The appearance of a white or gray coating on the grapes indicates that the plant is infected with a fungal infection. Similar symptoms indicate diseases such as mildew and oidium. There are many reasons for the appearance of fungus on the stems, vines and leaves of a grape bush.
Most often, grapes get sick due to improper care.
Reasons for appearance
A fungus is a microscopic organism that is spread throughout an area by wind, precipitation and weeds. It can exist for a long time in soil spores, maintaining a static state, which does not lead to infection of fruit and berry crops. However, with the advent of comfortable conditions, fungal spores become more active and begin to multiply quickly. The starting point for the development of the disease is, first of all, neglect of pruning of grapes. In dense plantings, where the vines are tangled and not enough light and fresh air passes through them, there is often excessive humidity and stuffiness - favorable conditions for all types of fungi. In addition, fungal infection can enter grape bushes through contaminated soil, which is rarely disinfected and fed; remnants of weeds that are not removed on time.
It should also be remembered that it is mainly weakened plants with weak immunity that are subject to infection. This may be caused by a lack of nutrients or, conversely, by their excess. This is especially true for nitrogen - if there is too much of this element in the soil, the grape bush is quickly depressed.
Influence of weather conditions:
- mildew develops in warm and damp weather;
- Oidium does not depend on humidity levels, but favors temperature. For infection to develop, a temperature within +5-30 degrees is required;
- gray mold is activated in conditions of low temperature and high humidity;
- Stuffiness and dampness are favorable for Alternaria blight.
Shocking variety
If you are determined to grow delicious berries on your plot, then you will need to pay a lot of attention to this. First of all, non-infectious diseases that are caused by heat or high humidity, poor soil or excess nutrients are dangerous for the vineyard. They can be easily avoided if you provide optimal conditions in your garden.
However, the list is not limited to this; there are hundreds more different infections. If you observe a white coating on the grapes, you will have to rack your brain as to what it is a consequence of. Infectious diseases spread throughout the vineyard very quickly. This leads to a significant loss of yield or death of the entire vine. Infection occurs through infected bushes, garden tools, as well as wind and water. Imagine all the risks, and you will understand how important constant monitoring of the garden is.
Signs of disease
You don’t need to think that white coating on grape leaves is just the beginning of the disease. In later stages, the green leaves turn brown and then die off altogether. As soon as the fungus “eats” all the foliage, it will move on to the shoots and fruits. Ignoring the disease can lead to the death of grapes within 30 days. Therefore, white, oily, matte spots on the vine and leaf blades should immediately alert you, because this indicates a rapidly developing infection that can lead to the death of the entire plant. You can verify the diagnosis by carefully examining all areas of the grape bush. Sporulation looks different for different diseases.
Oidium
Sporulation of powdery mildew looks like pubescent white spots that can appear not only on leaves, but also on stems, flowers, and fruits. As fungal spores age, the spots begin to darken and the infected areas become rougher and dry out. The leaf plate loses moisture, wrinkles, but does not fall off, but remains on the bush, continuing to infect still healthy areas. If black dots begin to appear on the leaves, this indicates the imminent death of the plant. If the fungus spreads to the fruits, they will soon wither and you cannot eat the berries. Productivity drops by 40-50%.
The danger of the disease is that it is not affected by the ambient temperature.
The fungus does not die even at sub-zero temperatures; it is able to overwinter in the plant tissues of grapes and become active in the spring. By the way! If you pick off the affected leaf, the plaque will go away after a while.
Mildew
Downy mildew is similar to oidium only on the back of the leaf - this is where the spores leave a powdery coating. On the outside, spots of different sizes have an oily structure. Color – dirty yellow. Gradually, the diseased lesions merge into one huge ulcer. Over time, the color changes to dark brown and even black. The leaf curls and falls off. Mildew also affects flowers and berries - they dry out completely, first becoming blue and therefore brown. The fungus first attacks the upper part of the vine, gradually moving down, capturing new territories. In most cases, at the time the disease is detected, the bush is already so severely affected that it cannot be treated.
Note!
It is almost impossible to notice this disease in the early stages, since the inside of the leaves is initially affected.
Alternaria blight
This fungal disease does not spare any organ of the grape bush. Alternaria can be identified by the silvery tint of the leaf blade. Gray spots contain necrosis, which is caused by infectious agents - the parasites Alternaria alternata and Alternaria tenussima. They penetrate the tissues of weakened plants. If chemical treatments are not carried out, the leaves and stems become covered first with light yellow and then with rusty and brown spots. Then the shoots and leaves dry out. The fungus then spreads from the leaves to the trunk and berries. The latter wrinkle and a metallic sheen appears on them. If the weather is hot and humid, the bush may die in 5 days.
If, during harvest, several infected berries get into the container with the collected bunches, they will infect all the fruits during storage, as a result, spoiling all the grapes.
