Agent: oomycete (fungus) Phytophthora infestans.
The harmfulness of this disease is that, despite a rather long period of development of the fungus, it can in a few days infect the entire crop of tomatoes and is the most common disease of a tomato. In addition, the agent of late blight is very viable, well preserved and hibernates successfully. It causes a decline in the quality of the crop and the death of plants, affects fruits and spoils seeds, and reduces resistance to other diseases.
Late blight is the most common disease of tomato, both in the open ground and in greenhouses. In addition to tomatoes, this disease can also infect other Solanaceous crops. Temperature jumps, excess moisture, poor airing of greenhouses, all this creates optimal conditions for the development of brown rot on tomatoes. Outwardly, the disease looks like dark spots on leaves, shoots, often even on a tomato, which causes them to rot. For this late blight is also called brown rot.
The first signs of the disease appear on the 7-10 day after infection. First of all, the lower leaves on the bush are infected. They appear dark brown and brown spots with a white border along the edge, which gradually expand. The same spots appear on infected fruits. The most vulnerable are the green fruits, as well as the young plants. Sets and flowers turn black and shed.
During the development of spots, focal points of infection increase to such a size that completely cover the entire leaf or stem and merge together. The fruits show characteristic signs of rot. It is necessary to get rid of them immediately - they are not suitable as food and as " seeds", but they are the carriers of infection in beds.
Late blight also infects potato, eggplant, and other solanaceous, so contamination from these crops is one of the root causes of the appearance of late blight on tomatoes. Also, not the last place among the causes of the appearance of late blight in the greenhouse occupies an excessive level of humidity and condensation. Because moisture is the carrier of the agent from sick plants to healthy ones. Prevention of this disease should be regular, because its pathogen rapidly spreads and develops on infected plants.
It is better to note the effectiveness of the following measures: