Powdery mildew on an apple tree, how to fight it? What is white plaque on leaves, its treatment

What is powdery mildew?

This is a common pest of garden shrubs and trees. This disease of fruit trees develops in conditions of high humidity and air temperature of +18...+25 degrees.

In such a situation, the apple tree’s resistance to infection decreases sharply.

In summer, when the weather is hot, the powdery mildew coating hardens and turns into a fruiting body, which transforms into a black mushroom .

This stops the spread of the disease. The layering dies, and the infection develops further in the buds of the tree in hot weather.

Who is the causative agent of the disease?

The source of powdery mildew is a fungus that affects all parts of the plant, including bark, leaves, and young buds.

A sign of the disease is a sticky white coating on the apple tree: on new shoots and leaves. This layer, after some time, becomes brown with dark dots.

The affected areas become deformed and, curling, wither . The shoots stop growing, curl up and dry out. What powdery mildew looks like on an apple tree is shown in the photo below.

Powdery mildew on an apple tree: 1 - mycelium and condia, 2 - affected parts.

Powdery mildew on trees affects the condition of the garden as a whole. Leaves fall from trees prematurely, and yields are significantly reduced. Severe frosts reduce the development of the disease.

Important! The mycelium of the fungus in infected buds disappears at a temperature of -20 degrees. At the end of severe frosts, the signs of the primary disease decrease. The source of the disease dies en masse.

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.

Disease development cycle

The infection development cycle includes two stages :

Marsupial;
Directly conidial.

The observed white coating on areas of plants is sporulation of conidia . The first stage of the disease appears in early spring when the buds open. During this period, a shrub or tree becomes infected with a fungus that has overwintered in the ovaries.

Condia appear, which serve as a source of secondary infection . The first stage of the disease lasts on average 30 days .

Then the marsupial stage begins in late May–early June . It is expressed in the appearance of black fruiting bodies with branched appendages on the shoots and leaves.

Marsupial stage.

Signs of tree damage

First, the leaves become covered with a whitish coating, reminiscent of flour.
Over time, the plaque thickens and takes on a brownish tint. The affected organs stop their growth, begin to curl and crumble.
Shoots damaged by powdery mildew first turn white, then turn brown, and at an advanced stage they die completely.
The flowers become covered with a whitish coating of thick consistency, which is why they bloom in a chaotic manner, become deformed and dry out. Such buds do not have time to develop fruit ovaries.
A grayish coating and deep cracks appear on the skin of apples.

Downy mildew

Powdery mildew as a disease spreads throughout the plant. Young branches and leaves, inflorescences, and sometimes fruits are affected .

Symptoms of infection first appear on the leaves of the apple tree . They are covered with a white coating. Diseased areas stop growing, curl, lose color and fall off.

On branches, the infection appears as a white powdery coating. Then it begins to darken, the shoots slow down, become crooked and finally die off. Young branches infected with powdery mildew freeze up to 50% of the total .

The inflorescences become diseased when the bud separates. The brushes are covered with a white coating of thick consistency, while drying quickly.

The ovary does not have time to form . Infected flowers develop poorly, bloom chaotically, and they themselves become deformed and dry out.

The apples themselves are also susceptible to disease . Sometimes a young ovary infected with powdery mildew forms a fruit.

With further development, a trace in the form of a net remains on its peel.

Varieties resistant to powdery mildew

When planting your garden, it is advisable to plant varieties of apple trees that are resistant to the infectious agent. Varieties such as:

Arbat,
Gold Rush,
Brigham Delicious,
Florina.

Advice! By doing this, you can save up to 80% of the garden's harvest.

Causes of damage to apple leaves

Preventing a disease is much easier than treating it, so it is important to know what triggers the development of powdery mildew.

The development of the disease is facilitated by violation of the growing conditions of the apple tree.

Possible causes of fungal damage to plantings:

excess nitrogen fertilizers in the soil, which contribute to the rapid growth of green mass, which provides the fungus with a large amount of food;
crown thickening;
high air humidity;
insufficient nutrition of apple trees;
low light;
prolonged heat;
poor ventilation of plantings;
fogs and heavy dew;
too deep anti-aging pruning, as a result of which the immunity of the apple tree weakens;
insufficient watering and, as a result, drying out of the soil;
sudden changes in humidity.

Causes of the disease

The reasons why the leaves of an apple tree turn white are considered to be:

Fog,
Dew,
Increased air temperature.

Added to these factors is a decrease in the resistance of trees and shrubs to the disease due to dry weather and lack of moisture.

The combination of these conditions leads to plant infection. The resistance of apple trees to the disease decreases due to sharp fluctuations in air humidity.

The source of infection, due to which the leaves of the apple tree turn white, overwinters in infected buds or as a fruiting body on branches and leaves.

The condia are then carried by the wind throughout the garden, infecting new healthy trees . In this way, the apple tree becomes infected a second time.

Powdery mildew manifests itself after the tree blooms and recurs several times at the beginning of the growing season. The incubation period of the disease lasts up to ten days and depends on weather conditions and the resistance of the apple tree to infection.

White coating on apple tree leaves: how to fight, treatment, what to do?

If a loose white coating has formed on the leaves of an apple tree, this means that the tree is affected by powdery mildew - the second most common disease of apple trees after scab.

Over time, the disease spreads to the shoots and trunk of the tree, which leads to its drying out and loss of 50 to 80% of the harvest .

White coating on the leaves, what is it?

The causative agent of powdery mildew is the parasitic powdery mildew fungus Erysiphales, which becomes active in late May-early June, at the stage of budding of apple trees.

The development of powdery mildew is favored by high humidity, so the disease often occurs after rain.

Favorable conditions for fungal development:

strong shade of plantings;
high air humidity;
air temperature is about 15 °C .

How to determine if an apple tree is affected by powdery mildew

The key to combating powdery mildew is treating plants at an early stage of the disease. To do this, it is necessary to detect it in time, preferably before the formation of a white coating.

The following symptoms of the disease are distinguished:

Buds affected by powdery mildew bloom later than expected ( an average of 4–5 days ).
The leaves and shoots of the apple tree are covered with a loose white coating, which is easily wiped off with a finger, but quickly grows back.
White coating on the leaves of an apple tree.
Inflorescences affected by the fungus lag behind in development, and the flower petals turn yellow.
Powdery mildew on apple tree ovaries.
Flowering is uneven.
Deformation of flower stamens, their drying out and falling off before the formation of the ovary.
If the apple tree is not treated in time, the white coating darkens over time and becomes gray-brown.
The leaves become covered with gray spots and curl.
The leaves curl, dry out and fall off.
At the last stage of the disease, the leaves become covered with small black dots.

Causes of damage to apple leaves

Preventing a disease is much easier than treating it, so it is important to know what triggers the development of powdery mildew.

The development of the disease is facilitated by violation of the growing conditions of the apple tree.

Possible causes of fungal damage to plantings:

excess nitrogen fertilizers in the soil, which contribute to the rapid growth of green mass, which provides the fungus with a large amount of food;
crown thickening;
high air humidity;
insufficient nutrition of apple trees;
low light;
prolonged heat;
poor ventilation of plantings;
fogs and heavy dew;
too deep anti-aging pruning, as a result of which the immunity of the apple tree weakens;
insufficient watering and, as a result, drying out of the soil;
sudden changes in humidity.

Basic rules of wrestling

In order to get rid of powdery mildew, the plantings must be treated with fungicides.

They are used both for direct control of fungus and for preventive spraying of trees. In addition, a number of folk remedies have proven themselves well in the fight against this disease.

Colloidal sulfur

Colloidal sulfur is an old and proven remedy for combating fungal diseases.

Colloidal sulfur has long been recognized as one of the most effective means of combating powdery mildew and scab. Trees are treated with sulfur according to the following scheme:

20 g of the substance is diluted in 10 liters of water. The resulting solution is sprayed on the apple tree before it begins to bloom.
The second treatment is carried out after flowering.
The apple trees are sprayed for the third time after 2–3 weeks .

The number of treatments can be increased if the tree is severely damaged.

Features of the use of colloidal sulfur:

the last spraying is carried out at least 20 days before harvest;
the effectiveness of the substance increases when treating trees early in the morning;
plantings cannot be processed during the flowering period;
It is not recommended to spray the apple tree with sulfur at temperatures above +35 °C , as this can lead to the formation of burns on the leaves;
at temperatures below +20 °C, the effectiveness of sulfur is reduced to zero;
Sulfur cannot be combined with other pesticides.

Fungicide "Topaz"

"Topaz" is a highly effective fungicide, the advantages of which include low price and effectiveness with low toxicity. The apple tree is sprayed with this preparation 2-3 times a season.

Topaz begins to act within three hours after treatment.

Solution dosage: 10–15 ml of substance per 10 liters of water .

Analogues of the drug:

"Topsin";
"Skor";
"TiovitJet";
"Ditan M-45";
"Rovral".

Natural biofungicide "Fitosporin"

This is an environmentally friendly product that does not pose a danger to human health. The plantings are sprayed with “Fitosporin” once every 2 weeks.

The main feature of Fitosporin is its ability to act at both low and high temperatures.

Spraying can be done in any weather conditions, but in damp and rainy weather it is better to treat the apple tree 2-3 hours after the rain.

Bordeaux mixture

This fungicide effectively copes not only with powdery mildew, but also with mildew, scab and gray mold.

Bordeaux mixture is a contact fungicide that has been tested for decades.

Features of application:

Apple trees are sprayed with 3% solution of Bordeaux mixture in March and a 1% solution during the growing season.
Bordeaux mixture is prepared from dry ingredients on the day the apple tree is processed.
To prepare 1% solution, you need to dissolve 100 g of copper sulfate in warm water (you can only use glass containers). Then the total volume of liquid must be brought to 5 liters , for which the required amount of cold water is added to the container. 100 g of quicklime is poured into 5 liters of water, after which the resulting milk of lime is expressed and mixed with copper sulfate.
To prepare 3% solution, the amount of components is increased to 300 g .
Dosage: 10 liters for an adult tree and 2 liters for young seedlings.
It is recommended to use Bordeaux mixture on the day the solution is prepared . If you plan to use it the next day, then you need to add 10 g of granulated sugar to the solution.

Soda ash and laundry soap

One of the most popular folk methods of combating powdery mildew is treatment with a solution of soda and soap.

Prepare the solution as follows:

50 g of soda ash is diluted with 10 liters of water.
A piece of laundry soap is finely rubbed, after which 40 g of the substance is poured into the resulting solution.
The mixture is thoroughly mixed until the soap is completely dissolved, after which the solution is ready for use.

Onion solution

One of the most gentle ways to treat apple trees affected by powdery mildew is spraying with onion infusion.

Onion infusion also helps against codling moth.

Algorithm for preparing the solution:

Peel the onions, putting the peels in a separate container.
200 g of husks are poured into 10 liters of boiling water.
The resulting mixture is infused for two days, after which the trees can be sprayed.

Potassium permanganate solution

Recommended dosage of the solution: 3 g of potassium permanganate per 10 liters of water. It is better to apply potassium permanganate after rain.

Milk solution

A milk solution to combat powdery mildew is prepared by mixing 7 liters of water and 2–3 liters of whey.
Then the resulting mixture is diluted with 1 tsp. copper sulfate.

