symptom
Celery leaf spot, also known as early blight, mainly damages leaves. The diseased leaves show yellow-green water-soaked spots at first, and then develop into round or irregular spots with a diameter of 4-10 mm. The lesions are taupe, and the edges are slightly darker and unclear. In severe cases, the lesions expand and merge into plaques, eventually causing the leaves to die. Lesions on stems or petioles are oval, 3-7 mm, grayish brown, slightly sunken. Whole plant lodging with severe disease. When the humidity is high, the above-mentioned diseased parts all grow a gray-white mold layer, that is, the conidiophores and conidia of the pathogen.
pathogen
Cercospora apii Fres., also known as Cercospora celery, belongs to the genus Cercospora in the fungal kingdom Ascomycota.
Transmission routes and disease conditions
The fungus survives the winter by attaching mycelium to seeds or diseased residues and diseased plants. When spring conditions are suitable, conidia are produced, which are spread by rain splash, wind, farm tools or agricultural operations, and directly invade from stomata or epidermis. The optimum temperature for growth is 25-30°C. The optimum temperature for conidia formation is 15-20°C, and the optimum temperature for germination is 28°C. High temperature and rainy or high temperature and drought, heavy condensation at night, and long duration are prone to disease. In particular, water shortage, fertilizer shortage, excessive irrigation or poor plant growth are severe.
Prevention method
① Choose disease-resistant varieties.
②Collect seeds from disease-free plants, and soak them in warm water at 48°C for 30 minutes if necessary.
③ Implement crop rotation for more than 2 years.
④ Reasonable dense planting, scientific irrigation, to prevent excessive humidity in the field.
⑤ Spray 500 times liquid of 70% propenezine wettable powder or 600-800 times liquid of 20% pentazole·carbendazim suspension concentrate, 800 times liquid liquid of 21% silazole·carbendazim suspension concentrate, 66% dicyanide Anthraquinone water dispersible granules 1800 times liquid.
⑥Under protected land conditions, 5% chlorothalonil dust agent can be used, 1kg per 667m2 each time. Or apply 45% chlorothalonil smoke agent, 200g per 667m2, once every 9 days, 2-3 times continuously or alternately.
