This disease - oidium - on other plants it is known as powdery mildew (real, not false, like peronosporosis), or ash. The fungus that causes the disease - Oidium Tuckeri Berk - was introduced from North America and was first discovered in England by the gardener Tucker in 1845. Five years later, powdery mildew covered the whole of Europe, and especially the French vineyards got from it, which they managed to save only thanks to the discovery that sulfur is an effective remedy against powdery mildew.
In the spring, after the start of the growth of shoots, on the bushes of grapes, you can find growths that are lagging behind in development. Leaves bloom on them curly, completely or partially covered with a grayish-white bloom. In June, this plaque covers the leaves on both sides, and the tops of the shoots, inflorescences and clusters look like they are strewn with flour or ash. Inflorescences affected by powdery mildew die off, the berries dry out, and those that are the size of a pea burst or, if the weather is dry, also dry out. Oidium can destroy most of the grape harvest, and almost all European plant varieties are affected by the disease.
In the photo: A vine affected by powdery mildew
The incubation period, that is, the time from the moment of infection to the appearance of mycelium plaque, is from 7 to 14 days. Mycelium grows best at a temperature of 25-30 ºC, but this does not mean that the disease does not develop at a lower temperature. Poor ventilation and abundance of foliage on the bush contributes to the spread and development of oidium.
If oidium is grape powdery mildew, then mildew for this culture is peronosporosis, or downy mildew. These are different diseases caused by different pathogens, and they are united by the fact that both diseases are fungal, as well as the fact that both mildew and powdery mildew are capable of destroying almost the entire grape harvest. The symptoms of these diseases are different from each other. We have already described the signs of mildew disease, and when grapes are infected with mildew, translucent yellowish oily spots appear on the upper side of the leaves, after fog or dew, a plaque forms on the underside of the affected leaves, which later turns brown and dries up. Most often, young leaves of grapes suffer from mildew, as well as inflorescences that turn brown from the disease, shoots on which blackening spots appear, and unripe berries, which, when infected, darken in the area of the stalk and crumble, and those grapes that remain on the bunch acquire sour taste. The berries ripened by the time of infection with the fungus are not affected by mildew.
The fight against powdery mildew is carried out by a whole range of measures, which includes agrotechnical methods, preventive measures, the use of chemicals and folk remedies. It is advisable to carry out measures to combat powdery mildew simultaneously with the destruction of mildew pathogens. Preventive measures against these diseases are the same, and as for the treatment with chemical preparations, at present, combined products are produced containing both sulfur, which destroy mildew pathogens, and copper or an organic fungicide, which have a detrimental effect on mildew.
How and with what to treat oidium on grapes? If the infection occurred during the last growing season, they begin to fight it as early as possible in the current season, however, keep in mind that treating the vineyard with sulfur at temperatures below 20 ºC will not give results, since it is at this temperature that solid sulfur turns into the necessary for destruction infections are vaporous. When processing grapes in hot weather, the leaves of the plant can get burned, so it is best to do the processing early in the morning or after 4:00 pm.
Treatments are carried out in 10-20 days, and in total such sessions should be carried out from 3 to 6. When spraying, a layer of sulfur should tightly cover each leaf of grapes. Damp sulfur is unsuitable for the destruction of infection.
Protection against powdery mildew is carried out with preparations Talendo, Karatan and Switch, which are used for preventive treatments of the vineyard, and for the treatment of already affected plants, in addition to colloidal sulfur, such fungicides as Tiovit Jet, Skor and Horus are effective.
You will not be able to avoid chemical treatment of grapes from powdery mildew, but it is quite possible to reduce the negative effect of chemical preparations. This is achieved by regular preventive measures.
Preventive treatments reduce the likelihood of fungal diseases affecting grapes and cause much less harm to plants than spraying with fungicides during treatment, since the concentration of the active chemical in preventive solutions is 3-4 times weaker than in medicinal solutions.
