Symptoms appear as wilting and a slow or rapid collapse of the plant.
The roots can appear brown and water-soaked instead of white. A water-soaked lesion can often appear at the base of the stem. Control can be achieved by using a two-year rotation with nonsusceptible plants, such as corn, to prevent the buildup of pathogenic organisms in the soil. Leaf blight, Alternaria dauci. Leaf blight is caused by a fungus and starts on the foliage as dark brown spots which grow together and may kill whole leaves.