How and what to treat the greenhouse in the spring from late blight

How to detect a disease

It is quite simple to determine the infection of plants with late blight. This disease mainly affects nightshade crops, so you should look for signs of its manifestation when examining tomatoes, eggplants, peppers, potatoes and physalis planted in a greenhouse. However, strawberries can also be attacked by a pest. Late blight begins with the appearance of dark gray-brown spots on the leaves of plants. At high air humidity, a fluffy white coating forms on the back of the leaf plates. Then dark spots appear on the stems.

Scheme of the development cycle of late blight

The affected leaves dry up, the peduncles also dry up and the inflorescences turn black. The fruits of diseased plants are covered with brown-brown spots that are hard to the touch, which grow along the surface and in depth, and then soften and begin to rot. On the tubers of potatoes infected with late blight, grayish areas with wrinkled skin appear, under which, when cut, one can see the "tongues" of reddish pathogen-affected tissue spreading inward. No wonder late blight is also known as brown rot or potato rot. The tubers affected by it, at first glance, and ripening green fruits become inedible even after a time after harvest, and diseased plants often die. In the middle of the 19th century, an outbreak of this disease in Ireland affected almost the entire potato crop, causing famine and massive immigration in the country.

What causes late blight

The causative agent of the disease is oomycetes, which have long been listed among fungi, and today they stand out as a separate group of special mycelial organisms. Late blight spends most of the time in the form of spores and only when favorable conditions begin to actively multiply. The most "favorite" late blight combination of high humidity and air heated to +25 - +30 ° C often occurs in the greenhouse. Under these conditions, spores can germinate and infect the plant in just an hour. A sharp fluctuation in temperature throughout the day, when a rather hot day is replaced by a cool night, causes abundant dew to fall out and the formation of fog. This is a favorable period for the activity of phytophthora.

Unlike polycarbonate structures, greenhouses with a film cover are more susceptible to disease outbreaks, since abundant condensation forms on the inside of the film when temperature drops. Phytophthora spores are washed off when irrigated into the soil, where they can survive even severe frosts. So the disease can appear in the greenhouse along with the soil.Spores persist for a long time and in the remains of infected plants, so they should be removed without fail and burned. Even improperly processed inventory can become a carrier of the disease.... Over long distances, tens of kilometers, spores are carried by the wind. So the pest can get into the greenhouse, which is located quite far from the source of the disease. Late blight can also penetrate along with the seedlings purchased on the market, since a visually beautiful-looking plant does not guarantee that it is not a carrier of the disease during the incubation period.

We treat plants

To date, there is no such remedy, the use of which would completely get rid of phytophthora. Since it is in a state of spores for most of its life cycle, neither chemical nor biological preparations finally destroy it. However, their use together with some other methods leads to a significant decrease in the number of spores and inhibition of the activity of the pest. That is, the fight against late blight is to a greater extent not in the treatment of diseased plants, but in the prevention of infection. Since spores can be almost everywhere, in the spring the greenhouse should be fumigated with special sulfur smoke bombs. Also, the walls and ceiling can be treated with such microbiological preparations as Fitosporin-M, Shining or Baikal EM.

Unlike chemical fungicides, these agents destroy pests due to the colonies of living microorganisms included in their composition, for which phytophthora spores are food. It is necessary to fight the disease if it is found in the greenhouse by removing and burning affected leaves and other parts of the plants. After that, foliar spraying of all nightshade crops with the mentioned microbiological preparations or fungicides containing copper should be carried out: copper sulfate, copper oxychloride, Bordeaux liquid, Barrier, Oxyhom, Ordan and others. These substances are also used for regular preventive treatment of plants. Seedlings should be thoroughly sprayed before planting in the greenhouse soil, and then after two weeks do it again.

It should be remembered that after using chemicals, vegetables can be eaten no earlier than three weeks after the last spraying. Among folk remedies, the treatment of nightshades planted in a greenhouse with garlic infusion is popular, which is prepared by adding 40 grams of chopped garlic to a bucket of water and infusing it throughout the day. The plant is sprayed in this case weekly. Since at an air temperature above +30 ° C, the development of the pest practically stops, then you can fight it periodically by arranging a steam room, closing all doors and windows for several hours on a sunny day, and then ventilate the greenhouse well. Since excess moisture contributes to the active reproduction of phytophthora, the plants should be watered only at the root. But it is highly undesirable to use underground watering or mulch the soil with polyethylene in a greenhouse.

Unlike open ground, in a greenhouse it is rarely possible to avoid when planting plants close to each other. This contributes to the rapid infection with late blight of all nightshade crops. Therefore, if, due to the size of the greenhouse, thickened planting schemes have to be used, then it is necessary to carry out the formation of plants in one stem. Since the disease often affects old leaves, the protective treatment consists in removing them during regular inspection of the plantings.

A good way to protect plants from phytophthora is a nightshade crop rotation, in which in the spring they are planted in the same greenhouse with an interval of three to four years.Also, a rather effective method to avoid infection will be the cultivation of hybrids that are especially resistant to infection or early ripening varieties, the harvest of which ripens before the beginning of the period of activity of the pest. Seeds for planting in a greenhouse should be purchased from those producers who pre-process them for pests and diseases.

How to process the soil

Since late blight in the greenhouse is stored mainly in the soil, the main fight against it is carried out on this "battlefield". The main thing in this case is to choose a way to treat the soil in such a way as to most effectively suppress the source of infection, that is, to destroy as many spores as possible.

The lack of copper salts in the soil contributes to the long-term preservation of pathogen spores, therefore, if infected plants are found in the fall, after harvesting, the top layer of soil about 5 centimeters thick is removed from the greenhouse, and in the spring the soil should be treated with a copper-containing fungicide or microbiological preparation.

The introduction of chemicals into the soil (Ordan, Oksikhom, Bordeaux liquid, etc.) requires refraining from using vegetables for food for a month after their use, but microbiological preparations (Fitosporin-M, Mikosan, Shining, Baikal EM, etc. .) you can cultivate the soil at any time. You should not use them only during the flowering period, when it can harm bees flying into the greenhouse for nectar.

Video "Handling greenhouses with your own hands"

If you want to know how and with what means you should treat greenhouses from late blight, then watch this video.