Content
Mildew on grapes is one of the most common fungal diseases of the crop. Downy mildew came to Europe from North America back in 1878. If you do not fight the disease, you can lose not only the harvest, but also the vine itself.
The first spring rain can bring mildew fungus from neighboring areas
What kind of disease is this and how is it dangerous?
The American grape disease mildew occurs in all grape plantations of the world. Downy mildew does not occur, perhaps, only in Central Asia, since there is no rain in this region in the summer.
The causative agent of the disease is the fungus Plasmopara viticola, which requires living plants to develop.Downy mildew spreads to plantations very quickly, so it is important not to miss preventive measures. The spores overwinter in the soil and retain their vitality for up to five years.
Downy mildew is dangerous for grapes, because 16 generations of the fungus develop in one season. There are other reasons why you need to fight mildew:
- Pests and parasites quickly spread to diseased plants;
- crop losses in the year of defeat and in the next season increase to 50%;
- the berries are practically unsuitable for processing;
- It is impossible to harvest cuttings from vines affected by downy mildew;
- Plants weakened by disease do not overwinter well.
First symptoms
Grape growers need to know the signs of downy mildew in order to immediately begin to combat it before it affects all plantings. The disease can be recognized by the following symptoms:
- “fat” yellowish spots appear on the upper part of the spreading leaf;
- on the back of the affected area there is white fluff, similar to flour.
After some time, the foliage dies and then falls off. Moreover, downy mildew affects not only the leaves, but also the vine, and then the berries. At first they turn blue, then darken (turn brown) and wrinkle, becoming unsuitable for consumption.
“Leathery” berries appear on the bunches due to mildew
Difference from other diseases
There is another disease with a similar name, “powdery mildew.” This is grape oidium. It is also capable of destroying almost the entire crop harvest. But the difference is that it can be recognized by a whitish coating, but not from the back, but from the upper part of the leaf blade. It is not oily and washes off easily.And already under the coating there are brown spots.
You can tell that oidium disease is developing on a vine by the smell of rotting fish.
Causes
The causative agent of mildew is the powdery mildew fungus Plasmopara viticola, which forms zoospores. They are carried by the wind over long distances, and damp and warm weather (8-24 °C) promotes the development of spores. Downy mildew affects only living plant tissues.
In hot, dry weather, zoospores die. Mildew has its own incubation period, which is determined by months:
- May, middle – from 15 to 18, end of the month – 12-15 days;
- June, beginning – 12-14, second half – 9-10, last ten days – up to 7 days;
- July, August – from five to six days.
How to deal with mildew on grapes
At the first signs of downy mildew, you need to urgently treat the plantings. To do this, you can use folk or special means. Each of them is good in its own way. Folk remedies are less effective, but they are safe and can be used at any time, even when the harvest is ripe.
Folk remedies for mildew on grapes
There are different ways to combat mildew that have been created and used for centuries. All these drugs are safe not only for humans, but also for insects.
Wood ash
To spray 1 kg of ash, pour 10 liters of water and leave for three days. Then filter, add three tablespoons of liquid soap. Use immediately. You can repeat every week.
Many winegrowers sprinkle their plantings with dry wood ash.
Soda
Baking soda or soda ash has long been used to combat downy mildew.About 50 g of powder is dissolved in 10 liters of water and 50 g of laundry or green soap is added.
Soda, iodine and manganese
This solution is prepared from 4 tbsp. l. soda, which is dissolved in warm water. Up to 20 drops of iodine are added there. Mix everything in 10 liters of water, pour in a little potassium permanganate and 3 tbsp. l. liquid soap (for the solution to stick). Spray grapes against mildew before flowering in cloudy, dry weather. Repeat every seven days.
Soda is one of the indispensable means for combating fungal diseases on grapes
Rotten hay
Place it in warm water and leave for five days to form Bacillus subtilis, which Plasmopara viticola is afraid of. The mother liquor is diluted in a ratio of 1:3. Grape bushes are treated for mildew all season every ten days.
The bucket needs to be filled with rotten hay, and only then add water, keep it in a warm place
Dairy products
Sour milk and whey are an excellent option for combating mildew and grape oidium. Powdery mildew does not like exposure to an acidic environment at all.