Prevention measures

The risk of powdery mildew can be minimized if a number of conditions are met:

Plantings must be watered moderately, preventing the soil from drying out. On the other hand, it is also not recommended to flood trees, since high humidity is an ideal environment for the spread of fungus.
You can increase the resistance of an apple tree to fungus by adding potassium and phosphorus fertilizers .
Do not overfeed trees with nitrogen.
Row spacing should be dug up periodically.
It is necessary to monitor the condition of the crown - when it thickens, a shadow is formed in which fungal infections develop faster.

Powdery mildew-resistant apple varieties

You can also protect yourself from powdery mildew by growing varieties that are resistant to this disease. These include the following:

Seedless Michurina;
Napoleon; Napoleon apples are removed from the branch in October and stored until the end of January.
Raika is red;
Titovka.

Conclusion

The most important thing in the fight against white plaque on apple tree leaves is not to delay treating the trees.

The easiest way to get rid of the fungus is in the first stages of the disease. If the necessary measures are not taken in time, the infection can spread to neighboring trees, which can infect the entire garden. Ultimately, up to 80% of the harvest can be lost.

Source: //frukti-yagodi.ru/boremsya-s-belym-nalyotom-na-listyax-yabloni/

Fighting methods

Powdery mildew, a chronic disease of apple trees, reduces orchard productivity .

The leaves fall prematurely, resulting in the loss of 50 to 80% of the fruit. Therefore, the question is quite relevant if powdery mildew appears on an apple tree: “How to deal with it?”

If, nevertheless, varieties of apple trees are planted in the garden that are susceptible to powdery mildew infection, it is necessary to master some methods of combating it :

In winter and spring, diseased shoots must be cut out regularly . This is done not only during bud break, but also after the tree has flowered.

Important! Cut branches must be destroyed, since the fungal spores are very viable. They can cover a distance of up to 1 km without losing their functions

These operations are aimed at combating the consequences of the disease and do not affect its development.

To protect trees from infection, they are sprayed with fungicides:

Trees are treated when the buds open, at the beginning of flowering and after it ends.
The procedure is repeated several times per season.
Up to 5 treatments of the garden with chemicals are carried out per year.

In summer, in hot weather, trees are treated more often. Maintain an interval of 6 - 8 days. When apple trees resistant to infection , spraying is carried out as the disease affects them. This may be one or two procedures.

It is important to treat with chemicals before the leaves appear.

Preventive measures

To obtain a good harvest of large, ripe apples, it is important not to take the development of diseases to extremes. Therefore, you need to start acting even before the first signs of powdery mildew appear, taking preventive measures.

Powdery mildew on roses

In summer, it is necessary to carry out preventive pruning of diseased shoots, if any, and collect fallen leaves. Pruning helps prevent the crown from thickening.

At the beginning of the fruit ripening period, phosphorus-potassium fertilizers are applied. This type of fertilizer not only affects the size, taste and color of apples, but also gives the tree additional strength to fight diseases and prepare for wintering. Fertilizers are applied not at the root, but in a circle around the trunk with a radius of 2 m.

Important! So, one of the most important points is the correct planting of the apple orchard. For planting, choose varieties that are resistant to powdery mildew. It is important to maintain sufficient distance between rows and between rows for the convenience of treating trees with preparations, pruning branches and harvesting. The distance affects the ventilation mode and prevents the branches from becoming waterlogged.

In the fall, it is dug to a depth of about 30 cm. This promotes the death of bacteria that have developed in the upper layer of soil and additionally enriches the root system with oxygen. Spraying with chemical and biological agents can also be carried out for preventive purposes. The main spraying is carried out during the following growing seasons:

bud maturation;
the beginning of flowering (when the buds soften);
when flowering is over;
the next 2 sprayings are repeated every 14 days.

In early spring, when the snow has just melted and the wood has dried, and in the fall, when the leaves have fallen, preventive spraying is carried out with a 3% solution of iron sulfate to destroy the remaining bacteria and prevent them from overwintering under the bark.

This is how you can easily and simply overcome diseases and pests of apple trees. But this can also be avoided if prevention is carried out in time. And then no powdery mildew will spoil the harvest!

