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Last quarter of the XIX century prigotovila growers of Europe serious tests in the form of previously unknown diseases of the culture, among which was the downy powdery mildew. In the Old World, the study of mildew, a dangerous disease of grape leaves and the whole plant as a whole, was begun in 1878, and after 18 years, the first case of a defeat in a vineyard was registered in Russia.
The entire above-ground part of the bush suffers from the microscopic fungus Plasmopara viticola settling on the grapes.
The uncontrolled development of the disease threatens with the drying of the shoots and the affected leaves, the berries form much less, and even the ovary that appears rots and decays. To cope with a serious enemy and not to lose most of the harvest can only be clearly presenting a picture of the disease, its development, and adhering to all measures to combat mildew on grapes.
Picture of mildew on grapes: photo and description of
The first signs of mildew are more often found on the leaves. At the beginning of the growing season, oily traces on their upper surface and an inconspicuous whitish coating on the back side of the leaf plate speak of the resettlement of the fungus. Moreover, a specific down, meaning sporulation, is better seen on the young parts of the shoots and leaves. Depending on the humidity and temperature of the air, the type of plant and the stage of development of the disease, grape leaves in the middle of the shoot are covered with reddish or yellowish spots of various shapes and sizes.
As the fungus infects and spreads, the leaf plate necrosis begins, but the loss of foliage leads to a general weakening of the bush and a deterioration in the quality of the berries.
The ingress of fungus on the shoots is not accompanied by the appearance of oily spots. Here you can immediately notice the grayish or brownish traces of drying fabric. The fastest mildew of grapes, as in the photo, affects the inflorescences, the young parts of the shoots and the ovary, which has not yet reached the size of a pea. At the same time, in wet conditions, a specific white bloom can, in two days already, completely cover blooming brushes and ovary clusters, which turn brown and die off quickly.
Berries, affected by the fungus at the stage of ripening or ripening, darken, shrink and dry. And on already ripe fruits mildew appears as pressed into the pulp, discolored spot in the area of the stem. Over time, and these berries become brown and showered.
The causative agent of the disease of vine leaves
Mildew or downy mildew is caused by a fungus, in the form of spores wintering directly under the bushes of grapes, in the foliage that fell on autumn. Due to its resistance to frost, the causative agent of downy mildew safely waits the cold season, and even at a temperature of +8 ° C it is activated and spreads with the wind or raindrops on the green parts of the bushes.
Infection of a plant occurs when the zoospore finds a stoma on leaf tissue and is fixed. To understand the course of the disease of grapes, and how to treat the leaves and other parts of the bush affected by the mildew, it is important to determine the cyclical nature of infection and reproduction.
The duration of the reproduction period of a harmful fungus depends on the temperature, and its favorable outcome depends on the humidity of the air. For the development of mildew on grapes optimal temperature can be considered from 20 to 27 ° C and the period when the bush remains wet for more than four hours in a row.
At this time, the incubation period for the disease of vine leaves is sharply reduced. During the season, the causative agent of the disease gives from 6 to 8 generations, while the incubation period on leaves and berries, becomes noticeably shorter by August. Until the temperature at night drops to + 12 ° C, a whitish fluff appears above the stomata, which is a congestion of sporiferors. Getting with the wind to new areas of the plant, especially in wet weather, the sporangia release new zoospores, and the circle of infestation of grapes with mildew, as in the photo, repeats.
Protective measures to combat mildew on grapes
The grower can take the first measures to protect against a dangerous disease even at the stage of laying the vineyard. Not all varieties have the same susceptibility to downy mildew. Even in the nineteenth century, it became clear that the fungus that caused serious damage to European plantations could not affect the yield and viability of American grapes. Moreover, in mildew-resistant plants, if spore penetration into the tissue occurs, then the further development of the fungus is not followed. In order not to observe lively the manifestations of diseases of grape diseases presented in the photo, and not to wonder how to treat the leaves and shoots, it is better to pick varieties rarely affected by mildew.
Today, breeders offer relatively powdery powdery mildew resistant varieties of table, as well as universal, as well as technical purposes.
These plants include the Murom variety, which gives early dark-colored dessert berries, Muscat Dniester, Autumn pink grapes, Moldova variety, Podarok Magaracha, and other varieties.
But even at cultivation of resistant varieties, it is impossible to do without obligatory preventive measures against mildew on grapes.
Cultivators have noticed that they are affected more often with downy mildew:
- young bushes and only seedlings planted from shkolka;
- plants that are regularly fertilized with products containing nitrogen but lacking potassium;
- landing with impermeable to air and sun thickened crown;
- bushes, under which weeds are preserved and fallen leaves are not removed;
- vineyards in regions with a humid warm climate.
Although the main measures to combat mildew grapes include the use of chemical processing agents, it is possible to enhance the effect of such preparations by adjusting regular planting care.
Reduce the risk of disease of the bushes will help:
- the location of the trellis along the direction of prevailing winds in a particular area;
- wide inter-row device;
- pruning of grapes, providing airing of all shoots;
- regulation of load on plants;
- high-quality garter shoots, debris, chasing and staving;
- timely removal of weeds and plowing or collection of fallen leaves.