Add 1 liter of serum and liquid soap to a 10-liter bucket so that the solution remains on the plant longer
Infusion horsetail
Many gardeners know this weed and remove it from the site. In fact, the plant helps in the fight against mildew. To obtain a solution, take 100 dry horsetail and boil it in 5 liters of water. After 12 hours, the infusion is filtered, combined with 50 g of liquid soap and sprayed on grape plantings infected with mildew.
Horsetail herb is sold in any pharmacy
Infusion fermented sour bread
Many winegrowers use fermented black bread to treat mildew on grapes.1 kg of dry crusts is poured into 10 liters of warm water, add 2 tbsp. l. granulated sugar and leave for 4-5 days. During this time, the liquid will begin to ferment. The resulting acidic environment with yeast fungi has a detrimental effect on mildew.
Before spraying, the infusion should be diluted with water at room temperature in a ratio of 1:3.
Dill
Some winegrowers hold dill in special esteem. They plant this fragrant plant along the entire perimeter of the vine site. In fact, dill does little to prevent downy mildew on grapes.
Planting dill will not harm the grapes, so you can grow it next to the vine
Preparations for mildew on grapes
Folk remedies for downy mildew are often used for prevention even when mildew has just appeared on grapes (isolated cases). If the damage is widespread, then you will have to use special compounds to rid the grapes of downy mildew.
Mildew medications can be:
- System. They are used not only for protection against mildew, but also for treatment. The drugs act on the disease “from the inside”, so no amount of rain can wash them away.
- Contact. These chemicals destroy mildew in the places where they are applied. Therefore, when working with them, you need to thoroughly “wash” all affected parts of the plants.
Any chemicals must be used strictly for their intended purpose.
- Biological. These are most often preventive drugs that can be used even at the stage of berry formation.
To avoid harm, you need to carefully study the recommendations on the packaging.
Agrotechnical measures
Most often, downy mildew breaks out on young grape plantings because they have low immunity. Sometimes folk recipes and chemical preparations are enough. Often the health of the vine largely depends on timely agrotechnical measures.
Agrotechnical measures against mildew:
- Ventilated areas are chosen for the grapes, and the rows are arranged so that they coincide with the direction of the winds.
- The vines are tied up and thinned to ensure air circulation.
- Be sure to feed the grapes with fertilizers containing potassium and phosphorus, and in the fall add a bucket of wood ash.
- Grape varieties resistant to mildew are planted.
- They prevent the growth of weeds and loosen the soil throughout the season.
- All cut parts of grapes that show signs of mildew are removed from the site and burned.
Pinching, pruning and chasing grapes should be carried out throughout the growing season
Preventive treatment of grapes against mildew
Prevention of mildew and other fungal diseases is necessary for grape plantings. Some of them occur in spring, some in autumn. In case of infection, it is no longer prevention that will be required, but specific treatment of the grapes.
How to treat grapes in spring against mildew
In the spring, it is important to have time to treat the grapevine from downy mildew before the first rain. To spray plantings and soil, use Nitrophen, which is diluted strictly according to the instructions.
When four leaves appear, Ridomil is diluted, and before the formation of tassels, the clusters are sprayed with Bordeaux mixture.
Treatment of grapes in autumn against mildew
Since grape mildew spores do not die during the wintering phase, it is necessary to carry out autumn work to prevent fungal diseases.
Stages of work:
- The foliage and mildew-affected parts of the grapes are collected in a heap and set on fire.
- The soil and plantings are sprayed with copper or iron sulfate.
- Depending on the region, the vine is covered for the winter.
Grape varieties resistant to mildew
There are not many grape varieties resistant to downy mildew. It is better for gardeners to start with representatives of the crop that have a high immunity to fungal diseases.
Resistant varieties:
- Victoria, Friendship;
- December, Pearl pink;
- Khasansky Bousa, Khasansky sweet;
- Super Extra, Bianchi.
It is important to first carefully read the descriptions and characteristics of grape varieties.
The Dneprovsky pink grape variety is also resistant to mildew
Conclusion
Mildew on grapes, like oidium, can be cured, the main thing is not to be late with the measures. You should carefully inspect the plantings so as not to miss the whitish fluff on the upper or lower side of the leaf blade.