Preventive measures are started in the fall: when preparing grapes for winter, they are treated with a solution of iron or copper sulfate, neutralizing the remains of the fungus. In early spring, even before the buds awaken, the vine is treated with Azophos solution, prepared according to the instructions. Nitrogen, which is part of the drug, enhances the effect of copper.
In the photo: Grapes affected by powdery mildew
Before flowering, the grapes are treated with a solution of two ten-gram bags of Ridomil Gold, one ampoule of Topaz and 40 drops of Ecosil in 8 liters of water. The next treatment - during the period of fruit formation - is carried out with the same solution, but instead of Ridomil, the drug Ordan is used. In the future, grapes are sprayed from mildew and other diseases, but these treatments may well restrain the development of oidium.
Provide good aeration of the soil and fresh air to each shrub in the vineyard.
We offer you a description of the chemicals used to destroy or inhibit the development of powdery mildew on grapes.
It should be remembered that the last treatment with chemicals that destroy mildew pathogens is carried out no later than 60 days before harvesting.
If you are a categorical opponent of the use of chemicals in the vineyard, then you can try to fight the powdery mildew with the help of less toxic folk remedies. For example:
Unfortunately, there are no grape varieties truly resistant to powdery mildew, but there are those that can adequately resist not only powdery mildew, but also other fungal diseases. As we have already mentioned, European grape varieties are the most vulnerable in this respect.
The variety Delight and its hybrids Talisman, Oval Delight (Baklanovsky), Ideal Delight, Gift to Zaporozhye, Timur and others showed high resistance to diseases. Among those resistant to powdery mildew and other fungal infections are the varieties Victoria, Kishmish Zaporozhye, Galbena-nou, Alex, White Miracle, Velvet Muscat, Platov's Jubilee, Gift to Ukraine, Pink Timur, Matryoshka, Denal, Golden Don, Lark, Caucasus, Sasha. The varieties obtained from the Vitis labrusca species have also proven themselves well: Alden, Alwood, Fredonia, Isabella large-fruited, New York Muscat, Pocklington, Supaga, Juodupe, Mars, Venus and Ainset Sidlis.
Among the grape varieties that are complexly resistant to diseases, the varieties Marinovsky, Platovsky, Crystal, Harmony, Millennium, Amethyst of Novocherkassk, Lancelot, Beautiful Flora, Kishmish Klyuchikova, Pleven, Eurostandard, Bogotyanovsky, Arochny, Anthony the Great and Nadezhda AZOS are distinguished by the highest resistance to fungi.
Growing grapes is a responsible and laborious process. Any wine grower, whether professional or amateur, wants his efforts to be rewarded with a rich harvest. But not everything depends on the will of a person, because vineyards sometimes get sick. Among the many ailments, mildew on grapes occupies a special place, which is considered one of the most dangerous diseases for this plant.
She is called mildew in another way. This is one of the most common and dangerous diseases of grapes. Powdery mildew affects many other plants as well. The spread of mildew is facilitated by the appearance of cold early morning dews, frequent rains, an air temperature of + 20– + 25 ° С. If you notice the appearance of powdery mildew as soon as possible, then the treatment will be successful. To do this, you need to periodically examine the grapes. If you see a rounded oily spot on the leaf, this should alert you. If the weather is wet, a powdery white coating will appear on the underside of the leaf, where the stain is. This means that the plant is really affected by powdery mildew.
Unless urgent action is taken, the affected tissue will begin to turn yellow and then dry out. The disease often spreads to the bunch of grapes. Here it appears as bright green spots. As a result, sap flow is disrupted, due to which flowers or berries dry up and crumble.
For prevention, it is necessary to cut off the grape bush in a timely manner, tie up the growing vines. In the fall, all fallen leaves must be raked, collected and burned, and the soil must be dug under the bush. It will help prevent powdery mildew by not thickening the branches (pruning unnecessary ones), as a result of which there will be better ventilation and illumination of the vine.
For the treatment of powdery mildew, "Acrobat MC" has proven itself well. Application: in 5 liters of water, you need to dissolve 20 g of drugs, this solution is enough to process an area of 100 square meters. m. First, use "Acrobat MC" for the prevention of downy mildew, if it does appear, then you need to repeat the treatments every two weeks. Last time - a month before picking berries.