But how to determine the processing time of the vine leaves from the disease, and how to treat the plant if the first signs of the disease have already appeared?
Spraying the grapes from mildew, as a measure to combat the dangerous disease
The timing of the chemical treatment of the vineyard with mildew depends primarily on the appearance of oily spots on the green parts of the plant. The effect of the protection will be greatest if by the time sporious spiders appear, the surface of the leaves, the inflorescences and the shoots will be completely covered with a layer of the preparation. This means that the treatment should be carried out shortly before the whitish, fluffy plaque becomes noticeable on the back side of the foliage.
The first spraying is done before flowering begins, and if last year the damage to the disease of grape leaves was severe, it is especially important to treat the vineyard as soon as the temperature rises above +8 ° C and the first heavy rainfall falls.
By choosing the time for the first treatment of the bushes, you can focus on the appearance of the first 3-4 leaves, and further spraying is planned based on the appearance on the vine and the development of the fungus.
Treatment of the bushes after flowering is aimed at protecting the ovary, after the calyx of the flower drops off the most susceptible to the disease. If the symptoms of the disease become visible when the grapes are actively flowering, the treatment is not delayed, but they are suitable, using products that do not contain copper. When the ovary is shown on the hands, treatments are necessary depending on the weather and the manifestation of the disease.
Bordeaux Powdery Mildew Grape Blend
The oldest and most proven remedy for mildew is Bordeaux fluid, a mixture of burnt lime and copper sulfate solutions. In addition to downy mildew, the agent is used against anthracnose and other grape diseases, therefore it can be used as a measure of comprehensive prevention and treatment. For the manufacture of the mixture can be taken as a finished, mass-produced product, and use individual components.
If the treatment is carried out before budding, the concentration of the vitriol in the solution is 3%, but when spraying the leaves and green parts of the plant, this content of the active element will cause a serious burn.
Therefore, for a later treatment and treatment of grapes, a Border blend is used to make a 1% composition immediately before the procedure.
From 5 liters of hot water and 100 grams of copper sulphate, carefully mixing, make a solution. Then, in a separate container in 10 liters of water, 75 grams of lime and also thoroughly stirred. A solution of copper sulphate is carefully poured into the milk of lime, the resulting product is mixed and filtered.
Bordeaux blend for the treatment of grapes should be used without delay, it must be remembered that its protective properties are lost after the first rain, which means that the treatment will have to be repeated. When spraying, special attention is paid to young shoots and the back side of the foliage.
Fungicides - preparations against fungal diseases
In order to process grapes with Bordeaux mixture to be more effective, the agent can be mixed with colloidal sulfur, which does not harm a person with a yellowish powder showing a bright effect against fungi and ticks. In this case, sulfur weakens the toxic effect of the copper drug, and the vine receives protection not only from mildew, but also from true powdery mildew.
Chloric oxide of copper is the main active ingredient in fungicides such as Abiga-peak and Hom, used against oidium, mildew and anthracnose grapes. An effective drug from the powdery mildew causative agent is Delan.
Today, for the treatment of mildew, besides Bordeaux liquid, there are a number of effective drugs in the arsenal of the grower, both containing copper and those based on other active ingredients.
Lime-sulfur decoction can be used as a substitute for Bordeaux mixture in the treatment of grapes or in addition to it. A brown or dark orange liquid with a predominant odor of hydrogen sulphide, ISO, is also active against mites and mushrooms that infect grapes.
Alirin-B and Planriz are representatives of the class of microbiological agents recommended for treating vines against gray mold, powdery mildew and mildew.
Fungicide Strobe for grapes
The active ingredient of this modern means is fixed on the treated parts of the plant, is released within a few weeks and does not allow the spores of the fungus to germinate, providing long-lasting and reliable protection of the vine from mildew and oidium.
Resistant to precipitation and not dangerous for the grapes Strobe:
- not only protects plants from fungi, stimulating oidium and mildew, but also contributes to the maturation of the shoots;
- is valid from 8 to 12 days;
- can be used with other drugs.
In this case, no more than three treatments of Strobe grapes per season are allowed.
Ridomil Gold for the prevention of mildew on grapes
This systemic fungicide is prophylactically used against downy mildew and other diseases of the grape. The tool is little toxic and compatible with other drugs, and when alternating with contact-action fungicides, Ridomil Gold is most effective.
Treatment of healthy vines at risk of mildew infection is carried out in dry, windless weather, when there is no danger of burns to the bush.
The effect of spraying lasts from 7 to 10 days. The advantages of using Ridomil Gold on grapes are that the :
- means, dried on the foliage and shoots, not washed off with dew and precipitation;
- protection extends to the untreated parts of the vine, including the increment formed after processing.
If there are signs of disease on the leaves of the vine, it is necessary to treat the plant with a fungicide of a curative action and only then, after a week, apply Ridomil Gold.
