Potato late blight begins to contract from the middle and lower leaves. Water-stained green-brown spots appear at the tip or leaf edge, and there is a wide gray-green halo around. When the humidity is high, the lesions rapidly expand into yellow-brown to dark brown. Large spots, gray-brown edges, and inconspicuous boundaries, often produce a circle of sparse white mold at the border of disease and health, especially after rain or early morning. The air is dry and the lesions become brown, dry, cracked or curled. The stems and petiole are infected, and irregular brown streaks are formed. In severe cases, the leaves are wilted and curled, and eventually the whole plant is black rot. Potato tubers are infected, and the primary light brown spots become irregular brown to purple-brown lesions. They are slightly sunken and the edges are not obvious. The subcutaneous potato is light brown to dark brown in the diseased part, eventually causing the potato to rot.
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Prevention and treatment methods: timely spraying and prevention in the early stage of the disease. Curzate choice of 72% WP 600-800 times, 64% of the anti-virus alum WP 500 times or 50% dimethomorph WP spraying. To ensure control, the condition is investigated 3-7 days after each spray . In order to avoid the emergence of drug resistance, the drugs should be used alternately, and the same agent should not be sprayed continuously for more than 3 times.
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(Source: Hebei Science and Technology News Author: Yutian County Agriculture and Animal Husbandry Su Yadong)
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