Alternaria (Ugni Blanc)
Initially, a form of fungus was known that attacked weakened and dead plant tissue. This fungus attacks all living tissues, which inevitably leads to the death of the bush.
Symptoms
Yellow-green spots appear on young leaves. With high humidity, they become covered with a greenish coating, reminiscent of mold. All foliage, shoots, fruits and roots are affected.
Development of the disease
The fungus Alternaria alternata attacks the green mass and fruits of garden plants in late spring. First, the leaves become covered with light yellow, round spots, about 1 cm in diameter. Then the affected areas turn gray, dry out and die. With further spread of the fungus, a coating forms on the bunches, and the berries become deformed. The shoots do not become woody, but remain silvery. The bark takes on a dirty white tint and becomes covered with dark spots.
Harm
The entire green mass of the bush is affected, as a result of which it is deprived of nutrition. Its frost resistance is significantly reduced. Seedlings and cuttings take root poorly and die.
Fighting methods
- At the first symptoms and for prevention, they are treated with Bordeaux mixture.
- Treatment with fungicides. Trichodermin, Ridomil, Quadris, Skor, Rapid Gold help well. Spraying is carried out once every 10 - 14 days.
Prevention
- After autumn pruning, all shoots and foliage must be burned.
- Preventive treatments are carried out in the spring.
Emergency help for plants
If you find foci of mycelium on grape leaves, then first of all they need to be treated with a manganese solution. Spraying is carried out every two weeks, while generously filling all parts of the bush with useful liquid. Potassium permanganate, of course, will not cure the bush completely, but it will significantly delay the reproduction of spores.
In parallel with the manganese solution, specialized drugs with a systemic mechanism of action are administered. Their active substance will penetrate into the plant fibers and begin to fight the pathogen using a contact method.
By the way!
Systemic drugs not only treat plants, but also have a protective function.
If possible, then in a few days you can prepare a solution from humus, which should also be used to treat the plantings if powdery mildew is noticed.
How to recognize mildew
At the initial stage of development of the disease, this is not at all easy. People usually realize that a vine is infected when it becomes serious. You will be very lucky if the summer turns out to be rainy. In damp weather, you can notice the fluff on the leaves and take action. But on hot days, even an experienced gardener will not notice the approaching disaster. You can completely get rid of mildew only by removing all the bushes from the ground. However, fungal spores can wait up to 20 years for a new vine to emerge. Its growth can be restrained annually with special fungicides, and preventive measures cannot be skipped.
Methods to combat plaque
When a white coating appears, regardless of what disease it is caused by, it is recommended to begin systematic spraying with sulfur-containing preparations. The fact is that sulfur absorbed by fungi is transformed into hydrogen sulfide, which has a detrimental effect on the mycelium. The sooner treatment is carried out, the faster it will be possible to suppress the development of infection.
Sulfur-based products can be used as a preventive measure. To do this, prepare a solution of 40 grams of sulfur and 10 liters of water. When the first signs appear, 100 grams of sulfur are already consumed per bucket of water. It is advisable to carry out sulfur treatment at a temperature of +20 degrees, otherwise it will not evaporate well. However, at temperatures above 27 degrees, the sulfur solution can cause leaf burn. Treatment is carried out 3-4 times per season with an interval of two weeks. Stop spraying when the berries on the bush begin to ripen.
Note!
All pesticide treatments should be stopped three weeks before harvest!
Colloidal sulfur is considered one of the most effective inorganic fungicides. It successfully fights gray mold, oidium and mildew. It also stops spider mites. Colloidal sulfur vapor penetrates the fungal organism and destroys it from the inside. the plant itself does not suffer. For processing grapes, the consumption rate of the drug is 80 grams per 10 liters of water. The resulting concentrate is enough to irrigate 60 square meters of plantings. The number of treatments per season is no more than 5.
If a white coating has just appeared, then spraying the bushes with a 1% solution of Bordeaux mixture will help stop sporulation. It is preferable to use this product regularly, starting in early spring, as soon as the winter shelter has been removed. If it is cool outside, it is better to use colloidal sulfur.
If the grape bushes are young enough and have not grown too large, then they can be treated with whey, which has proven itself in the fight against various fungi. Spraying should be carried out in the middle of the day, since milk protein is activated under the sun's rays. Against powdery mildew, a whey solution is prepared at the rate of 1 part milk to 3 parts water. The bushes are watered generously with the solution so that the liquid drips from the leaves. The natural fungicide is absolutely safe for plants, and therefore useful treatment can be carried out frequently, every 7-10 days.
Ready-made chemicals are mainly used against oidium. The best include Acrobat, Skor, Topaz, Tilt, Topsin, Tiovit Jet, Hom, Oksihom and others. Typically, these agents are treated twice, which is quite enough to suppress the spread of the disease.
