Causes of powdery mildew on apple trees, how to fight and what to do for treatment

The most common disease that significantly reduces the yield of fruit trees is powdery mildew. Heat-loving plants grown in temperate climates are at risk, but with uncharacteristic temperature conditions for the region and increased average annual humidity, powdery mildew also appears on apple trees, the most traditional fruit tree in the temperate climate zone.

What kind of disease is this

Fungal disease of garden fruit trees, shrubs, and root crops has several names, the most common are:

• underwear;
• powdery mildew;
• Ashtray.

What looks like a white coating on leaves, flowers, and fruits is the mycelium of microscopic fungi that multiply exponentially; every day a colony of pathogenic fungi covers larger and larger surface areas of leaves, bark and other outer parts of the plant.

The spores are easily carried by wind and insects, which means that if one tree on a site becomes diseased, it threatens to develop into a real epidemic of the entire garden.

A fungal disease develops on the bark, leaves and fruits. If at the early stage of damage in the fight against this scourge it is possible to save most of the crop, then if the apple tree is diseased at the stage of fruit ripening, losses can amount to up to 80% of the crop.

Who is the causative agent

The causative agent of powdery mildew is the marsupial fungi of the order Erysiphaceae (erysyphaceae), there are more than 700 species that cause powdery plaque - 100. Erysiphe, which causes Oidium, also belongs to this class.

Powdery mildew fungi are pyrenomycetes, each of the agricultural plants is susceptible to damage by representatives of a certain species:

• Blumeria graminis parasitizes cereals.
• Trifolia precipitates legumes.
• Sphaerotheca mors-uvae damages gooseberries and black currants.
• Betae threatens sugar beet yields.
• Cichoracearum spoils potatoes, tobacco, and pumpkins.
• Sphaerotheca lives on roses and other ornamental shrubs.
• Uncinula necator prefers grapes.
• Podosphaera is a common threat to fruit trees, including apple trees.

The peculiarity of parasitic mealy fungi is that their colony lives only as long as the plant is alive. Having attached to the surface of a leaf or stem at the beginning of summer, the mushrooms will die along with it.

Parasitic activity of fungi

The mycelium of the fungi that causes the disease is superficial with appressoria (suckers). To attach to the leaves, the fungi grow into plant cells with short hyphae with haustoria. During the growing season of the plant, fungi reproduce by conidia (asexual stage); in tropical climates, this may be the only stage. Conidia are arranged in islands or chains.

In a temperate continental climate, fungi have 2 stages of development - asexual and sexual (marsupial).

Like all mushrooms, Erysifaceae have fruiting bodies called cleistothecia. The spherical mushroom with a concave tip has appendages in the form of simple or branched outgrowths. Each of them contains from 1 to 22 asci; they, in turn, are a container for 2-8 ascospores. With such fertility, the mycelium will conquer the entire fruit tree in a matter of days if preventive and therapeutic measures are not taken in time.

Distribution area

The mycelium of marsupial fungi that cause leucorrhoea does not tolerate severe frosts; the mycelium can overwinter provided that it is located deep in the bark of a tree damaged in the previous season. Based on the harsh climatic conditions - severe frosts, short, dry, hot summers, fruit trees grown in Siberia and other northern regions are least often affected by powdery mildew.

Almost powdery mildew on fruit trees can be found in any corner of the world; the largest areas affected are observed in countries with a temperate continental climate.

The higher the air and soil humidity, the fewer sunny days in summer, the higher the risk. The most favorable conditions for the spread of pathogenic fungi are the Baltic states, the northwestern regions of the Leningrad region and the Moscow region. Slightly lower, powdery mildew causes damage to the crops of the Krasnodar Territory, Kazakhstan, Uzbekistan, Ukraine, Belarus, and Moldova.

Main causes and factors in the development of the disease

Between plants, the disease spreads conidially, methodically capturing new areas on the leaves and bark of the infected tree and neighboring drupes, berries, fruit trees and shrubs.

A favorable environment for mycelium is created by:

• soils with poor water conductivity;
• lack of sunlight at high air temperatures;
• mild winters with thaws;
• warm, swift spring after a snowy winter.

Under such natural conditions, the mycelium will develop quickly. At the spore maturation stage, winds and heavy rains will facilitate the reproduction and transmission of the disease.

Signs of tree infection

A white translucent coating formed on the shoots and leaves at the stage of the appearance of the first leaves is a sign of the manifestation of the disease. At the same time, the buds that have not yet blossomed begin to wither, become deformed, turn brown, wither and fall off.

The affected areas only initially appear white; the development of the disease is indicated by a denser silvery coating, which appears as such due to the formation of cleistothecia.

At first these are rare black dots; at a later stage, the fungal coating acquires a brown tint. The white coating on fruits is a short-term phenomenon. Apples affected by the fungus develop brown, woody spots and streaks on the skin.

What is dangerous for a tree

Despite the fact that plaque can easily be wiped off from leaves, shoots and even bark, the disease has already affected the epidermal cells of the plant - it has grown into them. The hyphae and haustoria remaining inside continue to parasitize, due to which after some time the spot becomes gray, brown or purple. The mycelium takes all the vital juices from its donor - the leaves dry out, the ovaries do not have time to form, and the existing fruits fall off prematurely or lose their presentation, and do not gain the standard weight for the variety.

The mycelium of fungi that causes powdery mildew on apple trees most often does not survive the winter, but under favorable reproduction conditions it can destroy an immature young seedling due to the compaction of the mycelium. Mature apple trees with chronic mildew stop bearing fruit long before the end of the typical period for the variety.

Please note: the incubation period is 4-9 days.

Preparations for powdery mildew on apple trees

A universal remedy for fungal infections and insect pests of fruit trees is colloidal sulfur. The trees are sprayed with a two percent solution during the budding period, until the cup of flowers opens. At the end of flowering, for preventive purposes, treatment is carried out with a one percent composition.

