[Fungus] Septoria citri Pass.
Septoria has saprophytic capabilities and pycnidia often form on dead twigs and leaves. Conidia from these pycnidia are spread by splashing water and may infect leaves and fruit. However, symptoms may not result for up to six months after infection.
Leaf - foliar lesions are blister-like, raised, black and 1-4 mm in diameter. Over time the center of the lesions become necrotic and pale brown. Pycnidia develop in the lesions especially following leaf drop when the lesion turns dark brown with dark margins. When conditions are favorable, the disease may cause severe leaf drop in the lower portion of the tree.
Fruit - early fruit lesions are small light tan to reddish brown pits 1-2 mm in diameter that extend no deeper than the flavedo. Older lesions are darker sunken 20-30 mm in diameter. Dark fruiting bodies, pycnidia, may develop in these lesions. Lesions may appear in the form of "tear stains" patterns. Spots are more evident on ripe fruit.
All citrus cultivar are susceptible. However, Valencia oranges, Navel oranges, lemons and grapefruit are frequently damaged.
This disease has been reported from most citrus producing areas throughout the world.