Pathogen: fungi of the genus Alternaria (Macrosporium)
Affects all the aerial parts of the plant, leading to premature wilting and death of tomatoes. The crop loss from this disease can reach 40%. In addition, the disease can manifest itself and after a while on the already harvested tomatoes.
Alternaria blight of tomato is a fungal disease of tomatoes and other solanaceous. There are no sorts tolerating to this disease. Fungus affects the whole plant: leaves, stems, stalks and fruits. The characteristic signs of the disease are dry, rounded spots with a clearly limited shape, brown and dark brown color.
Favorable conditions for the development of alternaria are dry hot weather (average air temperature is 25-30 °C) and a low amount of precipitation. Moisture that lingers on leaves (e.g, condensation or dew) can also be the cause of the spread of the disease. Despite the fact that this disease is more common among tomatoes in the open ground, in greenhouses, it is also often found. It should be noted that the symptoms of dry patchiness may vary slightly depending on the plant variety.
The first symptoms of contamination of tomatoes with alternaria can be observed even at the stage of transplanting the seedlings into the soil - these are small spots on the lower leaves of the plant (their diameter is about 4-7 mm), which later appear on the upper ones. The incubation period of the agent is only 2-3 days, then its active growth and spread begins.
With the development of alternaria, brown spots begin to increase in size and eventually reach 10-15 mm in diameter. On their surface becomes noticeable characteristic velvety coating of black color - the sporulation of the fungus began. Spots grow, merge with each other, covering most of the tomato. The plant lacks the vital substances necessary for growth and dies. Particularly active dry spotting affects only the fruit, which is fastened, which leads to their falling off or premature ripening.
The root cause of the appearance of an alternative in the greenhouse is already infected soil, plant remains with spores of the causative agent of the disease or infected seedlings, seeds of tomatoes. Therefore, the prevention of this disease has a high level of effectiveness: