Cercospora early blight

Small yellow spots, visible on both sides of the leaf, are the first symptom of early blight. Later the spots grow into gray, circular lesions that may be 0.25 to 0.75 inch in diameter. As leaf spots dry out, the tissue becomes papery in texture and often splits and cracks. Elongated lesions may develop on petioles. Under favorable conditions (temperatures between 60° and 86°F), the lesions will coalesce and cause a blighting effect on the leaves. The gray, fuzzy growth of the fungus may be observed in the centers of leaf and petiole lesions, but distinct structures (such as those found for celery late blight) are not formed by this pathogen. Even though the fungus growth is similar, do not confuse this disease with the early blight disease that occurs on tomato and potato, which is caused by an Alternaria sp. that does not infect celery.