Early blight is one of the most common and destructive diseases affecting celery, occurring in both open fields and protected environments. The pathogen primarily infects the leaves and petioles, leading to the formation of lesions that cause yellowing, wilting, and a significant decline in yield and quality. Prompt application of **pesticides** is essential to manage this disease effectively.
**Symptoms**
Infected leaves develop small, circular or irregularly shaped spots ranging from 5 to 10 mm in diameter. These spots have dark brown or purplish edges and a clear boundary with healthy tissue. Under humid conditions, a gray-white mold—comprising conidiophores and conidia of the pathogen—appears on the lesions. As the disease progresses, multiple spots may merge, causing the leaves to turn yellow and eventually die. On the petioles and flower stalks, initial lesions are oval or elongated, light brown, and slightly sunken. Over time, they develop into long, dark brown streaks. Affected areas may collapse, leading to yellowing or black rot, which can halt plant growth. Grayish-white mold also appears on the petioles and stems.
**Pathogen**
The causal agent is *Cercospora apii* Fres., a fungal pathogen that thrives under favorable environmental conditions.
**Disease Cycle**
The pathogen overwinters in infected plant debris and seeds. When conditions are suitable, it produces conidia that are spread by wind, rain, and human activities. The spores enter through natural openings or directly penetrate the leaf and stem surfaces. Infected seeds can also serve as a source of infection. In greenhouses, early blight can persist and later spread to open-field crops. High humidity, temperatures between 25°C and 30°C, and frequent dew accumulation promote disease development. Poor growing conditions such as water stress, nutrient deficiency, and weak plant growth further increase the risk of infection.
According to the **China Pesticide Network**, improper field management, excessive heat, large temperature fluctuations, and frequent dew formation can worsen the disease.
**Control Measures**
Selecting resistant varieties is an effective strategy. Varieties like Jinnan Shiqin No. 1, American Utah, Bailey Celery, California King, and Ventura show good resistance. 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, followed by cooling in cold water. Germination rates may decrease, so increasing the sowing rate by 10% is recommended. A germination test should be conducted first to assess the impact on seed viability.
At the early stages of infection, **fungicides** should be applied. Effective options include:
- 75% chlorothalonil wettable powder diluted 600–700 times
- 30% ethyl (or methyl) picoxystrobin at 1000 times dilution
- 50% fluazinam (immunized) at 800 times
- 32.5% benzoxypyrimidine (spike) at 1200 times
- 50% carbendazim WP at 500 times
- 72.56% copper oxychloride (Rumocarb) at 800 times
- 40% tetrachloroisophthalonitrile (tetrachlorodan) at 500 times
- 43% tebuconazole suspension at 8000 times
- 18.7% enoylpyrazole ester at 1000 times
- 60% azoxystrobin + Difenoconazole at 1000 times
- 40% mancozeb + sulfur suspension at 500 times
- 72% mancozeb + copper hydroxide at 800 times
Spray applications should be made every 7–10 days, with 2–3 consecutive treatments. For shed-grown celery, dust formulations such as 5% chlorothalonil (15 kg/ha) or 6.5% methyldiethanolamine (Methicillin) dust, or 45% chlorothalonil (3 kg/ha) can be used.
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