Alternaria leaf spot of Citrus

Alternaria symptoms once infection begins include small, dark, circular spots that regularly reach ½ inch in diameter. As they spread, alternaria leaf spots may change in color from black to tan or gray, with a yellow halo around the outside. Because spot development is heavily influenced by the environment, there are frequently noticeable concentric rings that spread from the initial point of infection. Sporulation causes these spots to develop a fuzzy texture.