Prevention and treatment of celery early blight

Early blight is one of the most significant diseases affecting celery, and it can occur in both open fields and protected environments. The pathogen primarily infects the leaves and petioles, leading to the formation of lesions that cause yellowing of the foliage or even entire plants, resulting in a significant decline in yield and quality. Prompt application of **pesticides** is essential to manage the disease effectively. **Symptoms** Infected leaves develop small, circular or irregularly shaped spots ranging from 5 to 10 mm in diameter. These lesions are typically brown with dark edges and have a clear boundary from healthy tissue. Under humid conditions, gray-white mold—composed of conidiophores and conidia of the pathogen—may appear on the affected areas. As the disease progresses, multiple lesions may merge, causing the leaves to yellow and wither. On the petioles and flower stalks, initial symptoms appear as elliptical or elongated, light brown spots that become sunken over time. Later, they develop into long, dark brown lesions, which can lead to collapse, yellowing, or black rot of the affected parts. Mold also appears on these areas. **Pathogen** The causal agent is the fungus *Cercospora apii* Fres., which is responsible for early blight in celery. **Disease Cycle** The pathogen survives in infected plant debris and soil. When environmental conditions are favorable, overwintering structures produce spores that are spread by wind, rain, and human activities. The spores can enter through stomata or directly penetrate the leaf and stem epidermis. Infected seeds can also serve as a source of infection. In greenhouses, the disease can persist and act as a reservoir for future outbreaks in open fields. Spores produced in the field can also infect fallen celery plants. The disease thrives at temperatures between 25°C and 30°C, especially when humidity is high, and there is frequent dew formation. Poor plant growth due to lack of water, nutrients, or improper cultivation practices can increase the severity of the disease. According to the **China Pesticide Network**, delayed protection, heat accumulation, and large temperature fluctuations between day and night can worsen the condition. **Control Measures** Selecting resistant varieties is an effective strategy. Some recommended varieties include Jinnan Shiqin No. 1, American Utah, Bailey Celery, California King, and Ventura. Seed treatment is also important. Seeds can be disinfected by soaking them in hot water at 48–49°C for 30 minutes or 52°C for 52 minutes while stirring, then quickly transferring to cool water to stop the process. After drying, the seeds can be sown. Due to potential germination loss, the seeding rate should be increased by about 10%. It is advisable to conduct a preliminary test to ensure the treatment does not negatively affect germination. At the first sign of disease, **fungicides** should be applied. Effective options include: - 75% chlorothalonil wettable powder diluted 600–700 times - 30% ethyl (or emulsifiable) fungus ester diluted 1000 times - 50% immunized (fluazidin) diluted 800 times - 32.5% pyraclostrobin (benzoxypyrimidine) diluted 1200 times - 50% carbendazim WP diluted 500 times - 72.56% mancozeb (Rumocarb) diluted 800 times - 40% tetrachloroisophthalonitrile wettable powder diluted 500 times - 43% tebuconazole suspension diluted 8000 times - 18.7% enopyrazole ester solution diluted 1000 times - 60% azoxystrobin + difenoconazole combination diluted 1000 times - 40% mancozeb + sulfur suspension agent diluted 500 times - 72% mancozeb + copper oxychloride water dispersible agent diluted 800 times Spraying should be done every 7–10 days, with 2–3 applications typically needed for effective control. For shed-grown celery, dust formulations such as 5% chlorothalonil (15 kg per hectare) or 6.5% methoxyfen (methicillin) dust, or 45% chlorothalonil (3 kg per hectare), can be used.

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