Tomato late blight is a disease caused by P. infestans fungus infestation, which has the characteristics of rapid onset, widespread epidemic and great harm. It is the main disease in the production of autumn tomatoes.
Seedlings, plants can be disease. Stems, leaves, and fruits can all be harmed, mainly destroying leaves and fruits. Seedlings of diseased seedlings appear dark green watery immersed lesions, which develop from the leaves to the main stem. The petioles and stems become dark brown and rotten. The whole plant is wilting and lodging, and when the humidity is high, the diseased part produces white mold layer. The base of the young stems develops, forming watery contractures, wilting or lodging of the seedlings.
In the adult stage, leaf lesions mostly start from the tips or leaf margins of the lower leaves. The lesions are dark green and irregular in shape at the beginning of the lesions. The lesions are not clearly visible at the boundary between the disease and the health. The lesions spread quickly in the wet, and the lesions on the back of the leaves are very fast. At the junction, white, loose molds may appear, and the lesions turn brown. When dry, the diseased department is dry, brittle and easily broken.
The lesions on stems were initially dark green, black in color, and slightly dark brown on the back, easily causing wilting or breaking of the diseased branches above the stem of the main stem. The victims suffer from fruit damage. They often form oil-immersed dark green to brown lesions on the fruit surface. They grow in an irregular, moire-like manner. The texture is hard and the flesh is dark brown. When the surface is wet, mildew develops on the surface of the lesion and quickly rots.
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