How to combat late blight on tomatoes in a greenhouse?

The fungus Phytophthora infestans has become a real scourge for greenhouse tomato growers. The outbreaks it causes have been compared to a flu epidemic. An entire tomato crop can be lost in just a few days. While the industry produces antifungal products, folk remedies for greenhouse late blight are also popular.

Symptoms of late blight

Brown spots on the first layer of leaves indicate the onset of the disease. The rate of disease development depends on the greenhouse's microclimate (humidity, soil, and air temperature). In the initial stage, the spots are small and undistributed. The undersides of the leaves may also be covered with a white, fluffy coating.

Within a few days, the spots rapidly increase in size, turning brown, and the affected leaves dry up and fall off. The disease continues to progress, infecting the stems, where black spots appear. The fruit then becomes affected. They may develop brown spots while still on the plant, or darken later during storage as they ripen.

The fungus affects all above-ground parts of the tomato bush:

• inflorescences;
• leaves;
• peduncles;
• fruit;
• stem.

Eating fruit infected with fungus can be dangerous due to the spores penetrating the flesh. Tomatoes can have an unpleasant flavor that will ruin the taste of any dish.

Reasons for occurrence

Unpredictable summer weather is the main cause of late blight on tomatoes grown outdoors and in greenhouses. Fungal spores are easily airborne and can migrate from infected potato plants into greenhouses. Nighttime cool spells and excessive soil and air humidity in greenhouses are the main causes of late blight.

Greenhouses without automatic ventilation systems can become covered in condensation during large daily temperature fluctuations and rainy weather. This dampness creates favorable conditions for fungus to thrive.

Excessive humidity can be caused by densely planted tomatoes and failure to remove side shoots and leaves in a timely manner. Densely planted tomatoes don't receive the necessary amount of sunlight, which affects their immune system and makes them more susceptible to fungal diseases.

Imbalanced nitrogen, phosphorus, and potassium levels in fertilizers also weakens the plant's immune system. Excess nitrogen in the soil weakens greenhouse tomatoes, making them more susceptible to infections. Phytophthora infestans spores overwinter in the soil, and outbreaks of late blight are inevitable if the greenhouse soil isn't treated against the fungus at the end of the summer season.

Chemicals against late blight

At the first signs of late blight, chemical treatments are used. To ensure effectiveness, greenhouse tomatoes are treated with different products throughout the season. This prevents the blight from becoming accustomed to the active ingredient.

Many gardeners traditionally use copper sulfate against late blight. Preparing a working solution doesn't take much time. Dissolve 2 tablespoons of the solution in a bucket of water and begin treating the bushes.

Systemic drugs

In the initial stages of the disease (spots on leaves), greenhouse tomatoes are treated with Quadris or Previkur. If the disease has affected leaves and stems, the following products are used:

• Bravo;
• Cuproxate;
• Infinito.

The drug Consento is worth mentioning separately; it protects tomato bushes from late blight and alternaria.

Biological drugs

Biological products are less harmful to the environment. Unlike chemical agents, they are less aggressive. Their mechanism of action involves selecting microorganisms that destroy the Phytophthora infestans fungus. These beneficial microorganisms are activated when they come into contact with water during the preparation of the working solution.

Fitosporin-M deservedly holds the most popular position in the fight and prevention of late blight. It shouldn't be used during the height of an epidemic; it's effective as a preventative measure (for treating seeds, soil, and seedlings) and at the first sign of symptoms.

A concentrated solution prepared from 200 g of paste and 400 ml of chlorine-free water at room temperature has an unlimited shelf life. Here are the methods for using it:

• Dissolve 4 drops of concentrate in a glass of water to obtain a liquid for soaking seeds before planting;
• to soak the roots of seedlings before transplanting, add 15 drops of the concentrated product to 5 liters of water;
• To treat the soil, 2 tablespoons of Fitosporin solution are required per bucket of water;
• A solution for spraying bushes is prepared from 10 liters of water and 3 teaspoons of concentrate.

