How to apply fungicides for effective control of carrot black spot
(1) Symptoms. Stems, leaves and petioles can all be infected. Leaf infection mostly starts from the leaf tip or edge, producing irregular dark brown to black lesions, with the surrounding tissue becoming increasingly discolored; when humidity is high, black mold grows on the lesions, and in severe cases the lesions merge, the leaf edges curl upward, and the leaves wither early. When stems are infected, the lesions are oblong, dark brown, ...
(1) Symptoms. Stems, leaves and petioles can all be infected. Leaf infection mostly starts from the leaf tip or edge, producing irregular dark brown to black lesions, with the surrounding tissue becoming increasingly discolored; when humidity is high, black mold grows on the lesions, and in severe cases the lesions merge, the leaf edges curl upward, and the leaves wither early. When stems are infected, the lesions are oblong, dark brown and slightly sunken.
(2) Conditions for onset. This disease is a fungal disease. The pathogen overwinters as mycelium or conidia on seeds or diseased plant debris. It spreads through airflow and causes secondary infection. Generally, fields during the rainy season and those with weak plant growth suffer more severe disease.
(3) Control methods. ① Promptly pull out diseased plants and bury them deeply. ② In dry weather, water promptly to prevent the soil from alternating between dry and wet; appropriately increase the application of phosphorus and potassium fertilizers so that the plants grow vigorously and their disease resistance increases. ③ Collect seeds from disease-free plants and store them separately. ④ Implement a crop rotation of more than 2 years. ⑤ Before sowing, treat seeds with 50% thiram wettable powder, or 40% seed-dressing dual powder, or 70% mancozeb, or 75% chlorothalonil, or 50% iprodione wettable powder. The fungicide dosage is 0.3% of the seed weight. ⑥ From the early stage of the disease, spray 75% chlorothalonil wettable powder 600-fold solution, or 58% metalaxyl-mancozeb wettable powder 400-500-fold solution, or 40% captan wettable powder 300-400-fold solution, or 50% iprodione wettable powder 1,500-fold solution, spraying once about every 10 days, for 3-4 consecutive treatments.