Phytophthora, which has crossed the threshold of harmfulness, is a real scourge of gardeners. The disease is especially dangerous in the confined space of greenhouses and greenhouses. In 2-3 days, under optimal conditions for the spread of the disease, up to 70% of the tomato crop dies. Late blight is spread by zoospores that overwinter on the remains of leaves, stems of various plants, in the soil, on fixtures and other construction and ancillary parts of greenhouses and near the greenhouse space. They retain their viability for 3–5 years and are able to survive 20-30 degree frosts in the soil. Therefore, thorough annual disinfection of the greenhouse is extremely necessary, which will destroy late blight spores and prevent the appearance of the disease in the new season.
Phytophthora in a greenhouse - methods of prevention and control. © Suzanne Arruda
Preparing the greenhouse for processing
A feature of many fungal diseases is the ability to persist for a long time in the soil, on structural parts of the greenhouse, in torn grass and tops. Therefore, greenhouse treatment includes several stages, excluding one of which it will not be possible to completely get rid of late blight.
All tools and equipment must be removed from the greenhouse and must be processed
The preparatory stage involves cleaning the greenhouse:
- Remove all tools and auxiliary equipment from the greenhouse: pegs, ropes, strings for tying, trellises, supports, etc.
- Uproot the tops and plant remains. If they have been infected with late blight, you will need to burn them to kill the spores. It is worth burning them in any case so that no pests or viruses remain in them.
- Pull out all the weeds. Burn.
Advice! All tools and equipment must be treated with copper sulfate to destroy the fungal spores that are probably present on them.
After cleaning the greenhouse, it is necessary to disinfect the soil.
What is late blight
Late blight is a dangerous fungal disease of various crops, which is caused by a protist of the oomycete division. Translated from Latin, the word Phytophthora means “plant destroyer.” And it is precisely combined with the action of this stimulant.
For reference!
Representatives of the Solanaceae category of flora suffer most from late blight. This includes tomatoes, potatoes, strawberries, buckwheat and other crops.
Reproduction of the fungal protist occurs due to zoospores that live on stems, last year's tubers, and even in the soil. And as soon as the conditions necessary for development arise, late blight wakes up and immediately spreads throughout the plants.
Just a greenhouse, that is, a damp and warm environment, is the most favorable for the accelerated spread and further reproduction of this disease. Phytophthora spores develop optimally on plant stems at air temperatures of +10˚ and humidity of about 65%.
In addition, spores develop not only on crops, but are sometimes located on the structure and the roof of the greenhouse itself. They penetrate into the soil during rain, harmful microorganisms are simply washed off from the leaves of plants, and also during strong winds.
The spores themselves are very light and easily inflate hundreds of meters. During its initial development, late blight is difficult to determine, and it spreads gradually, starting from small points.
The main signs of crop damage by late blight.
Whitish spots form on the back of the leaves, then they imperceptibly move onto the trunk and inflorescences of the plant. Slowly, darkened areas appear on the components of the crop, and rotting spots appear on the fruits with a brown tint.
On potato tubers, with the appearance of late blight in a polycarbonate greenhouse, black or brown areas also form. And if you peel the peel, you will see a dark red spot on the tuber. And if no action is taken against this disease, the plant is quickly destroyed by such a fungal parasite.
Soil disinfection
In the fall, the soil in the greenhouse needs to be dug up. This measure is necessary not only to prepare for spring planting. Digging reveals pest larvae that have buried themselves for the winter. Once on the surface, they will die on their own from low winter temperatures.
If you cannot replace greenhouse soil, then it must be disinfected
Advice! To get rid of pests and diseases, it is worth removing the top layer of soil (5 cm) from the greenhouse, where insects, larvae, microorganisms, viruses or fungal spores are usually stored.
You can disinfect the soil in a greenhouse in the fall using any of the following options:
- boiling water. Water the ground with hot water and cover with film. Hot steam kills most microorganisms and bacteria;
- copper sulfate. Water the soil with copper sulfate (1 tbsp) dissolved in a bucket of water. It is not recommended to repeat the procedure often, since copper can linger in the ground and enter plants and fruits, and subsequently accumulate in the human body;
Do not forget that it is better to disinfect the soil in the fall rather than in the spring before planting crops
- lime. Dry powder must be sprinkled on the soil. This procedure is allowed only in the fall, and in no case before planting seedlings in the spring;
- formalin. You will need to dig grooves, pour the substance into them, cover with a layer of earth and leave for 2 weeks. Afterwards, you need to ventilate the greenhouse well by opening all the windows for 2-3 weeks. Dig up the soil again to get rid of the smell;
- ready-made mixtures. Garden stores sell mixtures for autumn treatment of greenhouses; you can use one of them.
Prevention
In order to maximally protect the greenhouse from the appearance of late blight, the owner of the site needs to carry out preventive measures.
The main measures will be to carry out the following work:
- Moderate liming of the soil. Often in their garden plots, gardeners add lime in excessive amounts to neutralize acidified soil. However, it should be remembered that limed soil is an excellent environment for the development of late blight. If this happens, it is necessary to balance the composition of the soil: scatter peat and sand over the area, and then dig it up.
- Active development of late blight. Fungal spores develop well in damp conditions; therefore, tomatoes and potatoes should be watered as rarely as possible, but at the same time abundantly. You also need to ventilate the greenhouse with tomatoes more often. Humidity in a greenhouse structure can accumulate due to temperature changes, for example, at the end of the summer season, the nights are already cold, but the day is hot at the same time.
