Celery leaf spot has become a significant disease in winter and spring protected cultivation areas, greatly affecting both yield and quality of the crop. The disease primarily affects the leaves, but can also damage the petioles and stems. Leaf lesions appear in two forms: small and large spots. In the early stages, they manifest as light brown, oil-like spots that gradually expand into central brown necrotic areas. Small spots are usually less than 3 mm in diameter, with a yellow-brown margin and a yellow-white to gray-white center. Some may have a yellow halo around them. Large spots can grow up to 7–10 mm, with dark brown edges and a brown middle section. Both types of lesions contain small black spots, which are conidia. Petiole and stem lesions appear as diamond-shaped or oblong, slightly sunken, brown areas with a pale interior and scattered black spots. The pathogen responsible is *Septoria apiicola* (Speg.), also known as celery culm, *S. apii* (Chest.), referred to as celery shell spores, and *S. apii-graveolentis* (Dorogin), called celery large shell spores. All are fungi from the subphylum Ascomycota. The conidiospores are embedded in the epidermis, measuring 87–155 × 4–25–56 microns. They emerge through the spore orifice and spread via rain splash. Spores are colorless, transparent, and elongated, with a blunt tip and 0–7 septa, typically 3. Their size ranges from 35–55 × 2–3 microns. When germinating, the conidia may split into several sections, each producing germ tubes. Mycelium and conidia are killed at 48–49°C after 30 minutes. Germination occurs between 9–28°C, with optimal growth at 20–27°C. Growth slows above 27°C, and the pathogen only infects celery. The disease survives in the soil through mycelia and remnants of infected plant material, or through latent mycelium in seeds and seed coats. Endogenous conidiospores serve as primary and secondary inocula. They are released through spore orifices and spread by water splash, penetrating through stomata or the epidermis. The disease thrives under high humidity, with spore release and germination more likely when water droplets are present. Cool, wet, and rainy weather promotes disease development. In protected cultivation, poor ventilation, high humidity, low light, and weak plants increase susceptibility. Resistant varieties include Italian winter celery, summer celery, Florida 683 (susceptible to black heart disease under heat and drought), Utah 10-B, Emerson, June Bell, Early Green, Jinnan Ciqin (Tianjin), Daqin (Shanghai), and Beijing 8401 (developed from Shanghai Daqin). These can be selected based on local conditions. To manage the disease, choose resistant varieties such as Jinnan celery, winter celery, Xiaqin, Jinqin, Tianma, Shanghai Daqin, Ventura, American Glass Crisp, Celery 3, and Chunfeng. Use disease-free seeds or treat infected seeds. Store healthy seedlings for up to two years. Improve field management, apply balanced fertilizers, and enhance plant health. In open fields, apply 75% chlorothalonil WP at 600 times dilution, 40% Fuxing (fluorosiliconazole) at 8000 times, 45% Tecto suspension at 1000 times, or 50% mancozeb wettable powder at 1000 times. For ground protection, use 5% chlorothalonil or 6.5% thiram dust, or 45% chlorothalonil aerosol. Apply these treatments two to three times every 7–10 days for effective control.

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