A leaf spot is a limited, discoloured, diseased area of a leaf that is caused by fungal, bacterial or viral plant diseases, or by injuries from nematodes, insects, environmental factors, toxicity or herbicides. These discoloured spots or lesions often have a centre of necrosis. Symptoms can overlap across causal agents, however differing signs and symptoms of certain pathogens can lead to the diagnosis of the type of leaf spot disease. Prolonged wet and humid conditions promote leaf spot disease and most pathogens are spread by wind, splashing rain or irrigation that carry the disease to other leaves.

Cercospora is a genus of ascomycete fungi. Most species have no known sexual stage, and when the sexual stage is identified, it is in the genus Mycosphaerella. Most species of this genus cause plant diseases, and form leaf spots. It is a relatively well-studied genus of fungi, but there are countless species not yet described, and there is still much to learn about the best-known members of the genus.