Agent: fungus Cladosporium fulvum.
Harmful disease leads to the drying of tomato leaves, which in turn becomes the cause of complete drying up of the plant. Under good conditions, the fungus develops rapidly and infects a large area of plantations. That will reduce the yield by half from what is possible. In the case of improper treatment or the complete absence of any treatment, the spores-causative agents of the disease may persist for up to 10 years.
The brown mold of tomatoes is also called leaf mold or cladosporiosis. Particularly susceptible to this disease are tomatoes growing in conditions of closed ground. Favorable conditions for the development of this disease are excessive humidity (over 80%) with a warm temperature of +22 ... + 25°C and above. It is easy to recognize this disease by yellow or light green blurry spots on the lower leaves of plants, and by a light whitish coating on their upper leaves. In the course of the development of the disease, the plaque darkens to a brown color. In this case, tomato fruits, with the exception of small ones, practically do not suffer from this fungus.
The first signs of infection of tomatoes with brown spots become visible already in the period of the beginning of flowering of plants. Then from the outside of the leaves there are yellowish and light green spots, on the opposite side of the leaves you can see a brown plaque - spores of the fungus. The disease spreads from the top of the bush to the bottom.
If at the initial stage of the disease not to take any measures, very soon the scurf on the leaves will turn brown, sometimes becoming a dark brown tint. Fungus spreads throughout the tomato plant and begins to infect neghbour ones. Further, the spots may increase slightly, then darken to a yellow-brown color, metabolic processes deteriorate inside the leaves, they curl, wither and fall off. Following the leaves due to lack of nutrients, the entire plant also disappears.
Spread of the agent occurs when caring for plants through damage with air currents, drops of water. Also, the natural cause of brown spots in greenhouse are the spores of the fungus, which successfully hibernate in soil, on plant remains, and wooden frame of structures.
There are preventive measures: