Oidium of grapes (photo) and how to treat it

Powdery mildew is the scientific name for a fungal disease more commonly known as "powdery mildew." Spores attack grape leaves and fruit, rendering them unfit for consumption. Photos of powdery mildew on grapes, along with treatment and prevention methods, are provided below.

How to determine the presence of the disease?

Among grape diseases, oidium (see photo) is the most common, and most experienced gardeners know how to treat it. This doesn't diminish the danger of powdery mildew. This fungal infection is extremely resistant to high temperatures and frosts and can be transmitted through water, air, tools, and gardener's gloves.

Photo of grape oidiumIf not treated promptly, powdery mildew will terrify anyone. In advanced stages, powdery mildew attacks the fruit, causing them to darken, dry out, and crack right down to the pit. Leaves become covered with a white-gray coating, resembling a mixture of flour and ash, and curl up.

Old shoots become covered with brown spots and may fall off. Powdery mildew is most dangerous for fruit ovaries, as it can completely destroy the harvest if it gets on them. In the early stages, the fungus can be identified by the following signs:

1. Bumpy leaves. Even before the film appears, the leaf blades begin to curl slightly, with yellow spots visible in some areas.
2. On old shoots, the leaves become covered with brown spots that look like sunburn.
3. The ovaries and young fruits become covered with a thin coating, grow more slowly than their healthy neighbors, and show a clear lack of nutrition.
4. A fairly characteristic sign at any stage is the smell of herring near the vines.

Methods of control

Although the fungal disease attacks the leaves and fruits from the outside, not the inside (except in later stages), simply removing the plaque is impossible. The fungus uses special suckers and cannot be removed without damaging the surface on which it is located.

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Therefore, we need to take a different approach: use products that will kill the fungus. These are applied by spraying. The treatment must be carried out in two stages.

If the vine was infected last year, the procedure is scheduled when the temperature stabilizes at around 6°C (41°F). If there was no powdery mildew last year, then wait until the first 4-6 leaves appear.

If the disease is detected during the period of ovary formation, the chance of saving the crop is sharply reduced, but does not disappear completely.

Treatment can be carried out provided that at least 56 days pass between it and harvest.

Is it worth treating powdery mildew on grapes, as shown in the photo, in the fall, and how should the plantings be treated?

Yes, it is possible and necessary to combat powdery mildew in the fall if the disease was detected so late.

There is just one nuance to consider: some fungicides, especially those based on sulfur, only work well at temperatures between +18 and +22.

During the "Indian summer" period in September they still make sense, but with the onset of cold weather you will have to choose other means.

Sulfur

Sulfur has been used since the 19th century, when powdery mildew was first discovered in Europe. This substance is inexpensive and is found in almost every gardener's first aid kit. If stored properly, it will quickly kill powdery mildew.

Instructions for use:

1. Grind the sulfur to the finest possible powder. Pass it through a sieve to remove any lumps. Fine particles work best.
2. Dilute the product in warm water. The optimal air and water temperature for spraying is 18 to 22 degrees Celsius.
3. Wearing a respirator, thoroughly spray the bushes, paying attention to the back of the leaves.

Using sulfur at temperatures below 18°C ​​is not advisable. If cold weather sets in, you'll need to purchase a different product.

Professional fungicides

Rubigan, Bayleton, or Karatan are available at gardening stores. These are sulfur-based fungicides. Use them according to the instructions. These products are suitable for use in warm weather and can be applied after the grapes begin to bloom.

Folk remedies

If you've discovered powdery mildew on your grapes, as pictured, and don't know how to treat it, folk remedies are available. These can be used if professional fungicides are unavailable. They're ideal for when harvest time is approaching.

Commercially available medications can cause poisoning if they come into contact with fruit, but folk remedies are safer in this regard. The only drawback is the lack of guaranteed or weak results.

The best treatment options for grape leaves affected by powdery mildew, as shown in the photo:

1. Infusion of rotted hay. Pour 3 liters of water over a kilogram of hay and let it steep for 3 days. Strain the resulting infusion and spray it with a spray bottle.
2. Wood ash infusion. Add 1 kg of ash to 10 liters of water and mix thoroughly. Let it steep for 5 days, stirring daily. Strain the infusion and spray or water the vines.
3. Garlic water. Chop 150 grams (3 to 5 heads) of garlic and dilute it with 5 liters of warm water. Strain and use the solution as a spray.

In the long term, planting garlic, calendula, and sorrel near the vineyard can be helpful. The secretions of these plants protect the grapes from fungus.

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Prevention of oidium

Unfortunately, powdery mildew spreads very easily and quickly. Even if a gardener eradicates it from grapevines, it can persist on other plants. Comprehensive prevention is essential.

Key measures:

1. If affected leaves, branches, or fruits are found, they should be removed immediately. It's a good idea to trim off adjacent leaves as well, as they've likely also been contaminated with spores.
2. Spraying affected vines. Pruning alone is not enough: spores remain in the plant buds and can survive the winter. Applying a fungicide, sulfur, or other solution can be done every two weeks, provided it doesn't affect the harvest.
3. Thinning grapes. Fungus thrives in high humidity conditions, where the plant's leaves are tightly packed together. Vine shoots should be cut back or trained along a trellis at a certain distance from the main branch. Avoid growing grapes in poorly ventilated areas or in areas surrounded on all sides by building walls, tall shrubs, etc.
4. Regular watering and fertilizing are essential. Strong plants are less susceptible to disease. Grapes require adequate moisture, and regular additions of calcium and potassium to the soil are recommended.

In some regions, powdery mildew simply refuses to let go of vineyards. Powdery mildew thrives in southern regions, especially during rainy seasons. To avoid further harm to yourself and your plants, it's best to avoid standard varieties and instead choose specially bred ones.

Don't ignore powdery mildew. This fungal infection can significantly reduce vineyard yields if left untreated.