First, the symptoms: lettuce black spot disease, also known as ring disease or leaf blight, the disease is mainly harmful to the leaves. The typical symptom is the formation of round or nearly round brown plaques on the leaves, with a diameter of 3 to 15 mm, with concentric pattern. When wet, the surface of the lesions can produce black mildew, and the late lesions fill the whole leaves.
Second, prevention and treatment methods: strengthen cultivation management, increase the application of phosphorus, potassium fertilizer. Carry out rotations and remove old, sick and residual leaves in time. At the beginning of the disease, the following fungicides or formulas can be used for prevention and treatment: 10% difenoconazole water-dispersible granules 1500 times solution + 75% chlorothalonil WP 600 times solution; 25% nitrile emulsifiable concentrate 1000-2000 times Liquid +70% mancozeb WP 700 times solution; 25% prochloraz emulsifiable concentrate 800-1000 times solution + 75% chlorothalonil WP 600 times solution; 25% bromobacillus wettable powder 500-1000 Double solution +75% chlorothalonil WP 600 times solution; 2% azoxystrobin suspension 1000-2000 times solution; 77% copper hydroxide wettable powder 800 times solution; 47% spring leimycin · copper oxychloride The wettable powder is 600-800 times liquid; the 50% isourea suspension agent is 1000-2000 times liquid, etc., and the spray is evenly sprayed, and the spray is sprayed once every 7 to 10 days.
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