A harmless, at first glance, whitish coating on grapes can eventually lead to the death of both the shrub itself and the crop. In order to avoid unpleasant consequences, it is important to start the fight against diseases in a timely manner and not to forget about preventive measures.
How to deal with mildew?
White bloom on grapes in most cases is mildew (downy mildew) – a fairly common grape disease. The action of the fungus first appears on the inside of the plates, after which it “creeps” onto shoots, inflorescences and ovaries. The appearance of mildew to a novice gardener will be signaled by the presence of a grayish fluff on the leaves, especially noticeable in rainy weather, which turns brown over time. The fungus actively develops at temperatures from +20 to +27 ° C, accompanied by high humidity and poor ventilation. The disease can “move” in several ways: in the wind, on the paws of insects, or due to clothes and garden tools. Mildew hibernates in the soil and under fallen leaves.
If you do not react to the disease in a timely manner, then the grape bush may be so infected that it will only have to be destroyed. Oily dirty yellow spots, with which the leaf blades are covered on the outside, gradually merge into a single formation, thereby affecting the entire surface. The leaf turns dark brown and then black, it dries up and falls off. The same fate awaits the bunches of berries: they turn blue, turn brown and, finally, dry up.
In order to timely diagnose the disease, it is necessary to regularly inspect the vineyard. If leaf blades with suspicious spots are found, they should be immediately torn off and placed with the affected part on wet paper. If it is a mildew, then after a while a whitish coating will begin to appear on the back side. It should be borne in mind that the incubation period of the disease begins at the moment the spores hit the surface and continues until the appearance of oily formations.
As a rule, it lasts from 3 to 15 days. All parts of the plant covered with white bloom are cut off with a sharpened tool treated with alcohol.
If the presence of mildew is confirmed, then you need to do the following – immediately cut off all the affected parts, and then use contact fungicides. Copper-containing preparations are most suitable for this purpose:
- Bordeaux liquid;
- Anthracol;
- Ridomide;
- “Thanos”;
- Cuproxate.
Since contact fungicides only act on the area they cover, the surface of the leaves must be treated very carefully, paying special attention to their underside. Spraying with colloidal sulfur can be useful. In order to prepare a solution, it will be necessary to dilute 80 grams of the product in 10 liters of water. The resulting amount should be enough to process 60 square meters.
To prepare a sulfur solution, you need to dilute 30 grams of sulfur in 10 liters of water. After mixing the ingredients until smooth and filtering the resulting mixture, it will be necessary to pour the liquid into the spray bottle and use it to spray the leaves and clusters.
It is important that the temperature during the procedure exceeds +20 degrees so that the sulfur can evaporate. However, treatment can only be carried out in cloudy weather to avoid burns.
If rotting of flowers and berries has already begun in the vineyard, then you will have to use potent agents based on captafol, captan or folpet. On the contrary, at an early stage, you can try to get rid of white plaque using folk methods.
- For example, a glass of peeled garlic cloves will need to be ground in a blender or meat grinder, and then poured with a liter of water. After mixing the contents, cover it with a lid and put it in a dark place for 24 hours. The finished solution is filtered, diluted with 5 liters of water and used for spraying bushes.
- You can also use a solution of potassium permanganate, for the preparation of which it will be necessary to dilute 10 crystals in a liter of pure liquid. All aerial parts of the bush are processed with a pale pink solution, with special attention being paid to the back side of the leaf blades.
- Wood ash usually improves the situation. A kilogram of powder is diluted in a bucket of water. After mixing everything thoroughly, it will be necessary to leave the solution for 5-6 days. Before processing, each liter of the ash solution must be diluted with 10 liters of water.
It is also worth mentioning that it would be right to add soap shavings to each folk remedy, which allows you to keep the remedy on the surface for a long period. If a large part of the plant is affected, then it is better to destroy it by burning it. The vacated place must be disinfected, dug up and fed with mineral complexes. These activities should be carried out for a couple of years, and only then new crops should be planted on the updated fragment of the site. By the way, if one of the causes of the disease was high humidity, it will need to be reduced by removing the top layer of soil and placing peat mixed with sand instead.
Other diseases
Symptoms similar to mildew, that is, white bloom, also have oidium, alternariosis and a number of other diseases.
Oidium
Oidium affects all parts of the plant, including leaves, stems and brushes. This disease is especially dangerous for inflorescences and young ovaries, although it can also affect the entire aerial part of the grape bush, from the lower vines to the top. In the absence of timely treatment, the leaves begin to darken, dry out and crumble, and the flowers become covered with a grayish coating, from which they turn yellow and fall off. The fact that the grapes have become infected with oidium is evidenced by the appearance of a plaque on the lower part of the leaves. If you erase it, then brown spots will immediately show up. From above, the plate is covered with formations of white, gray or yellowish color.