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Folk remedies

A set of folk remedies is also used to protect apple trees. These include:

Pruning diseased branches;
Digging up soil around tree posts;
Application of phosphorus-potassium fertilizing ;
Spraying trees with infusions of insecticidal plants.

Soda

An effective way to combat powdery mildew is baking soda . There are many ways to prepare a solution. There are no clear proportions here.

One of the infusion options is this:

100 gr. Laundry soap is dissolved in ten liters of hot water.
Add two full tablespoons of soda,
Stir well.
Plants are treated with this solution three times every 7 to 10 days.

About powdery sundew

Trees and shrubs often suffer from the disease. The disease progresses with excessive humidity and warm temperatures of +18-25 ̊C. If an apple tree ripens in such conditions, it is less resistant to diseases. When it is hot in the summer, the sundew gradually begins to turn black and transform into a fungus. The disease no longer develops. As the fungus accumulates, it dies; the virus continues to develop in the buds of the apple tree at hot temperatures.

Preparations for powdery mildew on apple trees

Removing diseased branches and other agrotechnical measures do not completely destroy the causative agent of powdery mildew infection.

If a white coating has already appeared on the leaves of the apple tree, treatment is carried out by spraying with fungicides.

Treatment in the spring with these products is carried out:

In the budding phase;
Before flowering when dividing buds;
Immediately after flowering.

Subsequently, the garden is treated several more times throughout the season , as the disease becomes infected.

Basically, they try to spray with fungicides during the development of the purple bud and after flowering.

Periods and purposes of processing.

Most of the chemicals used protect the garden from other pests and diseases. Treating an apple tree with fungicides containing sulfur protects it from mites.

Chemical measures to combat powdery mildew include treating plants with such means as:

Topaz,
Topsin,
copper sulfate,
Colloidal sulfur.

Spray several times with warm solution.

In case of severe infection with powdery mildew, they resort to special treatment with fungicides based on tebuconazole, penconazole and flutriafol.

In the phase of loosening and dividing the bud , the first treatment is carried out, the second - after the tree blossoms, and the subsequent ones - twice after 10-14 days.

Special treatment against powdery mildew.

The garden is treated against powdery mildew with the following chemicals:

Hom, or copper oxychloride . This is a bluish powder. The product is diluted in a small container. The liquid is then diluted to the required volume. Processed in dry, windless weather. The air temperature should not exceed +30 degrees.
Tebuconazole . Systemic fungicide that penetrates the plant. Effectively affects powdery mildew infection and protects plants for three weeks after treatment.
Fitosporin . An environmentally friendly microbiological preparation based on living spores and cells. Trees are treated once every two weeks. Spraying can be done in any weather. In rainy weather, 2-3 hours before the rain starts or 3 hours after.
Cumulus, or colloidal sulfur . Inorganic fungicide in the form of granules. Used to combat fungi. During processing, the air temperature should not exceed 28 degrees. In hot weather, application is ineffective.
Urea . This is a nitrogen fertilizer in the form of granules. To feed trees, dissolve 200 grams in 10 liters of water.
Impact . Fungicide against fungi of low toxicity. It is advisable not to use during flowering plants. The drug protects the plant for up to 30 days . Used both in early spring and late autumn.

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.

Prevention measures

Mandatory application of fertilizers.
A preventive measure in the fight against powdery mildew in the garden is proper planting of the garden. Infection-resistant varieties of apple trees are selected for planting .

Throughout the season, agrotechnical measures are used in the garden , providing for proper tree care:

They try to prevent the crown from becoming too thick;
Maintaining optimal humidity levels in the garden;
Timely destruction of infected shoots;
Destruction of fallen leaves;
Digging up tree trunk circles is carried out.

In conclusion, here are some tips for combating powdery mildew in apple trees :

Carrying out zoning in the garden and selecting tree varieties.
The use of chemical treatments for trees in late autumn after the leaves have fallen.
Maintaining constant humidity in the garden, which makes the trees more resilient.
Spraying trees with chemicals.