Topaz, Ronilan, Topsin-M, Rovral are called upon to cope with gray rot. These drugs have a strong chemical effect on the fungus, but often cause resistance in one or another infectious agent. Therefore, these products need to be alternated with each other so that the fungus does not have time to get used to the chemical composition. If flowers or fruits begin to rot, they need to be treated with one of the preparations based on captan, folpet, or captafol.
If you are dealing with Alternaria blight, then it is preferable to choose copper-containing preparations for treating grapes. A copper-soda solution, which is prepared from soda ash (50 grams), grated soap (200 grams) with the addition of copper sulfate (10 grams), previously diluted in water, copes well with the disease. Also in the spring, fungicides with the active substance mancozeb of contact action are used (Mankodim, Ordan MC, Rapid Gold, Ridomil Gold, Ditan M-45). If the fungus has penetrated inside the plants, then systemic fungicides - Skor, Quadris, Strobi, Horus - will help in the fight against it.
Advice!
Spray thoroughly, also paying attention to the back of the leaves.
Treatment of oidium
If the grapes are covered with a white coating, you need to take immediate action. This is treatment with special antifungal drugs, such as Topaz and Strobi, Horus, Thiovit, Thanos. For treatment, you will need to repeat spraying after ten days. However, this disease is much easier to prevent than to treat. Agrotechnical techniques boil down to ventilating bushes by tying up shoots and pinching, as well as weed control. Follow the time limits for preventive treatment indicated for the treatment of mildew.
Preventive measures
The appearance of painful plaque can be prevented with the help of preventive techniques. So at the beginning of summer they spray with an ash solution. The product is prepared from 1 kilogram of wood ash and a bucket of water. For better adhesion, add grated soap to the mixture.
Iodine can prevent the appearance of oidium and mildew. A solution based on it is prepared from 10 liters of water and 10 milliliters of iodine. A popular preventive biological agent is Fitosporin-M. Plants are sprayed with it throughout the season.
In addition to useful spraying, it is important to observe agrotechnical literacy:
- destroy plant debris on which fungal spores are localized. You need to take all the grass outside the garden and burn it;
- do not plant crops close to grapes, which are more susceptible to fungal diseases;
- when buying grape seedlings for planting, choose healthy and well-developed bushes;
- Carry out sanitary pruning in early spring and autumn. In the summer, promptly remove branches and shoots that thicken the bush. Avoid crowding of plantings;
- use a sterile instrument for pruning. Before moving on to pruning the next bush, disinfect the pruning shears;
- water the grapes early in the morning so that the leaves have time to dry during the day;
- feed the grapes correctly - nitrogen is required only at the first stage of the growing season. Then the plant will only need phosphorus and potassium supplements.
Prevention
A gardener with certain experience and knowledge will definitely use modern methods on his site to avoid unpleasant consequences. It’s a little more difficult for beginners, but they too must learn to protect their garden. This is especially true for those who grow varietal grapes. The disease can affect even the most well-kept garden and spread through it with lightning speed.
At the beginning of spring, be sure to spray the vine with antifungal solutions. Late in the fall, before winding up the plant for hibernation, this procedure is repeated. But chemical treatment is not everything. Pay special attention to the soil. Grapes extract a huge amount of nutrients from it. If it is not fertilized, the vine will be susceptible to fungal diseases. It is advisable to use special mixtures for feeding that are sold in stores. Complexes that contain potassium, phosphorus, magnesium and other minerals are ideal.
It is very important to monitor the condition of the vine. The vineyard should be constantly moist, light and spacious. Therefore, the bush needs to be trimmed and tied up in a timely manner, and stepsons should be removed. A well-groomed vine is easier to inspect, and compliance with all these parameters is a kind of guarantee that the disease will bypass it.
Growing a vineyard is a troublesome, but very rewarding task. A well-groomed bush will thank you for your time with sweet berries that can be eaten directly or stored for the winter.
Will the affected grapes live?
Unfortunately, fungal diseases are difficult to treat. This is due to the fact that they are most often noticed on grapes when the infection has almost completely taken over them. It is impossible to cure such grapes, so you shouldn’t even waste time on futile attempts. Remember that while you are sorting through fungicidal preparations, the fungus is already targeting healthy bushes. Therefore, it is better to remove severely affected plants and direct all attention to saving still healthy bushes.
The land that is empty after the grapes are removed is carefully cultivated. It is dug up, disinfected, and complex mineral fertilizers are applied. It is not recommended to plant any plants in this place for the next two years. During this time, the earth will “rest” and get rid of harmful microorganisms.
Achievements of modern agricultural technicians
Only at first glance, the luxurious bunches grow without any effort from the gardener. The most beautiful and delicious varieties are always amazed first. Despite all the efforts of breeders, this law cannot be overcome. Only varieties with mediocre taste have a certain resistance to the most formidable diseases, including mildew. But if similar grapes, for example “Isabella” with sour blue berries, are crossed with a good sweet variety, then the resistance is noticeably reduced, and you can again notice a white coating on the grapes.
