Tomato early blight, also known as ringworm disease, is one of the important diseases of tomato. It is widely distributed. When the disease is severe, it often causes defoliation and fruit drop as a broken branch, which has a great impact on the yield. Generally, the yield is reduced by 10% to 30%, and the yield reduction in some areas is as high as 50%. Tomato early blight occurs from the seedling stage to the mature stage and can invade leaves, stems and fruits. At the initial stage of the damage to the leaves, small spots of dark brown or black round or oval shape are produced and gradually enlarged, with a diameter of 1-2 cm. The lesions are dark brown on the edges, grayish brown in the center, and concentric rings. When the humidity is high, black mold layer is formed on the lesion. Finally, the diseased leaves turn brown and fall off. Diseases are caused by the lower leaves of the plants and gradually spread upward. When the onset is severe, the lower leaves of the diseased plants die completely and even cause defoliation of the whole plant. Basal lesions often produce gray-brown, oval, and slightly sunken lesions on the branches, with concentric rings on them. Late stalk disease often covered with dark brown lesions, severe disease, can cause fragmentation. Spots on the fruit occur in cracked areas near the pedicle. The lesions are round or nearly round, brown or dark brown, slightly concave, and have concentric rings on them. When the humidity is high, black mold layer is also formed on the lesion. The fruit often falls off earlier. Fruit spots and calyces can also produce brown spots.
High temperatures and high humidity, especially in rainy and foggy weather, are most beneficial to early blight. In addition, lack of fertilizer, poor drainage in the field, plant growth and weakness, or plant length, poor ventilation and light transmission, can make the condition worse.
Chemical control: Can be sprayed with mancozeb, antiviral, chlorothalonil, metalaxyl manganese zinc. Mancozeb or chlorothalonil can also be used. After the onset of disease, the stem stalk is smeared. If the base of the stem is covered with dark brown spots, potassium permanganate can be used to irrigate the roots.
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