
• "Lillou"
• "Mascot".

Fighting the disease

To save grapes from powdery mildew, the fight against the disease must be comprehensive.

1. First of all, it is necessary to cut off all dead wood and thin out the infected bush. This is necessary to achieve good ventilation and sufficient sunlight for the shoots.
2. They stop feeding the diseased vine, since the plant will not be able to normally absorb fertilizers during this period.

How to process grapes from oidium?

It is advisable to process grapes using combined preparations. Copper in their composition will be detrimental to the fungus that causes the appearance of downy mildew, and sulfur will destroy the pathogens of powdery mildew.

Effective preparations for powdery mildew and mildew:

• "Oxyhom" - copper-based systemic fungicide. The first treatment is carried out when the first symptoms appear at the stage of bud formation. The second time the bush is sprayed at the final stage of flowering. The third spraying is done at the time of the formation of the ovaries. The vine is processed for the fourth time when the berries are the size of a pea.
• "Abiga Peak" - a remedy similar to "Oxyhom" effect, but used without reference to the stages of vegetation. The drug has a complex action against a number of fungal diseases in the vineyard. Processing is carried out 6 times per season.
• "Discort" - a fungicide of systemic action, which can be used to treat not only powdery mildew, but also black rot, rubella, black spot. Grape processing is carried out in 4 stages. The first spraying is in the budding phase, the second is when the berries are closed in a brush. The remaining two treatments are carried out with an interval of 1.5–2 weeks.
• "Medea" - a preparation similar to "Discort" according to the principle of action, used without taking into account the phases of the growing season. The first spraying with a working solution is carried out at the initial stage of the disease, further processing is required 2-3 times with an interval of 1-1.5 weeks. Can be used for prophylaxis.
• "Tiovit Jet" - a drug that has both fungicidal and acaricidal action. In addition to treating oidium, it will protect the grapes from the attack of spider mites. During the growing season, diseased plants will need 4 to 6 treatments.

The list of oidium remedies is extremely wide. To combat the disease can also be used:

• Horus,
• "Topaz",
• "Stroby"
• "Cumulus DF" and other drugs.

In warm weather, colloidal sulfur can be used for processing (the substance works effectively at a temperature of + 20 ° C or slightly higher). Chemical treatment should be carried out well before harvest in the morning or evening hours, using a face shield and closed clothing.

Will folk remedies help?

It is possible to use folk remedies for the treatment of powdery mildew only in the early stages of the disease.

• Well stops the development of fungus 0.5% solution of baking soda.
• Gardeners also use such a proven remedy as a solution of potassium permanganate: 5 g of substance per 20 liters of warm water.
• Ash infusion is considered an effective remedy for powdery mildew on grapes. This remedy, like the previous ones, is completely safe for the plant itself and beneficial insects. The infusion is prepared from 1 kg of ash and 10 liters of warm water. It is necessary to insist the composition for 5 days, periodically stirring the contents of the container. Before use, filter the infusion and add 40 g of crushed laundry soap to it for greater efficiency.
• Some people use mullein infusion (without bedding) to treat powdery mildew. Fertilizer consumption - 2–3 kg per bucket of water. The composition should be infused for 2-3 days.Before use, add 1 teaspoon of urea to it. Then the leaves are sprayed with infusion on both sides.
• Other plants, such as tansy, which are used to cultivate the soil under bushes, can help the grapes cope with the disease. It is necessary to prepare a decoction of 300 g of fresh or 30 g of dry raw materials (per 10 liters of water). First, the grass is poured with water and insisted for a day, then boiled for 2 hours, filtered and soaked in the ground, not forgetting about the aisles.

Those who have encountered the appearance of powdery mildew on their grapes already know that the disease, as luck would have it, affects the largest clusters, which are so sad to lose. In order not to resort to compulsory measures in the form of the use of chemicals, it is necessary to restrain the development of the fungus by appropriate agrotechnical methods. Diseased plants must be treated immediately.