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While powdery mildew is only a nuisance on plants in your own garden, this fungal disease is a real horror for farmers. Grapevines in particular suffer greatly from the infection and it is therefore necessary to prevent and combat possible infestation. Wine can be attacked by powdery mildew and downy mildew, which, along with phylloxera, is one of the biggest problems in viticulture. Even in the home garden is not to be trifled with.

Where does powdery mildew come from?

Powdery mildew and downy mildew, which affect grapevines, have only appeared in Europe since the mid-19th century. The fungi are originally from North America and were introduced there between 1845 and 1878, around the same time as phylloxera. Since that time, fungi and lice have been the biggest pests and diseases for winegrowing in Europe, since the native species are hardly resistant to powdery mildew and therefore fall victim to it in large numbers. This is what makes these fungi so dangerous, even on solitary vine shrubs kept purely for ornamental purposes or for low annual crop yields.

Notice: Not all types of mildew affect every plant. Powdery mildew fungi in particular specialize on a certain type of plant, and this also applies to wine, which suffers greatly from the infestation.

Powdery mildew in detail

Powdery mildew is a disease of various types of vines caused by the pathogen "Erysiphe necator", which belongs to the so-called fair-weather fungi. The disease caused by the sac fungus is also known under the names Oidium or Äscherich, which primarily indicates the grayish coloring of the plant as soon as the infestation is severely advanced. The sac fungus infects the wine by collecting on the surface of the plant parts and penetrating them via suction organs, more precisely into their cells. The fungus thus interferes with the nutrient balance of the grapevine and has a negative effect on it with the following symptoms:

  • white-grey spots form under and on the leaves
  • as well as net-like structures reminiscent of cobwebs
  • the more severely the vines are infested, the more parts of the plant are affected: shoots, flowers, buds, grapes
  • the layer looks mealy, slightly moldy
  • Leaves curl up
  • Flowers can no longer open
  • Grapes harden, turn gray or black in color and suffer seed breakage, becoming inedible
  • growth is restricted
  • Grapevine is gradually coming in
  • later stages: spots turn gray-brownish

Seed breakage in particular is devastating for viticulture, as the grapes can no longer be used to produce wine. Slightly infested fruits, on the other hand, cause an unpleasant aroma, so-called wine defects, which can greatly reduce the value of a product. Furthermore, the vines can be infested with other pathogens through seed breakage. However, infection by the fungi can occur at a temperature of over 7°C in spring, optimal temperatures are between 20°C and 27°C, but temperatures of up to 35°C are tolerated. They are therefore also called fair-weather mushrooms because they prefer warmth and drought. The following grape varieties are particularly susceptible to these fungi:

  • Blue Portuguese
  • blue burger
  • Muller Thurgau
  • Scheurebe
  • Sylvaner

Wrong mildew

Downy mildew is caused by the pathogen "Plasmopara viticola", which is a so-called pseudo- or egg fungus. Compared to powdery mildew, they are known as bad weather fungi and prefer a humid environment. The infestation is particularly effective as soon as the nights are damp. Rain is the best carrier of all mildew fungi, as it can infect the underside of leaves just by spraying up. In contrast to Erysiphe necator, the pseudofungi do not feed on the nutrients in the plant, but attack the cells directly and produce the characteristic coating through spores. In the event of an infestation, the following symptoms occur:

  • white, gray or slightly violet mealy coating forms on the underside of the leaf
  • The upper side of the leaves lightens and forms oil stains
  • Leaves wither over time
  • Plant can die completely
  • Leather berries, grapes no longer edible

The leatheriness is what winegrowers fear because the grapes die off completely when they are still young. They attack young shoots of the vines, dry them out and harden the skin. Once infested, the berries appear like raisins, which are unhealthy in color and tough as leather. As with the real thing, downy mildew can cause entire harvests to fail, which is devastating for viticulture. In contrast to powdery mildew, however, false mildew is not as specialized and has about the same effect on a wide range of grape varieties:

  • Müller-Thurgau
  • good noble
  • Portuguese
  • Limberger

Notice: Downy mildew begins to attack the wine at temperatures above 11°C. That said, this starts quite early in spring, especially when the snow has gone.

Powdery mildew on a plant leaf

prevent powdery mildew

Before you have to treat the vines with a spray or household remedy, you should plant and care for the vines in such a way that possible infestation is reduced or even prevented as much as possible. The fungi have the greatest opportunity to attack when the vines are in an unfavorable position or receive the wrong addition of nutrients - or dosage. With the following 7 tips you can ensure in advance that your wine is better protected from the fungi:

tip 1 Provide your vines with enough space, because this is the only way air can circulate between the plants. Also, when planting near walls, make sure they are far enough away. Recommended distance: between 100 and 200 cm.

tip 2 Herbs between or near the vines provide protection against powdery mildew. Due to the active ingredients they contain, these act against the spores of the fungi. These include above all:

  • chervil
  • basil
  • chives

tip 3 Do not fertilize too much and do not use large amounts of nitrogen when fertilizing, which acts as a breeding ground for the fungi.

tip 4 Be sure to protect the leaves from excessive moisture, especially from rain. Too much water leads to an unbalanced microclimate between the leaves of the plant, which in turn restricts air circulation and increases the risk of fungal infection.

tip 5 Water only in the morning or evening. To do this, only wet the location and the roots, not the stems or shoots from the wine.

tip 6 Weeds that are affected by powdery mildew and that grow near the vines should definitely be removed, as this is where the spores collect. However, never dispose of this in the compost, as from there the spores could spread via wind and rain.

tip 7 Regularly use strengthening decoctions, for example made from field horsetail. These ensure effective growth of the plant, which becomes stronger from within through the brew.