There are other chemicals available to combat mildew. These are copper-containing ones: "Aksikhom", "Hom", "Polykhom", "Kurzat". "Copper oxychloride", a 0.3% water-based solution is prepared from it. Good effect on the eradication of the disease and proven for a long time "Bordeaux mixture".
Good to knowhow it looks on grapes to be able to recognize it. This disease appears as a smoky white light coating. One gets the impression that the plant has been lightly powdered. It begins, as a rule, in early spring such symptoms are given by mildew, which covers plants and their fruits with microscopic fungi of its mold. Fungi adhere to plants by attaching themselves to their surface and sucking the juice out of them.
If powdery mildew is diagnosed, treatment should be started immediately. The incubation period lasts from the onset of sedimentation of the fungus to the formation of plaque - from about one week to two. In many ways, the speed of propagation depends on the air temperature. The infection can begin at a temperature of 5 degrees Celsius, but it will spread faster at 20 degrees and above. Studies have shown that the fungus spreads intensively in warm and damp weather, as well as if the grapes grow in poorly ventilated places and have a lot of leaves. It is believed that the virus hibernates quietly in the buds of grapes.
You can fight the development of the fungus with the help of a well-ventilated planting of grapes. The most acceptable option is spraying grapes using sulfur, which, when absorbed by the cells of the fungus, turns into hydrogen sulfide and destroys the pest. But keep in mind that solid sulfur must be vaporized. And this is possible only at temperatures above 18 degrees Celsius. The conclusion suggests itself - the process of pollination with sulfur at low temperatures simply will not give any results.
But there is also a "second side of the coin" - at too high temperatures, leaves and berries can get burned, so pollination with sulfur in the heat is also impossible. Better to do this in the early morning or late evening hours. And also, as the researchers noted, the smaller the sulfur particles, the greater the efficiency, which means that it is advisable to grind and sift sulfur for these purposes through a fine sieve. At the same time, please note that the substance must be stored in a dry room, otherwise there will be little sense from it.During the spraying process, a layer of sulfur should completely cover the entire green part of the bush.
In order to minimize the damage to the vine plantation by powdery mildew, experts recommend carrying out preventive treatments of the vines.
Such spraying is less harmful to plants than the treatment of grape bushes from the onset of the disease, since the dosage of fungicides in the working fluid used for prophylactic purposes is less than in medicinal ones.
Prevention begins in the autumn - after the end of leaf fall, grape whips should be sprayed with a solution of copper or iron sulfate.
You can also use Bordeaux liquid as a prophylactic against powdery mildew... These chemicals are capable of destroying fungus that may have remained on grape shoots after the summer season.
In the spring, before the beginning of sap flow in the vines, they carry out repeated preventive treatment of the vineyard. In this case, Azophos solution is used for preventive treatment, which is dissolved strictly according to the instructions. This preparation contains nitrogen, which enhances the effect of copper on the fungus.
During the budding period, vines from oidium are sprayed with a solution prepared as follows:
All these preparations are stirred in water and immediately processed the vines.
During the period of active ripening of the bunches, the treatment of the vines with the same solution should be repeated, only Ridomil is replaced with Ordan... In the future, gardeners must necessarily carry out spraying of vines against other diseases of this culture, but the fungicidal preparations used in this case inhibit the development of oidium.
It is also necessary to regularly loosen the soil in the vineyard and ensure regular ventilation of the vines.
Black spot, also a fungal infection, prefers warm and humid weather for its active development. Usually black spot is called the withering away of the shoots, but the professional growers call it escoriasis.
If most of the vine is covered with black fungal bodies, then it will be impossible to save it.
Preventive measures are the same as for anthracnose, and drugs to combat black spot are also fungicides.
Photo: signs of black spot on grapes
It is not easy to save the harvest, although it is not easy, but it is quite possible using effective fungicides, observing the frequency of treatments and taking preventive measures in time.