Gardeners who use Fitosporin-M to prevent late blight note good immunity and stress resistance in tomatoes.

The following biological preparations received good recommendations from gardeners:

• Baktofit;
• Phytophthora;
• Planriz.

These agents are used during the initial period of vegetation to prevent fungal diseases.

Simple folk remedies for protection against fungus

The advantage of folk remedies is that they are completely safe for our health. The fruits can be eaten immediately after processing without any fear.

Garlic infusion

One bucket of the infusion is enough for 20 tomato plants, using 0.5 liters per plant. To prepare, you need ½ teaspoon of potassium permanganate and 1.5 cups of garlic cloves. Chop the cloves, mix with the potassium permanganate, and add 2 liters of water.

The container can be glass or plastic, but it should have a lid. Let the garlic steep for about 30 minutes. Before use, strain the resulting infusion, dilute it with 10 liters of water, and water the plants at the roots.

Copper wire

Gardeners should have copper wire on hand. It can be used to protect tomato plants from late blight. There are two options:

• wrap the stem at the bottom with several turns of thin copper wire;
• Cut a piece (4 cm) of wire and stick it into the base of the stem, bending the ends to the ground.

These methods can only be used on mature bushes with thick stems.

Milk and dairy products

Lactic acid bacteria found in kefir, whey, and milk effectively combat fungus when sprayed on tomatoes. Use 100 ml of milk per liter of water, and dilute the whey 1:1. For enhanced effectiveness, add a few drops of iodine to the milk solution.

It's best to spray tomatoes after 7:00 PM, at sunset. The treatment will need to be repeated every two weeks. Milk and iodine are effective preventatives against fungal diseases. To prevent a late blight outbreak, spray healthy plants. The first treatment is carried out two weeks after transplanting the seedlings into the greenhouse.

Pharmaceutical products

On the pharmacy shelf, you can find medications that not only treat human illnesses but also protect greenhouse tomatoes from infection:

1. Trichopolum – a broad-spectrum antibiotic that effectively combats late blight without harming the plant itself. Dissolve two Trichopolum tablets in 1 liter of water and spray the plants in the greenhouse every 10 days.
2. Furacilin Apply three times per season. The first treatment is during flowering, the second during fruit formation, and the third at the end of summer. One furacilin tablet is needed per liter of water.
3. Calcium chloride It's used once during an epidemic; it stops the disease from progressing and prevents fruit spoilage. It's sold as a 10% solution. Use a 1200 ml bottle per 2 liters of water to prepare a 1% working solution.

Harvesting and storage

Diseased vines may still contain seemingly healthy green tomatoes without brown spots. They should be picked and dipped in warm water (60°C) for 15 seconds. Before ripening, the fruits should be thoroughly dried.

Tomato harvests can be saved by using preserves. Both red and green tomatoes can be used. Heat treatment kills the fungal spores. Eating preserves from tomatoes picked from diseased plants is safe.

Prevention

Saving a dying crop is no easy task. Experienced gardeners prefer to protect their crops from late blight as much as possible with simple preventative measures:

• select varieties (hybrids) with increased resistance to late blight;
• disinfect the soil for seedlings;
• process seeds;
• fertilize seedlings and adult plants during the growing season;
• in autumn and spring, the greenhouse is prepared for the new season;
• control the level of humidity and temperature in the greenhouse;
• compliance with the recommended planting scheme;
• use of drip irrigation and mulch.

Selecting a variety

Phytophthora begins to rage in greenhouses when the summer heat subsides, when it's still hot during the day and cools at night or during prolonged rains. Finding a perfect variety that's 100% resistant to the fungus is impossible. The solution is to choose ultra-early and early varieties that ripen before the fungus outbreak.

