Content
A white coating on grape berries and leaves is a characteristic sign of the disease affecting the crop. And if measures to protect the plant are not taken in a timely manner, then you should not count on a good harvest, not only in the current, but also in subsequent seasons. However, before you begin to treat grapes, you must first determine the disease that caused the appearance of white plaque. Because sometimes it can also be caused by the presence of a pest or a lack of certain nutrients in the soil.
It is impossible to completely exclude the possibility of a white coating appearing on grapes.
Why do grapes become covered with a white coating?
Grapes are considered a demanding crop. For the full development and regular fruiting of vines, certain conditions and proper care are required. If they do not comply, the plant’s immunity decreases and the likelihood of it being affected by diseases increases.Mistakes in agricultural technology can also contribute to the appearance of a white coating on the berries and leaves of grapes.
Provoking factors:
- prolonged stagnation of moisture in the soil;
- sudden temperature changes;
- dense plantings;
- insufficient ventilation of plants
- increased air humidity;
- lack of nutrients;
- bad light;
- inconsistency of climatic conditions.
Diseases of grapes with white bloom
There are several common cultural diseases that are characterized by the appearance of this symptom. Therefore, every gardener who grows grapes should know the distinctive features of white bloom, which will allow identifying the problem at an early stage of damage.
Oidium
This disease is also called powdery mildew. The causative agent is the fungus Uncinula necator Burri. Oidium first appeared in North America and then spread throughout the world.
The disease can be recognized by a white coating on the leaves, which is initially insignificant, but as powdery mildew progresses it completely covers the leaf. Subsequently, it acquires a grayish tint. White plaque interferes with the process of photosynthesis. As a result, the affected leaves wither and darken. In the absence of control measures, the disease spreads to shoots and inflorescences.
The berries, even if they set, subsequently crack under the influence of moldy fungi or dry out.
The incubation period of the disease is 7-14 days. Favorable conditions for the development of the fungus are a temperature of +23-25 ° C in combination with high humidity.White plaque with powdery mildew appears in late spring, early summer.
When affected by powdery mildew, the vine does not ripen
Mildew
The second name of the disease is downy mildew. The fungus attacks leaves, shoots and berries of grapes. The first mention of it appeared in 1878, when affected crops were discovered in North America. Subsequently, signs of mildew appeared in the south of France, and then the disease spread throughout the world. The causative agent is a fungus – Plasmopara viticola Berl. et Toni.
Mildew can be recognized at the initial stage of development by the oily spot that appears on young growing leaves. Subsequently, with increased humidity, a white coating appears on the back side of the plate on the affected areas, which indicates sporulation of the fungus.
Downy mildew is characterized by a rapid development process. And if yesterday the grapes looked quite healthy, today they may already have a “depressed” appearance. Subsequently, the affected leaf tissues die. And the white coating switches to inflorescences and clusters. The optimal conditions for the development of mildew are temperature +23-25 °C and high humidity.
If left untreated, grapes may die from downy mildew.
Alternaria blight
The causative agent of this disease is the fungus Alternaria solani Ell. et Mart Initially, small white tubercles appear on the grape leaves, inside which spores ripen. If you look closely, you can find necrotic areas in the center of such a spot. Signs of the disease also appear on the vine. After 5-6 days, with high humidity, the growths open and the fungal spores are carried by the wind.
Alternaria blight also affects grape bunches. In this case, a metallic sheen appears on the berries. As a result, the surface of the fruit becomes wrinkled and the taste quality decreases. Provoking factors for the development of fungus are elevated temperature and humidity for a long time.
To distinguish Alternaria from true and downy mildew, you need to lower the suspicious leaf into a container of water and place it in a warm place. After a few hours, a light olive coating should appear on the affected area, indicating Alternaria blight.
Alternaria blight is characterized by a short incubation period
Aspergillus rot
The causative agents of this disease are ten species of fungi from the genus Aspergillus. Aspergillus rot is common in the southern regions. It affects berries during prolonged drought and high air temperatures.
A characteristic sign of the lesion is light depressed spots on the berries, which then darken. Subsequently, they crack, and a white coating of mycelium and conidial sporulation appear on them in the form of a black-brown powdery mass. With severe damage, the bunches become completely black.
Aspergillosis develops when the sugar content in fruits reaches 8%
Gray rot
This disease in the form of a white thick coating can appear on the leaves, shoots and fruits of grapes. It affects the plant at any stage of development in the presence of favorable conditions - cold, damp weather. You can recognize it by the white coating on the top of the grape leaves, as well as the opening eyes and young shoots. Subsequently they turn brown and increase in size.
