This fungal disease is the main scourge of tomatoes, which affects them in the greenhouse and in the open field. The infection persists for a long time in the soil, especially if there is an insufficient presence of copper salts in it.
Especially often outbreaks of this disease occur in protected ground under a film shelter, because due to sudden temperature fluctuations during the day and at night, abundant condensation forms on the inner side of the film, and moisture accumulates on the plants.
Usually, the first signs of this disease first appear on the leaves of potatoes, and on tomatoes they can only be noticed after 8-10 days. The fact is that the causative agent of the disease is mainly stored on potato tubers, and at the first favorable conditions, the disease manifests itself on this crop, and then on tomatoes.
This disease can destroy the entire crop of fruits in 1-2 weeks. Therefore, the closer you plant the tomatoes to the potatoes, the faster and stronger this happens. In this case, late varieties of tomatoes and plants that were planted very late are especially affected.
All aerial parts of the plant are affected, but especially green fruits. First, small brown spots are formed on the upper side of plant leaves, scattered mainly along the edge of the leaf blade. At high humidity, a whitish bloom appears on the underside of the leaves. The leaves turn yellow and dry out.
Then the disease spreads to fruits, mostly green. Vague hard spots of various shapes and colors appear on the fruits - brown, green, vague. In this case, the rot zone rapidly increases in size and penetrates deep into the fruit.
But late blight causes special damage when ripening and storing green fruits, because the affected fruits are not suitable for food, since they turn into a continuous mucous mass.
The disease develops more strongly with strong fluctuations in day and night temperatures (cold nights and relatively warm days), in frequent rains, prolonged fogs, abundant dew, with thickened planting of plants. All this is facilitated by poor ventilation of greenhouses, high air humidity in them (over 80%), close planting of potatoes. In dry and hot weather, the development of the disease is significantly slowed down.
It is quite difficult to fight late blight in a garden or summer cottage, since the plantings of tomatoes and potatoes are practically close to each other. At the same time, every day we visit the tomato greenhouse and the potato plot countless times, transferring the infection from one place to another. That is why the fight against this disease should be, first of all, a systemic preventive, and only then a protective one.
First of all, this is the maximum possible spatial isolation of tomato and potato plantings from each other and the obligatory burning of all their plant residues in autumn. It is advisable to have 2 greenhouses on the site and every year to alternate planting tomatoes and cucumbers in them.
Disinfection of greenhouses in autumn with sulfur dioxide (100 g of sulfur per 1 cubic meter of greenhouse) or a solution of copper sulfate is mandatory. And if in the summer in this greenhouse the tomatoes were sick with late blight, then in the fall it is imperative to remove the top layer of soil 4-5 cm thick from the greenhouse.
Of great importance in the fight against late blight is the quality of seeds, especially of our own "production". It is best to sow tomato seeds 2-3 years ago, since during this period they are completely free from viral and other diseases.
It is very important to select and grow in a greenhouse, especially in the open field, of relatively disease-tolerant hybrids or early ripening varieties that have time to "give" the main harvest of fruits before the mass disease of plants with late blight. And in the trade there is now an abundance of such varieties. At the same time, it is better not to pursue cheapness and purchase seeds that have already been treated by the manufacturer from pests and diseases.
This is a very important event in our capricious weather and should not be neglected even by the most experienced "tomato". Do not confuse your tiny greenhouse with primitive ventilation with modern large-scale greenhouses, many of which even use electronics to regulate the climate inside the greenhouse.
You cannot thicken the plantings, and when using thickened planting schemes in greenhouses, form plants in only one stem. In this case, it is very important to remove old leaves on plants - in the open field up to the first brush, and in the greenhouse when growing tall tomatoes, remove old leaves up to the second and even up to the third brush. It should not be forgotten that these old leaves are primarily infected with infection.
Tomatoes (from planting to harvesting) must be fed with phosphorus-potassium fertilizers, while not forgetting about fertilizers containing copper (the easiest way is copper sulfate). A good prophylaxis against late blight is systematic, every 12-15 days, watering the plants over the leaves with a solution of "Fitosporin".
On the correct agricultural technology of tomatoes and the prevention of late blight - in the article Growing tomatoes in the garden.
An important element of the prevention of this disease is the watering of plants, or rather, not the watering itself, but the correctness of their implementation. They should be sparse, but abundant, in order to wet the soil well to the full depth of the roots. They need to be carried out only in the first half of the day, without soaking the leaves with water. Then you need to arrange the maximum possible ventilation (do not forget that tomatoes like drafts) so that the soil dries up by evening - this is a prerequisite for the prevention of diseases.
Let's be frank and try to remember how often we break this rule by watering tomatoes in the evening, and even over the leaves.
And the ideal conditions for watering tomatoes in a greenhouse and preventing diseases is underground watering of plants and continuous mulching of the soil with plastic wrap.
And now let's briefly consider the measures to eradicate this disease and, above all, the treatment of plants with an old, but very effective Bordeaux liquid or other more modern preparations.
If in your greenhouse late blight has a permanent "registration", then tomato seedlings for prevention purposes must already be sprayed with 0.5% Bordeaux liquid before planting it in the greenhouse. After 15 days, the treatment must be repeated, but with 1% Bordeaux liquid.
If there are signs of a disease in the greenhouse, then the treatment must be repeated every 15 days until the browning of the fruits begins. You can eat such fruits a week after the last treatment.
Approximately the same result is obtained by treating tomatoes with copper chloride. Its solution is easier and faster to prepare than Bordeaux liquid, but it is more poisonous. Numerous modern means of protection are also effective - "Barrier", "Barrier", "Oxyhom", "Hom", etc.
But in all these cases, the fruits can be eaten only 3 weeks after the last treatment with this drug. During this "forbidden" time, it is advisable to spray the plants with an infusion of garlic (1 glass of garlic pulp per 10 liters of water).
An important detail if you weren't paying attention. All these drugs must be started as early as possible, while the causative agent of the disease has not penetrated into the fetal tissue.
It is very important to harvest the fruits until they are fully ripe, i.e. at the stage of green ripening (green, but reaching normal size) or blange (starting to turn slightly pink) fruits. If there is a disease in the greenhouse, complete harvesting of the fruits must be completed by the end of August.
In order to prevent already removed fruits, you can lower the fruits for 10 minutes in a warm solution of potassium permanganate (pink) with a temperature of 40 degrees. It is impossible to make the solution too dark, because you can burn the skin of the fruit.Then rinse them with water, wipe dry, isolate them from each other by wrapping each fruit in paper, and put them in storage.
Well, if you are not at all sure that the tomatoes you have removed are healthy, then you can try to save them. To do this, dip the tomatoes for 1-1.5 minutes in hot water with a temperature of 58-60 ° C (but not higher, otherwise you will just "cook" the tomatoes), then in cold water, and then wipe them dry and ripen them at a temperature of 25 degrees ... But at the same time, keep in mind that after such a heat treatment, the fruits very often lose their elasticity and are not stored for a long time.