How to recognize

Powdery mildew of an apple tree appears mainly simultaneously on leaves and shoots in the form of a powdery white coating. As the disease develops, the green part of the plant becomes deformed, acquiring a lanceolate appearance, the leaf blades become rough, curl and gradually dry out. Infected inflorescences differ:

yellow-green color;
developmental delay;
uneven flowering;
obvious deformation of stamens and petals on flowers.

All this ultimately leads to the flowers drying out and falling off without the formation of ovaries. Infected shoots initially have a white coating, which over time changes to brown-gray, turning into dark. Diseased petioles and leaves become covered with a whitish-gray coating, which becomes reddish as the disease develops. Read about the beneficial properties and secrets of growing lettuce at this link.

On some young ovaries, external mycelium (marsupial fungus) appears, which gradually disappears, but a rusty mesh remains on the skin of the fruit.

What fungus affects the apple tree?

Powdery mildew often affects melons and berry bushes: gooseberries, currants, acacia, hawthorn. Mushrooms Erysiphales, Phyllactinia guttata of the family Erysiphaceae of the class Ascomycetes live only on apple trees. This type of fungus does not affect other crops.

Candida education

The development cycle of fungal infection of apple trees is divided into two stages:

Candida formation (germinated spores), they die only at -20 °C. They appear in spring as white spots. If you look at them under a magnifying glass, mycelium will be visible - the webs of the fungus. A coating similar to flour is ripe mycelial spores.
Marsupial, begins 30 days after the defeat. Black fruiting bodies with branched appendages (dark dots on the leaves) appear.

Powdery mildew is a harmful pest. Spores are carried by the wind, birds, with tools, and on clothing. The pathogen inhibits plant growth and inhibits photosynthesis.

The foliage curls and dries out. Buds and inflorescences are affected. The yield is reduced by up to 80%, the winter hardiness of the tree deteriorates, and part of the crown has to be cut out.

Biology

The pathogen affects apple trees of various varieties. In some cases it appears on the pear, but in this case it does not cause much harm.

During the winter season, the pathogen persists as mycelium in fruit and leaf buds. In some cases, the fungus overwinters in the teleomorph stage.

Conidial sporulation develops in early spring on the affected parts of the plant. The teleomorphic stage of the pathogen is formed somewhat later, in May - July, depending on the climate of the region. The formation of asci and ascospores is completed by the end of the growing season and mature cleistothecia overwinter on the shoots. However, in most cases, cleistothecia are destroyed by spring under the influence of various microorganisms. Therefore, the marsupial stage of the pathogen does not play a special role in the spread of infection.

In the development cycle of the pathogen, two types of infection are observed: primary and secondary. The first appears in early spring, during the phase of swelling and bud opening, and is carried out by the mycelium of the fungus, which has overwintered in the buds. Secondary infection is the result of a new infection, the source of which is conidia. A noticeable manifestation of conidial sporulation appears during the phase of bud separation and reaches its intensity after flowering simultaneously with the growth of young shoots.

The average length of the incubation period of the disease is 4-10 days. Its duration depends on weather conditions and plant resistance.

It has been established that in hot weather, when the plant is weakened, its resistance to powdery mildew also decreases. At this time, an increase in the intensity of sporulation and distribution of conidia is observed. The development of powdery mildew is promoted by sharp fluctuations in humidity.

The most favorable temperature for infection is +18°C-+25°C with simultaneous high saturation of the air with vaporous moisture. In drops of water, as well as when the temperature drops, conidia do not germinate. Under unfavorable conditions, their viability lasts 12-14 days.

At an air temperature of -20°C and below, the mycelium located in the infected kidneys dies. At the same time, the kidneys themselves die, but the supply of infectious agents is also reduced. After harsh winters, primary infection is significantly reduced.