Although this does not guarantee that the wine will not be infested, these measures can greatly reduce the probability. Above all, fresh air and the right nutrient balance are important for the vines so that they can fight mildew on their own, because weakened plants in particular are literally at the mercy of the fungi. However, if your wine is infested, you must first identify which fungus it is, as there are different treatment measures available for the two types. Or as an alternative, plant vines that are really mildew resistant.

powdery mildew on plant leaf

"Resistant" varieties

Wine comes in many varieties and some of these have been bred heavily for fungal resistance for several years to resist mildew infestation. This is particularly important for organic viticulture, since no aggressive spraying agents may be used here. These grape varieties all come from Europe and are for the most part resistant to powdery mildew and are much better suited than the classic vines that are typical of wine growing in Europe. American vines, for example, are resistant to powdery mildew, but are not so well suited for cultivation in Germany. You should choose one of the following varieties:

  • Regent: red
  • Cabernet Blanc: white
  • Baron: red
  • Reberger: red
  • Muscat Bleu: red
  • Villaris: white
  • Felicia: white
  • Cal 6-04: white

We especially recommend the Regent grape variety, which has shown itself to be extremely resistant to powdery mildew and other fungal diseases in recent decades. If the location is optimally chosen and fertilized accordingly, infestation by the fungi is almost impossible. The other grape varieties are also very suitable, especially with good care, and can save you a lot of trouble. The crop yield of the Regent is also not without. Please note that these vines can also suffer from powdery mildew if they are over- or under-fertilized and if there is too much moisture.

combat powdery mildew

You can either treat the vines with chemical sprays or home remedies, which are much gentler. You should avoid using chemicals in your own garden at all costs, as they could endanger not only you but also your neighbors, domestic animals and wild animals. Before each treatment, remove affected leaves and shoots to also curb the spread. You can fight the fungus with the following means:

  • special sprays from the trade on an ecological basis
  • skimmed or raw milk
  • baking powder
  • ablutions
  • herbal broths
  • Bring beneficial insects into the garden

Ecological sprays from the trade

There are more and more products on the market that you can use to efficiently combat the fungi on your vines. These are not even harmful because they are created on an ecological basis and thus literally get to the root of the problem. The following manufacturers are recommended here:

  • Compo
  • Neudorff

These manufacturers are well-known in horticulture and offer you copper-based drugs to combat them, which are effective against fungi. These are administered via a conventional squirt bottle according to the dosage information on the packaging and can be used even in the case of a severe infestation. It is important that you then dispose of the pack in the recycling collection.

Powdery mildew on the rhododendron

milk

Skimmed and raw milk can be used quite well against an initial infestation. To do this, proceed as follows:

  • mix 100 milliliters of raw or skimmed milk with 600 milliliters of water
  • fill the agent in a spray bottle
  • treat the plants extensively with the product every four days

The milk is particularly good for the early stages of infestation and acts as a precaution against the fungus as the fats in the milk act against the spores.

baking powder

The baking soda solution is good for fighting mildew as it contains lecithin and is so effective against the fungi. The mix is created like this:

  • first mix together 10 ml of baking soda, 10 g of rapeseed oil and a drop of washing-up liquid
  • then dilute the mixture with a liter of rain or mineral water
  • put this in a spray bottle and spray the wine every 10 to 12 days
  • spray in the evening, as this is when the solution can easily soak in without reacting with the sunlight

ablutions

Fight mildew with a targeted washing of the entire plant. While plants should not be kept too wet, it is worth hosing down with a garden hose sprayed with mineral water or rainwater. Then you should carefully dry the vines with a cloth. This is particularly useful for light infestations, but must be repeated quite often.

herbal broths

You can combat powdery mildew extremely well with herbal broths, as the ingredients work against the spores. Use medicinal herbs for this, for example: horsetail, Canadian goldenrod, nettles, tansy or rhubarb leaves (not medicinal herbs, but still effective). Proceed as follows:

  • Chop up 300 grams of fresh herb or 30 g of dried herb, horsetail works best
  • soak it in 10 liters of water for 12 to 24 hours
  • simmer for 15 minutes the next day
  • dilute this brew in a ratio of 1:5 with water
  • sprinkle the vines every four days

beneficials

As an alternative, you can also bring beneficial insects into the garden. Ladybugs and sawflies, which feed extensively on the fungi, should be mentioned here. They also maintain the garden's natural balance while fighting mildew.

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