Late blight (late blight) on tomatoes: photos, control methods

What is late blight

Phytophthora are fungus-like microorganisms that reproduce by zoospores. They parasitize vegetable crops of the nightshade family. Late blight of tomatoes is most often caused. Pathogens attack leaves, stems of seedlings and fruits.

Fungal spores tolerate low temperatures well, quickly become active in a humid, warm climate and begin to multiply rapidly.

Preventive treatment of contaminated soil before winter or spring will help avoid the loss of a new crop.

Causes (causative agent) of late blight

The causative agent belongs to phycomycete fungi from the peronosporaceae family. Phytophthora are mycelial organisms, pseudofungi, division oomycetes, parasites of higher plants, capable of a parasitic lifestyle. During ontogenesis, they exhibit pathogenic properties in relation to the plant.

The sources of the phytopathogen are in the soil and in plant debris - this is the primary source of infection. As well as infected garden tools. Spores can also be found on the walls and roof of the greenhouse.

Humid weather, especially during the growing season, favors the persistence and spread of infection. It spreads especially quickly in rainy years, as well as during a sharp change in day and night temperatures, accompanied by heavy dew and fog.

Development factors

Late blight of tomatoes is spreading at lightning speed. The peak of infection occurs at the end of June. The disease is transmitted from a plant infected with spores to healthy seedlings.

It is possible to spread spores by wind from neighboring garden plots that contain diseased vegetable crops of the nightshade family. A summer resident can bring the infection into his greenhouse or garden along with his clothes after contact with infected plants.

The speed at which the fungus spreads is also influenced by the following factors:

  • prolonged rains;
  • violation of agrotechnical conditions for growing tomatoes;
  • weeds that activate fungal growth;
  • density of seedlings.

High humidity, 20-25 degrees Celsius are optimal conditions for the growth of the fungus. Therefore, rainy summers often cause outbreaks of late blight.

Failure to observe crop rotation and infrequent weeding of vegetable crops are the reasons for the appearance of the disease on a personal plot. Therefore, experienced gardeners do not recommend planting nightshades for longer than 4-5 years in the same place.

You should also avoid such things as potatoes and tomatoes. Fungal spores found in infected tubers can spread to tomatoes and vice versa.

The activation of late blight is primarily facilitated by weeds such as woodlice, quinoa, and sow thistle. Their appearance in the garden must be carefully monitored and promptly destroyed.

Tomato bushes planted close to each other create favorable conditions for the development of pathogenic microorganisms (lack of light, high humidity). Therefore, plants should be planted at a distance of at least 0.5 meters from each other.

The mechanism of spread of late blight

The body of the fungus itself is located in the intercellular space. Under favorable conditions during the growing season, zoosporangia germinate in drops of moisture, forming zoospores, or an infectious sprout, which penetrates plant tissue. Depending on external conditions (temperature and humidity), the incubation period can be from 6 to 10 days. The spread of the disease is also associated with the formation of reproductive structures – oospores – in the late blight pathogen.

What does late blight look like?

It is quite difficult to recognize a fungal disease at the initial stage. Therefore, in order not to miss the disease, you should examine the tomato bushes from time to time to identify the first signs of infection.

In closed ground with high humidity, the disease initially manifests itself in the form of a white fluffy coating on the back side of the leaf blade. These symptoms are a signal to treat tomatoes against late blight in the greenhouse.

In open ground, the leaves of seedlings may turn light green in places. Also locally, leaf blades and stems begin to darken, dry out and curl. The manifestation of the disease on seedlings and tomatoes can be clearly seen in the photos below.

Diseased fruits are covered with gray, brown, lilac-brown or black spots. A tomato affected by late blight becomes very hard to the touch.

The location of the rot is always dry, which makes it possible to differentiate late blight from other types of fungi and bacteria.

Fruits that seem healthy at first glance may already be affected by the fungus if there are infected tomatoes on the branches nearby. Manifestations of late blight may occur later, after harvest.

With secondary infection, the fruits quickly and completely rot, emitting a specific putrefactive odor.


Manifestations of late blight

Late blight on tomatoes can be diagnosed by the following visible manifestations:

  1. A white coating is noticeable on the foliage
  2. The lower part of the leaves darkens and becomes covered with brown spots. Then the entire leaf blade turns black and dries out. The plant sheds its leaves
  3. The stems of the plant darken and also dry out over time.
  4. Brown spots form on the fruits, the tomatoes mummify or begin to rot. Brown stains appear on harvested unripe tomatoes after 1–2 days of storage.

A characteristic symptom of fungal infection is that the spots can be gray or brown and, as a rule, have an irregular shape. Tomato fruits become diseased through the stalk, so they may look healthy in appearance. Late blight spots appear even at the stage of tomato ripening.

