Alternaria species cause small, dark specks to emerge on leaves and later enlarge into circular, tan spots. If conditions are favorable, dark green spores of the pathogen will grow on the spots. Such growth causes the spots to have concentric rings in them. Old leafspots become papery in texture and may tear. When the dry tissue falls out, a shothole effect results. It prefers cool moist conditions. The pathogen infects carrots and many other vegetables. Spores are spread by winds and splashing water. The fungus does not survive in soil, but is carried over in seed, on weed or volunteer hosts, or on undecomposed crop residue.