The disease quickly spreads throughout the bush. The green parts of the plant gradually turn black or dark brown. A powdery coating appears on the fruits, which later transforms into dirty gray spots. The clusters stop developing in size, and the grapes themselves turn brown and dry out. With late infection, the berries can also crack and rot. To save the vineyard from oidium, it is necessary to immediately respond to the appearance of a specific smell of rotting fish.
A whitish coating on any part of the bush should also alert. The culture should also be treated with contact fungicides:
- “Horus”;
- “Topaz”;
- “Tiovit”;
- “Strobe”.
As a rule, a double treatment is enough to stop the spread of a fungal disease.
Alternaria
A symptom of the defeat of the vineyard by Alternaria is the silvering of the leaf blade. Gradually, the surface becomes covered with light yellow spots, which then rust and turn brown. The shoots of the bush dry out in the same way as the leaves. Then the fungus moves to the trunk and berries. All this happens very quickly – in hot, humid weather, the grapes will die in 5 days. Moreover, if damaged berries, shriveled and covered with a metallic sheen, are in the same basket with healthy fruits, the entire crop will be destroyed.
A culture infected with Alternaria should be sprayed with copper-containing agents. If the spores have time to penetrate the tissues of the shrub, it will be necessary to treat with systemic drugs, such as:
- “Horus”;
- “Quadris”;
- “Strobe”.
In spring, it makes sense to spray contact fungicides on the bushes. We must not forget that when a disease occurs, all the affected parts of the plant are immediately utilized and, if possible, the top layer of the soil is changed. The remaining specimens are treated with a three percent solution of Bordeaux liquid or copper sulfate.
After 10 days, it makes sense to feed the grapes with preparations that include microorganisms, for example, such as “Emochka”. To do this, 10 milliliters of the substance are diluted in 100 liters of liquid. After another 10 days, the culture is again treated with Bordeaux liquid or copper sulphate. A good effect on the state of the vineyard is a copper-soda solution, to create which 50 grams of soda ash, 200 grams of soap chips and 10 grams of copper sulphate, previously diluted in water, are combined.
If at first glance it is difficult to understand what exactly the plant has become infected with, it is worth starting with the implementation of universal “saving” measures. To contain the reproduction of spores, it will be necessary to spray the grapes with a manganese solution once every two weeks. In parallel, systemic preparations should be introduced, as well as plantings should be treated with a solution of humus. Sulfur-containing preparations always help to fight against white plaque. This happens due to the fact that the sulfur absorbed by the fungi is transformed into hydrogen sulfide, which, in turn, negatively affects the mycelium. With a weak whitish solution, Bordeaux liquid will effectively cope.
Young bushes can be sprayed with whey. Such processing is necessarily carried out under the sun’s rays in order to activate the action of milk protein. The solution is prepared from a part of milk and three parts of water.
In all cases, we must not forget that pesticide treatments should be stopped three weeks before harvest.
Preventive measures
In order to provide the necessary prevention of diseases in grapes, it is necessary to understand why the culture is generally affected by white bloom. Fungal spores infect plants with weak immunity and mechanical damage. Often those specimens that are attacked by various pests also suffer. The causes of the development of the disease can be improper care and inappropriate conditions. In the first case, the problem is the lack of pruning, and hence the thickening, due to which the vines and dense foliage interfere with the penetration of air and light. The resulting high humidity and stuffiness become ideal conditions for the spread of the disease. The same can be said about waterlogging of the soil.
In order to prevent the defeat of the bushes by various diseases, it is necessary to engage in prevention in time.
- The main preventive measures include cleaning procedures. It is important to free the site from fallen leaves, tops, plant residues and weeds.
- Of course, preventive spraying with potassium permanganate and sulfuric solutions plays an important role, which are held in early spring and autumn before wintering.
- Grapes need proper nutrition: thus, nitrogen benefits the culture only at the beginning of the growing season, and then the plant already requires potassium and phosphorus. Sanitary pruning should be carried out at least twice a year, freeing the vineyard from excess stems, branches and green mass. Thinning should only be done with sterilized instruments. Watering the grapes requires regular, but moderate.
- In order not to experience problems with grapes, the plant will have to pay due attention even at the stage of acquiring seedlings. It is better to buy planting material in trusted specialized stores, giving preference to healthy and well-developed samples.
When planting, it is important to keep sufficient gaps between individual bushes. You should also not place nearby crops that are susceptible to similar fungal diseases.
The following video will talk about remedies for powdery mildew on grapes.
