Leaf spots can occur on any carrot tissue above ground. However, symptoms are usually most severe and obvious along leaflet margins. Infection sites initially appear as a brown or black spot with a yellow margin. As the disease progresses, the leaflets become yellowed and curl at the margins. Lesions on leaf petioles, stems, and flower parts are usually elongated and dark brown.
Solutions
Cercospora and Alternaria leaf spots are favored by moist conditions. The fungi are seedborne but can be spread by wind and splashing water. Keep foliage dry and avoid overhead sprinklers. Remove infected plants, and destroy diseased crop material by plowing it under to ensure decomposition. Some varieties may show resistance.
