Mealy dew (or ash) is a fungal disease that affects most plant crops, and tomatoes are no exception. In this article we will learn how powdery mildew looks on tomatoes and how to deal with it.
What is dangerous and where does it come from
Mealy dew is dangerous in that it takes nutrients from the plant, interferes with the processes of photosynthesis, respiration, makes the tomato bush unstable even to slight cold snaps. Powdery mildew first affects the leaves of culture - they wither and fall, new leaves from dormant buds may appear in their place, but they will not be complete and will not help the plant in any way. 
There are no signs of disease outside on the stem and fruits, but the bush will not survive for long. Powdery mildew pathogens on tomatoes are spores of two types of fungi: Leveilluia taurica and Oidiopsis sicula.
There are several reasons for the appearance and development of these fungi:
- high humidity at a temperature of 15 ° C to 30 ° C;
- significant nitrogen content in the soil;
- thick landing;
- non-compliance with irrigation regime.
Also, the cause of infection can be the transfer of spores from a diseased plant to a healthy one.
This can occur in the following ways:
- through the air;
- through splashes of water that beat off from an infected bush;
- you can transfer the fungus on your hands (by touching the diseased tomato, and then to the healthy one);
- through parasitic insects.
Did you know? Powdery mildew spores can “travel” in the wind for tens of kilometers.
Signs of appearance on tomatoes
Mealy dew manifests itself on the outside of the leaves of a tomato as white (maybe with a green or yellow shade) or yellow powdery spots, which gradually spread throughout the leaf. Further rings may appear that resemble brown spot infection. With conditions conducive to the development of the disease, "flour" appears on both sides of the leaves.
Mealy dew also affects gooseberries, grapes, cucumbers, roses.
Disease prevention
To avoid powdery mildew on tomatoes, you should stick to certain prevention rules:
- It is recommended to spray the bushes with a solution of manganese monthly;
- do not use nitrogen fertilizers;
- It is necessary to carry out spraying with special prophylactic drugs, for example, “Gumat”, “Epin”, “Rajok”;
- If you grow tomatoes in a greenhouse, frequent airing should be carried out to avoid moisture stagnation; also recommend changing the ground every year;
- to prevent the emergence of aphids and other parasites, because they carry the spores of the fungus of the pathogen;
- often loosen the ground so that it dries out and is saturated with oxygen.
- alternate planting crops in the garden.
Important! Planting tomatoes in the same place where you grew them this season is possible only after 3-5 years.
How to fight in case of defeat
There are many ways to get rid of powdery mildew on tomatoes. You can handle any chemical, biological substance or use a folk remedy, but certain actions need to be performed in any case.
The first step is to completely cut off all infected leaves and flower stalks, and then burn them in a fire. And only then process shrubs and soil with potassium permanganate or other special substances from powdery mildew.
Important! It is recommended to carefully replace the soil under the plant, because it contains a huge amount of pathogen mycelium.
Biological preparations
In stores and in the markets you can find an uncountable amount of biological preparations for powdery mildew, but, based on the many positive reviews in various agricultural forums, you can separately select such drugs: "Appin", "Immunocytofit", "Fuzaksin", "Monofilin", "Baktofit", "Gumat".
These drugs increase resistance to fungal and viral diseases not only in tomatoes, but also in other crops. They are suitable both as a prophylactic and for the treatment of powdery mildew in the early stages. 
Chemicals
The use of chemical preparations (fungicides) is recommended only in the case of severe damage to the bush by a fungus.
The most effective fungicides include: "Topaz", "Skor", "Amistar", "Kvadris", "Tiovit Jet", "Cumulus". Treatment with such drugs should be carried out strictly following the manufacturer's instructions and precautions.
Important! All fungicides can not be stored in diluted form, so the solution should be used immediately after preparation.
Folk remedies
Folk remedies for powdery mildew on tomatoes are more suitable for the treatment of the early stage of the disease and as a prophylactic agent. Now we will get acquainted with the most effective recipes. 
- Soda and soap solution. Such a solution is prepared as follows: for 10 liters of warm water, 50 g of ordinary baking soda and a small amount of laundry soap are taken. All ingredients must be thoroughly mixed. Prepare the solution sprayed plants 2 times a week, trying to get the solution on both sides of the leaves.
- Serum treatment. For this tool, we need the usual whey, which is mixed with water in proportions: 1 liter of serum to 10 liter of water. After spraying the tomatoes with such a means, a thin film will appear on the leaves, which will not allow the fungus mycelium to breathe, which, in turn, will lead to the death of the disease. Repeat the spraying procedure should be 3-4 times with an interval of 3 days.
- Bordeaux fluid treatment and prophylaxis. The solution is prepared very simply: 100 g of the liquid should be diluted in 10 liters of warm water. Processing of such a mixture is carried out 2 or 3 weeks before planting tomatoes in open ground, or when the disease manifests its symptoms.
- Infusion of wood ash. The infusion is prepared at the rate of 1 kg of ash per 10 liters of water (the water should be very hot, but not boiling). The ash is dissolved in water and left to infuse for a week. Then the infusion should be poured into another bucket or sprayer, the old one should be poured in such a way that settled ash will remain in the first bucket. The remaining ash can be mixed with water and used for watering.
Did you know? Mycelium fungi can live in the soil for about 20 years.
Mealy dew is a very contagious disease that is difficult to treat, and if you notice the slightest signs of it, you should immediately begin to fight it. But still the best way to combat powdery mildew is its prevention.