Progresses in high humidity and poorly ventilated plantings. At the same time, the water content in the fruit decreases, and the sugar content increases. But if it rains, this provokes massive rotting of the crop.
White bloom due to gray rot also appears on one-year-old vines
Felt mite (grape itch)
White spots on grape leaves can also appear as a result of damage to the plant by felt mites or itching (Eriophyes vitis Pgst). This microscopic pest infects leaves and feeds on plant sap. As a result, characteristic swellings appear on the plates. On the reverse side of the leaf, the affected areas are covered with a thick, felty white coating.
Felt leaf larvae overwinter in the bud scales. And with the arrival of spring warmth, the pest’s life cycle resumes. Signs of itching usually appear on the lower leaves of grapes.
Grape itch does not cause serious damage to grapes
Chlorosis
The disease develops when there is an increased content of lime in the soil or a lack of iron. As a result, the leaf blades lose their green pigment and become almost white, but the veins retain a rich shade. This leads to disruption of the photosynthesis process. As a result, the plant does not receive the necessary nutrition, which weakens it. This leads to shedding of the ovary and failure of the berries and young vines to ripen.
Rainy, cold weather promotes chlorosis
What to do if there is a white coating on the leaves and bunches of grapes
The bushes should be treated immediately when a white coating appears on the grapes, before the disease or pest spreads throughout the plantation. To do this, you can use chemical and folk remedies.
Drugs
Fungicides should be used to combat fungal diseases. When processing, you need to spray the solution on the leaves, paying special attention to their back side, shoots and berries. It is better not to carry out the procedure during flowering.
Effective preparations for the appearance of white plaque on grapes:
- Bordeaux mixture;
- Cupritox;
- Home;
- colloidal sulfur;
- Quadris.
To combat felt itching, insecticides should be used: Bi-58, Actellik, Fufanon.
If chlorosis occurs, iron chelate should be used. It is recommended to spray the affected plants with the drug and water it. Repeat the procedure every seven days until the color of the leaves is restored.
Folk remedies
You can also treat grapes for mold using folk remedies. But it should be understood that if the disease spreads massively, they will be ineffective. They are best used as a preventive measure, and also when the use of chemicals is unacceptable: during the flowering and ripening of berries.
Effective folk remedies for white plaque:
- Dissolve 1 tsp. with a slide of permanent potassium in 10 liters of water. Mix the solution thoroughly and spray the affected crops.
- Mix 1 kg of mullein with 3 liters of water and leave for three days. Then stir the resulting mixture and strain. Dilute the concentrate in a 1:3 ratio with water and leave for another three hours. Then spray the grapes.
- Add 40 g of soda ash to 10 liters of water.Mix the solution and process the grapes.
- Chop 150 g of garlic and pour a bucket of water over it, strain and immediately spray the plant. Repeat the treatment after three days.
Prevention
To prevent grapes from becoming covered with a white coating, you need to know how to treat them as a preventive measure. This will reduce the likelihood of damage to a minimum.
Experienced winegrowers recommend using 1% copper and iron sulfate, as well as colloidal sulfur, in early spring and late autumn.
Other measures to prevent the appearance of white plaque:
- remove plant debris;
- carry out annual sanitary pruning;
- tie the lashes in a timely manner;
- do not allow plantings to become dense;
- water only when the soil dries 5-7 cm deep;
- Regularly loosen the soil at the base of the grapes.
Grape varieties resistant to diseases
To successfully grow grapes, you need to select zoned varieties of the crop. Inadequacy of conditions leads to weakening of plants and, as a result, their damage by diseases and pests.
Resistant varieties:
- Timur;
Timur's growing season is 105-115 days
- Harold;
Harold - a promising hybrid form of culture
- Carménère;
Carménère is from Bordeaux
- Delight;
Delight is characterized by increased resistance to frost and disease
- Rochefort.
Rochefort has great growth power
Is it possible to eat infected grapes?
In most cases, when a white coating appears on the grapes, the fruits become watery and lose their sugar content. Therefore, any desire to use them disappears. But in the case of gray rot and felt itching, the berries are quite edible.The main thing is to wait the required period of time before harvesting after using chemicals.
Conclusion
The white coating on grape berries, as well as shoots and leaves, will not disappear on its own, since this sign indicates that the plant needs the help of a gardener. Lack of control measures can cause the death of the bush. Therefore, when warning signs appear, you need to act quickly so that the problem does not become widespread.
