Causes and methods of treatment for black plaque on cucumber leaves in a greenhouse

Cucumbers are one of the most favorite crops for gardeners. Achievements of modern breeding make it possible to grow this wonderful vegetable not only in garden plots, but even on window sills and balconies. However, this is a southern plant that loves warmth and sun, therefore in northern latitudes it is often grown indoors.

Greenhouse cucumbers are subject to the same diseases, as all melons and gourds. In the article we will talk about black plaque on cucumber leaves in a greenhouse, the reasons for its development and how to deal with it.

Reasons for the appearance of black plaque

In a greenhouse, it is easy to create optimal conditions for growing a cucumber crop. To get a good harvest, it is enough to observe the temperature regime, ventilate the room, monitor the humidity and illumination.

However, even in such conditions, plants are susceptible to disease. Their development is provoked by the violation of agricultural standards, the use of small greenhouses and greenhouses, the cultivation of crops in one structure that require different care conditions.

A common problem when growing cucumbers in a greenhouse is black bloom on the leaves and fruits. There are a number of reasons for the appearance of the disease.

Causes and methods of treatment for black plaque on cucumber leaves in a greenhouse

Black leaf mold

This is a disease caused by the development of a harmful fungus. It affects not only the leaves, but also the stems of the cucumber bush.

The development of the disease begins with the appearance of small light brown spots on the leaves, similar to burns. After a while, the specks merge into one whole, forming large blots of dead tissue.

First of all, the fungus attacks old leaves. If the infection is not dealt with, it passes on to the stems, petioles and greens, which dry up, become covered with a black bloom.

The impetus for the development of the disease is a sharp change in day and night temperatures in a greenhouse or greenhouse. Blinding, pinching and pinching injuries to cucumber bushes contribute to the development and spread of the fungus.

If the pathogen is not dealt with, it will spread to all crops nearby. The fungus is resistant to temperature extremes, hibernates on plant debris, in the soil, on structures of greenhouses and greenhouses. Seed material can also be a source of disease.

Sooty fungus

Sooty fungus (rabble) is another fungal disease that affects greenhouse plantings. The infection is most harmful to young vegetables.

The mushroom hibernates in the soil, on plant remains. With the onset of warmth, it activates and affects the culture. They recognize the ailment by small black spots on foliage and fruits, resembling soot. If you do not take action, then the fungus affects the entire bush, covering the leaves, stems and fruits with a black coating.

The reason for the development of sooty fungus is pestssuch as aphids and whiteflies. Parasites cover the tops with sweet secretions, on which the infection multiplies.

Leaf spot

Leaf spot is a common disease that affects not only cucumber, but also many other crops. The infection is caused by fungi (mycoses), bacteria (bacteriosis) or viruses. Nematodes are another cause of foliage staining.

The variety of causative agents of the disease complicates the fight against it. Progressive spotting is most dangerous for young plants.The disease leads to disruption of photosynthesis, drying and leaf fall, depletion of the culture and its death.


A fungus of this type infects the leaves and stems of cucumbers, leads to wilting of greenery and lashes of the plant, and subsequently to the complete death of the bush.

The pathogen enters the vegetable from the soil. First, small roots are affected, then larger ones. Through the roots through the vessels, the fungus enters the whips and leaves. Gradually, the stem becomes thinner, becomes brown. Soon the entire bush withers and perishes.

A frequent impetus to the development of the disease is excessive watering. Recognizing Fusarium is easy: just look at the cross-section of a cucumber stem (as in the photo). In a diseased plant, the core of the stem is brown.

Causes and methods of treatment for black plaque on cucumber leaves in a greenhouse

Methods of dealing with black plaque

What if a problem is found? When the first dark spots appear, they immediately take measures to combat the disease. If the cause of the infection is not eliminated, it will spread first to the entire bush, and then to neighboring plants.

First of all, all affected leaves and lashes of the culture are cut and destroyed. After that, the bushes are treated with special agents to destroy the causative agent of the disease.


Chemicals have shown the greatest effectiveness in the fight against fungal diseases. When the first signs of damage appear, cucumber bushes are sprayed with a 0.7-1.0% solution of Bordeaux mixture or a 0.5% suspension of copper oxychloride. The treatment is repeated after 8-10 days.

The Topaz fungicide has proven itself well. It is a chemical agent that has a systemic effect. The main substance - penconazole - inhibits the activity of phytopathogenic fungi during the breeding season. Spraying is carried out in accordance with the instructions. The drug is used before and after flowering.