When treating with a universal fungicide - Bordeaux mixture, for the first spraying take a 3% solution, for the second you will need a 1% solution. To effectively protect apple trees from re-infection, the penconazole drug “Topaz” is recommended; it penetrates deeply into the tissues of the tree and fights the pathogen from the inside, and not just the superficial manifestations of the disease.

Just like Topaz, the following are in demand among gardeners:

• granular urea;
• "Impact"
• "Cumulus";
• "Tebuconazole";
• "Topsin";
• "Fitosporin".

If you don’t have specialized chemicals on hand, there are several options for how to treat your apple tree when the first signs of ash fly are detected.

Folk remedies

Three simple recipes have been used effectively by amateur gardeners for a long time. Recommended proportions for 10 liters of water:

1. 50 g of soda ash with 40 g of grated laundry soap.
2. 3 g potassium permanganate (potassium permanganate);
3. "Hom" - copper oxychloride, 40 g.

These products, in combination with fertilizing, give a good preventive effect; when the disease manifests itself, such spraying gives the gardener a reprieve for 3-4 days. Severe lesions must be treated with specialized means. Sometimes it makes sense to sacrifice the harvest of one season in order to protect the tree.

Control measures

In addition to spraying three times with fungicides per season, it is necessary to strictly dose fertilizing. Nitrogen fertilizers increase the ability to develop not only agricultural crops, but also the fungi that parasitize them - if the recommended norms of nitrogen fertilizers are exceeded, the mycelium will spread especially quickly. Potassium and phosphorus fertilizers reduce its vital activity.

Prevention at the stage of the initial growing season is important, but how to deal with powdery mildew during fruit ripening? Folk remedies do not affect the quality of the fruit; if there is an increased risk of plant infection with powdery mildew, it is recommended to spray apple trees with potassium permanganate or a solution of soda with laundry soap once every 10-14 days.

If the tree is infected, the manifestations of the disease are not only on the leaves, but also on the branches and trunk, then you cannot do without Topaz or a fungicide similar in action to it. The first 2 sprayings are carried out at intervals of 3-4 days. Further, until the fruits ripen, it is necessary to carry out prevention.

Treatment of an adult tree

Treating a tall apple tree with a dense crown is difficult; spraying is carried out not only on the surface of the leaves; it is necessary to treat the branches, trunk, and lower part of the leaves. To do this, you will need an assistant pumping the solution and personal protective equipment - glasses, a suit that maximally protects areas of the body.

What to do with an apple tree when an entire branch of an adult plant is affected? It is easier to remove and burn it; in such a case, a stepladder, pruning shears, hacksaw, and garden pitcher should always be at hand. To prevent the development of powdery mildew after winter from mycelium that has overwintered in the soil:

• Mulch is removed from under the tree.
• In spring and autumn, the trunk is whitewashed.
• There should not be any last year's leaves or fruits on the site.

Manifestations of the disease on apples do not affect the taste, but the apples will be less juicy. If pathogens can be overcome using folk remedies or gentle dosages of chemicals, then the crop can be used for food.

Attention! You can find out after what treatments apples are suitable for eating on the packaging of professional products. The manufacturer's instructions will be relevant if the recommended proportions are strictly observed during use.

How to save young seedlings

To protect apple tree seedlings during the planting season, they are soaked for a day in a weak solution of potassium permanganate (potassium permanganate). The water should acquire a light pinkish tint; a strong solution can cause burns and the plant will hurt. To improve the survival rate of a seedling, it is better to use growth stimulants, and it is better to refuse nitrogen fertilizing, because in the first season a harvest is not expected from an apple tree (on any rootstock).

Prevention

When selecting a site for planting, you should avoid proximity to plants affected by the fungus, protect it on the leeward side, but do not plant it in the shade of a house or a monolithic fence. It is imperative to adhere to the intervals recommended for specific heights of fruit trees.

It is necessary to thin out the crown, remove affected and old (non-fruit-bearing) branches, remove fallen leaves and fruits, carry out mulching and whitewashing, and apply potash and phosphorus fertilizers.

How to fertilize an apple tree in the fall against disease?

A 1-1.5 percent solution of sodium phosphate strengthens the plant, helps to establish the formation of strong, healthy buds, and strengthens the plant’s immunity to diseases.

Seasonal processing

Phosphate spraying is carried out on apple trees and other fruit trees after harvesting, but before the leaves have fallen and turned yellow. The solution is absorbed through the leaf blades, thereby protecting the plant from infection with powdery mildew and other fungal diseases after winter.

On varieties of late-ripening apple trees, the leaves fall off before the tree is harvested; in this case, phosphate must be applied through the soil with the last watering of the season. Thinning the thickening tree crown prevents the rapid spread of the disease; whitewashing the trunk makes it difficult for hyphae and haustoria to penetrate the plant bark.

Varieties resistant to powdery mildew

The resistance of an apple tree to certain strains of diseases in plants, as in all living organisms, is determined by a gene that is strongest in apple trees of selected varieties:

• Amulet;
• Argo;
• Gloucester;
• Duet;
• Marshmallow;
• Golden summer;
• Carmen;
• Red poppy;
• Red amber;
• Kupava;
• Linda;
• Mutsu;
• Orion;
• Palette;
• Prestige;
• Dawn;
• Redfree;
• fontanel;
• Union;
• Talida;
• Mascot;
• Fortune;
• Fairy.

This is not a complete list of apple trees resistant to powdery mildew. For each region, other varieties with high resistance rates can be found in local nurseries. When choosing an apple tree variety, it is necessary to remember that immunity to one disease in an apple tree can be compensated by weak resistance to other types of pathogens.