Tomatoes showed good resistance:

1. Budenovka. Large-fruited (300 g), mid-season (100-110 days) variety with indeterminate bushes (height 1.5-1.7 m), yield of about 20 kg/m² with a planting pattern of 3 bushes per 1 m².
2. Evpator F1. A hybrid with indeterminate bushes (height 1.8 m), mid-season, medium-sized fruits (100-150 g), red, yield up to 4.5 kg per bush.
3. La-La-Fa F1. A hybrid with determinate bushes (height 1.5 m), mid-season (110-115 days), medium-sized fruits (120-150 g), red with glossy skin and excellent taste, up to 3 kg of fruit are harvested from 1 bush.
4. Andromeda F1. Early hybrid (90-115 days), bushes 0.7 m tall, fruits are red, pink, yellow, weighing from 75 to 125 g, yield from 6 to 10 kg/m².

Seed and soil treatment

The soil, even purchased, must be treated 1-2 weeks before sowing seeds for seedlings:

• warm up for 30 minutes at a temperature of 90 °C;
• spill with potassium permanganate;
• pour with garlic infusion;
• treated with a solution of phytosporin.

Tomato seeds are first calibrated and then treated with potassium permanganate or Fitosporin solutions. Seeds collected from late blight-affected bushes are heat-treated for at least two hours at 50°C.

Greenhouse maintenance

Phytophthora infestans spores remain viable in soil and plant debris for many years, so a thorough cleaning of the greenhouse is necessary at the end of each season:

• remove plant debris and ligatures;
• wash glass (polycarbonate) with laundry soap;
• clean load-bearing structures from dust and dirt, treat wooden parts with a solution of lime and copper sulfate.

About once every 3-4 years, remove the top 5 to 7 cm of soil and take it to a compost heap for regeneration. At the same time, replenish the fertility of the greenhouse soil by adding:

• peat;
• humus;
• compost;
• sand.

Treat greenhouse soil with Karbation; the air temperature during treatment should be above zero (18°C). The product is toxic, so personal protective equipment is required when handling it. Its use is recommended if the greenhouse is infested with late blight.

Care instructions

Protecting tomatoes grown indoors from late blight is much easier than protecting those grown outdoors. A greenhouse equipped with vents makes it easy to control the microclimate (temperature and humidity). Furthermore, gardeners should follow these greenhouse care guidelines:

• follow the recommended planting pattern;
• shape the bushes, removing unnecessary shoots;
• use supports to tie up bushes;
• Mulch the bed with dry grass, peat, black film.

Spores enter the greenhouse through air-driven doors. The source of contamination can be vegetables grown outdoors, such as potatoes, eggplants, and peppers.

Reviews

Elena, Nikolaev

I read a recipe in an old gardening magazine about pine shoots for late blight. I used them to treat my tomatoes four times this summer, and the blight was virtually gone. I made a decoction from freshly picked pine shoots. I first kept them in the refrigerator's vegetable drawer for 10 days, then finely chopped them. I added 2 cups of water to 1 cup of chopped shoots, brought them to a boil, and simmered them over very low heat for about 3 minutes. I cooled the decoction, added 5 cups of water, and sprayed the tomatoes in the greenhouse. I first treated the tomatoes two weeks after transplanting, and the remaining three sprays were done approximately every three weeks.

Sergey, Magnitogorsk

I have successfully managed to combat late blight on tomatoes in a greenhouse. The weather was damp, and the first signs of late blight appeared on the bushes. We didn't hesitate and almost immediately treated them with a solution of iodine and salt, and literally the next day with Fitosporin. We simultaneously stopped watering, pulled out weeds, and picked off the affected leaves. The last tomatoes were harvested in early September, and the late blight was contained.

Tatyana, Moscow region

I treat the trunks of diseased tomato plants with a paste made from water, chalk, and potassium permanganate. I apply it with a small brush and remove the diseased leaves. This method is simple but effective, and it always helps me stop the spread of late blight.