Apium graveolens var. dulce
Cercospora Blight (fungus – Cercospora apii): Symptoms begin as small, yellowish spots on both sides of the foliage. Spots enlarge quickly changing from yellow to ash-gray with the tissue drying in affected areas. The fungus also attacks leaf petioles and stems. Under conditions of high humidity and warm weather, a gray velvety growth can be seen on the surface of affected spots. The fungus is seed-borne and spores can also be blown in air currents for long distances. Warm temperatures are required for fungus development. Control is obtained by using disease-free seed treated with fungicides and spraying plants with a protective fungicide at regular intervals when disease represents a threat.
Late Blight (fungi – Septoria apiicola): Small, yellowish spots develop on the underside of the leaves which later spread to the entire foliage. Spots enlarge and turn brown, similar to lesions caused by Cercospora. Minute, black fruiting bodies can be found scattered in the affected areas. Lesions with fruiting structures can be seen on petioles and stems. High humidity, free water, and cool temperatures favor disease development. Fungicides recommended for Cercospora blight will also control late blight.
Stalk Rot (fungi – Rhizoctonia solani): A serious disease of celery that is favored by high temperatures and moist conditions. Symptoms are first seen as small lesions on the base of the petioles, near the ground. As the disease progresses, the spots are enlarged, appear watersoaked at first, turning later to a brick-red color. When matured, the spots are sunken and turn to a dark brown color that is characteristic of the disease. The lesion can be a few or numerous, making it necessary to trim a lot of the leaves, thus reducing quality and yield. Shallow planting on raised beds and fungicide applications serve to reduce disease losses.
Root Knot (nematode – Meloidogyne spp.): (See Nematode)