Blackening of fruits is a symptom not only of late blight, but also the result of excessive watering, dry soil or excess fertilizer. Late blight can easily be confused with other diseases on tomatoes - their distinctive features are collected in the table.

Folk remedies

One of the safer methods for dealing with late blight on tomatoes is considered to be the use of folk remedies by gardeners. Most often at home, solutions prepared from:

  • iodine;
  • brilliant greens;
  • whey;
  • kefir;

Fungi are afraid of an acidic environment, so summer residents often use kefir or whey to combat late blight.

2 liters of any fermented milk product is mixed with 8-10 liters of water. Add 20-30 drops of iodine or brilliant green to the solution.

Late blight on tomatoes in a greenhouse is no less common than in open ground. To combat its spores, you can use the above method with fermented milk products. It is equally effective for both open and protected ground.

Fungi are afraid of iodine vapor, so gardeners often use this product to destroy pathogenic microorganisms in greenhouses and greenhouses. In order to protect the plants, you will need several bottles of medicinal liquid and tea bags (you can use already used ones).

Infusion bags are immersed in iodine. After the excess liquid has drained from the glass, they are hung throughout the greenhouse. For 1 sq. m. you will need 1 iodized sachet.

After 2 weeks, the manipulations are carried out again. This procedure ensures the disinfection of greenhouses and prevents relapses of the disease.


The name of the fungus “phytophthora” translated means “destroying plants.” The disease can affect an entire plant in just 3 days, and the entire planting on the site in 1.5–2 weeks. In the case of tomatoes, the disease is very dangerous because it affects the plant during the period of fruit ripening, when it is impossible to fight it.

Phytophthora may contain:

  • on seeds
  • in the ground
  • on gardening tools
  • plant remains
  • in the material from which the greenhouse or greenhouse is made

Most often, manifestations of late blight become noticeable on tomatoes in late July - early August. This period is characterized by hot days and cold nights.

Late blight on leaves

The infection is transmitted mainly from potatoes. Fungal spores overwinter in the soil of a potato field or in tubers.

Favorable conditions for the active life of a unicellular microorganism:

  • high air humidity
  • low temperature
  • soil with high lime content
  • unthinned planting where fresh air does not circulate well
  • sudden temperature changes
  • morning dew and frequent fogs
  • weakened plants, in the care of which the rules of agricultural technology are not followed

General recommendations for treatment against late blight

It is important to know not only how to save tomatoes from late blight, but also how not to harm the plants and your health. Therefore, before processing, a number of recommendations should be followed:

  • Spraying should be carried out in calm weather to ensure uniform distribution of substances.
  • Plants should be treated before the first ovary. All treatments must be completed 20 days before harvest.
  • The frequency of treatments depends on the condition of the plants. It is advisable to repeat the procedure after 2 weeks, even if the tomatoes look healthy.
  • Chemical treatment is carried out no more than 2 times, then you can use Bordeaux mixture or copper chloride preparation.

To prevent resistance, the use of different groups of fungicides should be alternated.

Late blight of Saintpaulia (violets)

Saintpaulias usually suffer from late blight when there is excess moisture in the air and rare ventilation of the room. The disease can be determined by the following signs: weak plant growth, loss of turgor (elasticity) in the leaves, discoloration of the leaf blades. Further development of the disease leads to the death of plants.

It is extremely difficult to rid Saintpaulia of late blight. It is better to immediately isolate the diseased plant from healthy ones.

Basic measures to prevent Saintpaulia late blight:

  • use only proven soil and pots;
  • When preparing the soil yourself, the soil must be sterilized before planting.

Do not forget that any disease, including late blight, is much easier to prevent than to cure. To do this, it is necessary to observe crop rotation, apply phosphorus and potassium fertilizers, not thicken the plantings and promptly remove plant parts affected by late blight, preventing the spread of the disease. Follow these simple rules and may your harvest be healthy!

How to prevent relapses of late blight

The following recommendations will help you avoid re-infection with a fungal disease:

  • observe crop rotation (change plots every 4-5 years);
  • avoid crowding of plants;
  • tear off the lower leaves of tomatoes before the first ovary for better ventilation and more light flow;
  • do not create a compost heap in the garden;
  • remove nightshade tops from the site and destroy them;
  • water the plants strictly at the roots;
  • when growing indoors, ventilate the greenhouse;
  • Do not use fresh manure as fertilizer.

After planting in a permanent place, it is recommended to treat with biological fungicides for preventive purposes. Fitosporin M for tomatoes has proven itself to be such a product.


Spraying tomatoes

It is better to prevent a disease than to subsequently spend a lot of time and effort on its treatment, especially since preventive measures give good results.

If chemicals are used for prevention, then the first treatment must be carried out at the stage of ovary formation, and then it is carried out every ten days. Another option to prevent infection is to water the tomatoes every other time with water with the addition of fungicides.