Fungal diseases are capable of developing resistance and immunity to fungicides. Therefore, the chemicals used alternate.

Biological methods

If you are concerned about using chemicals on your site, there is a good alternative - biofungicides. They are used to treat plants and prevent diseases. The products are environmentally safe, harmless to humans, animals, birds and insects.

Biofungicides include drugs such as Fitosporin, Pseudobacterin, Gamair.


Fitosporin is a well-known and widely used elicitor that enhances the plant's own defense and immunity. The drug is available in the form of a paste, powder, solution.

Causes and methods of treatment for black plaque on cucumber leaves in a greenhouseThe paste is effective in the processing of soil and humus, it is used to protect root crops when laying for winter storage. Powder and solution are used for plant treatment and prevention.

The agent becomes active when the temperature rises to +7 ° C. It is advisable to use the drug for cultivating land from early spring.


Pseudobacterin - a biofungicide used to fight fungal and bacterial diseases... It has a pronounced growth-stimulating effect, without reducing the quality of vegetables and fruits.

The product is compatible with other pesticides and agrochemicals.


Gamair is a microbiological fungicide that is effective against a range of fungal diseases such as root rot, powdery mildew, downy mildew, black and gray rot, rust. Gamair is available in the form of water-soluble tablets. It is used for both treatment and prophylactic purposes.

Traditional methods

When the first signs of black plaque appear on the leaves, it is advisable to start treatment with safe folk methods.

Among the variety of such methods of combating fungal diseases, the replacement method is considered the most effective. Its essence lies in the displacement of the fungus by more active beneficial microorganisms. These useful substitutes are found in natural dairy products - milk and whey.

To prepare the solution, the product is mixed with water in a ratio of 1:10 and the cucumber bushes are sprayed with a spray bottle. Beneficial microorganisms destroy the harmful fungus on the leaves and lashes of the culture, thereby stopping the development of the disease. Not only the sick, but all healthy plants in the greenhouse are sprayed.

At the initial stages of the development of the infection, spraying with infusions of herbs (nettle, tansy, wormwood) helps.

Important! Spraying is carried out early in the morning or in the evening. Sunlight on wet leaves causes burns.

Treatment of bushes with a mixture of ash and laundry soap diluted in water is effective, as well as spraying with a solution of soda and soap.

Preventive measures

Any disease, including that of a vegetable crop, is easier to prevent than to cure. Therefore, special attention is paid to the prevention of diseases when growing plants.

Important! Excessive thickening of plantings is one of the main causes of the onset and development of fungal diseases.

Prevention measures include:

  1. Treatment of seed and soil before planting with a solution of biofungicides. If in the previous season there were a lot of fungal diseases on the site, then the soil is treated 3-4 times.
  2. Compliance with agrotechnical rules for growing vegetables. When planting seedlings, they maintain the prescribed distance between the bushes. Weak, sick, damaged leaves, shoots are promptly removed.
  3. Autumn cleaning of the garden area from fallen leaves and plant debris, creating a fertile soil for the development of fungus and mold.
  4. Timely application of not only nitrogen, but also phosphorus-potassium fertilizers. An excess of nitrogenous fertilizers in the soil contributes to the occurrence of diseases.

Read also:

What are red cucumbers (Tladianta Doubtful), what are they good for.

How to pinch cucumbers correctly - when and why it is needed.

How to get rid of whitefly in a greenhouse on cucumbers.

Recommendations of experienced gardeners

Causes and methods of treatment for black plaque on cucumber leaves in a greenhouse

By itself, the black bloom on cucumber leaves does not do much harm to the culture. However, its appearance indicates the contamination of the plantings or the wrong growing conditions.

Fungal diseases arise and actively spread on weakened plants infected with pests. Pests such as aphids, thrips, whiteflies leave sticky, sugary secretions on which the fungus grows.

Advice! At the first sign of pests, take action to eliminate them.

The fungus loves high humidity in the soil and air. Therefore, when growing cucumbers in a greenhouse, it is important to maintain optimal air humidity in the room and to prevent waterlogging of the soil.

Dense plantings and excessive growth of greenery impede the flow of air to the bushes and contribute to the emergence and spread of fungal diseases.

Important! The application of potash fertilizers to the soil in spring and autumn protects plants from infections.


Black bloom on cucumber leaves interferes with the natural process of photosynthesis and therefore plant development and fruit growth. The reason for the appearance of plaque lies in fungal diseases. Controlling pests such as aphids, whiteflies, and controlling soil and air moisture will prevent the development of infections and black plaque on leaves and stems.

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