- Weakened immunity. When plants are poorly developed, various parasites stick to them. To boost the immune system, crops need to be promptly fed with microelements: manganese, iodine, potassium and phosphorus.
- Maintaining crop rotation. When planting nightshade crops, you need to take into account the impact of other plants on them in order to avoid the development of late blight. So for potatoes, excellent predecessors are cucumbers, zucchini, squash, cabbage and a number of other plants, and for tomatoes - legumes, onions, pumpkin, some varieties of cabbage, cucumbers, etc.
- Hybrids. A sure way to obtain abundant harvests and at the same time prevent the development of late blight is to plant hybrid plants that are protected from diseases by selection.
On a note! To prevent the development of late blight, potato and tomato plantings should not be placed next to each other, since both of these crops are nightshade crops, which means they have the same properties.
And of course, we must not forget about the treatment of greenhouses. Such disinfection can be done not only through chemicals and fumigation of the room, but also through planting green manure in the fall.
Greenhouse treatment
First of all, you need to wash the greenhouse. This can be done with ordinary soapy water. You can also add drugs that kill the fungus to the solution. It is necessary to wash all structural parts, windows and partitions. External processing is carried out similarly. Infusions of garlic, tobacco ash or mustard powder are often used. Sometimes such procedures are enough to kill the spores.
The walls of the greenhouse should also be thoroughly washed.
If the late blight infection was large-scale, you should use one of these methods:
- Bordeaux mixture, copper sulfate or potassium permanganate. After making the solution, you need to carefully spray all the parts of the structure. It's better to use a spray bottle.
- Fitosporin. Dilute the solution according to the instructions and disinfect the surface of the greenhouse. The treatment should be carried out only at temperatures above +10°C; at low temperatures the drug will not have any effect.
- Lime. Suppress the lime and coat all parts of the greenhouse. At the same time, make sure that the solution gets into the cracks and into all corners. After treatment, the greenhouse must be closed for 2 days. Metal parts will need to be doused with boiling water, wooden parts will need to be cleaned with a brush. Ventilate by opening doors and windows for 2 weeks and repeat the procedure.
- Fumigation with sulfur. Cutting sulfur needs to be crushed, combined with ash and placed in metal containers. They need to be evenly distributed throughout the greenhouse and the substance should be set on fire. At the same time, observe all safety precautions: the substance is toxic and dangerous.
Fumigation of a greenhouse against late blight - Fumigation with a sulfur bomb. Place the checkers on iron baking sheets and place them at equal distances around the greenhouse. Light it and leave it for 2 weeks. Then thoroughly ventilate the greenhouse.
Attention! Fumigation should be carried out if the greenhouse is located away from the house and living quarters, since sulfur emits a dangerous gas with a strong unpleasant odor.
Sulfur has a negative effect on metal parts of the structure, so it should not be used in greenhouses whose frame is made of metal.
When should you treat for late blight - in spring or autumn?
Late blight loves warm, moist environments. Therefore, when the temperature outside is above 20 °C during the day and cool at night, microorganisms begin to multiply intensively.
It is better to process in the spring with the onset of warmth, until the fruits are ripe. And it makes sense to disinfect the greenhouse in the fall, because the fungus can survive in the cold due to spores.
Soil preparation
The soil in the greenhouse must be replaced every 3-5 years, even if no diseases were observed in the greenhouse. And if infected with late blight, you can replace it completely: remove a 10 cm layer and place it in a prepared ridge. Sprinkle the soil with lime. In summer you need to mix or dig up this soil. After a year or two, it can be reused in a greenhouse or garden.
If you do not have the opportunity to replace the soil, then be sure to apply fertilizer for the winter.
For laying in a greenhouse, you cannot use ordinary soil from the garden. It is also most likely infested or contains pests. It is better to prepare the soil yourself, add:
- humus, manure;
- sand, sawdust;
- wood ash.
After the soil has been brought into the greenhouse, it should be treated with copper sulfate or potassium permanganate. You can spread mulch on the surface. Sometimes straw, corn tops or spruce branches are laid on top of the beds, after which the greenhouse is carefully closed for the winter.
Some useful tips
Some amateur agronomists leave the windows in the greenhouse open for the winter so that the remaining microorganisms can be affected by frost. At temperatures below -15-20°C, any bacteria, microorganisms, viruses and spores will die. The ground will also freeze a few centimeters and be similarly disinfected. Thus, nature will complete the disinfection of the greenhouse.
Greenhouse support
When preparing a greenhouse for winter, it is also worth remembering a few expert tips:
- Put up supports. Winter may be snowy and snow accumulated on the roof can damage the structure. It is better to protect yourself from this than to repair or buy a greenhouse again in the spring.
- If the greenhouse is film-based: remove the film. Structural elements can be wrapped with tarpaulin or other material so that the frame does not collapse from humidity and exposure to low temperatures.
- If the greenhouse is glass: it is necessary to take care of the integrity of the structure. Provide for the possibility of snow accumulation on the roof. It may be better to remove some of the glass so that it does not get damaged.
- If the greenhouse is made of polycarbonate: leave the windows open. This will prevent ice from forming on the material.
In winter, you can bring snow into the greenhouse and spread it on the beds. This way the soil will be well saturated with moisture.