After fruits appear on the plant, no chemicals are used; gardeners switch to means of protection and prevention that are safe for humans. So, it is recommended to use:

  1. Rock salt in solution with water in a ratio of 100 g per 5 liters. Even green fruits are sprayed with this brine: the salt forms an invisible protective film on them
  2. Weekly you can spray with a solution of fermented kefir or fermented baked milk (1 liter of dairy product per 10 liters of clean water)
  3. Spraying with infusion of garlic, nettle, onion, bird cherry leaves

Green tomatoes picked for ripening can be subjected to heat treatment as a preventive measure: heated for 2–3 minutes at a temperature of 60 degrees. Fruits affected by the fungus should not be eaten.

Excess nitrogen in the soil can provoke the appearance of fungus.

How to reduce the risk of infection

Tomatoes in the garden

Tips on how to reduce the likelihood of tomatoes becoming infected with late blight:

  1. Before planting, planting material must be treated or treated with fungicides.
  2. Soil with excess lime content is fertilized with peat
  3. When planting tomato seedlings, calcined river sand is placed at the bottom of each hole.
  4. It is worth adhering to the basic principles of crop rotation: bad predecessors for planting tomatoes on the plot are melon, carrots, cauliflower and beets
  5. Thin out the planting in a timely manner so that air circulates around each plant.
  6. The lower leaves on the stems of tomatoes should be removed, and the soil under the planting should be mulched
  7. Tomatoes should be watered early in the morning or late in the evening, strictly under the stem, to prevent splashing and moisture getting on the leaves.
  8. It is necessary to loosen the rows
  9. Watering should be reduced when air humidity is high.
  10. Fertilize tomatoes with complex mineral mixtures, the application of which strengthens the plant’s immunity
  11. Do not plant different members of the Solanaceae family nearby. If this is not possible, then plant bush plants between the beds for protection: peas, corn, beans
  12. You can replant tomatoes in the same place only after 4–5 years

The best choice for combined planting with tomatoes would be garlic, parsley, cabbage, basil, spinach, and carrots. You need to avoid the proximity of tomatoes with other nightshades, fennel and beets.

Varieties resistant to late blight

There are no completely immune varieties. Hybrids exhibit relative stability:

  • Lark;
  • La-La-Fa;
  • Union 8 and many others.

Resistant varieties are also infected with late blight, but later than others. In addition, they are able to recover from the disease if infected leaves are removed from them and sprayed with a systemic preparation.

Possible mistakes when fighting late blight

When preventing and combating the disease, there are many mistakes that only make the situation worse. These include the following:

  • Watering a sick plant. This is not only pointless, but also harmful: after all, it is already infected and can infect other plants;
  • "Rain" method of irrigation. Tomatoes should be watered only at the root, excluding the above-ground part;
  • Excess nitrogen in the soil if you overfeed the plant. The best fertilizers for it are potassium and phosphorus;
  • Using several methods at once. Choose one and then alternate after a few days.

Ash solution for treating tomatoes from late blight

Ash is an excellent natural septic tank that disinfects and deoxidizes the soil. It is impossible not to note the mineral benefits of ash - the content of potassium, phosphorus, calcium and sodium. The main thing is that the soot is obtained from natural forests.

Only then will it be suitable for preparing an ash solution:

  • 1 glass of ash is poured into 1 liter of water;
  • The solution is stirred and infused for 24 hours;
  • Next, the resulting solution (without sediment) is diluted with 5 liters of warm purified water.

The advantage of the ash solution is its versatility - the treatment can be foliar or root. To enhance the effect, ash can be mixed with a 5% soap solution in a 1:1 ratio.

Copper wire for treating late blight on tomatoes

Despite the popularity of various solutions, vegetable growers are always looking for new means to combat fungal diseases.

It turns out that cutting copper wire into the trunk of a tomato helps to harden the vegetable and destroy fungal spores using copper (it is not without reason that copper sulfate is one of the effective remedies for late blight).

The thematic procedure goes as follows:

  • Copper wire with a diameter of no more than 1 mm is cleaned and cut into 4-5 cm pieces;
  • One end of each segment is bent into a hook so that the wire can be easily removed from the barrel if necessary;
  • The sharp end of a copper piece cuts into the trunk of a 100-day-old seedling or adult plant at a 10-centimeter height from the ground.

From the moment of “implantation” the tomato does not need such a chemical element as copper. The need to use drugs against late blight is reduced by 2-4 times. In addition, copper wire protects against other fungal spores.

Why is late blight dangerous?

Late blight is scary because the disease is invisible at the first stage , especially since the spores are very tenacious. They can remain dormant for a long time on the greenhouse structure, in the ground, and even on plant seeds. Spots appear on the tomatoes themselves, which gradually spread to the entire fruit, while it becomes deformed and begins to rot.

During decay, a sharply unpleasant odor appears. If the disease spreads, you can lose up to 70% of the tomato harvest.

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